How to check if my string is equal to null

Question

I want to perform some action ONLY IF my string has a meaningful value  So  I tried this   if   myString equals        doSomething     and this  if   myString equals null     doSomething     and this  if     myString equals       amp  amp    myString equals null      doSomething     and this  if     myString equals       amp  amp   myString  null     doSomething     and this  if   myString length   gt 0    doSomething     And in all cases my program doSomething in spite on the fact that my string IS EMPTY  It equals to null  So  what is wrong with that   ADDED   I found the reason of the problem  The variable was declared as a string and  as a consequence  null assigned to this variable was transformed to  null   So  if   myString equals  null    works

User · Answer

Try   myString  null  amp  amp  myString length   gt 0

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I been using StringUtil isBlank string    It tests if a string is blank  null  emtpy  or only whitespace   So this one is the best so far  Here is the orignal method from the docs            Tests if a string is blank  null  emtpy  or only whitespace        r n   t  etc         param string string to test        return if string is blank            public static boolean isBlank String string            if  string    null    string length      0              return true           int l   string length            for  int i   0  i  lt  l  i                  if   StringUtil isWhitespace string codePointAt i                    return false                    return true

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Okay this is how datatypes work in Java   You have to excuse my English  I am prob  not using the right vocab  You have to differentiate between two of them  The base datatypes and the normal datatypes  Base data types pretty much make up everything that exists  For example  there are all numbers  char  boolean etc   The normal data types or complex data types is everything else   A String is an array of chars  therefore a complex data type   Every variable that you create is actually a pointer on the value in your memory  For example   String s   new String  This is just a test      the variable  s  does NOT contain a String  It is a pointer  This pointer points on the variable in your memory  When you call System out println anyObject   the toString   method of that object is called  If it did not override toString from Object  it will print the pointer  For example   public class Foo      public static void main String   args            Foo f   new Foo            System out println f             gt  gt  gt  gt   gt  gt  gt  gt   gt  gt  gt  gt Foo 330bedb4   Everything behind the     is the pointer  This only works for complex data types  Primitive datatypes are DIRECTLY saved in their pointer  So actually there is no pointer and the values are stored directly   For example   int i   123    i does NOT store a pointer in this case  i will store the integer value 123  in byte ofc    Okay so lets come back to the    operator  It always compares the pointer and not the content saved at the pointer s position in the memory   Example   String s1   new String  Hallo    String s2   new String  Hallo     System out println s1    s2     gt  gt  gt  gt  gt  false   This both String have a different pointer  String equals String other  however compares the content  You can compare primitive data types with the      operator because the pointer of two different objects with the same content is equal   Null would mean that the pointer is empty  An empty primitive data type by default is 0  for numbers   Null for any complex object however means  that object does not exist   Greetings

User · Answer

If myString is null  then calling myString equals null  or myString equals     will fail with a NullPointerException  You cannot call any instance methods on a null variable   Check for null first like this   if  myString    null  amp  amp   myString equals              do something     This makes use of short-circuit evaluation to not attempt the  equals if myString fails the null check

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I would encourage using an existing utility  or creating your own method   public static boolean isEmpty String string        return string    null    string length      0      Then just use it when you need it   if    StringUtils isEmpty string          do something     As noted above  the    and  amp  amp  operators short circuit   That means as soon as they can determine their value they stop   So if  string    null  is true  the length part does not need to be evaluated  as the expression would always be true   Likewise with  amp  amp   where if the left side is false  the expression is always false and need not be evaluated further   As an additional note  using length is generally a better idea than using  equals   The performance is slightly better  not much   and doesn t require object creation  though most compilers might optimize this out

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if str isEmpty      str  null   do whatever you want

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You need to check that the myString object is null   if  myString    null        doSomething

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You can check string equal to null using this   String Test   null   Test     compareTo  null     If the result is 0 then  Test        null

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if  myString    null  amp  amp  myString length    gt  0                your magic here       Incidently  if you are doing much string manipulation  there s a great Spring class with all sorts of useful methods    http   static springsource org spring docs 2 5 x api org springframework util StringUtils html

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In Android you can check this with utility method isEmpty from TextUtils   public static boolean isEmpty CharSequence str        return str    null    str length      0      isEmpty CharSequence str  method check both condition  for null and length

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If your string is null  calls like this should throw a NullReferenceException   myString equals null   But anyway  I think a method like this is what you want   public static class StringUtils       public static bool isNullOrEmpty String myString                 return myString    null       equals myString             Then in your code  you can do things like this   if   StringUtils isNullOrEmpty myString         doSomething

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I always use like this    if  mystr    null  amp  amp   mystr isEmpty         DO WHATEVER YOU WANT OR LEAVE IT EMPTY  else       DO WHATEVER YOU WANT OR LEAVE IT EMPTY     or you can copy this to your project   private boolean isEmptyOrNull String mystr       if  mystr    null  amp  amp   mystr isEmpty     return true        else   return false        and just call it like     boolean b   isEmptyOrNull yourString     it will return true if is empty or null b true if is empty or null  or you can use try catch and catch when it is null

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I tried most of the examples given above for a null in an android app l was building and IT ALL FAILED  So l came up with a solution that worked anytime for me   String test   null     If  test equals  null             go ahead string is not null      So simply concatenate an empty string as l did above and test against  null  and it works fine  In fact no exception is thrown

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I think that myString is not a string but an array of strings  Here is what you need to do   String myNewString   join myString      if   myNewString equals              Do something

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WORKING       if  myString    null  amp  amp   myString isEmpty              return true            else           return false         Updated For Kotlin we check if the string is null or not by following return myString isNullOrEmpty      Returns  true  if this nullable String is either  null  or empty  false otherwise  return myString isEmpty      Returns  true  if this char sequence is empty  contains no characters   false otherwise

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This should work   if  myString    null  amp  amp   myString equals          doSomething     If not  then myString likely has a value that you are not expecting   Try printing it out like this   System out println       myString           Using the     symbols to surround the string will show you if there is extra whitespace in there that you re not accounting for

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For me the best check if a string has any meaningful content in Java is this one   string    null  amp  amp   string trim   isEmpty     First you check if the string is null to avoid NullPointerException and then you trim all space characters to avoid checking strings that only have whitespaces and finally you check if the trimmed string is not empty  i e has length 0

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Apache commons StringUtils isNotEmpty is the best way to go

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I had this problem in android and i use this way  Work for me    String test   null  if test     null       Do work     But in java code I use    String test   null  if test    null      Do work     And     private Integer compareDateStrings BeanToDoTask arg0  BeanToDoTask arg1  String strProperty        String strDate0   BeanUtils getProperty arg0  strProperty   logger debug  strDate0       strDate0       String strDate1   BeanUtils getProperty arg1  strProperty   logger debug  strDate1       strDate1       return compareDateStrings strDate0  strDate1      private Integer compareDateStrings String strDate0  String strDate1        int cmp   0      if  isEmpty strDate0             if  isNotEmpty strDate1                 cmp   -1            else               cmp   0                  else if  isEmpty strDate1             cmp   1        else           cmp   strDate0 compareTo strDate1             return cmp     private boolean isEmpty String str        return str    null    str isEmpty      private boolean isNotEmpty String str        return  isEmpty str

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I d do something like this     myString    null  amp  amp  myString length    gt  0         doSomething     System out println  Non valid String       Testing for null checks whether myString contains an instance of String  length   returns the length and is equivalent to equals      Checking if myString is null first will avoid a NullPointerException

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You have to check with null if str    null

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If myString is in fact null  then any call to the reference will fail with a Null Pointer Exception  NPE    Since java 6  use  isEmpty instead of length check  in any case NEVER create a new empty String with the check    if  myString    null  amp  amp    myString isEmpty         doSomething        Incidentally if comparing with String literals as you do  would reverse the statement so as not to have to have a null check  i e   if   some string to check  equals myString      doSomething         instead of    if  myString    null  amp  amp   myString equals  some string to check         doSomething

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Exception may also help   try        define your myString   catch  Exception e         in that case  you may affect    to myString    myString

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if  myString    null  amp  amp   myString isEmpty           doSomething       As further comment  you should be aware of this term in the equals contract   From Object equals Object       For any non-null reference value x  x equals null  should return false     The way to compare with null is to use x    null and x    null   Moreover  x field and x method   throws NullPointerException if x    null

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I prefer to use   if  StringUtils isBlank myString        checks if myString is whitespace  empty  or null        do something     Read StringUtils isBlank   vs String isEmpty

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If you are working in Android then you can use the simple TextUtils class  Check the following code   if  TextUtils isEmpty myString       do something     This is simple usage of code  Answer may be repeated  But is simple to have single and simple check for you

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Every time i have to deal with strings  almost every time  I stop and wonder which way is really the fastest way to check for an empty string  Of course the string Length    0 check should be the fastest since Length is a property and there shouldn t be any processing other than retrieving the value of the property  But then I ask myself  why is there a String Empty  It should be faster to check for String Empty than for length  I tell myself  Well i finnaly decided to test it out  I coded a small Windows Console app that tells me how long it takes to do a certain check for 10 million repitions  I checked 3 different strings  a NULL string  an Empty string  and a    string  I used 5 different methods  String IsNullOrEmpty    str    null  str    null    str    String Empty  str    null    str        str    null    str length    0  Below are the results   String IsNullOrEmpty   NULL   62 milliseconds Empty   46 milliseconds      46 milliseconds  str    null NULL   31 milliseconds Empty   46 milliseconds      31 milliseconds  str    null    str    String Empty NULL   46 milliseconds Empty   62 milliseconds      359 milliseconds  str    null    str       NULL   46 milliseconds Empty   343 milliseconds      78 milliseconds  str    null    str length    0 NULL   31 milliseconds Empty   63 milliseconds      62 milliseconds   According to these results  on average checking for str    null is the fastest  but might not always yield what we re looking for  if str   String Empty or str       it results in false  Then you have 2 that are tied in second place  String IsNullOrEmpty   and str    null    str length    0  Since String IsNullOrEmpty   looks nicer and is easier  and faster  to write I would recommend using it over the other solution

[java] How to check if my string is equal to null?

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