HashCode() of arrays

Question

Hi,
I want to put some vectors into a set, so I wrote the following code:
Set<double[]> set = new HashSet<double[]>();
double[] x = new double[] { 1., 2., 3. },
         y = x.clone();
set.add(x);
set.add(y);
System.out.println(set.size()); // prints "2"The problem is that the standard hashCode() implementation of java arrays does not take into account the array values. That's why the vectors x and y hash differently. My question: How can I change this behaviour? The only way I see would be to encapsulate the array into its own class and override the hashCode() method, e.g. using Arrays.hashCode(double[] x).
I think that's pretty ugly :-( Is there a better way to do this?
Thanks!
gogo_

Answer 1

Yes, indeed, the Arrays class might be helpful, as I pointed out in my original posting.
I would like to know how to change the default hashCode() for arrays. The Arrays class just gives me one possible way to compute a different hash value, but this function will not be used when I put the array into a HashSet.
For example, when sorting a collection, it is always possible to provide the sort method with a different comparator then the default one. That's what I am looking for here. The only solution I found is the code below. Really ugly. Especially when you have more than one array type, this code needs to be duplicated again and again. You cannot even use Generics because it's an array of primitive types!
It can't be that hard!! I have added some extra duke stars.
Thanks for your time
gogo_
import java.util.Arrays;
import java.util.HashSet;
import java.util.Set;
public class Test {
    private static class DoubleArray {
        double[] x;
        DoubleArray(double[] x) {
            this.x = x;
        @Override
        public boolean equals(Object obj) {
            if (obj == null)
                return false;
            if (getClass() != obj.getClass())
                return false;
            final DoubleArray other = (DoubleArray) obj;
            return Arrays.equals(x, other.x);
        @Override
        public int hashCode() {
            return Arrays.hashCode(x);
    public static void main(String[] ignored) {
        DoubleArray x = new DoubleArray(new double[] { 1., 2., 3. }),
                    y = new DoubleArray(new double[] { 1., 2., 3. });
        Set<DoubleArray> set = new HashSet<DoubleArray>();
        set.add(x);
        set.add(y);
        System.out.println(set.size()); // prints "1"
}