How does Java compare Sets?

Question

I have a class

class Foo
{
   int x;
   Set<Integer> set;
}

When I build a set Set<Foo> , it compiles and runs. Comparing integers are simple, but how does Java compare two sets?

Should I override as

        if(this.toBeLocalized != that.toBeLocalized)
        {
            if(this.set.size() == that.set.size())
            {
                Set<Integer> ref = new HashSet<>();
                ref.addAll(this.set);
                ref.removeAll(that.set);
                if(ref == null)
                {
                    return 0;
                }
            }
        }
        return -1;
    }

Or there is a comparison for sets?

Answer 1

this is implementation of methd equals from class AbstractSet , and most of implementations of Set will extends it

  public boolean equals(Object o) {
    if (o == this)
        return true;

    if (!(o instanceof Set))
        return false;
    Collection c = (Collection) o;
    if (c.size() != size())
        return false;
        try {
            return containsAll(c);
        } catch (ClassCastException unused)   {
            return false;
        } catch (NullPointerException unused) {
            return false;
        }
    }

Answer 2

Set already defines .equals() , and all implementations of Set are required to implement it the way the doc says (and, of course, it goes for .hashCode() as well).

So you just have to:

set1.equals(set2)

Note that the contract stipulate that order of elements does not matter , so [1, 2, 3] and [2, 1, 3] are equal. This is unlike List where order does matter.