deepEquals - Lists are equal, Sets are not

Question

I have a class M with hashCode() and equals() generated by Eclipse (please see below).

Two lists with equal M's are equal, Two sets with equal M's are not equal.

Is this a bug in deepEquals() or am I confused?

import java.util.ArrayList;
import java.util.Arrays;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Set;
class M {
    @Override public int hashCode() {
        final int prime=31;
        int result=1;
        result=prime*result+Arrays.hashCode(b);
        return result;
    }
    @Override public boolean equals(Object obj) {
        if(this==obj) return true;
        if(obj==null) return false;
        if(getClass()!=obj.getClass()) return false;
        M other=(M)obj;
        if(!Arrays.deepEquals(b,other.b)) return false;
        return true;
    }
    int[][] b=new int[3][3];
}
public class SetEquality {
    static List<Object> list(Object o) {
        ArrayList<Object> l=new ArrayList<>();
        l.add(o);
        return l;
    }
    static Set<Object> set(Object o) {
        Set<Object> l=new LinkedHashSet<>();
        l.add(o);
        return l;
    }
    public static void main(String[] args) {
        M f=new M();
        M g=new M();
        List<Object> listWithF=list(f);
        List<Object> listWithG=list(g);
        System.out.println("lists: "+listWithF.equals(listWithG));
        Set<Object> setWithF=set(f);
        Set<Object> setWithG=set(g);
        System.out.println("sets: "+setWithF.equals(setWithG));
    }
}

Answer 1

The problem is that your objects aren't returning equal hashcodes. You need to use Arrays.deepHashCode() instead (see e.g. http://ideone.com/qPyWLh).

This appears to be a known bug in Eclipse: https://bugs.eclipse.org/bugs/show_bug.cgi?id=422717.