Java Operator for checking null - What is it Not Ternary

Question

I was reading an article linked from a slashdot story  and came across this little tidbit      Take the latest version of Java  which   tries to make null-pointer checking   easier by offering shorthand syntax   for the endless pointer testing  Just   adding a question mark to each method   invocation automatically includes a   test for null pointers  replacing a   rat s nest of if-then statements  such   as         public String getPostcode Person person          String ans  null        if  person    null            Name nm  person getName            if  nm   null              ans  nm getPostcode                            return ans             With this     public String getFirstName Person person          return person  getName    getGivenName             I ve scoured the internet  okay  I spent at least 15 minutes googling variations on  java question mark   and got nothing  So  my question  is there any official documentation on this  I found that C  has a similar operator  the      operator   but I d like to get the documentation for the language I m working in  Or  is this just a use of the ternary operator that I ve never seen before   Thanks   EDIT  Link to the article  http   infoworld com d developer-world 12-programming-mistakes-avoid-292

User · Answer

This syntax does not exist in Java  nor is it slated to be included in any of the upcoming versions that I know of

User · Answer

One way to workaround the lack of     operator using Java 8 without the overhead of try-catch  which could also hide a NullPointerException originated elsewhere  as mentioned  is to create a class to  pipe  methods in a Java-8-Stream style   public class Pipe lt T gt        private T object       private Pipe T t            object   t             public static lt T gt  Pipe lt T gt  of T t            return new Pipe lt  gt  t              public  lt S gt  Pipe lt S gt  after Function lt   super T    extends S gt  plumber            return new Pipe lt  gt  object    null   null   plumber apply object               public T get             return object             public T orElse T other            return object    null   other   object            Then  the given example would become   public String getFirstName Person person        return Pipe of person  after Person  getName  after Name  getGivenName  get           EDIT   Upon further thought  I figured out that it is actually possible to achieve the same only using standard Java 8 classes   public String getFirstName Person person        return Optional ofNullable person  map Person  getName  map Name  getGivenName  orElse null       In this case  it is even possible to choose a default value  like   lt no first name gt    instead of null by passing it as parameter of orElse

User · Answer

There you have it  null-safe invocation in Java 8   public void someMethod         String userName   nullIfAbsent new Order    t - gt  t getAccount   getUser            getName        static  lt T  R gt  R nullIfAbsent T t  Function lt T  R gt  funct        try           return funct apply t         catch  NullPointerException e            return null

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There was a proposal for it in Java 7  but it was rejected   http   tech puredanger com java7  null

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I m not sure this would even work  if  say  the person reference was null  what would the runtime replace it with  A new Person  That would require the Person to have some default initialization that you d expect in this case  You may avoid null reference exceptions but you d still get unpredictable behavior if you didn t plan for these types of setups   The    operator in C  might be best termed the  coalesce  operator  you can chain several expressions and it will return the first that isn t null  Unfortunately  Java doesn t have it  I think the best you could do is use the ternary operator to perform null checks and evaluate an alternative to the entire expression if any member in the chain is null   return person    null             person getName      null                 person getName   getGivenName      You could also use try-catch   try      return person getName   getGivenName      catch NullReferenceException       return

User · Answer

If this is not a performance issue for you  you can write  public String getFirstName Person person      try        return person getName   getGivenName        catch  NullPointerException ignored         return null

User · Answer

Java does not have the exact syntax but as of JDK-8  we have the Optional API with various methods at our disposal  So  the C  version with the use of null conditional operator   return person  getName    getGivenName       can be written as follows in Java with the Optional API    return Optional ofNullable person                   map e - gt  e getName                     map e - gt  e getGivenName                     orElse null     if any of person  getName or getGivenName is null then null is returned

User · Answer

See  https   blogs oracle com darcy project-coin -the-final-five-or-so  specifically  Elvis and other null safe operators     The result is that this feature was considered for Java 7  but was not included

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If someone is looking for an alternative for old java versions  you can try this one I wrote          Strong typed Lambda to return NULL or DEFAULT VALUES instead of runtime errors      if you override the defaultValue method  if the execution result was null it will be used in place            Sample         It won t throw a NullPointerException but null      lt pre gt       code     new RuntimeExceptionHandlerLambda lt String gt                Override         public String evaluate                 String x   null              return x trim                      get             lt pre gt              author Robson Farias         public abstract class RuntimeExceptionHandlerLambda lt T gt         private T result       private RuntimeException exception       public abstract T evaluate         public RuntimeException getException             return exception             public boolean hasException             return exception    null             public T defaultValue             return result             public T get             try               result   evaluate              catch  RuntimeException runtimeException                exception   runtimeException                    return result    null   defaultValue     result

User · Answer

You can test the code which you have provided and it will give syntax error So  it is not supported in Java   Groovy does support it and it was proposed for Java 7  but never got included    However  you can use the Optional provided in Java 8  This might help you in achieving something on similar line  https   docs oracle com javase 8 docs api java util Optional html http   www oracle com technetwork articles java java8-optional-2175753 html  Example Code for Optional

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Since Android does not support Lambda Functions unless your installed OS is    24  we need to use reflection      Example using doIt function with sample classes public void Test         testEntry new Entry null        testEntry new Entry new Person new Name  Bob          static void testEntry Entry entry        doIt doIt doIt entry    getPerson     getName     getName          Helper to safely execute function  public static  lt T R gt  R doIt T obj  String methodName        try          if  obj    null              return  R obj getClass   getDeclaredMethod methodName  invoke obj         catch  Exception ignore              return null         Sample test classes     static class Entry           Person person          Entry Person person    this person   person            Person getPerson     return person               static class Person           Name name          Person Name name    this name   name            Name getName     return name               static class Name           String name          Name String name    this name   name            String getName                 System out print   Name     name                     return name

User · Answer

That s actually Groovy s safe-dereference operator   You can t use it in pure Java  sadly   so that post is simply wrong  or more likely slightly misleading  if it s claiming Groovy to be the  latest version of Java

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It is possible to define util methods which solves this in an almost pretty way with Java 8 lambda   This is a variation of H-MANs solution but it uses overloaded methods with multiple arguments to handle multiple steps instead of catching NullPointerException   Even if I think this solution is kind of cool I think I prefer Helder Pereira s seconds one since that doesn t require any util methods    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

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The original idea comes from groovy   It was proposed for Java 7 as part of Project Coin  https   wiki openjdk java net display Coin 2009 Proposals TOC  Elvis and Other Null-Safe Operators   but hasn t been accepted yet   The related Elvis operator    was proposed to make x    y shorthand for x    null   x   y  especially useful when x is a complex expression

[java] Java "?" Operator for checking null - What is it? (Not Ternary!)

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