@Override
    public int hashCode()
    {
        return Long.hashCode(numberAndGeneration);
    }
@Test
    void checkHashCode()
    {
        // same object number 100 0
        assertEquals(new COSObjectKey(100, 0).hashCode(),
                new COSObjectKey(100, 0).hashCode());

        // different object numbers/same generation numbers 100 0 vs. 200 0
        assertNotEquals(new COSObjectKey(100, 0).hashCode(),
                new COSObjectKey(200, 0).hashCode());

        // different object numbers/different generation numbers/ sum of both numbers are equal 100 0 vs. 99 1
        assertNotEquals(new COSObjectKey(100, 0).hashCode(),
                new COSObjectKey(99, 1).hashCode());
    }