how to compare the Java Byte array

Question

public class ByteArr        public static void main String   args           Byte   a     byte 0x03   byte 0x00   byte 0x00   byte 0x00           Byte   b     byte 0x03   byte 0x00   byte 0x00   byte 0x00           byte   aa     byte 0x03   byte 0x00   byte 0x00   byte 0x00           byte   bb     byte 0x03   byte 0x00   byte 0x00   byte 0x00            System out println a           System out println b           System out println a    b           System out println a equals b             System out println aa           System out println bb           System out println aa    bb           System out println aa equals bb              I do not know why all of them print false   When I run  java ByteArray   the answer is  false false false false    I think the a   equals b   but the JVM is telling me I am wrong  why

User · Answer

They are returning false because you are testing for object identity rather than value equality. This returns false because your arrays are actually different objects in memory.

If you want to test for value equality should use the handy comparison functions in java.util.Arrays

e.g.

import java.util.Arrays;

'''''

Arrays.equals(a,b);

User · Answer

have you looked at Arrays equals     Edit  if  as per your comment  the issue is using a byte array as a HashMap key then see this question

User · Answer

why a   doesn t equals b    Because equals function really called on Byte   or byte   is Object equals Object obj   This functions only compares object identify   don t compare the contents of the array

User · Answer

As byte   is mutable it is treated as only being  equals   if its the same object   If you want to compare the contents you have to use Arrays equals a  b   BTW  Its not the way I would design it

User · Answer

I looked for an array wrapper which makes it comparable to use with guava TreeRangeMap  The class doesn t accept comparator   After some research I realized that ByteBuffer from JDK has this feature and it doesn t copy original array which is good  More over you can compare faster with ByteBuffer  asLongBuffer 8 bytes at time  also doesn t copy   By default ByteBuffer  wrap byte    use BigEndian so order relation is the same as comparing individual bytes

User · Answer

Use Arrays equals   if you want to compare the actual content of arrays that contain primitive types values  like byte    System out println Arrays equals aa  bb      Use Arrays deepEquals for comparison of arrays that contain objects

User · Answer

If you re trying to use the array as a generic HashMap key  that s not going to work  Consider creating a custom wrapper object that holds the array  and whose equals      and hashcode      method returns the results from the java util Arrays methods  For example     import java util Arrays   public class MyByteArray      private byte   data             constructors  getters methods  setter methods  etc          Override    public int hashCode           return Arrays hashCode data             Override    public boolean equals Object obj          if  this    obj           return true        if  obj    null           return false        if  getClass      obj getClass             return false        MyByteArray other    MyByteArray  obj        if   Arrays equals data  other data            return false        return true             Objects of this wrapper class will work fine as a key for your HashMap lt MyByteArray  OtherType gt  and will allow for clean use of equals      and hashCode      methods

User · Answer

There s a faster way to do that   Arrays hashCode arr1     Arrays hashCode arr2

User · Answer

Cause they re not equal  ie  they re different arrays with equal elements inside   Try using Arrays equals   or Arrays deepEquals

User · Answer

Because neither    nor the equals   method of the array compare the contents  both only evaluate object identity     always does  and equals   is not overwritten  so the version from Object is being used    For comparing the contents  use Arrays equals

User · Answer

You can also use a ByteArrayComparator from Apache Directory  In addition to equals it lets you compare if one array is greater than the other

User · Answer

Arrays equals is not enough for a comparator  you can not check the map contain the data  I copy the code from Arrays equals  modified to build a Comparator   class ByteArrays      public static  lt T gt  SortedMap lt byte    T gt  newByteArrayMap             return new TreeMap lt  gt  new ByteArrayComparator                public static SortedSet lt byte   gt  newByteArraySet             return new TreeSet lt  gt  new ByteArrayComparator                static class ByteArrayComparator implements Comparator lt byte   gt             Override         public int compare byte   a  byte   b                if  a    b                    return 0                            if  a    null    b    null                    throw new NullPointerException                               int length   a length              int cmp              if   cmp   Integer compare length  b length      0                    return cmp                             for  int i   0  i  lt  length  i                      if   cmp   Byte compare a i   b i       0                        return cmp                                               return 0

User · Answer

You can also use org apache commons lang ArrayUtils isEquals

User · Answer

Try for this   boolean blnResult   Arrays equals byteArray1  byteArray2     I am also not sure about this  but try this may be it works

User · Answer

Java byte compare   public static boolean equals byte   a  byte   a2            if  a    a2              return true          if  a    null    a2    null              return false           int length   a length          if  a2 length    length              return false           for  int i   0  i  lt  length  i                if  a i     a2 i                   return false           return true

[java] how to compare the Java Byte[] array?

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