java - 锁定java同步方法

Question

我正在尝试使用同步方法编写一个带有线程的 Java 程序。但是我无法理解当另一个线程调用 java 中的同步方法时，我如何显示一个线程已经在运行。谁能用简单的例子解释一下

Answer 1

这是一个人为的例子，它显示了交织和阻塞过程。在我的机器上打印:

Thread[Thread-0,5,main] is going to call the synchronized method
Thread[Thread-1,5,main] is going to call the synchronized method
Thread[Thread-0,5,main] is in the synchronized method
Thread[Thread-0,5,main] is exiting the method
Thread[Thread-1,5,main] is in the synchronized method
Thread[Thread-1,5,main] is exiting the method

可以看到只有一个线程进入了同步块(synchronized block)，而另一个在等待。

public class Test1 {

    public static void main(String[] args) throws Exception {
        final Test1 test = new Test1();
        Runnable r = new Runnable() {
            @Override
            public void run() {
                System.out.println(Thread.currentThread() + " is going to call the synchronized method");
                test.method();
            }
        };
        new Thread(r).start();
        new Thread(r).start();
    }

    public synchronized void method() {
        System.out.println(Thread.currentThread() + " is in the synchronized method");
        try {
            Thread.sleep(1000);
        } catch (InterruptedException ex) {
        }
        System.out.println(Thread.currentThread() + " is exiting the method");
    }
}