@Override
	public V putIfAbsent(K key, V value) {
		if (null != this.inverse) {
			this.inverse.putIfAbsent(value, key);
		}
		return super.putIfAbsent(key, value);
	}
@Test
	public void putIfAbsentTest(){
		final BiMap<String, Integer> biMap = new BiMap<>(new HashMap<>());
		biMap.put("aaa", 111);
		biMap.put("bbb", 222);

		biMap.putIfAbsent("ccc", 333);
		assertEquals(new Integer(333), biMap.get("ccc"));
		assertEquals("ccc", biMap.getKey(333));
	}