浅谈HashMap，LinkedHashMap，ConcurrentHashMap、synchronizedMap（四.synchronizedMap）

╰+哭是因爲堅強的太久メ 2022-05-27 07:47 140阅读 0赞

直接看synchronizedMap源码吧，相对来说简单很多了。

public static <K,V> Map<K,V> synchronizedMap(Map<K,V> m) {
            // 返回一个synchronizedMap对象。
            return new SynchronizedMap<>(m);
        }
    
        /** * @serial include */
        private static class SynchronizedMap<K,V>
            implements Map<K,V>, Serializable {
            private static final long serialVersionUID = 1978198479659022715L;
    
            private final Map<K,V> m;     // Backing Map
            final Object      mutex;        // Object on which to synchronize
    
            SynchronizedMap(Map<K,V> m) {
                this.m = Objects.requireNonNull(m);
                mutex = this;
            }
    
            SynchronizedMap(Map<K,V> m, Object mutex) {
                this.m = m;
                this.mutex = mutex;
            }
    
            public int size() {
                synchronized (mutex) {
       return m.size();}
            }
            public boolean isEmpty() {
                synchronized (mutex) {
       return m.isEmpty();}
            }
            public boolean containsKey(Object key) {
                synchronized (mutex) {
       return m.containsKey(key);}
            }
            public boolean containsValue(Object value) {
                synchronized (mutex) {
       return m.containsValue(value);}
            }
            public V get(Object key) {
                synchronized (mutex) {
       return m.get(key);}
            }
    
            public V put(K key, V value) {
                synchronized (mutex) {
       return m.put(key, value);}
            }
            public V remove(Object key) {
                synchronized (mutex) {
       return m.remove(key);}
            }
            public void putAll(Map<? extends K, ? extends V> map) {
                synchronized (mutex) {m.putAll(map);}
            }
            public void clear() {
                synchronized (mutex) {m.clear();}
            }
    
            private transient Set<K> keySet;
            private transient Set<Map.Entry<K,V>> entrySet;
            private transient Collection<V> values;
    
            public Set<K> keySet() {
                synchronized (mutex) {
                    if (keySet==null)
                        keySet = new SynchronizedSet<>(m.keySet(), mutex);
                    return keySet;
                }
            }
    
            public Set<Map.Entry<K,V>> entrySet() {
                synchronized (mutex) {
                    if (entrySet==null)
                        entrySet = new SynchronizedSet<>(m.entrySet(), mutex);
                    return entrySet;
                }
            }
    
            public Collection<V> values() {
                synchronized (mutex) {
                    if (values==null)
                        values = new SynchronizedCollection<>(m.values(), mutex);
                    return values;
                }
            }
    
            public boolean equals(Object o) {
                if (this == o)
                    return true;
                synchronized (mutex) {
       return m.equals(o);}
            }
            public int hashCode() {
                synchronized (mutex) {
       return m.hashCode();}
            }
            public String toString() {
                synchronized (mutex) {
       return m.toString();}
            }
    
            // Override default methods in Map
            @Override
            public V getOrDefault(Object k, V defaultValue) {
                synchronized (mutex) {
       return m.getOrDefault(k, defaultValue);}
            }
            @Override
            public void forEach(BiConsumer<? super K, ? super V> action) {
                synchronized (mutex) {m.forEach(action);}
            }
            @Override
            public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
                synchronized (mutex) {m.replaceAll(function);}
            }
            @Override
            public V putIfAbsent(K key, V value) {
                synchronized (mutex) {
       return m.putIfAbsent(key, value);}
            }
            @Override
            public boolean remove(Object key, Object value) {
                synchronized (mutex) {
       return m.remove(key, value);}
            }
            @Override
            public boolean replace(K key, V oldValue, V newValue) {
                synchronized (mutex) {
       return m.replace(key, oldValue, newValue);}
            }
            @Override
            public V replace(K key, V value) {
                synchronized (mutex) {
       return m.replace(key, value);}
            }
            @Override
            public V computeIfAbsent(K key,
                    Function<? super K, ? extends V> mappingFunction) {
                synchronized (mutex) {
       return m.computeIfAbsent(key, mappingFunction);}
            }
            @Override
            public V computeIfPresent(K key,
                    BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
                synchronized (mutex) {
       return m.computeIfPresent(key, remappingFunction);}
            }
            @Override
            public V compute(K key,
                    BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
                synchronized (mutex) {
       return m.compute(key, remappingFunction);}
            }
            @Override
            public V merge(K key, V value,
                    BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
                synchronized (mutex) {
       return m.merge(key, value, remappingFunction);}
            }
    
            private void writeObject(ObjectOutputStream s) throws IOException {
                synchronized (mutex) {s.defaultWriteObject();}
            }
        }

我们可以看到其实synchronizedMap中的方法，基本都是调用Map的方法，只不过是在前面加上synchronized锁而已，以此来保证Map的线程安全。