6)computeIfAbsent(K key, Function<? super K, ? extends V> mappingFunction);//当key不存在时才put，如果key存在则无效
/** * 当key不存在时才put，如果key存在则无效 * 如：computeIfAbsent(keyC, k -> genValue(k)); * Function返回值作为新的value,Function只有一个参数 * @param key * @param mappingFunction * @return */ @Override public V computeIfAbsent(K key, Function<? super K, ? extends V> mappingFunction) { if (mappingFunction == null) throw new NullPointerException(); int hash = hash(key); Node<K,V>[] tab; Node<K,V> first; int n, i; int binCount = 0; TreeNode<K,V> t = null; Node<K,V> old = null; if (size > threshold || (tab = table) == null || (n = tab.length) == 0) n = (tab = resize()).length; if ((first = tab[i = (n - 1) & hash]) != null) { if (first instanceof TreeNode) old = (t = (TreeNode<K,V>)first).getTreeNode(hash, key); else { Node<K,V> e = first; K k; do { if (e.hash == hash && ((k = e.key) == key || (key != null && key.equals(k)))) { old = e; break; } ++binCount; } while ((e = e.next) != null); } V oldValue; if (old != null && (oldValue = old.value) != null) { afterNodeAccess(old); return oldValue; } } V v = mappingFunction.apply(key); if (v == null) { return null; } else if (old != null) { old.value = v; afterNodeAccess(old); return v; } else if (t != null) t.putTreeVal(this, tab, hash, key, v); else { tab[i] = newNode(hash, key, v, first); if (binCount >= TREEIFY_THRESHOLD - 1) treeifyBin(tab, hash); } ++modCount; ++size; afterNodeInsertion(true); return v; }7)computeIfPresent(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction);//compute方法的补充，如果key存在，则覆盖新的BiFunction计算出的value值，如果不存在则跳过
/** * compute方法的补充，如果key存在，则覆盖新的BiFunction计算出的value值，如果不存在则跳过 * @param key * @param remappingFunction * @return */ public V computeIfPresent(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction) { if (remappingFunction == null) throw new NullPointerException(); Node<K,V> e; V oldValue; int hash = hash(key); if ((e = getNode(hash, key)) != null && (oldValue = e.value) != null) { V v = remappingFunction.apply(key, oldValue); if (v != null) { e.value = v; afterNodeAccess(e); return v; } else removeNode(hash, key, null, false, true); } return null; }8)V replace(K key, V value);//替换新值
/** * 如果key存在不为空，则替换新的value值 */ @Override public V replace(K key, V value) { Node<K,V> e; if ((e = getNode(hash(key), key)) != null) { V oldValue = e.value; e.value = value; afterNodeAccess(e); return oldValue; } return null; }9)replace(K key, V oldValue, V newValue);//判断oldValue是否是当前key的值，再替换新值
/** * 如果key存在不为空并且oldValue等于当前key的值，则替换新的value值 */ @Override public boolean replace(K key, V oldValue, V newValue) { Node<K,V> e; V v; if ((e = getNode(hash(key), key)) != null && ((v = e.value) == oldValue || (v != null && v.equals(oldValue)))) { e.value = newValue; afterNodeAccess(e); return true; } return false; }