Comparing integer Arrays in Java. Why does not == work?

Question

I\'m learning Java and just came up with this subtle fact about the language: if I declare two integer Arrays with the same elements and compare them using == t

Answer 1

No. ==compares numerical (or boolean) values, or references, only.

http://docs.oracle.com/javase/specs/jls/se7/html/jls-15.html#jls-15.21

You're probably looking for the Arrays.equals (a,b) method

Answer 2

If you use == operator with Object you are comparing the references, not the values.
If you use == operator with primitive types (int, long, boolean...) you are checking if they have the same values.

int[] a = {1, 2, 3};
int[] b = {1, 2, 3};

System.out.println(a == b); //return false;

System.out.println(a[0] == b[0]); //return true;



String[] a1 = {"Cat", "Dog", "Mouse"};
String[] b2 = {"Cat", "Dog", "Mouse"};

System.out.println(a1 == b1); //return false;

System.out.println(a1[0] == b1[0]); //return false; Because String are Object

You can use the Arrays.equals(array1, array2) method.

Answer 3

Use Arrays.equals(arr1, arr2) method.

The == operator just checks if two references point to the same object.

Test:

int[] a = {1, 2, 3};
int[] b = a;    
System.out.println(a == b);   // returns true as b and a refer to the same array  

int[] a = {1, 2, 3};
int[] b = {1, 2, 3};
System.out.println(Arrays.equals(a, b));   //returns true as a and b are meaningfully equal