concurrent test for hashset on JDK8

HashSetTest.java

import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
import java.util.concurrent.CyclicBarrier;

public class HashSetTest {

    private static Set<String> set = new HashSet<String>();

    public static boolean update(final Set<String> subList) {
        boolean updated = !set.equals(subList);
        set.addAll(subList);

        Iterator<String> it = set.iterator();
        while (it.hasNext()) {
            String next = it.next();
            boolean exist = subList.contains(next);

            if (!exist) {
                it.remove();
                updated = true;
            }
        }

        return updated;
    }

    public static void main(String[] args) throws Exception {
        int threads = 10;
        final CyclicBarrier barrier = new CyclicBarrier(threads + 1);
        for (int i = 0; i < threads; i++) {
            new Thread() {
                public void run() {
                    try {
                        barrier.await();
                        Set<String> newSet = new HashSet<String>();
                        newSet.add("a");
                        newSet.add("b");
                        while (update(newSet)) {
                            System.out.println(set.size() + " " + set);
                        }
                        barrier.await();
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            }.start();
        }
        barrier.await();
        barrier.await();
    }
}