Question

在下面的代码中，我试图打印vector对象的线程名称和哈希码值，但输出不是预期的。此外，由于哈希码值与vector对象不一致，因此单例被破坏。

public class ThreadTestVector implements Runnable {

private static Vector<String> vector;

public static synchronized Vector<String> getInstance() {
    if (vector == null) {
        vector = new Vector<String>();
    }
    return vector;
}

@Override
public synchronized void run() {

    Vector<String> vector = getInstance();

    for (int i = 0; i < 10; i++) {
        vector.add(Thread.currentThread().getName());
    }
    for (int i = 0; i < vector.size(); i++) {
        System.out.println(vector.get(i) + " Hash Code "
                + vector.hashCode());
    }
    // clear the vector for values already printed
    vector.clear();
}

public static void main(String[] args) throws Exception {
    Runnable r = new ThreadTestVector();
    Runnable r1 = new ThreadTestVector();
    Runnable r2 = new ThreadTestVector();
    Runnable r3 = new ThreadTestVector();
    Thread t1 = new Thread(r);
    Thread t2 = new Thread(r1);
    Thread t3 = new Thread(r2);
    Thread t4 = new Thread(r3);
    t1.start();
    // Thread.sleep(100);
    t2.start();
    // Thread.sleep(100);
    t3.start();
    // Thread.sleep(100);
    t4.start();

}

}

执行输出模式后执行 Thread-0哈希码924221025
Thread-0哈希码1030242113
Thread-0哈希码1030242113
Thread-0哈希码1030242113
Thread-0哈希码-119973247
Thread-0哈希码1030242113
Thread-0哈希码1030242113
Thread-0哈希码1030242113
Thread-0哈希码1030242113
Thread-0哈希码1030242113
Thread-0哈希码1030242113
Thread-0哈希码1030242113
Thread-0哈希码1030242113
Thread-0哈希码1030242113
Thread-1哈希码1030242113
Thread-1哈希码1030242113
Thread-1哈希码1030242113
Thread-1哈希码1030242113
Thread-1哈希码1030242113
Thread-1哈希码1030242113
Thread-1哈希码1030242113
Thread-1哈希码1030242113
Thread-1哈希码1030242113
Thread-1哈希码1030242113
Thread-2哈希码1030242113
Thread-2哈希码1030242113
Thread-2哈希码1030242113
Thread-2哈希码1030242113
Thread-2哈希码1030242113
Thread-2哈希码1030242113
Thread-2哈希码1030242113
Thread-2哈希码1030242113
Thread-2哈希码1030242113
Thread-2哈希码1030242113
Thread-3哈希码1030242113
Thread-3哈希码1030242113
Thread-3哈希码1030242113
Thread-3哈希码1030242113
Thread-3哈希码1030242113
Thread-3哈希码1030242113
Thread-3哈希码1030242113
Thread-3哈希码1030242113
Thread-3哈希码1030242113
Thread-3哈希码1030242113
Thread-0哈希码1901327073
Thread-0哈希码1030242113
Thread-0哈希码1030242113

这些都是混乱的，哈希码值也不同。

如何修复它以便以同步方式打印输出并且哈希码值是一致的？

Answer 1

你应该同步矢量

if (vector != null) {
 synchronized(vector) {
for (int i = 0; i < 10; i++) {
        vector.add(Thread.currentThread().getName());
    }
    for (int i = 0; i < vector.size(); i++) {
        System.out.println(vector.get(i) + " Hash Code "
                + vector.hashCode());
    }
    // clear the vector for values already printed
    vector.clear();
}
}

Answer 2

散列码值不同，因为Vector的散列码是根据其内容计算的。

因此，您为哈希码获取不同的值并不奇怪。

同步不适用于给定的代码示例

2 个答案: