Avoiding NullPointerException in Java

Question

I use object    null a lot to avoid NullPointerException  What is an alternative to  if  someobject    null        someobject doCalc

User · Answer

If null-values are not allowed

If your method is called externally, start with something like this:

public void method(Object object) {
  if (object == null) {
    throw new IllegalArgumentException("...");
  }

Then, in the rest of that method, you'll know that object is not null.

If it is an internal method (not part of an API), just document that it cannot be null, and that's it.

Example:

public String getFirst3Chars(String text) {
  return text.subString(0, 3);
}

However, if your method just passes the value on, and the next method passes it on etc. it could get problematic. In that case you may want to check the argument as above.

If null is allowed

This really depends. If find that I often do something like this:

if (object == null) {
  // something
} else {
  // something else
}

So I branch, and do two completely different things. There is no ugly code snippet, because I really need to do two different things depending on the data. For example, should I work on the input, or should I calculate a good default value?

It's actually rare for me to use the idiom "if (object != null && ...".

It may be easier to give you examples, if you show examples of where you typically use the idiom.

User · Answer

Common  problem  in Java indeed   First  my thoughts on this   I consider that it is bad to  eat  something when NULL was passed where NULL isn t a valid value  If you re not exiting the method with some sort of error then it means nothing went wrong in your method which is not true  Then you probably return null in this case  and in the receiving method you again check for null  and it never ends  and you end up with  if    null   etc    So  IMHO  null must be a critical error which prevents further execution  that is  where null is not a valid value    The way I solve this problem is this   First  I follow this convention    All public methods   API always check its arguments for null All private methods do not check for null since they are controlled methods  just let die with nullpointer exception in case it wasn t handled above  The only other methods which do not check for null are utility methods  They are public  but if you call them for some reason  you know what parameters you pass  This is like trying to boil water in the kettle without providing water      And finally  in the code  the first line of the public method goes like this   ValidationUtils getNullValidator   addParam plans   plans   addParam persons   persons   validate      Note that addParam   returns self  so that you can add more parameters to check   Method validate   will throw checked ValidationException if any of the parameters is null  checked or unchecked is more a design taste issue  but my ValidationException is checked    void validate   throws ValidationException    The message will contain the following text if  for example   plans  is null    Illegal argument value null is encountered for parameter  plans    As you can see  the second value in the addParam   method  string  is needed for the user message  because you cannot easily detect passed-in variable name  even with reflection  not subject of this post anyway       And yes  we know that beyond this line we will no longer encounter a null value so we just safely invoke methods on those objects   This way  the code is clean  easy maintainable and readable

User · Answer

I m a fan of  fail fast  code  Ask yourself - are you doing something useful in the case where the parameter is null  If you don t have a clear answer for what your code should do in that case    I e  it should never be null in the first place  then ignore it and allow a NullPointerException to be thrown  The calling code will make just as much sense of an NPE as it would an IllegalArgumentException  but it ll be easier for the developer to debug and understand what went wrong if an NPE is thrown rather than your code attempting to execute some other unexpected contingency logic - which ultimately results in the application failing anyway

User · Answer

Wherever you pass an array or a Vector  initialise these to empty ones  instead of null   - This way you can avoid lots of checking for null and all is good     public class NonNullThing       Vector vectorField   new Vector        int   arrayField   new int 0       public NonNullThing               etc

User · Answer

You can make one generic Method for object and string so that you can use it through out in your application- This could help you and your colleagues   Create a class eg  StringUtilities and add the method eg  getNullString public static String getNullString Object someobject       if null  someobject           return null      else if someobject getClass   isInstance  quot  quot    amp  amp                String someobject  trim   equalsIgnoreCase  quot null quot                  String someobject  trim   equalsIgnoreCase  quot  quot             return null      else if someobject getClass   isInstance  quot  quot            return  String someobject      else         return someobject toString   trim       And simply call this method as  if  StringUtilities getNullString someobject     null         Do something

User · Answer

If you consider an object should not be null  or it is a bug  use an assert  If your method doesn t accept null params say it in the javadoc and use an assert    You have to check for object    null only if you want to handle the case where the object may be null     There is a proposal to add new annotations in Java7 to help with null   notnull params  http   tech puredanger com java7  jsr308

User · Answer

Functional approach may help to wrap the repetitive null checks and execute anonymous code like the below sample       BiConsumer lt Object  Consumer lt Object gt  gt  consumeIfPresent     s f  - gt           if s  null                f accept s                         consumeIfPresent accept null   s - gt  System out println s         consumeIfPresent accept  test    s - gt  System out println s         BiFunction lt Object  Function lt Object Object gt  Object gt  executeIfPresent     a b  - gt           if a  null                return b apply a                     return null             executeIfPresent apply null   s - gt   System out println s  return s          executeIfPresent apply  test    s - gt   System out println s  return s

User · Answer

You can use FindBugs  They also have an Eclipse plugin  that helps you find duplicate null checks  among other things   but keep in mind that sometimes you should opt for defensive programming  There is also Contracts for Java which may be helpful

User · Answer

If you use  or planning to use  a Java IDE like JetBrains IntelliJ IDEA  Eclipse or Netbeans or a tool like findbugs then you can use annotations to solve this problem   Basically  you ve got  Nullable and  NotNull   You can use in method and parameters  like this    NotNull public static String helloWorld         return  Hello World       or   Nullable public static String helloWorld         return  Hello World       The second example won t compile  in IntelliJ IDEA    When you use the first helloWorld   function in another piece of code   public static void main String   args        String result   helloWorld        if result    null            System out println result             Now the IntelliJ IDEA compiler will tell you that the check is useless  since the helloWorld   function won t return null  ever   Using parameter  void someMethod  NotNull someParameter        if you write something like   someMethod null     This won t compile   Last example using  Nullable   Nullable iWantToDestroyEverything     return null      Doing this  iWantToDestroyEverything   something      And you can be sure that this won t happen      It s a nice way to let the compiler check something more than it usually does and to enforce your contracts to be stronger  Unfortunately  it s not supported by all the compilers   In IntelliJ IDEA 10 5 and on  they added support for any other  Nullable  NotNull implementations   See blog post More flexible and configurable  Nullable  NotNull annotations

User · Answer

All in all to avoid statement if  object    null                 since java 7 you can use Objects methods  Objects isNull object  Objects nonNull object  Objects requireNonNull object  Objects equals object1  object2   since java 8 you can use Optional class  when to use    object ifPresent obj - gt        java 8 object ifPresentOrElse obj - gt          - gt        java 9  rely on method contract  JSR 305  and use Find Bugs  Mark your code with annotations  javax annotation Nullable and  javax annotation Nonnnul  Also Preconditions are available  Preconditions checkNotNull object    In special cases  for example for Strings and Collections  you can use apache-commons  or Google guava  utility methods     public static boolean isEmpty CharSequence cs    apache CollectionUtils public static boolean isEmpty Collection coll    apache StringUtils public static boolean isEmpty Map map    apache MapUtils public static boolean isNullOrEmpty  Nullable String string    Guava Strings   When you need to assign default value when null use apache commons lang   public static Object defaultIfNull Object object  Object defaultValue

User · Answer

One more alternative   The following simple function helps to hide the null-check  I don t know why  but I haven t found it as part of the same common library    public static  lt T gt  boolean isNull T argument        return  argument    null       You could now write  if   isNull someobject         someobject doCalc        which is IMO a better way of expressing    null

User · Answer

You can also use the Checker Framework  with JDK 7 and beyond  to statically check for null values  This might solve a lot of problems  but requires running an extra tool that currently only works with OpenJDK AFAIK  https   checkerframework org

User · Answer

This is a very common problem for every Java developer  So there is official support in Java nbsp 8 to address these issues without cluttered code   Java 8 has introduced java util Optional lt T gt   It is a container that may or may not hold a non-null value  Java 8 has given a safer way to handle an object whose value may be null in some of the cases  It is inspired from the ideas of Haskell and Scala   In a nutshell  the Optional class includes methods to explicitly deal with the cases where a value is present or absent  However  the advantage compared to null references is that the Optional lt T  class forces you to think about the case when the value is not present  As a consequence  you can prevent unintended null pointer exceptions   In above example we have a home service factory that returns a handle to multiple appliances available in the home  But these services may or may not be available functional  it means it may result in a NullPointerException  Instead of adding a null if condition before using any service  let s wrap it in to Optional lt Service    WRAPPING TO OPTION lt T   Let s consider a method to get a reference of a service from a factory  Instead of returning the service reference  wrap it with Optional  It lets the API user know that the returned service may or may not available functional  use defensively  public Optional lt Service gt  getRefrigertorControl           Service s   new  RefrigeratorService                       return Optional ofNullable s          As you see Optional ofNullable   provides an easy way to get the reference wrapped  There are another ways to get the reference of Optional  either Optional empty    amp  Optional of    One for returning an empty object instead of retuning null and the other to wrap a non-nullable object  respectively   SO HOW EXACTLY IT HELPS TO AVOID A NULL CHECK   Once you have wrapped a reference object  Optional provides many useful methods to invoke methods on a wrapped reference without NPE   Optional ref   homeServices getRefrigertorControl    ref ifPresent HomeServices  switchItOn     Optional ifPresent invokes the given Consumer with a reference if it is a non-null value  Otherwise  it does nothing    FunctionalInterface public interface Consumer lt T gt    Represents an operation that accepts a single input argument and returns no result  Unlike most other functional interfaces  Consumer is expected to operate via side-effects  It is so clean and easy to understand  In the above code example  HomeService switchOn Service  gets invoked if the Optional holding reference is non-null   We use the ternary operator very often for checking null condition and return an alternative value or default value  Optional provides another way to handle the same condition without checking null  Optional orElse defaultObj  returns defaultObj if the Optional has a null value  Let s use this in our sample code   public static Optional lt HomeServices gt  get         service   Optional of service orElse new HomeServices          return service      Now HomeServices get   does same thing  but in a better way  It checks whether the service is already initialized of not  If it is then return the same or create a new New service  Optional lt T  orElse T  helps to return a default value   Finally  here is our NPE as well as null check-free code   import java util Optional  public class HomeServices       private static final int NOW   0      private static Optional lt HomeServices gt  service   public static Optional lt HomeServices gt  get         service   Optional of service orElse new HomeServices          return service     public Optional lt Service gt  getRefrigertorControl         Service s   new  RefrigeratorService                  return Optional ofNullable s      public static void main String   args           Get Home Services handle        Optional lt HomeServices gt  homeServices   HomeServices get        if homeServices    null            Optional lt Service gt  refrigertorControl   homeServices get   getRefrigertorControl            refrigertorControl ifPresent HomeServices  switchItOn            public static void switchItOn Service s                            The complete post is NPE as well as Null check-free code     Really

User · Answer

For utility classes  you can check that parameters are not null   In all other cases  you may not have to  Use encapsulation as much as possible  thus reducing the places you feel tempted to check for null

User · Answer

Only for this situation -  Not checking if a variable is null before invoking an equals method  a string compare example below    if   foo equals  bar                   will result in a NullPointerException if foo doesn t exist   You can avoid that if you compare your Strings like this   if    bar  equals foo

User · Answer

Since Java 7 the class java util Objects exists   But since Java 8  you can use Objects isNull var  and Objects nonNull var  methods of Objects class to do the null pointer check   For example   String var1   null  Date var2   null  Long var3   null   if Objects isNull var1   amp  amp  Objects isNull var2   amp  amp  Objects isNull var3       System out println  All Null    else if  Objects nonNull var1   amp  amp  Objects nonNull var2   amp  amp  Objects nonNull var3       System out println  All Not Null

User · Answer

Depending on what kind of objects you are checking you may be able to use some of the classes in the apache commons such as  apache commons lang and apache commons collections  Example    String foo      if  StringUtils isBlank  foo             do something     or  depending on what you need to check    String foo      if  StringUtils isEmpty  foo             do something     The StringUtils class is only one of many  there are quite a few good classes in the commons that do null safe manipulation   Here follows an example of how you can use null vallidation in JAVA when you include apache library commons-lang-2 4 jar   public DOCUMENT read String xml  ValidationEventHandler validationEventHandler        Validate notNull validationEventHandler  ValidationHandler not Injected        return read new StringReader xml   true  validationEventHandler       And if you are using Spring  Spring also has the same functionality in its package  see library spring-2 4 6 jar    Example on how to use this static classf from spring org springframework util Assert   Assert notNull validationEventHandler  ValidationHandler not Injected

User · Answer

First of all  we can t really remove all null conditions  We can reduce them using  NotNull and  Nullable annotations  as mentioned already   But this needs to be backed by some framework  This is where OVal can help   The basic idea is object parameters constructor should always satisfy preconditions  You can have a whole lot of preconditions such as Nullable  NotNull and OVal would take care that an object should be in a consistent state when invoked   I guess OVal internally uses AspectJ to validate the preconditions    Guarded public class BusinessObject     public BusinessObject  NotNull String name          this name   name                 For example      Throws a ConstraintsViolatedException because parameter name is null BusinessObject bo   new BusinessObject null

User · Answer

Never initialise variables to null  If  1  is not possible  initialise all collections and arrays to empty collections arrays    Doing this in your own code and you can avoid    null checks   Most of the time null checks seem to guard loops over collections or arrays  so just initialise them empty  you won t need any null checks      Bad ArrayList lt String gt  lemmings  String   names   void checkLemmings         if  lemmings    null  for lemming  lemmings               do something               Good ArrayList lt String gt  lemmings   new ArrayList lt String gt     String   names        void checkLemmings         for lemming  lemmings               do something           There is a tiny overhead in this  but it s worth it for cleaner code and less NullPointerExceptions

User · Answer

I like articles from Nat Pryce  Here are the links    Avoiding Nulls with Polymorphic Dispatch Avoiding Nulls with  Tell  Don t Ask  Style   In the articles there is also a link to a Git repository for a Java Maybe Type which I find interesting  but I don t think it alone could decrease the checking code bloat  After doing some research on the Internet  I think    null code bloat could be decreased mainly by careful design

User · Answer

One Option you have   Use checker framework s  RequiresNonNull on methods  for ex you get this if you call a method annotated as such  with a null argument  It will fail during compile  even before your code runs  since at runtime it will be NullPointerException   RequiresNonNull value       1     static void check  Boolean x        if  x  System out println  true        else System out println  false       public static void main String   args          check null         gets    ERROR  found     null  ERROR  required   Initialized  NonNull Boolean  ERROR  - gt   Help 1    There are other methods like Use Java 8 s Optional  Guava Annotations  Null Object pattern etc  Does not matter as long as you obtain your goal of avoiding   null

User · Answer

This to me sounds like a reasonably common problem that junior to intermediate developers tend to face at some point  they either don t know or don t trust the contracts they are participating in and defensively overcheck for nulls   Additionally  when writing their own code  they tend to rely on returning nulls to indicate something thus requiring the caller to check for nulls   To put this another way  there are two instances where null checking comes up    Where null is a valid response in terms of the contract  and Where it isn t a valid response     2  is easy   Either use assert statements  assertions  or allow failure  for example   NullPointerException    Assertions are a highly-underused Java feature that was added in 1 4   The syntax is   assert  lt condition gt    or  assert  lt condition gt     lt object gt    where  lt condition gt  is a boolean expression and  lt object gt  is an object whose toString   method s output will be included in the error   An assert statement throws an Error  AssertionError  if the condition is not true   By default  Java ignores assertions   You can enable assertions by passing the option -ea to the JVM   You can enable and disable assertions for individual classes and packages   This means that you can validate code with the assertions while developing and testing  and disable them in a production environment  although my testing has shown next to no performance impact from assertions   Not using assertions in this case is OK because the code will just fail  which is what will happen if you use assertions   The only difference is that with assertions it might happen sooner  in a more-meaningful way and possibly with extra information  which may help you to figure out why it happened if you weren t expecting it    1  is a little harder   If you have no control over the code you re calling then you re stuck   If null is a valid response  you have to check for it   If it s code that you do control  however  and this is often the case   then it s a different story   Avoid using nulls as a response   With methods that return collections  it s easy  return empty collections  or arrays  instead of nulls pretty much all the time   With non-collections it might be harder   Consider this as an example  if you have these interfaces   public interface Action     void doSomething       public interface Parser     Action findAction String userInput       where Parser takes raw user input and finds something to do  perhaps if you re implementing a command line interface for something   Now you might make the contract that it returns null if there s no appropriate action   That leads the null checking you re talking about   An alternative solution is to never return null and instead use the Null Object pattern   public class MyParser implements Parser     private static Action DO NOTHING   new Action         public void doSomething        do nothing              public Action findAction String userInput                   if      we can t find any actions              return DO NOTHING                Compare   Parser parser   ParserFactory getParser    if  parser    null         now what       this would be an example of where null isn t  or shouldn t be  a valid response   Action action   parser findAction someInput   if  action    null         do nothing   else     action doSomething        to  ParserFactory getParser   findAction someInput  doSomething      which is a much better design because it leads to more concise code   That said  perhaps it is entirely appropriate for the findAction   method to throw an Exception with a meaningful error message -- especially in this case where you are relying on user input   It would be much better for the findAction method to throw an Exception than for the calling method to blow up with a simple NullPointerException with no explanation   try       ParserFactory getParser   findAction someInput  doSomething      catch ActionNotFoundException anfe        userConsole err anfe getMessage         Or if you think the try catch mechanism is too ugly  rather than Do Nothing your default action should provide feedback to the user   public Action findAction final String userInput           Code to return requested Action if found        return new Action             public void doSomething                 userConsole err  Action not found      userInput

User · Answer

You can couple your Class with Unit Testing using a framework like JUnit  This way your code will be clean  no useless checkings  and you will be sure your instances wont be null   This is one good reason  of many  to use Unit Testing

User · Answer

Functional approach may help to wrap the repetitive null checks and execute anonymous code like the below sample       BiConsumer lt Object  Consumer lt Object gt  gt  consumeIfPresent     s f  - gt           if s  null                f accept s                         consumeIfPresent accept null   s - gt  System out println s         consumeIfPresent accept  test    s - gt  System out println s         BiFunction lt Object  Function lt Object Object gt  Object gt  executeIfPresent     a b  - gt           if a  null                return b apply a                     return null             executeIfPresent apply null   s - gt   System out println s  return s          executeIfPresent apply  test    s - gt   System out println s  return s

User · Answer

The best way to avoid Null Checks in Java  is to properly handle and use exceptions  Null Checks in my experience have become more common and required as you move closer to the front-end  because it s closer to the user who may supply invalid information through the UI  such as  no value  being submitted for a field   One may argue that you should be able to control what the UI is doing  lest you forget most UI is done through a third party library of some kind  which for example  may return either NULL or an Empty String for a blank text box  depending on the situation or the library  You can combine the two like this  try     myvar   get user supplied value       if   myvar    myvar length      0    alert the user somehow    return        process user input myvar     catch  Exception ex      handle exception ex      Another approach people take is to say  if  myvar  amp  amp  myvar length    gt  0         You could also throw an exception  which is what I prefer  if   myvar    myvar length      0     throw new Exception  quot You must supply a name  quot        But that s up to you

User · Answer

Sometimes  you have methods that operate on its parameters that define a symmetric operation   a f b    lt - gt  b f a     If you know b can never be null  you can just swap it  It is most useful for equals  Instead of foo equals  bar    better do  bar  equals foo

User · Answer

OK  I now this has been technically answered a million times but I have to say this because this is an un-ending discussion with Java programmers   Sorry but I disagree will almost all of above  The reason we have to be testing for null in Java is because must Java programmers don   t know how to handle memory    I say this because I have a long experience programming in C   and we don   t do this  In other words  you don   t need to  And note that  in Java  if you hit a dangling pointer you get a normal exception  in C   this exception normally is not caught and terminates the program   Don   t want to do this  Then follow some simple rules ala C C     Don   t instantiate things so easily  think that every  new  can get you in lots of trouble and FOLLOW these simple rules   A class shall access memory in only 3 ways -    It can  HAVE  class members  and they will follow these rules    ALL  HAS  members are created  new  in the constructor  You will close  de allocate in destructor or equivalent close   function in Java for that same class and in NO other     This means that you need to have in mind  just like Java does  who is the owner or parent of each resource and respect that ownership   An object is only deleted by the class who created it  Also -    Some members will be  USED  but not own or  HAVE   This are  OWN  in another class and passed as arguments to the constructor  Since these are owned by another class  we will NEVER delete or close this  only the parent can  A method in a class can also  instantiate local objects for internal use which will NEVER pass out side of the class  or they should have been normal  has  objects    Finally for all this to work  you need to have a disciplined design with classes in hierarchy form and making no cycles   Under this design  AND following the above rules  there is no way that a child class in a hierarchy design will ever access a pointer which was destroyed  because that means that a parent was destroyed before a child  which the hierarchical acyclic design will not allow it   Finally  also remember when starting your system you should build from top to bottom of the hierarchy and destroy bottom to top  You will never have a null pointer anywhere  or someone is violating the rules

User · Answer

Depending on what kind of objects you are checking you may be able to use some of the classes in the apache commons such as  apache commons lang and apache commons collections  Example    String foo      if  StringUtils isBlank  foo             do something     or  depending on what you need to check    String foo      if  StringUtils isEmpty  foo             do something     The StringUtils class is only one of many  there are quite a few good classes in the commons that do null safe manipulation   Here follows an example of how you can use null vallidation in JAVA when you include apache library commons-lang-2 4 jar   public DOCUMENT read String xml  ValidationEventHandler validationEventHandler        Validate notNull validationEventHandler  ValidationHandler not Injected        return read new StringReader xml   true  validationEventHandler       And if you are using Spring  Spring also has the same functionality in its package  see library spring-2 4 6 jar    Example on how to use this static classf from spring org springframework util Assert   Assert notNull validationEventHandler  ValidationHandler not Injected

User · Answer

Depending on what kind of objects you are checking you may be able to use some of the classes in the apache commons such as  apache commons lang and apache commons collections  Example    String foo      if  StringUtils isBlank  foo             do something     or  depending on what you need to check    String foo      if  StringUtils isEmpty  foo             do something     The StringUtils class is only one of many  there are quite a few good classes in the commons that do null safe manipulation   Here follows an example of how you can use null vallidation in JAVA when you include apache library commons-lang-2 4 jar   public DOCUMENT read String xml  ValidationEventHandler validationEventHandler        Validate notNull validationEventHandler  ValidationHandler not Injected        return read new StringReader xml   true  validationEventHandler       And if you are using Spring  Spring also has the same functionality in its package  see library spring-2 4 6 jar    Example on how to use this static classf from spring org springframework util Assert   Assert notNull validationEventHandler  ValidationHandler not Injected

User · Answer

Only for this situation -  Not checking if a variable is null before invoking an equals method  a string compare example below    if   foo equals  bar                   will result in a NullPointerException if foo doesn t exist   You can avoid that if you compare your Strings like this   if    bar  equals foo

User · Answer

If undefined values are not permitted   You might configure your IDE to warn you about potential null dereferencing  E g  in Eclipse  see Preferences   Java   Compiler   Errors Warnings Null analysis   If undefined values are permitted   If you want to define a new API where undefined values make sense  use the Option Pattern  may be familiar from functional languages   It has the following advantages    It is stated explicitly in the API whether an input or output exists or not  The compiler forces you to handle the  undefined  case  Option is a monad  so there is no need for verbose null checking  just use map foreach getOrElse or a similar combinator to safely use the value  example     Java 8 has a built-in Optional class  recommended   for earlier versions  there are library alternatives  for example Guava s Optional or FunctionalJava s Option  But like many functional-style patterns  using Option in Java  even 8  results in quite some boilerplate  which you can reduce using a less verbose JVM language  e g  Scala or Xtend   If you have to deal with an API which might return nulls  you can t do much in Java  Xtend and Groovy have the Elvis operator    and the null-safe dereference operator     but note that this returns null in case of a null reference  so it just  defers  the proper handling of null

User · Answer

You can couple your Class with Unit Testing using a framework like JUnit  This way your code will be clean  no useless checkings  and you will be sure your instances wont be null   This is one good reason  of many  to use Unit Testing

User · Answer

Here is my approach     class MyObjectHandler   public static final int EXCEPTION    -3   public static final int INACCESSIBLE    -2    public static int doSomething  MyObject obj  MyObjectParameter    input        int returnValue  0       try               if  obj    null                        returnValue   obj doSomething input                     else                       returnValue   MyObjectHandler INACCESSIBLE                      catch  Exception e                e printStack            returnValue   MyObjectHandler EXCEPTION            finally               return returnValue                   Then your code will be just like   import xx xx xx MyObjectHandler  import xx xx xx MyObjectParameter   class Test        public static void main                   MyObject obj   null           MyObjectHandler doSomething obj  null

User · Answer

Wow  I almost hate to add another answer when we have 57 different ways to recommend the NullObject pattern  but I think that some people interested in this question may like to know that there is a proposal on the table for Java 7 to add  null-safe handling  mdash a streamlined syntax for if-not-equal-null logic   The example given by Alex Miller looks like this   public String getPostcode Person person        return person  getAddress    getPostcode            The    means only de-reference the left identifier if it is not null  otherwise evaluate the remainder of the expression as null  Some people  like Java Posse member Dick Wall and the voters at Devoxx really love this proposal  but there is opposition too  on the grounds that it will actually encourage more use of null as a sentinel value     Update  An official proposal for a null-safe operator in Java 7 has been submitted under Project Coin  The syntax is a little different than the example above  but it s the same notion     Update  The null-safe operator proposal didn t make it into Project Coin  So  you won t be seeing this syntax in Java 7

User · Answer

We have been using Apache libraries  Apache Commons  for this issue   ObjectUtils equals object  null    or  CollectionUtils isEmpty myCollection     or   StringUtils isEmpty  string      I like the previous answer before  as a practice  of providing initial default values or empty sets for collections to minimize the need   These can be simple uses that keep you from having NullPointerException or using an empty collection   This doesnt answer the question for what to do with the null object  but these provide some checks for basic validations of the object or collection    Hope this helps

User · Answer

Null object pattern can be used as a solution for this problem  For that  the class of the someObject should be modified    public abstract class SomeObject      public abstract boolean isNil       public class NullObject extends SomeObject       Override    public boolean isNil           return true         public class RealObject extends SomeObject       Override    public boolean isNil           return false           Now istead of checking    if  someobject    null        someobject doCalc        We can use   if   someObject isNil         someobject doCalc        Reference   https   www tutorialspoint com design pattern null object pattern htm

User · Answer

Only for this situation -  Not checking if a variable is null before invoking an equals method  a string compare example below    if   foo equals  bar                   will result in a NullPointerException if foo doesn t exist   You can avoid that if you compare your Strings like this   if    bar  equals foo

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With Java 8 comes the new java util Optional class that arguably solves some of the problem  One can at least say that it improves the readability of the code  and in the case of public APIs make the API s contract clearer to the client developer   They work like that   An optional object for a given type  Fruit  is created as the return type of a method  It can be empty or contain a Fruit object   public static Optional lt Fruit gt  find String name  List lt Fruit gt  fruits       for  Fruit fruit   fruits          if  fruit getName   equals name              return Optional of fruit                   return Optional empty        Now look at this code where we search a list of Fruit  fruits  for a given Fruit instance   Optional lt Fruit gt  found   find  lemon   fruits   if  found isPresent         Fruit fruit   found get       String name   fruit getName        You can use the map   operator to perform a computation on--or extract a value from--an optional object   orElse   lets you provide a fallback for missing values   String nameOrNull   find  lemon   fruits       map f - gt  f getName         orElse  empty-name      Of course  the check for null empty value is still necessary  but at least the developer is conscious that the value might be empty and the risk of forgetting to check is limited   In an API built from scratch using Optional whenever a return value might be empty  and returning a plain object only when it cannot be null  convention   the client code might abandon null checks on simple object return values     Of course Optional could also be used as a method argument  perhaps a better way to indicate optional arguments than 5 or 10 overloading methods in some cases   Optional offers other convenient methods  such as orElse that allow the use of a default value  and ifPresent that works with lambda expressions   I invite you to read this article  my main source for writing this answer  in which the NullPointerException  and in general null pointer  problematic as well as the  partial  solution brought by Optional are well explained  Java Optional Objects

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With Java 8 comes the new java util Optional class that arguably solves some of the problem  One can at least say that it improves the readability of the code  and in the case of public APIs make the API s contract clearer to the client developer   They work like that   An optional object for a given type  Fruit  is created as the return type of a method  It can be empty or contain a Fruit object   public static Optional lt Fruit gt  find String name  List lt Fruit gt  fruits       for  Fruit fruit   fruits          if  fruit getName   equals name              return Optional of fruit                   return Optional empty        Now look at this code where we search a list of Fruit  fruits  for a given Fruit instance   Optional lt Fruit gt  found   find  lemon   fruits   if  found isPresent         Fruit fruit   found get       String name   fruit getName        You can use the map   operator to perform a computation on--or extract a value from--an optional object   orElse   lets you provide a fallback for missing values   String nameOrNull   find  lemon   fruits       map f - gt  f getName         orElse  empty-name      Of course  the check for null empty value is still necessary  but at least the developer is conscious that the value might be empty and the risk of forgetting to check is limited   In an API built from scratch using Optional whenever a return value might be empty  and returning a plain object only when it cannot be null  convention   the client code might abandon null checks on simple object return values     Of course Optional could also be used as a method argument  perhaps a better way to indicate optional arguments than 5 or 10 overloading methods in some cases   Optional offers other convenient methods  such as orElse that allow the use of a default value  and ifPresent that works with lambda expressions   I invite you to read this article  my main source for writing this answer  in which the NullPointerException  and in general null pointer  problematic as well as the  partial  solution brought by Optional are well explained  Java Optional Objects

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Java 8 has introduced a new class Optional in java util package   Advantages of Java 8 Optional   1   Null checks are not required  2   No more NullPointerException at run-time  3   We can develop clean and neat APIs     Optional - A container object which may or may not contain a non-null value  If a value is present  isPresent   will return true and get   will return the value   For more details find here oracle docs  - https   docs oracle com javase 8 docs api java util Optional html

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There has a good way to check the null value from JDK  It is Optional java that has a sea of methods to resolve these problems  Such as follow     Returns an   code Optional  describing the specified value  if non-null   otherwise returns an empty   code Optional     param  the class of the value  param value the possibly-null value to describe  return an   code Optional  with a present value if the specified value is non-null  otherwise an empty   code Optional      public static  lt T gt  Optional lt T gt  ofNullable T value        return value    null   empty     of value             Return   code true  if there is a value present  otherwise   code false       return   code true  if there is a value present  otherwise   code false     public boolean isPresent     return value    null          If a value is present  invoke the specified consumer with the value  otherwise do nothing    param consumer block to be executed if a value is present  throws NullPointerException if value is present and   code consumer  is null    public void ifPresent Consumer lt   super T gt  consumer    if  value    null  consumer accept value         It is really  really useful to help javer

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This to me sounds like a reasonably common problem that junior to intermediate developers tend to face at some point  they either don t know or don t trust the contracts they are participating in and defensively overcheck for nulls   Additionally  when writing their own code  they tend to rely on returning nulls to indicate something thus requiring the caller to check for nulls   To put this another way  there are two instances where null checking comes up    Where null is a valid response in terms of the contract  and Where it isn t a valid response     2  is easy   Either use assert statements  assertions  or allow failure  for example   NullPointerException    Assertions are a highly-underused Java feature that was added in 1 4   The syntax is   assert  lt condition gt    or  assert  lt condition gt     lt object gt    where  lt condition gt  is a boolean expression and  lt object gt  is an object whose toString   method s output will be included in the error   An assert statement throws an Error  AssertionError  if the condition is not true   By default  Java ignores assertions   You can enable assertions by passing the option -ea to the JVM   You can enable and disable assertions for individual classes and packages   This means that you can validate code with the assertions while developing and testing  and disable them in a production environment  although my testing has shown next to no performance impact from assertions   Not using assertions in this case is OK because the code will just fail  which is what will happen if you use assertions   The only difference is that with assertions it might happen sooner  in a more-meaningful way and possibly with extra information  which may help you to figure out why it happened if you weren t expecting it    1  is a little harder   If you have no control over the code you re calling then you re stuck   If null is a valid response  you have to check for it   If it s code that you do control  however  and this is often the case   then it s a different story   Avoid using nulls as a response   With methods that return collections  it s easy  return empty collections  or arrays  instead of nulls pretty much all the time   With non-collections it might be harder   Consider this as an example  if you have these interfaces   public interface Action     void doSomething       public interface Parser     Action findAction String userInput       where Parser takes raw user input and finds something to do  perhaps if you re implementing a command line interface for something   Now you might make the contract that it returns null if there s no appropriate action   That leads the null checking you re talking about   An alternative solution is to never return null and instead use the Null Object pattern   public class MyParser implements Parser     private static Action DO NOTHING   new Action         public void doSomething        do nothing              public Action findAction String userInput                   if      we can t find any actions              return DO NOTHING                Compare   Parser parser   ParserFactory getParser    if  parser    null         now what       this would be an example of where null isn t  or shouldn t be  a valid response   Action action   parser findAction someInput   if  action    null         do nothing   else     action doSomething        to  ParserFactory getParser   findAction someInput  doSomething      which is a much better design because it leads to more concise code   That said  perhaps it is entirely appropriate for the findAction   method to throw an Exception with a meaningful error message -- especially in this case where you are relying on user input   It would be much better for the findAction method to throw an Exception than for the calling method to blow up with a simple NullPointerException with no explanation   try       ParserFactory getParser   findAction someInput  doSomething      catch ActionNotFoundException anfe        userConsole err anfe getMessage         Or if you think the try catch mechanism is too ugly  rather than Do Nothing your default action should provide feedback to the user   public Action findAction final String userInput           Code to return requested Action if found        return new Action             public void doSomething                 userConsole err  Action not found      userInput

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If you are using java8 or later go for the isNull yourObject  from java util Objects   Example -  String myObject   null   Objects isNull myObject     will return true   Usage  The below code returns a non null value  if the name is not null then that value will be returned else the default value will be returned    final String name    Jobin   String nonNullValue   Optional ofNullable name  filter Objects  nonNull  orElse  DefaultName

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May I answer it more generally   We usually face this issue when the methods get the parameters in the way we not expected  bad method call is programmer s fault   For example  you expect to get an object  instead you get a null  You expect to get an String with at least one character  instead you get an empty String      So there is no difference between   if object    null        you called my method badly       or  if str length      0        you called my method badly again      They both want to make sure that we received valid parameters  before we do any other functions   As mentioned in some other answers  to avoid above problems you can follow the Design by contract pattern  Please see http   en wikipedia org wiki Design by contract    To implement this pattern in java  you can use core java annotations like javax annotation NotNull or use more sophisticated libraries like Hibernate Validator   Just a sample   getCustomerAccounts  NotEmpty String customerId  Size min   1  String accountType    Now you can safely develop the core function of your method without needing to check input parameters  they guard your methods from unexpected parameters   You can go a step further and make sure that only valid pojos could be created in your application   sample from hibernate validator site   public class Car        NotNull    private String manufacturer       NotNull     Size min   2  max   14     private String licensePlate       Min 2     private int seatCount

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With Java 8  you could pass a supplier to a helper method like below   if CommonUtil resolve   - gt  a b   c    isPresent           Above replaces boiler plate code like below   if a  null  amp  amp  a b    null  amp  amp  a b   c    null           CommonUtil java   public static  lt T gt  Optional lt T gt  resolve Supplier lt T gt  resolver            try               T result   resolver get                return Optional ofNullable result             catch  NullPointerException var2                return Optional empty

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I ve tried the NullObjectPattern but for me is not always the best way to go  There are sometimes when a  no action  is not appropiate   NullPointerException is a Runtime exception that means it s developers fault and with enough experience it tells you exactly where is the error   Now to the answer   Try to make all your attributes and its accessors as private as possible or avoid to  expose them to the clients at all  You can have the argument values in the constructor of course  but by reducing the scope you don t let the client class pass an invalid value  If you need to modify the values  you can always create a new object   You check the values in the constructor only once and in the rest of the methods you can be almost sure that the values are not null   Of course  experience is the better way to understand and apply this suggestion   Byte

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One Option you have   Use checker framework s  RequiresNonNull on methods  for ex you get this if you call a method annotated as such  with a null argument  It will fail during compile  even before your code runs  since at runtime it will be NullPointerException   RequiresNonNull value       1     static void check  Boolean x        if  x  System out println  true        else System out println  false       public static void main String   args          check null         gets    ERROR  found     null  ERROR  required   Initialized  NonNull Boolean  ERROR  - gt   Help 1    There are other methods like Use Java 8 s Optional  Guava Annotations  Null Object pattern etc  Does not matter as long as you obtain your goal of avoiding   null

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I prefer this  public void simpleFunc SomeObject someObject       someObject   someObject    null   someObject   new SomeObject null       someObject doSomething        Of course in my example SomeObject handles gracefully a null parameter  For example logging such event and doing nothing more

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Guava  a very useful core library by Google  has a nice and useful API to avoid nulls  I find UsingAndAvoidingNullExplained very helpful   As explained in the wiki      Optional lt T gt  is a way of replacing a nullable T reference with a   non-null value  An Optional may either contain a non-null T reference    in which case we say the reference is  present    or it may contain   nothing  in which case we say the reference is  absent    It is never   said to  contain null     Usage   Optional lt Integer gt  possible   Optional of 5   possible isPresent       returns true possible get       returns 5

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It is possible to define util methods which handles nested null-checks in an almost pretty way with Java 8 lambdas   void example         Entry entry   new Entry           This is the same as H-MANs solution      Person person   getNullsafe entry  e - gt  e getPerson                Get object in several steps     String givenName   getNullsafe entry  e - gt  e getPerson    p - gt  p getName    n - gt  n getGivenName            Call void methods     doNullsafe entry  e - gt  e getPerson    p - gt  p getName    n - gt  n nameIt                    Return result of call to f1 with o1 if it is non-null  otherwise return null     public static  lt R  T1 gt  R getNullsafe T1 o1  Function lt T1  R gt  f1        if  o1    null  return f1 apply o1       return null      public static  lt R  T0  T1 gt  R getNullsafe T0 o0  Function lt T0  T1 gt  f1  Function lt T1  R gt  f2        return getNullsafe getNullsafe o0  f1   f2      public static  lt R  T0  T1  T2 gt  R getNullsafe T0 o0  Function lt T0  T1 gt  f1  Function lt T1  T2 gt  f2  Function lt T2  R gt  f3        return getNullsafe getNullsafe o0  f1  f2   f3           Call consumer f1 with o1 if it is non-null  otherwise do nothing     public static  lt T1 gt  void doNullsafe T1 o1  Consumer lt T1 gt  f1        if  o1    null  f1 accept o1      public static  lt T0  T1 gt  void doNullsafe T0 o0  Function lt T0  T1 gt  f1  Consumer lt T1 gt  f2        doNullsafe getNullsafe o0  f1   f2      public static  lt T0  T1  T2 gt  void doNullsafe T0 o0  Function lt T0  T1 gt  f1  Function lt T1  T2 gt  f2  Consumer lt T2 gt  f3        doNullsafe getNullsafe o0  f1  f2   f3       class Entry       Person getPerson     return null       class Person       Name getName     return null       class Name       void nameIt          String getGivenName     return null         This answer was first posted here

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Since Java 7 the class java util Objects exists   But since Java 8  you can use Objects isNull var  and Objects nonNull var  methods of Objects class to do the null pointer check   For example   String var1   null  Date var2   null  Long var3   null   if Objects isNull var1   amp  amp  Objects isNull var2   amp  amp  Objects isNull var3       System out println  All Null    else if  Objects nonNull var1   amp  amp  Objects nonNull var2   amp  amp  Objects nonNull var3       System out println  All Not Null

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Asking that question points out that you may be interested in error handling strategies   How and where to handle errors is a pervasive architectural question   There are several ways to do this  My favorite  allow the Exceptions to ripple through - catch them at the  main loop  or in some other function with the appropriate responsibilities   Checking for error conditions and handling them appropriately can be seen as a specialized responsibility  Sure do have a look at Aspect Oriented Programming  too - they have neat ways to insert if  o    null   handleNull   into your bytecode

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If null-values are not allowed

If your method is called externally, start with something like this:

public void method(Object object) {
  if (object == null) {
    throw new IllegalArgumentException("...");
  }

Then, in the rest of that method, you'll know that object is not null.

If it is an internal method (not part of an API), just document that it cannot be null, and that's it.

Example:

public String getFirst3Chars(String text) {
  return text.subString(0, 3);
}

However, if your method just passes the value on, and the next method passes it on etc. it could get problematic. In that case you may want to check the argument as above.

If null is allowed

This really depends. If find that I often do something like this:

if (object == null) {
  // something
} else {
  // something else
}

So I branch, and do two completely different things. There is no ugly code snippet, because I really need to do two different things depending on the data. For example, should I work on the input, or should I calculate a good default value?

It's actually rare for me to use the idiom "if (object != null && ...".

It may be easier to give you examples, if you show examples of where you typically use the idiom.

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I highly disregard answers that suggest using the null objects in every situation  This pattern may break the contract and bury problems deeper and deeper instead of solving them  not mentioning that used inappropriately will create another pile of boilerplate code that will require future maintenance   In reality if something returned from a method can be null and the calling code has to make decision upon that  there should an earlier call that ensures the state    Also keep in mind  that null object pattern will be memory hungry if used without care  For this - the instance of a NullObject should be shared between owners  and not be an unigue instance for each of these   Also I would not recommend using this pattern where the type is meant to be a primitive type representation - like mathematical entities  that are not scalars  vectors  matrices  complex numbers and POD Plain Old Data  objects  which are meant to hold state in form of Java built-in types  In the latter case you would end up calling getter methods with arbitrary results  For example what should a NullPerson getName   method return    It s worth considering such cases in order to avoid absurd results

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You can also use the Checker Framework  with JDK 7 and beyond  to statically check for null values  This might solve a lot of problems  but requires running an extra tool that currently only works with OpenJDK AFAIK  https   checkerframework org

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Depending on what kind of objects you are checking you may be able to use some of the classes in the apache commons such as  apache commons lang and apache commons collections  Example    String foo      if  StringUtils isBlank  foo             do something     or  depending on what you need to check    String foo      if  StringUtils isEmpty  foo             do something     The StringUtils class is only one of many  there are quite a few good classes in the commons that do null safe manipulation   Here follows an example of how you can use null vallidation in JAVA when you include apache library commons-lang-2 4 jar   public DOCUMENT read String xml  ValidationEventHandler validationEventHandler        Validate notNull validationEventHandler  ValidationHandler not Injected        return read new StringReader xml   true  validationEventHandler       And if you are using Spring  Spring also has the same functionality in its package  see library spring-2 4 6 jar    Example on how to use this static classf from spring org springframework util Assert   Assert notNull validationEventHandler  ValidationHandler not Injected

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In Java 8 you can use type T for local-variable field method-argument method-return-type if it never assigned null  and do not check for null  or type Optional lt T gt  if it can be null  Then use method map for processing T - gt  and method flatMap for processing T - gt  Optional lt R gt    class SomeService        Inject     private CompanyDao companyDao          return Optional lt String gt      public Optional lt String gt  selectCeoCityByCompanyId0 int companyId            return companyDao selectById companyId                   map Company  getCeo                   flatMap Person  getHomeAddress                   flatMap Address  getCity                 return String   default value     public String selectCeoCityByCompanyId1 int companyId            return companyDao selectById companyId                   map Company  getCeo                   flatMap Person  getHomeAddress                   flatMap Address  getCity                   orElse  UNKNOWN                  return String   exception     public String selectCeoCityByCompanyId2 int companyId  throws NoSuchElementException           return companyDao selectById companyId                   map Company  getCeo                   flatMap Person  getHomeAddress                   flatMap Address  getCity                   orElseThrow NoSuchElementException  new            interface CompanyDao          real situation  no company for such id - gt  use Optional lt Company gt       Optional lt Company gt  selectById int id      class Company          company always has ceo - gt  use Person      Person ceo      public Person getCeo    return ceo      class Person          person always has name - gt  use String     String firstName         person can be without address - gt  use Optional lt Address gt      Optional lt Address gt  homeAddress   Optional empty         public String getFirstName    return firstName          public Optional lt Address gt  getHomeAddress    return homeAddress      class Address           address always contains country - gt  use String     String country          city field is optional - gt  use Optional lt String gt      Optional lt String gt  city   Optional empty         String getCountry    return country           Optional lt String gt  getCity    return city

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I follow below guidelines to avoid null checks    Avoid lazy initialization of member variables as much as possible  Initialize the variables in declaration itself  This will handle NullPointerExceptions   Decide on mutability of member variables early in the cycle  Use language constructs like final keyword effectively   If you know that augments for method won t be changed  declare them as final  Limit the mutation of data as much as possible  Some variables can be created in a constructor and can never be changed  Remove public setter methods unless they are really required   E g  Assume that one class in your application  A java  is maintaining a collection like HashMap   Don t provide public getter method in A java and allow B java to directly add an element in Map  Instead provide an API in A java  which adds an element into collection       Avoid a getMap   put key value     recommended  public void addElement Object key  Object value             Have null checks for both key and value here   single place        map put key value      And finally  use try   catch   finally   blocks at right places effectively

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Null is not a  problem   It is an integral part of a complete modeling tool set  Software aims to model the complexity of the world and null bears its burden  Null indicates  No data  or  Unknown  in Java and the like  So it is appropriate to use nulls for these purposes  I don t prefer the  Null object  pattern  I think it rise the  who will guard the guardians  problem   If you ask me what is the name of my girlfriend I ll tell you that I have no girlfriend  In the Java language I ll return null   An alternative would be to throw meaningful exception to indicate some problem that can t be  or don t want to be  solved right there and delegate it somewhere higher in the stack to retry or report data access error to the user      For an  unknown question  give  unknown answer    Be null-safe where this is correct from business point of view  Checking arguments for null once inside a method before usage relieves multiple callers from checking them before a call   public Photo getPhotoOfThePerson Person person        if  person    null          return null         Grabbing some resources or intensive calculation        using person object anyhow      Previous leads to normal logic flow to get no photo of a non-existent girlfriend from my photo library   getPhotoOfThePerson me getGirlfriend      And it fits with new coming Java API  looking forward   getPhotoByName me getGirlfriend    getName      While it is rather  normal business flow  not to find photo stored into the DB for some person  I used to use pairs like below for some other cases  public static MyEnum parseMyEnum String value      throws IllegalArgumentException public static MyEnum parseMyEnumOrNull String value     And don t loathe to type  lt alt gt     lt shift gt     lt j gt   generate javadoc in Eclipse  and write three additional words for you public API  This will be more than enough for all but those who don t read documentation           return photo or null       or          return photo  never null      This is rather theoretical case and in most cases you should prefer java null safe API  in case it will be released in another 10 years   but NullPointerException is subclass of an Exception  Thus it is a form of Throwable that indicates conditions that a reasonable application might want to catch  javadoc   To use the first most advantage of exceptions and separate error-handling code from  regular  code  according to creators of Java  it is appropriate  as for me  to catch NullPointerException   public Photo getGirlfriendPhoto         try           return appContext getPhotoDataSource   getPhotoByName me getGirlfriend   getName           catch  NullPointerException e            return null            Questions could arise   Q  What if getPhotoDataSource   returns null  A  It is up to business logic  If I fail to find a photo album I ll show you no photos  What if appContext is not initialized  This method s business logic puts up with this  If the same logic should be more strict then throwing an exception it is part of the business logic and explicit check for null should be used  case 3   The new Java Null-safe API fits better here to specify selectively what implies and what does not imply to be initialized to be fail-fast in case of programmer errors   Q  Redundant code could be executed and unnecessary resources could be grabbed  A  It could take place if getPhotoByName   would try to open a database connection  create PreparedStatement and use the person name as an SQL parameter at last  The approach for an unknown question gives an unknown answer  case 1  works here  Before grabbing resources the method should check parameters and return  unknown  result if needed   Q  This approach has a performance penalty due to the try closure opening  A  Software should be easy to understand and modify firstly  Only after this  one could think about performance  and only if needed  and where needed   source   and many others    PS  This approach will be as reasonable to use as the separate error-handling code from  regular  code principle is reasonable to use in some place  Consider the next example   public SomeValue calculateSomeValueUsingSophisticatedLogic Predicate predicate        try           Result1 result1   performSomeCalculation predicate           Result2 result2   performSomeOtherCalculation result1 getSomeProperty             Result3 result3   performThirdCalculation result2 getSomeProperty             Result4 result4   performLastCalculation result3 getSomeProperty             return result4 getSomeProperty          catch  NullPointerException e            return null           public SomeValue calculateSomeValueUsingSophisticatedLogic Predicate predicate        SomeValue result   null      if  predicate    null            Result1 result1   performSomeCalculation predicate           if  result1    null  amp  amp  result1 getSomeProperty      null                Result2 result2   performSomeOtherCalculation result1 getSomeProperty                 if  result2    null  amp  amp  result2 getSomeProperty      null                    Result3 result3   performThirdCalculation result2 getSomeProperty                     if  result3    null  amp  amp  result3 getSomeProperty      null                        Result4 result4   performLastCalculation result3 getSomeProperty                         if  result4    null                            result   result4 getSomeProperty                                                                              return result      PPS  For those fast to downvote  and not so fast to read documentation  I would like to say that I ve never caught a null-pointer exception  NPE  in my life  But this possibility was intentionally designed by the Java creators because NPE is a subclass of Exception  We have a precedent in Java history when ThreadDeath is an Error not because it is actually an application error  but solely because it was not intended to be caught  How much NPE fits to be an Error than ThreadDeath  But it is not  Check for  No data  only if business logic implies it   public void updatePersonPhoneNumber Long personId  String phoneNumber        if  personId    null          return      DataSource dataSource   appContext getStuffDataSource        Person person   dataSource getPersonById personId       if  person    null            person setPhoneNumber phoneNumber           dataSource updatePerson person         else           Person   new Person personId           person setPhoneNumber phoneNumber           dataSource insertPerson person             and  public void updatePersonPhoneNumber Long personId  String phoneNumber        if  personId    null          return      DataSource dataSource   appContext getStuffDataSource        Person person   dataSource getPersonById personId       if  person    null          throw new SomeReasonableUserException  What are you thinking about            person setPhoneNumber phoneNumber       dataSource updatePerson person       If appContext or dataSource is not initialized unhandled runtime NullPointerException will kill current thread and will be processed by Thread defaultUncaughtExceptionHandler  for you to define and use your favorite logger or other notification mechanizm   If not set  ThreadGroup uncaughtException will print stacktrace to system err  One should monitor application error log and open Jira issue for each unhandled exception which in fact is application error  Programmer should fix bug somewhere in initialization stuff

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I m a fan of  fail fast  code  Ask yourself - are you doing something useful in the case where the parameter is null  If you don t have a clear answer for what your code should do in that case    I e  it should never be null in the first place  then ignore it and allow a NullPointerException to be thrown  The calling code will make just as much sense of an NPE as it would an IllegalArgumentException  but it ll be easier for the developer to debug and understand what went wrong if an NPE is thrown rather than your code attempting to execute some other unexpected contingency logic - which ultimately results in the application failing anyway

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Probably the best alternative for Java 8 or newer is to use the Optional class    Optional stringToUse   Optional of  optional is there    stringToUse ifPresent System out  println     This is especially handy for long chains of possible null values  Example   Optional lt Integer gt  i   Optional ofNullable wsObject getFoo         map f - gt  f getBar         map b - gt  b getBaz         map b - gt  b getInt       Example on how to throw exception on null   Optional optionalCarNull   Optional ofNullable someNull   optionalCarNull orElseThrow IllegalStateException  new     Java 7 introduced the Objects requireNonNull method which can be handy when something should be checked for non-nullness  Example   String lowerVal   Objects requireNonNull someVar   input cannot be null or empty   toLowerCase

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We have been using Apache libraries  Apache Commons  for this issue   ObjectUtils equals object  null    or  CollectionUtils isEmpty myCollection     or   StringUtils isEmpty  string      I like the previous answer before  as a practice  of providing initial default values or empty sets for collections to minimize the need   These can be simple uses that keep you from having NullPointerException or using an empty collection   This doesnt answer the question for what to do with the null object  but these provide some checks for basic validations of the object or collection    Hope this helps

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Java 8 has introduced a new class Optional in java util package   Advantages of Java 8 Optional   1   Null checks are not required  2   No more NullPointerException at run-time  3   We can develop clean and neat APIs     Optional - A container object which may or may not contain a non-null value  If a value is present  isPresent   will return true and get   will return the value   For more details find here oracle docs  - https   docs oracle com javase 8 docs api java util Optional html

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With Java 8  you could pass a supplier to a helper method like below   if CommonUtil resolve   - gt  a b   c    isPresent           Above replaces boiler plate code like below   if a  null  amp  amp  a b    null  amp  amp  a b   c    null           CommonUtil java   public static  lt T gt  Optional lt T gt  resolve Supplier lt T gt  resolver            try               T result   resolver get                return Optional ofNullable result             catch  NullPointerException var2                return Optional empty

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I prefer this  public void simpleFunc SomeObject someObject       someObject   someObject    null   someObject   new SomeObject null       someObject doSomething        Of course in my example SomeObject handles gracefully a null parameter  For example logging such event and doing nothing more

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OK  I now this has been technically answered a million times but I have to say this because this is an un-ending discussion with Java programmers   Sorry but I disagree will almost all of above  The reason we have to be testing for null in Java is because must Java programmers don   t know how to handle memory    I say this because I have a long experience programming in C   and we don   t do this  In other words  you don   t need to  And note that  in Java  if you hit a dangling pointer you get a normal exception  in C   this exception normally is not caught and terminates the program   Don   t want to do this  Then follow some simple rules ala C C     Don   t instantiate things so easily  think that every  new  can get you in lots of trouble and FOLLOW these simple rules   A class shall access memory in only 3 ways -    It can  HAVE  class members  and they will follow these rules    ALL  HAS  members are created  new  in the constructor  You will close  de allocate in destructor or equivalent close   function in Java for that same class and in NO other     This means that you need to have in mind  just like Java does  who is the owner or parent of each resource and respect that ownership   An object is only deleted by the class who created it  Also -    Some members will be  USED  but not own or  HAVE   This are  OWN  in another class and passed as arguments to the constructor  Since these are owned by another class  we will NEVER delete or close this  only the parent can  A method in a class can also  instantiate local objects for internal use which will NEVER pass out side of the class  or they should have been normal  has  objects    Finally for all this to work  you need to have a disciplined design with classes in hierarchy form and making no cycles   Under this design  AND following the above rules  there is no way that a child class in a hierarchy design will ever access a pointer which was destroyed  because that means that a parent was destroyed before a child  which the hierarchical acyclic design will not allow it   Finally  also remember when starting your system you should build from top to bottom of the hierarchy and destroy bottom to top  You will never have a null pointer anywhere  or someone is violating the rules

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Rather than Null Object Pattern -- which has its uses -- you might consider situations where the null object is a bug   When the exception is thrown  examine the stack trace and work through the bug

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Another alternative to the    null check is  if you can t get rid of it design-wise    Optional ofNullable someobject  ifPresent someobject - gt  someobject doCalc       or  Optional ofNullable someobject  ifPresent SomeClass  doCalc     With SomeClass being someobject s type   You can t get a return value back from doCalc   though  so only useful for void methods

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Probably the best alternative for Java 8 or newer is to use the Optional class    Optional stringToUse   Optional of  optional is there    stringToUse ifPresent System out  println     This is especially handy for long chains of possible null values  Example   Optional lt Integer gt  i   Optional ofNullable wsObject getFoo         map f - gt  f getBar         map b - gt  b getBaz         map b - gt  b getInt       Example on how to throw exception on null   Optional optionalCarNull   Optional ofNullable someNull   optionalCarNull orElseThrow IllegalStateException  new     Java 7 introduced the Objects requireNonNull method which can be handy when something should be checked for non-nullness  Example   String lowerVal   Objects requireNonNull someVar   input cannot be null or empty   toLowerCase

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public class Null    public static void main String   args        String str1   null      String str2    quot  quot        if isNullOrEmpty str1           System out println  quot First string is null or empty  quot        else         System out println  quot First string is not null or empty  quot         if isNullOrEmpty str2           System out println  quot Second string is null or empty  quot        else         System out println  quot Second string is not null or empty  quot       public static boolean isNullOrEmpty String str        if str    null  amp  amp   str isEmpty            return false      return true       Output str1 is null or empty  str2 is null or empty   In the above program  we ve two strings str1 and str2  str1 contains null value and str2 is an empty string  We ve also created a function isNullOrEmpty   which checks  as the name suggests  whether the string is null or empty  It checks it using a null check using    null and isEmpty   method of string  In plain terms  if a string isn t a null and isEmpty   returns false  it s not either null or empty  Else  it is  However  the above program doesn t return empty if a string contains only whitespace characters  spaces   Technically  isEmpty   sees it contains spaces and returns false  For string with spaces  we use the string method trim   to trim out all the leading and trailing whitespace characters

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If you consider an object should not be null  or it is a bug  use an assert  If your method doesn t accept null params say it in the javadoc and use an assert    You have to check for object    null only if you want to handle the case where the object may be null     There is a proposal to add new annotations in Java7 to help with null   notnull params  http   tech puredanger com java7  jsr308

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All in all to avoid statement if  object    null                 since java 7 you can use Objects methods  Objects isNull object  Objects nonNull object  Objects requireNonNull object  Objects equals object1  object2   since java 8 you can use Optional class  when to use    object ifPresent obj - gt        java 8 object ifPresentOrElse obj - gt          - gt        java 9  rely on method contract  JSR 305  and use Find Bugs  Mark your code with annotations  javax annotation Nullable and  javax annotation Nonnnul  Also Preconditions are available  Preconditions checkNotNull object    In special cases  for example for Strings and Collections  you can use apache-commons  or Google guava  utility methods     public static boolean isEmpty CharSequence cs    apache CollectionUtils public static boolean isEmpty Collection coll    apache StringUtils public static boolean isEmpty Map map    apache MapUtils public static boolean isNullOrEmpty  Nullable String string    Guava Strings   When you need to assign default value when null use apache commons lang   public static Object defaultIfNull Object object  Object defaultValue

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Rather than Null Object Pattern -- which has its uses -- you might consider situations where the null object is a bug   When the exception is thrown  examine the stack trace and work through the bug

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Just don t ever use null  Don t allow it   In my classes  most fields and local variables have non-null default values  and I add contract statements  always-on asserts  everywhere in the code to make sure this is being enforced  since it s more succinct  and more expressive than letting it come up as an NPE and then having to resolve the line number  etc     Once I adopted this practice  I noticed that the problems seemed to fix themselves  You d catch things much earlier in the development process just by accident and realize you had a weak spot    and more importantly   it helps encapsulate different modules  concerns  different modules can  trust  each other  and no more littering the code with if   null else constructs   This is defensive programming and results in much cleaner code in the long run  Always sanitize the data  e g  here by enforcing rigid standards  and the problems go away   class C       private final MyType mustBeSet      public C MyType mything           mustBeSet Contract notNull mything            private String name     lt unknown gt       public void setName String s          name   Contract notNull s            class Contract       public static  lt T gt  T notNull T t    if  t    null    throw new ContractException  argument must be non-null    return t        The contracts are like mini-unit tests which are always running  even in production  and when things fail  you know why  rather than a random NPE you have to somehow figure out

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In addition to using assert you can use the following   if  someobject    null           Handle null here then move on      This is slightly better than   if  someobject    null

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The best way to avoid Null Checks in Java  is to properly handle and use exceptions  Null Checks in my experience have become more common and required as you move closer to the front-end  because it s closer to the user who may supply invalid information through the UI  such as  no value  being submitted for a field   One may argue that you should be able to control what the UI is doing  lest you forget most UI is done through a third party library of some kind  which for example  may return either NULL or an Empty String for a blank text box  depending on the situation or the library  You can combine the two like this  try     myvar   get user supplied value       if   myvar    myvar length      0    alert the user somehow    return        process user input myvar     catch  Exception ex      handle exception ex      Another approach people take is to say  if  myvar  amp  amp  myvar length    gt  0         You could also throw an exception  which is what I prefer  if   myvar    myvar length      0     throw new Exception  quot You must supply a name  quot        But that s up to you

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Null object pattern can be used as a solution for this problem  For that  the class of the someObject should be modified    public abstract class SomeObject      public abstract boolean isNil       public class NullObject extends SomeObject       Override    public boolean isNil           return true         public class RealObject extends SomeObject       Override    public boolean isNil           return false           Now istead of checking    if  someobject    null        someobject doCalc        We can use   if   someObject isNil         someobject doCalc        Reference   https   www tutorialspoint com design pattern null object pattern htm

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Wow  I almost hate to add another answer when we have 57 different ways to recommend the NullObject pattern  but I think that some people interested in this question may like to know that there is a proposal on the table for Java 7 to add  null-safe handling  mdash a streamlined syntax for if-not-equal-null logic   The example given by Alex Miller looks like this   public String getPostcode Person person        return person  getAddress    getPostcode            The    means only de-reference the left identifier if it is not null  otherwise evaluate the remainder of the expression as null  Some people  like Java Posse member Dick Wall and the voters at Devoxx really love this proposal  but there is opposition too  on the grounds that it will actually encourage more use of null as a sentinel value     Update  An official proposal for a null-safe operator in Java 7 has been submitted under Project Coin  The syntax is a little different than the example above  but it s the same notion     Update  The null-safe operator proposal didn t make it into Project Coin  So  you won t be seeing this syntax in Java 7

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Common  problem  in Java indeed   First  my thoughts on this   I consider that it is bad to  eat  something when NULL was passed where NULL isn t a valid value  If you re not exiting the method with some sort of error then it means nothing went wrong in your method which is not true  Then you probably return null in this case  and in the receiving method you again check for null  and it never ends  and you end up with  if    null   etc    So  IMHO  null must be a critical error which prevents further execution  that is  where null is not a valid value    The way I solve this problem is this   First  I follow this convention    All public methods   API always check its arguments for null All private methods do not check for null since they are controlled methods  just let die with nullpointer exception in case it wasn t handled above  The only other methods which do not check for null are utility methods  They are public  but if you call them for some reason  you know what parameters you pass  This is like trying to boil water in the kettle without providing water      And finally  in the code  the first line of the public method goes like this   ValidationUtils getNullValidator   addParam plans   plans   addParam persons   persons   validate      Note that addParam   returns self  so that you can add more parameters to check   Method validate   will throw checked ValidationException if any of the parameters is null  checked or unchecked is more a design taste issue  but my ValidationException is checked    void validate   throws ValidationException    The message will contain the following text if  for example   plans  is null    Illegal argument value null is encountered for parameter  plans    As you can see  the second value in the addParam   method  string  is needed for the user message  because you cannot easily detect passed-in variable name  even with reflection  not subject of this post anyway       And yes  we know that beyond this line we will no longer encounter a null value so we just safely invoke methods on those objects   This way  the code is clean  easy maintainable and readable

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Sometimes  you have methods that operate on its parameters that define a symmetric operation   a f b    lt - gt  b f a     If you know b can never be null  you can just swap it  It is most useful for equals  Instead of foo equals  bar    better do  bar  equals foo

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For utility classes  you can check that parameters are not null   In all other cases  you may not have to  Use encapsulation as much as possible  thus reducing the places you feel tempted to check for null

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I like articles from Nat Pryce  Here are the links    Avoiding Nulls with Polymorphic Dispatch Avoiding Nulls with  Tell  Don t Ask  Style   In the articles there is also a link to a Git repository for a Java Maybe Type which I find interesting  but I don t think it alone could decrease the checking code bloat  After doing some research on the Internet  I think    null code bloat could be decreased mainly by careful design

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Java 8 has introduced a new class Optional in java util package  It is used to represent a value is present or absent  The main advantage of this new construct is that No more too many null checks and NullPointerException  It avoids any runtime NullPointerExceptions and supports us in developing clean and neat Java APIs or Applications  Like Collections and arrays  it is also a Container to hold at most one value  Below are some useful link you can follow https   www mkyong com java8 java-8-optional-in-depth  https   dzone com articles java-8-optional-avoid-null-and

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I ve tried the NullObjectPattern but for me is not always the best way to go  There are sometimes when a  no action  is not appropiate   NullPointerException is a Runtime exception that means it s developers fault and with enough experience it tells you exactly where is the error   Now to the answer   Try to make all your attributes and its accessors as private as possible or avoid to  expose them to the clients at all  You can have the argument values in the constructor of course  but by reducing the scope you don t let the client class pass an invalid value  If you need to modify the values  you can always create a new object   You check the values in the constructor only once and in the rest of the methods you can be almost sure that the values are not null   Of course  experience is the better way to understand and apply this suggestion   Byte

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You can avoid most a lot to avoid NullPointerException by just following most of the others answers to the Question  I just want to add few more ways which have been introduced in  Java 9 to handle this scenario gracefully and also showcase a few of the older ones can also be used and thus reducing your efforts    public static boolean isNull Object obj   Returns true if the provided reference is null otherwise returns false   Since Java 1 8 public static boolean nonNull Object obj   Returns true if the provided reference is non-null otherwise returns false   Since Java 1 8 public static  lt T gt  T requireNonNullElse  T obj  T defaultObj   Returns the first argument if it is non-null and otherwise returns the non-null second argument   Since Java 9 public static  lt T gt  T requireNonNullElseGet  T obj  Supplier lt   extends T gt  supplier   Returns the first argument if it is non-null and otherwise returns the non-null value of supplier get     Since Java 9 public static  lt T gt  T requireNonNull  T obj  Supplier lt String gt  messageSupplier   Checks that the specified object reference is not null and throws a customized NullPointerException otherwise   Since Java 1 8   Further details about the above functions can be found here

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Null is not a  problem   It is an integral part of a complete modeling tool set  Software aims to model the complexity of the world and null bears its burden  Null indicates  No data  or  Unknown  in Java and the like  So it is appropriate to use nulls for these purposes  I don t prefer the  Null object  pattern  I think it rise the  who will guard the guardians  problem   If you ask me what is the name of my girlfriend I ll tell you that I have no girlfriend  In the Java language I ll return null   An alternative would be to throw meaningful exception to indicate some problem that can t be  or don t want to be  solved right there and delegate it somewhere higher in the stack to retry or report data access error to the user      For an  unknown question  give  unknown answer    Be null-safe where this is correct from business point of view  Checking arguments for null once inside a method before usage relieves multiple callers from checking them before a call   public Photo getPhotoOfThePerson Person person        if  person    null          return null         Grabbing some resources or intensive calculation        using person object anyhow      Previous leads to normal logic flow to get no photo of a non-existent girlfriend from my photo library   getPhotoOfThePerson me getGirlfriend      And it fits with new coming Java API  looking forward   getPhotoByName me getGirlfriend    getName      While it is rather  normal business flow  not to find photo stored into the DB for some person  I used to use pairs like below for some other cases  public static MyEnum parseMyEnum String value      throws IllegalArgumentException public static MyEnum parseMyEnumOrNull String value     And don t loathe to type  lt alt gt     lt shift gt     lt j gt   generate javadoc in Eclipse  and write three additional words for you public API  This will be more than enough for all but those who don t read documentation           return photo or null       or          return photo  never null      This is rather theoretical case and in most cases you should prefer java null safe API  in case it will be released in another 10 years   but NullPointerException is subclass of an Exception  Thus it is a form of Throwable that indicates conditions that a reasonable application might want to catch  javadoc   To use the first most advantage of exceptions and separate error-handling code from  regular  code  according to creators of Java  it is appropriate  as for me  to catch NullPointerException   public Photo getGirlfriendPhoto         try           return appContext getPhotoDataSource   getPhotoByName me getGirlfriend   getName           catch  NullPointerException e            return null            Questions could arise   Q  What if getPhotoDataSource   returns null  A  It is up to business logic  If I fail to find a photo album I ll show you no photos  What if appContext is not initialized  This method s business logic puts up with this  If the same logic should be more strict then throwing an exception it is part of the business logic and explicit check for null should be used  case 3   The new Java Null-safe API fits better here to specify selectively what implies and what does not imply to be initialized to be fail-fast in case of programmer errors   Q  Redundant code could be executed and unnecessary resources could be grabbed  A  It could take place if getPhotoByName   would try to open a database connection  create PreparedStatement and use the person name as an SQL parameter at last  The approach for an unknown question gives an unknown answer  case 1  works here  Before grabbing resources the method should check parameters and return  unknown  result if needed   Q  This approach has a performance penalty due to the try closure opening  A  Software should be easy to understand and modify firstly  Only after this  one could think about performance  and only if needed  and where needed   source   and many others    PS  This approach will be as reasonable to use as the separate error-handling code from  regular  code principle is reasonable to use in some place  Consider the next example   public SomeValue calculateSomeValueUsingSophisticatedLogic Predicate predicate        try           Result1 result1   performSomeCalculation predicate           Result2 result2   performSomeOtherCalculation result1 getSomeProperty             Result3 result3   performThirdCalculation result2 getSomeProperty             Result4 result4   performLastCalculation result3 getSomeProperty             return result4 getSomeProperty          catch  NullPointerException e            return null           public SomeValue calculateSomeValueUsingSophisticatedLogic Predicate predicate        SomeValue result   null      if  predicate    null            Result1 result1   performSomeCalculation predicate           if  result1    null  amp  amp  result1 getSomeProperty      null                Result2 result2   performSomeOtherCalculation result1 getSomeProperty                 if  result2    null  amp  amp  result2 getSomeProperty      null                    Result3 result3   performThirdCalculation result2 getSomeProperty                     if  result3    null  amp  amp  result3 getSomeProperty      null                        Result4 result4   performLastCalculation result3 getSomeProperty                         if  result4    null                            result   result4 getSomeProperty                                                                              return result      PPS  For those fast to downvote  and not so fast to read documentation  I would like to say that I ve never caught a null-pointer exception  NPE  in my life  But this possibility was intentionally designed by the Java creators because NPE is a subclass of Exception  We have a precedent in Java history when ThreadDeath is an Error not because it is actually an application error  but solely because it was not intended to be caught  How much NPE fits to be an Error than ThreadDeath  But it is not  Check for  No data  only if business logic implies it   public void updatePersonPhoneNumber Long personId  String phoneNumber        if  personId    null          return      DataSource dataSource   appContext getStuffDataSource        Person person   dataSource getPersonById personId       if  person    null            person setPhoneNumber phoneNumber           dataSource updatePerson person         else           Person   new Person personId           person setPhoneNumber phoneNumber           dataSource insertPerson person             and  public void updatePersonPhoneNumber Long personId  String phoneNumber        if  personId    null          return      DataSource dataSource   appContext getStuffDataSource        Person person   dataSource getPersonById personId       if  person    null          throw new SomeReasonableUserException  What are you thinking about            person setPhoneNumber phoneNumber       dataSource updatePerson person       If appContext or dataSource is not initialized unhandled runtime NullPointerException will kill current thread and will be processed by Thread defaultUncaughtExceptionHandler  for you to define and use your favorite logger or other notification mechanizm   If not set  ThreadGroup uncaughtException will print stacktrace to system err  One should monitor application error log and open Jira issue for each unhandled exception which in fact is application error  Programmer should fix bug somewhere in initialization stuff

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The way to avoid unnecessary null-checks is simple to state   You need to know which variables can be null  and which cannot  and you need to be confident about which category a given variable fall into   But  although it can be stated simply enough  achieving it is harder  The key lies in the confident part  because how can you be sure that a variable can t be null   There are no quick-fix  easy answers to this  but here are some pointers    Clean code  The most important thing for being able to reason about the behaviour of a piece of code is that it is written in a matter that is easy to understand  Name your variables based on what they represent  name your methods after what they do  apply the Single responsibility principle  the S in SOLID  http   en wikipedia org wiki SOLID  object-oriented design   it means that each piece of code should have a single responsibility  and do this and nothing else   Once your code is clean  it is much easier to reason about it  also across multiple tiers layers of code  With messy code  trying to understand what a method does might make you forget why you are reading the method in the first place   Tip  Read  Clean Code  by Robert C  Martin  Avoid returning null values  If a null value would keep your program from functioning correctly  throw an exception instead  make sure to add the appropriate error-handling   Cases where returning a null value might be acceptable is for instance trying to fetch an object from the database  In these cases  write code that handles the null values  and make a note behind your ear that here we have something that might return null  Handle returned null values as close to the caller of the method returning null as possible  don t just blindly pass it back up the call-chain   Never EVER pass explicit null values as parameters  at least not across classes   If you are ever in a position where passing a null-parameter is the only option  creating a new method that does not have this parameter is the way to go   Validate your input  Identify the  entry-points  to your application  They can everything from webservices  REST-services  remote EJB classes  controllers  etc  For each method in these entry-points  ask yourself   Will this method execute correctly if this parameter is null   If the answer is no  add Validate notNull someParam   Can t function when someParam is null      This will throw an IllegalArgumentException if the required parameter is missing  The good thing about this type of validation in the entry-points  is that you can then easily assume in the code being executed from the entry-point  that this variable will never be null  Also  if this fails  being at the entry-point  debugging is made a lot easier than it would if you just got a NullPointerException deep down in your code  since a failure like this can only mean one thing  The client didn t send you all the required information  In most cases you want to validate all input parameters  if you find yourself in a position where you need to allow a lot of null-values  it might be a sign of a badly designed interface  which needs refactoring additions to suite the needs of the clients  When working with Collections  return an empty one rather than null   When working with a database  utilize not null-constraints  In that way  you ll know that a value read from the database cannot be null  and you won t have to check for it  Structure your code and stick with it  Doing this allows you to make assumptions about the behaviour of the code  for instance if all input to your application is validated  then you can assume that these values will never be null   If you are not already doing it  write automated tests of your code  By writing tests  you will reason about your code  and you will also become more confident that it does what it s supposed to  Also  automated tests guards you from blunders during refactoring  by letting you know immediatly that this piece of code is not doing what it used to    You still have to null-check of course  but it can trimmed down to the bare minimum  i e  the situation where know you might be getting a null-value  instead of everywhere just to be sure   When it comes to null-checks  i actually prefer to use the ternary operator  but use with care  when you start nesting them they come really messy    public String nullSafeToString final Object o        return o    null   o toString      null

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Kotlin with null safety is elegant alternative  but it means a larger change

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I ve tried the NullObjectPattern but for me is not always the best way to go  There are sometimes when a  no action  is not appropiate   NullPointerException is a Runtime exception that means it s developers fault and with enough experience it tells you exactly where is the error   Now to the answer   Try to make all your attributes and its accessors as private as possible or avoid to  expose them to the clients at all  You can have the argument values in the constructor of course  but by reducing the scope you don t let the client class pass an invalid value  If you need to modify the values  you can always create a new object   You check the values in the constructor only once and in the rest of the methods you can be almost sure that the values are not null   Of course  experience is the better way to understand and apply this suggestion   Byte

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Asking that question points out that you may be interested in error handling strategies   How and where to handle errors is a pervasive architectural question   There are several ways to do this  My favorite  allow the Exceptions to ripple through - catch them at the  main loop  or in some other function with the appropriate responsibilities   Checking for error conditions and handling them appropriately can be seen as a specialized responsibility  Sure do have a look at Aspect Oriented Programming  too - they have neat ways to insert if  o    null   handleNull   into your bytecode

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Kotlin with null safety is elegant alternative  but it means a larger change

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You can avoid most a lot to avoid NullPointerException by just following most of the others answers to the Question  I just want to add few more ways which have been introduced in  Java 9 to handle this scenario gracefully and also showcase a few of the older ones can also be used and thus reducing your efforts    public static boolean isNull Object obj   Returns true if the provided reference is null otherwise returns false   Since Java 1 8 public static boolean nonNull Object obj   Returns true if the provided reference is non-null otherwise returns false   Since Java 1 8 public static  lt T gt  T requireNonNullElse  T obj  T defaultObj   Returns the first argument if it is non-null and otherwise returns the non-null second argument   Since Java 9 public static  lt T gt  T requireNonNullElseGet  T obj  Supplier lt   extends T gt  supplier   Returns the first argument if it is non-null and otherwise returns the non-null value of supplier get     Since Java 9 public static  lt T gt  T requireNonNull  T obj  Supplier lt String gt  messageSupplier   Checks that the specified object reference is not null and throws a customized NullPointerException otherwise   Since Java 1 8   Further details about the above functions can be found here

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Rather than Null Object Pattern -- which has its uses -- you might consider situations where the null object is a bug   When the exception is thrown  examine the stack trace and work through the bug

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Another suggestion is to program defensively - where your classes functions provide default values that are known and safe  and where null is reserved for true errors exceptions   For example  instead of functions that return Strings returning null when there is a problem  say converting a number to a string   have them return an empty String       You still have to test the return value before proceeding  but there would be no special cases for exceptions  An additional benefit of this style of programming is that your program will be able to differentiate and respond accordingly between normal operations and exceptions

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This is the most common error occurred for most of the developers   We have number of ways to handle this   Approach 1   org apache commons lang Validate   using apache framework   notNull Object object  String message    Approach 2   if someObject  null      simply checking against null     Approach 3    isNull  Nullable     using annotation based validation   Approach 4      by writing static method and calling it across whereever we needed to check the validation  static  lt T gt  T isNull someObject e        if e    null         throw new NullPointerException            return e

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Wherever you pass an array or a Vector  initialise these to empty ones  instead of null   - This way you can avoid lots of checking for null and all is good     public class NonNullThing       Vector vectorField   new Vector        int   arrayField   new int 0       public NonNullThing               etc

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I follow below guidelines to avoid null checks    Avoid lazy initialization of member variables as much as possible  Initialize the variables in declaration itself  This will handle NullPointerExceptions   Decide on mutability of member variables early in the cycle  Use language constructs like final keyword effectively   If you know that augments for method won t be changed  declare them as final  Limit the mutation of data as much as possible  Some variables can be created in a constructor and can never be changed  Remove public setter methods unless they are really required   E g  Assume that one class in your application  A java  is maintaining a collection like HashMap   Don t provide public getter method in A java and allow B java to directly add an element in Map  Instead provide an API in A java  which adds an element into collection       Avoid a getMap   put key value     recommended  public void addElement Object key  Object value             Have null checks for both key and value here   single place        map put key value      And finally  use try   catch   finally   blocks at right places effectively

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I find Guava Preconditions to be very useful in this case  I don t like leaving nulls to null pointer exception since the only way to understand an NPE is by locating the line number  Line numbers in production version and development version can be different   Using Guava Preconditions  I can check null parameters and define a meaningful exception message in one line   For example   Preconditions checkNotNull paramVal   Method foo received null paramVal

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Another alternative to the    null check is  if you can t get rid of it design-wise    Optional ofNullable someobject  ifPresent someobject - gt  someobject doCalc       or  Optional ofNullable someobject  ifPresent SomeClass  doCalc     With SomeClass being someobject s type   You can t get a return value back from doCalc   though  so only useful for void methods

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One more alternative   The following simple function helps to hide the null-check  I don t know why  but I haven t found it as part of the same common library    public static  lt T gt  boolean isNull T argument        return  argument    null       You could now write  if   isNull someobject         someobject doCalc        which is IMO a better way of expressing    null

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You can use an interceptor before the method call  That is what aspect-oriented programming focus on   Suppose M1 Object test  is a method and M2 is a method where we apply an aspect before a method call  M2 Object test2   If test2    null then call M1  otherwise do another thing  It works for all methods with whom you want to apply an aspect for  If you want to apply an aspect for an instance field and constructor you can use AspectJ  Spring can also be the best choice for a method aspect

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You can use FindBugs  They also have an Eclipse plugin  that helps you find duplicate null checks  among other things   but keep in mind that sometimes you should opt for defensive programming  There is also Contracts for Java which may be helpful

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If you are using java8 or later go for the isNull yourObject  from java util Objects   Example -  String myObject   null   Objects isNull myObject     will return true   Usage  The below code returns a non null value  if the name is not null then that value will be returned else the default value will be returned    final String name    Jobin   String nonNullValue   Optional ofNullable name  filter Objects  nonNull  orElse  DefaultName

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Wow  I almost hate to add another answer when we have 57 different ways to recommend the NullObject pattern  but I think that some people interested in this question may like to know that there is a proposal on the table for Java 7 to add  null-safe handling  mdash a streamlined syntax for if-not-equal-null logic   The example given by Alex Miller looks like this   public String getPostcode Person person        return person  getAddress    getPostcode            The    means only de-reference the left identifier if it is not null  otherwise evaluate the remainder of the expression as null  Some people  like Java Posse member Dick Wall and the voters at Devoxx really love this proposal  but there is opposition too  on the grounds that it will actually encourage more use of null as a sentinel value     Update  An official proposal for a null-safe operator in Java 7 has been submitted under Project Coin  The syntax is a little different than the example above  but it s the same notion     Update  The null-safe operator proposal didn t make it into Project Coin  So  you won t be seeing this syntax in Java 7

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May I answer it more generally   We usually face this issue when the methods get the parameters in the way we not expected  bad method call is programmer s fault   For example  you expect to get an object  instead you get a null  You expect to get an String with at least one character  instead you get an empty String      So there is no difference between   if object    null        you called my method badly       or  if str length      0        you called my method badly again      They both want to make sure that we received valid parameters  before we do any other functions   As mentioned in some other answers  to avoid above problems you can follow the Design by contract pattern  Please see http   en wikipedia org wiki Design by contract    To implement this pattern in java  you can use core java annotations like javax annotation NotNull or use more sophisticated libraries like Hibernate Validator   Just a sample   getCustomerAccounts  NotEmpty String customerId  Size min   1  String accountType    Now you can safely develop the core function of your method without needing to check input parameters  they guard your methods from unexpected parameters   You can go a step further and make sure that only valid pojos could be created in your application   sample from hibernate validator site   public class Car        NotNull    private String manufacturer       NotNull     Size min   2  max   14     private String licensePlate       Min 2     private int seatCount

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If null-values are not allowed

If your method is called externally, start with something like this:

public void method(Object object) {
  if (object == null) {
    throw new IllegalArgumentException("...");
  }

Then, in the rest of that method, you'll know that object is not null.

If it is an internal method (not part of an API), just document that it cannot be null, and that's it.

Example:

public String getFirst3Chars(String text) {
  return text.subString(0, 3);
}

However, if your method just passes the value on, and the next method passes it on etc. it could get problematic. In that case you may want to check the argument as above.

If null is allowed

This really depends. If find that I often do something like this:

if (object == null) {
  // something
} else {
  // something else
}

So I branch, and do two completely different things. There is no ugly code snippet, because I really need to do two different things depending on the data. For example, should I work on the input, or should I calculate a good default value?

It's actually rare for me to use the idiom "if (object != null && ...".

It may be easier to give you examples, if you show examples of where you typically use the idiom.

User · Answer

It is possible to define util methods which handles nested null-checks in an almost pretty way with Java 8 lambdas   void example         Entry entry   new Entry           This is the same as H-MANs solution      Person person   getNullsafe entry  e - gt  e getPerson                Get object in several steps     String givenName   getNullsafe entry  e - gt  e getPerson    p - gt  p getName    n - gt  n getGivenName            Call void methods     doNullsafe entry  e - gt  e getPerson    p - gt  p getName    n - gt  n nameIt                    Return result of call to f1 with o1 if it is non-null  otherwise return null     public static  lt R  T1 gt  R getNullsafe T1 o1  Function lt T1  R gt  f1        if  o1    null  return f1 apply o1       return null      public static  lt R  T0  T1 gt  R getNullsafe T0 o0  Function lt T0  T1 gt  f1  Function lt T1  R gt  f2        return getNullsafe getNullsafe o0  f1   f2      public static  lt R  T0  T1  T2 gt  R getNullsafe T0 o0  Function lt T0  T1 gt  f1  Function lt T1  T2 gt  f2  Function lt T2  R gt  f3        return getNullsafe getNullsafe o0  f1  f2   f3           Call consumer f1 with o1 if it is non-null  otherwise do nothing     public static  lt T1 gt  void doNullsafe T1 o1  Consumer lt T1 gt  f1        if  o1    null  f1 accept o1      public static  lt T0  T1 gt  void doNullsafe T0 o0  Function lt T0  T1 gt  f1  Consumer lt T1 gt  f2        doNullsafe getNullsafe o0  f1   f2      public static  lt T0  T1  T2 gt  void doNullsafe T0 o0  Function lt T0  T1 gt  f1  Function lt T1  T2 gt  f2  Consumer lt T2 gt  f3        doNullsafe getNullsafe o0  f1  f2   f3       class Entry       Person getPerson     return null       class Person       Name getName     return null       class Name       void nameIt          String getGivenName     return null         This answer was first posted here

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Java 7 has a new java util Objects utility class on which there is a requireNonNull   method  All this does is throw a NullPointerException if its argument is null  but it cleans up the code a bit  Example   Objects requireNonNull someObject   someObject doCalc        The method is most useful for checking just before an assignment in a constructor  where each use of it can save three lines of code   Parent Child child       if  child    null          throw new NullPointerException  child            this child   child      becomes  Parent Child child       this child   Objects requireNonNull child   child

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Java 7 has a new java util Objects utility class on which there is a requireNonNull   method  All this does is throw a NullPointerException if its argument is null  but it cleans up the code a bit  Example   Objects requireNonNull someObject   someObject doCalc        The method is most useful for checking just before an assignment in a constructor  where each use of it can save three lines of code   Parent Child child       if  child    null          throw new NullPointerException  child            this child   child      becomes  Parent Child child       this child   Objects requireNonNull child   child

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I highly disregard answers that suggest using the null objects in every situation  This pattern may break the contract and bury problems deeper and deeper instead of solving them  not mentioning that used inappropriately will create another pile of boilerplate code that will require future maintenance   In reality if something returned from a method can be null and the calling code has to make decision upon that  there should an earlier call that ensures the state    Also keep in mind  that null object pattern will be memory hungry if used without care  For this - the instance of a NullObject should be shared between owners  and not be an unigue instance for each of these   Also I would not recommend using this pattern where the type is meant to be a primitive type representation - like mathematical entities  that are not scalars  vectors  matrices  complex numbers and POD Plain Old Data  objects  which are meant to hold state in form of Java built-in types  In the latter case you would end up calling getter methods with arbitrary results  For example what should a NullPerson getName   method return    It s worth considering such cases in order to avoid absurd results

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This is the most common error occurred for most of the developers   We have number of ways to handle this   Approach 1   org apache commons lang Validate   using apache framework   notNull Object object  String message    Approach 2   if someObject  null      simply checking against null     Approach 3    isNull  Nullable     using annotation based validation   Approach 4      by writing static method and calling it across whereever we needed to check the validation  static  lt T gt  T isNull someObject e        if e    null         throw new NullPointerException            return e

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You can use an interceptor before the method call  That is what aspect-oriented programming focus on   Suppose M1 Object test  is a method and M2 is a method where we apply an aspect before a method call  M2 Object test2   If test2    null then call M1  otherwise do another thing  It works for all methods with whom you want to apply an aspect for  If you want to apply an aspect for an instance field and constructor you can use AspectJ  Spring can also be the best choice for a method aspect

User · Answer

If null-values are not allowed

If your method is called externally, start with something like this:

public void method(Object object) {
  if (object == null) {
    throw new IllegalArgumentException("...");
  }

Then, in the rest of that method, you'll know that object is not null.

If it is an internal method (not part of an API), just document that it cannot be null, and that's it.

Example:

public String getFirst3Chars(String text) {
  return text.subString(0, 3);
}

However, if your method just passes the value on, and the next method passes it on etc. it could get problematic. In that case you may want to check the argument as above.

If null is allowed

This really depends. If find that I often do something like this:

if (object == null) {
  // something
} else {
  // something else
}

So I branch, and do two completely different things. There is no ugly code snippet, because I really need to do two different things depending on the data. For example, should I work on the input, or should I calculate a good default value?

It's actually rare for me to use the idiom "if (object != null && ...".

It may be easier to give you examples, if you show examples of where you typically use the idiom.

User · Answer

Another suggestion is to program defensively - where your classes functions provide default values that are known and safe  and where null is reserved for true errors exceptions   For example  instead of functions that return Strings returning null when there is a problem  say converting a number to a string   have them return an empty String       You still have to test the return value before proceeding  but there would be no special cases for exceptions  An additional benefit of this style of programming is that your program will be able to differentiate and respond accordingly between normal operations and exceptions

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If you use  or planning to use  a Java IDE like JetBrains IntelliJ IDEA  Eclipse or Netbeans or a tool like findbugs then you can use annotations to solve this problem   Basically  you ve got  Nullable and  NotNull   You can use in method and parameters  like this    NotNull public static String helloWorld         return  Hello World       or   Nullable public static String helloWorld         return  Hello World       The second example won t compile  in IntelliJ IDEA    When you use the first helloWorld   function in another piece of code   public static void main String   args        String result   helloWorld        if result    null            System out println result             Now the IntelliJ IDEA compiler will tell you that the check is useless  since the helloWorld   function won t return null  ever   Using parameter  void someMethod  NotNull someParameter        if you write something like   someMethod null     This won t compile   Last example using  Nullable   Nullable iWantToDestroyEverything     return null      Doing this  iWantToDestroyEverything   something      And you can be sure that this won t happen      It s a nice way to let the compiler check something more than it usually does and to enforce your contracts to be stronger  Unfortunately  it s not supported by all the compilers   In IntelliJ IDEA 10 5 and on  they added support for any other  Nullable  NotNull implementations   See blog post More flexible and configurable  Nullable  NotNull annotations

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Asking that question points out that you may be interested in error handling strategies   How and where to handle errors is a pervasive architectural question   There are several ways to do this  My favorite  allow the Exceptions to ripple through - catch them at the  main loop  or in some other function with the appropriate responsibilities   Checking for error conditions and handling them appropriately can be seen as a specialized responsibility  Sure do have a look at Aspect Oriented Programming  too - they have neat ways to insert if  o    null   handleNull   into your bytecode

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I find Guava Preconditions to be very useful in this case  I don t like leaving nulls to null pointer exception since the only way to understand an NPE is by locating the line number  Line numbers in production version and development version can be different   Using Guava Preconditions  I can check null parameters and define a meaningful exception message in one line   For example   Preconditions checkNotNull paramVal   Method foo received null paramVal

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If undefined values are not permitted   You might configure your IDE to warn you about potential null dereferencing  E g  in Eclipse  see Preferences   Java   Compiler   Errors Warnings Null analysis   If undefined values are permitted   If you want to define a new API where undefined values make sense  use the Option Pattern  may be familiar from functional languages   It has the following advantages    It is stated explicitly in the API whether an input or output exists or not  The compiler forces you to handle the  undefined  case  Option is a monad  so there is no need for verbose null checking  just use map foreach getOrElse or a similar combinator to safely use the value  example     Java 8 has a built-in Optional class  recommended   for earlier versions  there are library alternatives  for example Guava s Optional or FunctionalJava s Option  But like many functional-style patterns  using Option in Java  even 8  results in quite some boilerplate  which you can reduce using a less verbose JVM language  e g  Scala or Xtend   If you have to deal with an API which might return nulls  you can t do much in Java  Xtend and Groovy have the Elvis operator    and the null-safe dereference operator     but note that this returns null in case of a null reference  so it just  defers  the proper handling of null

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Java 8 has introduced a new class Optional in java util package  It is used to represent a value is present or absent  The main advantage of this new construct is that No more too many null checks and NullPointerException  It avoids any runtime NullPointerExceptions and supports us in developing clean and neat Java APIs or Applications  Like Collections and arrays  it is also a Container to hold at most one value  Below are some useful link you can follow https   www mkyong com java8 java-8-optional-in-depth  https   dzone com articles java-8-optional-avoid-null-and

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Only for this situation -  Not checking if a variable is null before invoking an equals method  a string compare example below    if   foo equals  bar                   will result in a NullPointerException if foo doesn t exist   You can avoid that if you compare your Strings like this   if    bar  equals foo

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The Google collections framework offers a good and elegant way to achieve the null check   There is a method in a library class like this   static  lt T gt  T checkNotNull T e       if  e    null          throw new NullPointerException            return e      And the usage is  with import static        void foo int a  Person p       if  checkNotNull p  getAge    gt  a                      else                          Or in your example   checkNotNull someobject  doCalc

User · Answer

The Google collections framework offers a good and elegant way to achieve the null check   There is a method in a library class like this   static  lt T gt  T checkNotNull T e       if  e    null          throw new NullPointerException            return e      And the usage is  with import static        void foo int a  Person p       if  checkNotNull p  getAge    gt  a                      else                          Or in your example   checkNotNull someobject  doCalc

User · Answer

I ve tried the NullObjectPattern but for me is not always the best way to go  There are sometimes when a  no action  is not appropiate   NullPointerException is a Runtime exception that means it s developers fault and with enough experience it tells you exactly where is the error   Now to the answer   Try to make all your attributes and its accessors as private as possible or avoid to  expose them to the clients at all  You can have the argument values in the constructor of course  but by reducing the scope you don t let the client class pass an invalid value  If you need to modify the values  you can always create a new object   You check the values in the constructor only once and in the rest of the methods you can be almost sure that the values are not null   Of course  experience is the better way to understand and apply this suggestion   Byte

User · Answer

The Google collections framework offers a good and elegant way to achieve the null check   There is a method in a library class like this   static  lt T gt  T checkNotNull T e       if  e    null          throw new NullPointerException            return e      And the usage is  with import static        void foo int a  Person p       if  checkNotNull p  getAge    gt  a                      else                          Or in your example   checkNotNull someobject  doCalc

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Java 8 now has Optional class that wraps the object in consideration and if a value is present  isPresent   will return true and get   will return the value   http   www oracle com technetwork articles java java8-optional-2175753 html

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Asking that question points out that you may be interested in error handling strategies   How and where to handle errors is a pervasive architectural question   There are several ways to do this  My favorite  allow the Exceptions to ripple through - catch them at the  main loop  or in some other function with the appropriate responsibilities   Checking for error conditions and handling them appropriately can be seen as a specialized responsibility  Sure do have a look at Aspect Oriented Programming  too - they have neat ways to insert if  o    null   handleNull   into your bytecode

User · Answer

Ultimately  the only way to completely solve this problem is by using a different programming language    In Objective-C  you can do the equivalent of invoking a method on nil  and absolutely nothing will happen  This makes most null checks unnecessary  but it can make errors much harder to diagnose  In Nice  a Java-derived language  there are two versions of all types  a potentially-null version and a not-null version  You can only invoke methods on not-null types  Potentially-null types can be converted to not-null types through explicit checking for null  This makes it much easier to know where null checks are necessary and where they aren t

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Sometimes  you have methods that operate on its parameters that define a symmetric operation   a f b    lt - gt  b f a     If you know b can never be null  you can just swap it  It is most useful for equals  Instead of foo equals  bar    better do  bar  equals foo

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Here is my approach     class MyObjectHandler   public static final int EXCEPTION    -3   public static final int INACCESSIBLE    -2    public static int doSomething  MyObject obj  MyObjectParameter    input        int returnValue  0       try               if  obj    null                        returnValue   obj doSomething input                     else                       returnValue   MyObjectHandler INACCESSIBLE                      catch  Exception e                e printStack            returnValue   MyObjectHandler EXCEPTION            finally               return returnValue                   Then your code will be just like   import xx xx xx MyObjectHandler  import xx xx xx MyObjectParameter   class Test        public static void main                   MyObject obj   null           MyObjectHandler doSomething obj  null

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Java 8 now has Optional class that wraps the object in consideration and if a value is present  isPresent   will return true and get   will return the value   http   www oracle com technetwork articles java java8-optional-2175753 html

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Just don t ever use null  Don t allow it   In my classes  most fields and local variables have non-null default values  and I add contract statements  always-on asserts  everywhere in the code to make sure this is being enforced  since it s more succinct  and more expressive than letting it come up as an NPE and then having to resolve the line number  etc     Once I adopted this practice  I noticed that the problems seemed to fix themselves  You d catch things much earlier in the development process just by accident and realize you had a weak spot    and more importantly   it helps encapsulate different modules  concerns  different modules can  trust  each other  and no more littering the code with if   null else constructs   This is defensive programming and results in much cleaner code in the long run  Always sanitize the data  e g  here by enforcing rigid standards  and the problems go away   class C       private final MyType mustBeSet      public C MyType mything           mustBeSet Contract notNull mything            private String name     lt unknown gt       public void setName String s          name   Contract notNull s            class Contract       public static  lt T gt  T notNull T t    if  t    null    throw new ContractException  argument must be non-null    return t        The contracts are like mini-unit tests which are always running  even in production  and when things fail  you know why  rather than a random NPE you have to somehow figure out

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Rather than Null Object Pattern -- which has its uses -- you might consider situations where the null object is a bug   When the exception is thrown  examine the stack trace and work through the bug

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You can make one generic Method for object and string so that you can use it through out in your application- This could help you and your colleagues   Create a class eg  StringUtilities and add the method eg  getNullString public static String getNullString Object someobject       if null  someobject           return null      else if someobject getClass   isInstance  quot  quot    amp  amp                String someobject  trim   equalsIgnoreCase  quot null quot                  String someobject  trim   equalsIgnoreCase  quot  quot             return null      else if someobject getClass   isInstance  quot  quot            return  String someobject      else         return someobject toString   trim       And simply call this method as  if  StringUtilities getNullString someobject     null         Do something

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In Java 8 you can use type T for local-variable field method-argument method-return-type if it never assigned null  and do not check for null  or type Optional lt T gt  if it can be null  Then use method map for processing T - gt  and method flatMap for processing T - gt  Optional lt R gt    class SomeService        Inject     private CompanyDao companyDao          return Optional lt String gt      public Optional lt String gt  selectCeoCityByCompanyId0 int companyId            return companyDao selectById companyId                   map Company  getCeo                   flatMap Person  getHomeAddress                   flatMap Address  getCity                 return String   default value     public String selectCeoCityByCompanyId1 int companyId            return companyDao selectById companyId                   map Company  getCeo                   flatMap Person  getHomeAddress                   flatMap Address  getCity                   orElse  UNKNOWN                  return String   exception     public String selectCeoCityByCompanyId2 int companyId  throws NoSuchElementException           return companyDao selectById companyId                   map Company  getCeo                   flatMap Person  getHomeAddress                   flatMap Address  getCity                   orElseThrow NoSuchElementException  new            interface CompanyDao          real situation  no company for such id - gt  use Optional lt Company gt       Optional lt Company gt  selectById int id      class Company          company always has ceo - gt  use Person      Person ceo      public Person getCeo    return ceo      class Person          person always has name - gt  use String     String firstName         person can be without address - gt  use Optional lt Address gt      Optional lt Address gt  homeAddress   Optional empty         public String getFirstName    return firstName          public Optional lt Address gt  getHomeAddress    return homeAddress      class Address           address always contains country - gt  use String     String country          city field is optional - gt  use Optional lt String gt      Optional lt String gt  city   Optional empty         String getCountry    return country           Optional lt String gt  getCity    return city

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Wherever you pass an array or a Vector  initialise these to empty ones  instead of null   - This way you can avoid lots of checking for null and all is good     public class NonNullThing       Vector vectorField   new Vector        int   arrayField   new int 0       public NonNullThing               etc

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There has a good way to check the null value from JDK  It is Optional java that has a sea of methods to resolve these problems  Such as follow     Returns an   code Optional  describing the specified value  if non-null   otherwise returns an empty   code Optional     param  the class of the value  param value the possibly-null value to describe  return an   code Optional  with a present value if the specified value is non-null  otherwise an empty   code Optional      public static  lt T gt  Optional lt T gt  ofNullable T value        return value    null   empty     of value             Return   code true  if there is a value present  otherwise   code false       return   code true  if there is a value present  otherwise   code false     public boolean isPresent     return value    null          If a value is present  invoke the specified consumer with the value  otherwise do nothing    param consumer block to be executed if a value is present  throws NullPointerException if value is present and   code consumer  is null    public void ifPresent Consumer lt   super T gt  consumer    if  value    null  consumer accept value         It is really  really useful to help javer

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The Google collections framework offers a good and elegant way to achieve the null check   There is a method in a library class like this   static  lt T gt  T checkNotNull T e       if  e    null          throw new NullPointerException            return e      And the usage is  with import static        void foo int a  Person p       if  checkNotNull p  getAge    gt  a                      else                          Or in your example   checkNotNull someobject  doCalc

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This is a very common problem for every Java developer  So there is official support in Java nbsp 8 to address these issues without cluttered code   Java 8 has introduced java util Optional lt T gt   It is a container that may or may not hold a non-null value  Java 8 has given a safer way to handle an object whose value may be null in some of the cases  It is inspired from the ideas of Haskell and Scala   In a nutshell  the Optional class includes methods to explicitly deal with the cases where a value is present or absent  However  the advantage compared to null references is that the Optional lt T  class forces you to think about the case when the value is not present  As a consequence  you can prevent unintended null pointer exceptions   In above example we have a home service factory that returns a handle to multiple appliances available in the home  But these services may or may not be available functional  it means it may result in a NullPointerException  Instead of adding a null if condition before using any service  let s wrap it in to Optional lt Service    WRAPPING TO OPTION lt T   Let s consider a method to get a reference of a service from a factory  Instead of returning the service reference  wrap it with Optional  It lets the API user know that the returned service may or may not available functional  use defensively  public Optional lt Service gt  getRefrigertorControl           Service s   new  RefrigeratorService                       return Optional ofNullable s          As you see Optional ofNullable   provides an easy way to get the reference wrapped  There are another ways to get the reference of Optional  either Optional empty    amp  Optional of    One for returning an empty object instead of retuning null and the other to wrap a non-nullable object  respectively   SO HOW EXACTLY IT HELPS TO AVOID A NULL CHECK   Once you have wrapped a reference object  Optional provides many useful methods to invoke methods on a wrapped reference without NPE   Optional ref   homeServices getRefrigertorControl    ref ifPresent HomeServices  switchItOn     Optional ifPresent invokes the given Consumer with a reference if it is a non-null value  Otherwise  it does nothing    FunctionalInterface public interface Consumer lt T gt    Represents an operation that accepts a single input argument and returns no result  Unlike most other functional interfaces  Consumer is expected to operate via side-effects  It is so clean and easy to understand  In the above code example  HomeService switchOn Service  gets invoked if the Optional holding reference is non-null   We use the ternary operator very often for checking null condition and return an alternative value or default value  Optional provides another way to handle the same condition without checking null  Optional orElse defaultObj  returns defaultObj if the Optional has a null value  Let s use this in our sample code   public static Optional lt HomeServices gt  get         service   Optional of service orElse new HomeServices          return service      Now HomeServices get   does same thing  but in a better way  It checks whether the service is already initialized of not  If it is then return the same or create a new New service  Optional lt T  orElse T  helps to return a default value   Finally  here is our NPE as well as null check-free code   import java util Optional  public class HomeServices       private static final int NOW   0      private static Optional lt HomeServices gt  service   public static Optional lt HomeServices gt  get         service   Optional of service orElse new HomeServices          return service     public Optional lt Service gt  getRefrigertorControl         Service s   new  RefrigeratorService                  return Optional ofNullable s      public static void main String   args           Get Home Services handle        Optional lt HomeServices gt  homeServices   HomeServices get        if homeServices    null            Optional lt Service gt  refrigertorControl   homeServices get   getRefrigertorControl            refrigertorControl ifPresent HomeServices  switchItOn            public static void switchItOn Service s                            The complete post is NPE as well as Null check-free code     Really

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If you consider an object should not be null  or it is a bug  use an assert  If your method doesn t accept null params say it in the javadoc and use an assert    You have to check for object    null only if you want to handle the case where the object may be null     There is a proposal to add new annotations in Java7 to help with null   notnull params  http   tech puredanger com java7  jsr308

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Guava  a very useful core library by Google  has a nice and useful API to avoid nulls  I find UsingAndAvoidingNullExplained very helpful   As explained in the wiki      Optional lt T gt  is a way of replacing a nullable T reference with a   non-null value  An Optional may either contain a non-null T reference    in which case we say the reference is  present    or it may contain   nothing  in which case we say the reference is  absent    It is never   said to  contain null     Usage   Optional lt Integer gt  possible   Optional of 5   possible isPresent       returns true possible get       returns 5

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This to me sounds like a reasonably common problem that junior to intermediate developers tend to face at some point  they either don t know or don t trust the contracts they are participating in and defensively overcheck for nulls   Additionally  when writing their own code  they tend to rely on returning nulls to indicate something thus requiring the caller to check for nulls   To put this another way  there are two instances where null checking comes up    Where null is a valid response in terms of the contract  and Where it isn t a valid response     2  is easy   Either use assert statements  assertions  or allow failure  for example   NullPointerException    Assertions are a highly-underused Java feature that was added in 1 4   The syntax is   assert  lt condition gt    or  assert  lt condition gt     lt object gt    where  lt condition gt  is a boolean expression and  lt object gt  is an object whose toString   method s output will be included in the error   An assert statement throws an Error  AssertionError  if the condition is not true   By default  Java ignores assertions   You can enable assertions by passing the option -ea to the JVM   You can enable and disable assertions for individual classes and packages   This means that you can validate code with the assertions while developing and testing  and disable them in a production environment  although my testing has shown next to no performance impact from assertions   Not using assertions in this case is OK because the code will just fail  which is what will happen if you use assertions   The only difference is that with assertions it might happen sooner  in a more-meaningful way and possibly with extra information  which may help you to figure out why it happened if you weren t expecting it    1  is a little harder   If you have no control over the code you re calling then you re stuck   If null is a valid response  you have to check for it   If it s code that you do control  however  and this is often the case   then it s a different story   Avoid using nulls as a response   With methods that return collections  it s easy  return empty collections  or arrays  instead of nulls pretty much all the time   With non-collections it might be harder   Consider this as an example  if you have these interfaces   public interface Action     void doSomething       public interface Parser     Action findAction String userInput       where Parser takes raw user input and finds something to do  perhaps if you re implementing a command line interface for something   Now you might make the contract that it returns null if there s no appropriate action   That leads the null checking you re talking about   An alternative solution is to never return null and instead use the Null Object pattern   public class MyParser implements Parser     private static Action DO NOTHING   new Action         public void doSomething        do nothing              public Action findAction String userInput                   if      we can t find any actions              return DO NOTHING                Compare   Parser parser   ParserFactory getParser    if  parser    null         now what       this would be an example of where null isn t  or shouldn t be  a valid response   Action action   parser findAction someInput   if  action    null         do nothing   else     action doSomething        to  ParserFactory getParser   findAction someInput  doSomething      which is a much better design because it leads to more concise code   That said  perhaps it is entirely appropriate for the findAction   method to throw an Exception with a meaningful error message -- especially in this case where you are relying on user input   It would be much better for the findAction method to throw an Exception than for the calling method to blow up with a simple NullPointerException with no explanation   try       ParserFactory getParser   findAction someInput  doSomething      catch ActionNotFoundException anfe        userConsole err anfe getMessage         Or if you think the try catch mechanism is too ugly  rather than Do Nothing your default action should provide feedback to the user   public Action findAction final String userInput           Code to return requested Action if found        return new Action             public void doSomething                 userConsole err  Action not found      userInput

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The way to avoid unnecessary null-checks is simple to state   You need to know which variables can be null  and which cannot  and you need to be confident about which category a given variable fall into   But  although it can be stated simply enough  achieving it is harder  The key lies in the confident part  because how can you be sure that a variable can t be null   There are no quick-fix  easy answers to this  but here are some pointers    Clean code  The most important thing for being able to reason about the behaviour of a piece of code is that it is written in a matter that is easy to understand  Name your variables based on what they represent  name your methods after what they do  apply the Single responsibility principle  the S in SOLID  http   en wikipedia org wiki SOLID  object-oriented design   it means that each piece of code should have a single responsibility  and do this and nothing else   Once your code is clean  it is much easier to reason about it  also across multiple tiers layers of code  With messy code  trying to understand what a method does might make you forget why you are reading the method in the first place   Tip  Read  Clean Code  by Robert C  Martin  Avoid returning null values  If a null value would keep your program from functioning correctly  throw an exception instead  make sure to add the appropriate error-handling   Cases where returning a null value might be acceptable is for instance trying to fetch an object from the database  In these cases  write code that handles the null values  and make a note behind your ear that here we have something that might return null  Handle returned null values as close to the caller of the method returning null as possible  don t just blindly pass it back up the call-chain   Never EVER pass explicit null values as parameters  at least not across classes   If you are ever in a position where passing a null-parameter is the only option  creating a new method that does not have this parameter is the way to go   Validate your input  Identify the  entry-points  to your application  They can everything from webservices  REST-services  remote EJB classes  controllers  etc  For each method in these entry-points  ask yourself   Will this method execute correctly if this parameter is null   If the answer is no  add Validate notNull someParam   Can t function when someParam is null      This will throw an IllegalArgumentException if the required parameter is missing  The good thing about this type of validation in the entry-points  is that you can then easily assume in the code being executed from the entry-point  that this variable will never be null  Also  if this fails  being at the entry-point  debugging is made a lot easier than it would if you just got a NullPointerException deep down in your code  since a failure like this can only mean one thing  The client didn t send you all the required information  In most cases you want to validate all input parameters  if you find yourself in a position where you need to allow a lot of null-values  it might be a sign of a badly designed interface  which needs refactoring additions to suite the needs of the clients  When working with Collections  return an empty one rather than null   When working with a database  utilize not null-constraints  In that way  you ll know that a value read from the database cannot be null  and you won t have to check for it  Structure your code and stick with it  Doing this allows you to make assumptions about the behaviour of the code  for instance if all input to your application is validated  then you can assume that these values will never be null   If you are not already doing it  write automated tests of your code  By writing tests  you will reason about your code  and you will also become more confident that it does what it s supposed to  Also  automated tests guards you from blunders during refactoring  by letting you know immediatly that this piece of code is not doing what it used to    You still have to null-check of course  but it can trimmed down to the bare minimum  i e  the situation where know you might be getting a null-value  instead of everywhere just to be sure   When it comes to null-checks  i actually prefer to use the ternary operator  but use with care  when you start nesting them they come really messy    public String nullSafeToString final Object o        return o    null   o toString      null

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In addition to using assert you can use the following   if  someobject    null           Handle null here then move on      This is slightly better than   if  someobject    null

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Ultimately  the only way to completely solve this problem is by using a different programming language    In Objective-C  you can do the equivalent of invoking a method on nil  and absolutely nothing will happen  This makes most null checks unnecessary  but it can make errors much harder to diagnose  In Nice  a Java-derived language  there are two versions of all types  a potentially-null version and a not-null version  You can only invoke methods on not-null types  Potentially-null types can be converted to not-null types through explicit checking for null  This makes it much easier to know where null checks are necessary and where they aren t

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Never initialise variables to null  If  1  is not possible  initialise all collections and arrays to empty collections arrays    Doing this in your own code and you can avoid    null checks   Most of the time null checks seem to guard loops over collections or arrays  so just initialise them empty  you won t need any null checks      Bad ArrayList lt String gt  lemmings  String   names   void checkLemmings         if  lemmings    null  for lemming  lemmings               do something               Good ArrayList lt String gt  lemmings   new ArrayList lt String gt     String   names        void checkLemmings         for lemming  lemmings               do something           There is a tiny overhead in this  but it s worth it for cleaner code and less NullPointerExceptions

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First of all  we can t really remove all null conditions  We can reduce them using  NotNull and  Nullable annotations  as mentioned already   But this needs to be backed by some framework  This is where OVal can help   The basic idea is object parameters constructor should always satisfy preconditions  You can have a whole lot of preconditions such as Nullable  NotNull and OVal would take care that an object should be in a consistent state when invoked   I guess OVal internally uses AspectJ to validate the preconditions    Guarded public class BusinessObject     public BusinessObject  NotNull String name          this name   name                 For example      Throws a ConstraintsViolatedException because parameter name is null BusinessObject bo   new BusinessObject null

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public class Null    public static void main String   args        String str1   null      String str2    quot  quot        if isNullOrEmpty str1           System out println  quot First string is null or empty  quot        else         System out println  quot First string is not null or empty  quot         if isNullOrEmpty str2           System out println  quot Second string is null or empty  quot        else         System out println  quot Second string is not null or empty  quot       public static boolean isNullOrEmpty String str        if str    null  amp  amp   str isEmpty            return false      return true       Output str1 is null or empty  str2 is null or empty   In the above program  we ve two strings str1 and str2  str1 contains null value and str2 is an empty string  We ve also created a function isNullOrEmpty   which checks  as the name suggests  whether the string is null or empty  It checks it using a null check using    null and isEmpty   method of string  In plain terms  if a string isn t a null and isEmpty   returns false  it s not either null or empty  Else  it is  However  the above program doesn t return empty if a string contains only whitespace characters  spaces   Technically  isEmpty   sees it contains spaces and returns false  For string with spaces  we use the string method trim   to trim out all the leading and trailing whitespace characters

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Sometimes  you have methods that operate on its parameters that define a symmetric operation   a f b    lt - gt  b f a     If you know b can never be null  you can just swap it  It is most useful for equals  Instead of foo equals  bar    better do  bar  equals foo

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public static  lt T gt  T ifNull T toCheck  T ifNull        if  toCheck    null               return ifNull            return toCheck

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Wherever you pass an array or a Vector  initialise these to empty ones  instead of null   - This way you can avoid lots of checking for null and all is good     public class NonNullThing       Vector vectorField   new Vector        int   arrayField   new int 0       public NonNullThing               etc

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If you consider an object should not be null  or it is a bug  use an assert  If your method doesn t accept null params say it in the javadoc and use an assert    You have to check for object    null only if you want to handle the case where the object may be null     There is a proposal to add new annotations in Java7 to help with null   notnull params  http   tech puredanger com java7  jsr308

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This to me sounds like a reasonably common problem that junior to intermediate developers tend to face at some point  they either don t know or don t trust the contracts they are participating in and defensively overcheck for nulls   Additionally  when writing their own code  they tend to rely on returning nulls to indicate something thus requiring the caller to check for nulls   To put this another way  there are two instances where null checking comes up    Where null is a valid response in terms of the contract  and Where it isn t a valid response     2  is easy   Either use assert statements  assertions  or allow failure  for example   NullPointerException    Assertions are a highly-underused Java feature that was added in 1 4   The syntax is   assert  lt condition gt    or  assert  lt condition gt     lt object gt    where  lt condition gt  is a boolean expression and  lt object gt  is an object whose toString   method s output will be included in the error   An assert statement throws an Error  AssertionError  if the condition is not true   By default  Java ignores assertions   You can enable assertions by passing the option -ea to the JVM   You can enable and disable assertions for individual classes and packages   This means that you can validate code with the assertions while developing and testing  and disable them in a production environment  although my testing has shown next to no performance impact from assertions   Not using assertions in this case is OK because the code will just fail  which is what will happen if you use assertions   The only difference is that with assertions it might happen sooner  in a more-meaningful way and possibly with extra information  which may help you to figure out why it happened if you weren t expecting it    1  is a little harder   If you have no control over the code you re calling then you re stuck   If null is a valid response  you have to check for it   If it s code that you do control  however  and this is often the case   then it s a different story   Avoid using nulls as a response   With methods that return collections  it s easy  return empty collections  or arrays  instead of nulls pretty much all the time   With non-collections it might be harder   Consider this as an example  if you have these interfaces   public interface Action     void doSomething       public interface Parser     Action findAction String userInput       where Parser takes raw user input and finds something to do  perhaps if you re implementing a command line interface for something   Now you might make the contract that it returns null if there s no appropriate action   That leads the null checking you re talking about   An alternative solution is to never return null and instead use the Null Object pattern   public class MyParser implements Parser     private static Action DO NOTHING   new Action         public void doSomething        do nothing              public Action findAction String userInput                   if      we can t find any actions              return DO NOTHING                Compare   Parser parser   ParserFactory getParser    if  parser    null         now what       this would be an example of where null isn t  or shouldn t be  a valid response   Action action   parser findAction someInput   if  action    null         do nothing   else     action doSomething        to  ParserFactory getParser   findAction someInput  doSomething      which is a much better design because it leads to more concise code   That said  perhaps it is entirely appropriate for the findAction   method to throw an Exception with a meaningful error message -- especially in this case where you are relying on user input   It would be much better for the findAction method to throw an Exception than for the calling method to blow up with a simple NullPointerException with no explanation   try       ParserFactory getParser   findAction someInput  doSomething      catch ActionNotFoundException anfe        userConsole err anfe getMessage         Or if you think the try catch mechanism is too ugly  rather than Do Nothing your default action should provide feedback to the user   public Action findAction final String userInput           Code to return requested Action if found        return new Action             public void doSomething                 userConsole err  Action not found      userInput

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public static  lt T gt  T ifNull T toCheck  T ifNull        if  toCheck    null               return ifNull            return toCheck

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Wow  I almost hate to add another answer when we have 57 different ways to recommend the NullObject pattern  but I think that some people interested in this question may like to know that there is a proposal on the table for Java 7 to add  null-safe handling  mdash a streamlined syntax for if-not-equal-null logic   The example given by Alex Miller looks like this   public String getPostcode Person person        return person  getAddress    getPostcode            The    means only de-reference the left identifier if it is not null  otherwise evaluate the remainder of the expression as null  Some people  like Java Posse member Dick Wall and the voters at Devoxx really love this proposal  but there is opposition too  on the grounds that it will actually encourage more use of null as a sentinel value     Update  An official proposal for a null-safe operator in Java 7 has been submitted under Project Coin  The syntax is a little different than the example above  but it s the same notion     Update  The null-safe operator proposal didn t make it into Project Coin  So  you won t be seeing this syntax in Java 7

[java] Avoiding NullPointerException in Java

If null-values are not allowed

If null is allowed

Examples related to java

Examples related to nullpointerexception

Examples related to null