Java:同步方法如何与同步静态方法同步？

Question

代码片段：

public class SyncTest {

public static void main(String[] args) {
    new SyncTest().test();
}

private void test() {
    final Outputer outputer = new Outputer();

    // Thread 1
    new Thread(new Runnable() {
        @Override
        public void run() {
            while (true) {
                try {
                    Thread.sleep(50);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                outputer.outPut("一二三四五六七八九");
            }
        }
    }).start();

    // Thread2
    new Thread(new Runnable() {
        @Override
        public void run() {
            while (true) {
                try {
                    Thread.sleep(50);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                Outputer.outPut2("123456789");  
            }
        }
    }).start();
}

static class Outputer {
    public void outPut( String name) {          
        int len = name.length();
        synchronized (Outputer.this) {                          // lock is Outputer.class
            for (int i = 0; i < len; i++) {
                System.out.print(name.charAt(i));
            }
            System.out.println();
        }
    }
    public static synchronized void outPut3( String name) {     // lock also is Outputer.class
        int len = name.length();
        for (int i = 0; i < len; i++) {
            System.out.print(name.charAt(i));
        }
        System.out.println();
    }
}

}

输出：

123456789 1一2二三四五六七八九3456789

显然没有同步，请帮忙，谢谢

Answer 1

您需要指定类实例而不是this，因此两者都使用相同的Monitor对象

static class Outputer {
    public void outPut( String name) {          
        int len = name.length();
        synchronized (Outputer.class) {      // Outputer.this is not the same as Outputer.class
            for (int i = 0; i < len; i++) {
                System.out.print(name.charAt(i));
            }
            System.out.println();
        }
    }
}

或者，您可以使用一个单独的监视器对象，因此这是显式的，它将被使用：

static class Outputer {
    private static Object syncronisationMonitor = new Object();

    // nonstatic method
    public void outPut( String name) {          
        synchronized (syncronisationMonitor ) { // we use the same monitor as in the static method                        
           [...]
        }
    }

    //static method
    public static void outPut3( String name) {    
        synchronized (syncronisationMonitor ) {  // we use the same monitor as in the non-static method                                               
            [...]
        }
    }
}