This is odd. A co-worker asked about the implementation of myArray.hashCode() in java. I thought I knew but then I ran a few tests. Check the code below. The odd thing I noticed is that when I wrote the first sys out the results were different. Note that it's almost like it's reporting a memory address and modifying the class moved the address or something. Just thought I would share.
int[] foo = new int[100000];
java.util.Random rand = new java.util.Random();
for(int a = 0; a < foo.length; a++) foo[a] = rand.nextInt();
int[] bar = new int[100000];
int[] baz = new int[100000];
int[] bax = new int[100000];
for(int a = 0; a < foo.length; a++) bar[a] = baz[a] = bax[a] = foo[a];
System.out.println(foo.hashCode() + " ----- " + bar.hashCode() + " ----- " + baz.hashCode() + " ----- " + bax.hashCode());
// returns 4097744 ----- 328041 ----- 2083945 ----- 2438296
// Consistently unless you modify the class. Very weird
// Before adding the comments below it returned this:
// 4177328 ----- 4097744 ----- 328041 ----- 2083945
System.out.println("Equal ?? " +
(java.util.Arrays.equals(foo, bar) && java.util.Arrays.equals(bar, baz) &&
java.util.Arrays.equals(baz, bax) && java.util.Arrays.equals(foo, bax)));
The java.lang.Array
hashCode
method is inherited from Object
, which means the hashcode depends on the reference. To get the hashcode based on the content of the array use Arrays.hashCode
.
Beware though its a shallow hashcode implementation. A deep implementation is also present Arrays.deepHashCode
.