JDK java.util.concurrent.ConcurrentSkipListSet.equals(Object o) implementation efficiency

[Tenghuan He]

Hi, all

I found that the equalsimplementation of
java.util.concurrent.ConcurrentSkipListSet in JDK as follows:

public boolean equals(Object o) {
    // Override AbstractSet version to avoid calling size()
    if (o == this)
        return true;
    if (!(o instanceof Set))
        return false;
    Collection<?> c = (Collection<?>) o;
    try {
        return containsAll(c) && c.containsAll(this);
    } catch (ClassCastException unused) {
        return false;
    } catch (NullPointerException unused) {
        return false;
    }}


Since ConcurrentSkipListSet extends NavigableSet which extends SortedSet,
the following equalsimplementation seems more reasonable for a compare
object which also extends SortedSet.

public boolean myEquals(Object o) {
        // Override AbstractSet version to avoid calling size()
        if (o == this)
            return true;
        if (!(o instanceof Set))
            return false;
        if (o instanceof SortedSet) {
            Iterator iter1 = ((SortedSet) o).iterator();
            Iterator iter2 = iterator();

            while (iter1.hasNext() && iter2.hasNext()) {
                if (!iter1.next().equals(iter2.next())) {
                    return false;
                }
            }
            return !(iter1.hasNext() || iter1.hasNext());
        }
        Collection<?> c = (Collection<?>) o;
        try {
            return containsAll(c) && c.containsAll(this);
        } catch (ClassCastException unused) {
            return false;
        } catch (NullPointerException unused) {
            return false;
        }
    }

A simple test has shown the performance improvement

public class Test {
    public static void main(String[] args) {
        ConcurrentSkipListSet<Integer> set1 = new
ConcurrentSkipListSet<Integer>();
        ConcurrentSkipListSet<Integer> set2 = new
ConcurrentSkipListSet<Integer>();

        for (int i = 0; i < 10000000; i++) {
            set1.add(i);
            set2.add(i);
        }

        long ts = System.currentTimeMillis();
        System.out.println(set1.equals(set2));
        System.out.println(System.currentTimeMillis() - ts);

        ts = System.currentTimeMillis();
        System.out.println(myset1.myEquals(myset2));
        System.out.println(System.currentTimeMillis() - ts);
    }}

Output result

true2713true589


Any ideas? (Related question on SO:
https://stackoverflow.com/questions/44198103/jdk-java-util-concurrent-concurrentskiplistset-equalsobject-o-implementation-e

Thanks & Best Regards

Tenghuan He