Comparing two integer arrays in Java

Question

I am trying to write code to compare two arrays  In the first array I have put my own digits  but the second the array takes numbers from the input file  The size of this array is determined by the first number in the file while the first array is always of size 10  The length must be the same for both arrays as well as the numbers   My code is below   public static void compareArrays int   array1  int   array2        boolean b   false      for  int i   0  i  lt  array2 length  i               for  int a   0  a  lt  array1 length  a                   if  array2 i     array1 a                     b   true                  System out println  true                  else                   b   false                  System out println  False                    break

User · Answer

None of the existing answers involve using a comparator  and therefore cannot be used in binary trees or for sorting  So I m just gonna leave this here   public static int compareIntArrays int   a  int   b        if  a    null            return b    null   0   -1            if  b    null            return 1            int cmp   a length - b length      if  cmp    0            return cmp            for  int i   0  i  lt  a length  i              cmp   Integer compare a i   b i            if  cmp    0                return cmp                      return 0

User · Answer

From what I see you just try to see if they are equal  if this is true  just go with something like this   boolean areEqual   Arrays equals arr1  arr2     This is the standard way of doing it   Please note that the arrays must be also sorted to be considered equal  from the JavaDoc      Two arrays are considered equal if both arrays contain the same number   of elements  and all corresponding pairs of elements in the two arrays   are equal  In other words  two arrays are equal if they contain the   same elements in the same order    Sorry for missing that

User · Answer

The length of the arrays must be the same and the numbers just be the same throughout 1st number in arrays must be the sasme and so on    Based on this comment  then you already have your algorithm    Check if both arrays have the same length   array1 length    array2 length The numbers must be the same in the same position   array1 x     array2 x    Knowing this  you can create your code like this  this is not Java code  it s an algorithm    function compareArrays int   array1  int   array2         if  array1    null  return false     if  array2    null  return false      if array1 length    array2 length then return false      for i  lt - 0 to array1 length - 1         if array1 i     array2 i  return false      return true     Note  your function should return a boolean  not being a void  then recover the return value in another variable and use it to print the message  true  or  false    public static void main String   args        int   array1      int   array2        initialize the arrays          fill the arrays with items          call the compare function     boolean arrayEquality   compareArrays array1  array2       if  arrayEquality            System out println  arrays are equals          else           System out println  arrays are not equals

User · Answer

If you know the arrays are of the same size it is provably faster to sort then compare  Arrays sort array1  Arrays sort array2  return Arrays equals array1  array2    If you do not want to change the order of the data in the arrays then do a System arraycopy first

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public static void compareArrays int   array1  int   array2            boolean b   true          if  array1    null  amp  amp  array2    null             if  array1 length    array2 length                b   false            else               for  int i   0  i  lt  array2 length  i                        if  array2 i     array1 i                           b   false                                                                  else            b   false                    System out println b

User · Answer

use Arrays equals ary1 ary2       returns boolean value  EDIT you can use Arrays deepEquals ary1 ary2  to compare 2D arrays as well  also check this link for comparision comparision between Arrays equls ar1 ar2  and Arrays deepEquals ar1 ar2   Java Arrays equals   returns false for two dimensional arrays  EDIT 2 if you dont want to use these library methods then you can easily implement your method like this   public static boolean ArrayCompare int   a  int   a2        if  a  a2       checks for same array reference         return true      if  a  null    a2  null      checks for null arrays         return false       int length   a length      if  a2 length    length      arrays should be of equal length         return false       for  int i 0  i lt length  i        compare array values         if  a i     a2 i               return false       return true

User · Answer

For the sake of completeness  you should have a method which can check all arrays       public static  lt E gt  boolean compareArrays E   array1  E   array2          boolean b   true        for  int i   0  i  lt  array2 length  i              if  array2 i  equals array1 i         For String Compare            System out println  true              else              b   false             System out println  False                             return b

User · Answer

Even though there is something easy like  equals  I d like to point out TWO mistakes you made in your code  The first  when you go through the arrays  you say b is true or false  Then you start again to check  because of the for-loop  But each time you are giving b a value  So  no matter what happens  the value b gets set to is always the value of the LAST for-loop  Next time  set boolean b   true  if equal   true  do nothing  if equal   false  b false   Secondly  you are now checking each value in array1 with each value in array2  If I understand correctly  you only need to check the values at the same location in the array  meaning you should have deleted the second for-loop and check like this  if  array2 i     array1 i    Then your code should function as well   Your code would work like this   public static void compareArrays int   array1  int   array2        boolean b   true      for  int i   0  i  lt  array2 length  i              if  array2 i     array1 i                 System out println  true              else               b   false              System out println  False                         return b       But as said by other  easier would be  Arrays equals ary1 ary2

User · Answer

You can check array equality with the Apache Commons ArrayUtils isEquals   method

User · Answer

Here my approach it may be useful to others   public static void compareArrays int   array1  int   array2        if  array1 length    array2 length                   System out println  Not Equal              else               int temp   0          for  int i   0  i  lt  array2 length  i         Take any one of the array size             temp    array1 i    array2 i       with help of xor operator to find two array are equal or not                                    if  temp    0                          System out println  Equal                      else               System out println  Not Equal

[java] Comparing two integer arrays in Java

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