### Question:
ConcurrentOpenHashMap { public V putIfAbsent(K key, V value) { checkNotNull(key); checkNotNull(value); long h = hash(key); return getSection(h).put(key, value, (int) h, true, null); } ConcurrentOpenHashMap();  ConcurrentOpenHashMap(int expectedItems);  ConcurrentOpenHashMap(int expectedItems, int concurrencyLevel); long size(); long capacity(); boolean isEmpty(); V get(K key); boolean containsKey(K key); V put(K key, V value); V putIfAbsent(K key, V value); V computeIfAbsent(K key, Function<K, V> provider); V remove(K key); boolean remove(K key, Object value); void clear(); void forEach(BiConsumer<? super K, ? super V> processor); int removeIf(BiPredicate<K, V> filter); List<K> keys(); List<V> values();  }### Answer:
@Test public void testPutIfAbsent() { ConcurrentOpenHashMap<Long, String> map = new ConcurrentOpenHashMap<>(); assertEquals(map.putIfAbsent(1L, "one"), null); assertEquals(map.get(1L), "one"); assertEquals(map.putIfAbsent(1L, "uno"), "one"); assertEquals(map.get(1L), "one"); }