hashmap怎么变成线程安全的

// synchronizedMap方法
public static Map synchronizedMap(Map m) {
return new SynchronizedMap>(m);
}
// SynchronizedMap类
private static class SynchronizedMap
implements Map, Serializable {
private static final long serialVersionUID = 1978198479659022715L;

private final Map m; // Backing Map
final Object mutex; // Object on which to synchronize

SynchronizedMap(Map m) {
this.m = Objects.requireNonNull(m);
mutex = this;
}

SynchronizedMap(Map 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);}
}
// 省略其他方法
}

用ConcurrentHashMap， 这个是线程安全的