How can I check whether an array is null empty

Question

I have an int array which has no elements and I m trying to check whether it s empty   For example  why is the condition of the if-statement in the code below never true   int   k   new int 3    if  k    null        System out println k length

User · Answer

Method to check array for null or empty also is present on org apache commons lang   import org apache commons lang ArrayUtils   ArrayUtils isEmpty array

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I tested as below  Hope it helps    Integer   integers1   new Integer 10           System out println integers1 length     it has length 10 but it is empty  It is not null array         for  Integer integer   integers1                System out println integer     prints all 0s              But if I manually add 0 to any index  now even though array has all 0s elements   still it is not empty           integers1 2    0          for  Integer integer   integers1                System out println integer     Still it prints all 0s but it is not empty               but that manually added 0 is different              Even we manually add 0  still we need to treat it as null  This is semantic logic           Integer   integers2   new Integer 20           integers2   null    array is nullified           integers2 3    null    If I had int   -- because it is priitive -- then I can t write this line           if  integers2    null                System out println  null Array

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An int array without elements is not necessarily null  It will only be null if it hasn t been allocated yet  See this tutorial for more information about Java arrays   You can test the array s length   void foo int   data      if data length    0      return

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I believe that what you want is  int   k   new int 3    if  k    null        Note     and not    as above     System out println k length       You newed it up so it was never going to be null

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if you are trying to check that in spring frame work then isEmpty method in objectUtils class helps  public static boolean isEmpty  Nullable Object   array            return  array    null    array length    0

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I am from  net background  However  java c  are more less same   If you instantiate a non-primitive type  array in your case   it won t be null  e g  int   numbers   new int 3   In this case  the space is allocated  amp  each of the element has a default value of 0   It will be null  when you don t new it up  e g    int   numbers   null     changed as per  Joachim s suggestion  if  numbers    null       System out println  yes  it is null  Please new it up

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You can also check whether there is any elements in the array by finding out its length  then put it into if-else statement to check whether it is null    int   k   new int 3   if k length    0      do something

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The point here very simply is that the variable k isn t null because it points to the array  It doesn t matter that the array itself is empty  The null test in your post would only evaluate to true if the variable k didn t point to anything

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There s a key difference between a null array and an empty array  This is a test for null   int arr     null  if  arr    null      System out println  array is null         Empty  here has no official meaning  I m choosing to define empty as having 0 elements   arr   new int 0   if  arr length    0      System out println  array is empty        An alternative definition of  empty  is if all the elements are null   Object arr     new Object 10   boolean empty   true  for  int i 0  i lt arr length  i        if  arr i     null        empty   false      break          or  Object arr     new Object 10   boolean empty   true  for  Object ob   arr      if  ob    null        empty   false      break

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An int array is initialised with zero so it won t actually ever contain nulls  Only arrays of Object s will contain null initially

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In Java 8  you achieve this with the help of streams allMatch method   For primitive   int   k   new int 3   Arrays stream k  allMatch element - gt  element    0    For Object   Objects   k   new Objects 3   Arrays stream k  allMatch Objects  nonNull

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ArrayUtils isNotEmpty testArrayName  from the package org apache commons lang3 ensures Array is not null or empty

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Look at its length   int   i        if  i length    0         no elements in the array   Though it s safer to check for null at the same time   if  i    null    i length    0

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public boolean empty         boolean isEmpty   true      int i   0      for  int j   0  j  lt  array length  j              if  array j     0                i                        if  i    0            isEmpty   false            return isEmpty      This is as close as I got to checking if an int array is empty  Although this will not work when the ints in the array are actually zero  It ll work for  1 2 3   and it ll still return false if  2 0  but  0  will return true

[java] How can I check whether an array is null / empty?

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