多线程(九)： HashTable、HashMap和ConcurrentHashMap

版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/vbirdbest/article/details/81749089

public class HashTest {
    static Map<String, Integer> map = new HashMap<String, Integer>();
    // static Map<String, Integer> map = new Hashtable<>();
    public static void main(String[] args) {
        for (int i = 0; i < 2; i++) {
            new Thread(() -> {
                int raddom = new Random().nextInt();
                String threadName = Thread.currentThread().getName();
                map.put(threadName, raddom);

                System.out.println(Thread.currentThread().getName() + "\t" + map.get(threadName));
            }).start();
        }
    }
}

HashMap

public class HashMap<K,V> extends AbstractMap<K,V>
    implements Map<K,V>, Cloneable, Serializable {

    public V put(K key, V value);

    public V get(Object key);
}

// 可以通过Collections将非线性安全转为线程安全
Map<Object, Object> map = Collections.synchronizedMap(new HashMap<>());

Hashtable

public class Hashtable<K,V> extends Dictionary<K,V> implements Map<K,V>, Cloneable, java.io.Serializable {
    // 线程安全 同步方法synchronized
    public synchronized V put(K key, V value);

    // 线程安全 同步方法synchronized
    public synchronized V get(Object key);
}    

上面示例使用Hashtable就会每次都能获取到数据