public boolean contains(long item1, long item2) {
        lock.readLock().lock();
        try {
            RoaringBitmap bitSet = map.get(item1);
            return bitSet != null && bitSet.contains(item2, item2 + 1);
        } finally {
            lock.readLock().unlock();
        }
    }
@Test
    public void testContains() {
        ConcurrentBitmapSortedLongPairSet set = new ConcurrentBitmapSortedLongPairSet();
        assertFalse(set.contains(1, 1));

        int items = 10;
        for (int i = 0; i < items; i++) {
            set.add(1, i);
        }

        for (int i = 0; i < items; i++) {
            assertTrue(set.contains(1, i));
        }

        assertFalse(set.contains(1, 10000));
    }