目录

一、背景

二、方法

1.forEach()

2.replaceAll()

3.putIfAbsent()

4.computeIfAbsent()

5.computeIfPresent()

6.compute()

7.merge()

三、实现类

一、背景

二、方法

1.forEach()

default void forEach(BiConsumer<? super K, ? super V> action) {Objects.requireNonNull(action);for (Map.Entry<K, V> entry : entrySet()) {K k;V v;try {k = entry.getKey();v = entry.getValue();} catch(IllegalStateException ise) {// this usually means the entry is no longer in the map.throw new ConcurrentModificationException(ise);}action.accept(k, v);}}

2.replaceAll()

default void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {Objects.requireNonNull(function);for (Map.Entry<K, V> entry : entrySet()) {K k;V v;try {k = entry.getKey();v = entry.getValue();} catch(IllegalStateException ise) {// this usually means the entry is no longer in the map.throw new ConcurrentModificationException(ise);}// ise thrown from function is not a cme.v = function.apply(k, v);try {entry.setValue(v);} catch(IllegalStateException ise) {// this usually means the entry is no longer in the map.throw new ConcurrentModificationException(ise);}}}

3.putIfAbsent()

default V putIfAbsent(K key, V value) {V v = get(key);if (v == null) {v = put(key, value);}return v;}

4.computeIfAbsent()

default V computeIfAbsent(K key,Function<? super K, ? extends V> mappingFunction) {Objects.requireNonNull(mappingFunction);V v;if ((v = get(key)) == null) {V newValue;if ((newValue = mappingFunction.apply(key)) != null) {put(key, newValue);return newValue;}}return v;}

5.computeIfPresent()

default V computeIfPresent(K key,BiFunction<? super K, ? super V, ? extends V> remappingFunction) {Objects.requireNonNull(remappingFunction);V oldValue;if ((oldValue = get(key)) != null) {V newValue = remappingFunction.apply(key, oldValue);if (newValue != null) {put(key, newValue);return newValue;} else {remove(key);return null;}} else {return null;}}

6.compute()

default V compute(K key,BiFunction<? super K, ? super V, ? extends V> remappingFunction) {Objects.requireNonNull(remappingFunction);V oldValue = get(key);V newValue = remappingFunction.apply(key, oldValue);if (newValue == null) {// delete mappingif (oldValue != null || containsKey(key)) {// something to removeremove(key);return null;} else {// nothing to do. Leave things as they were.return null;}} else {// add or replace old mappingput(key, newValue);return newValue;}}

7.merge()

default V merge(K key, V value,BiFunction<? super V, ? super V, ? extends V> remappingFunction) {Objects.requireNonNull(remappingFunction);Objects.requireNonNull(value);V oldValue = get(key);V newValue = (oldValue == null) ? value :remappingFunction.apply(oldValue, value);if(newValue == null) {remove(key);} else {put(key, newValue);}return newValue;}

三、实现类