java多线程之线程锁

MyThread.java:

class MyThread implements Runnable {
    int i = 1;

    public void run() {
        // 线程锁，一个线程执行本处代码时，其他线程等待本线程执行完毕后再执行；
        // 如果不加线程锁，则线程会得到同一个数；
        synchronized (this) {
            if (i <= 0) {
                return;
            }
            System.out.println(Thread.currentThread().getName() + "--->" + i);
            i--;
        }
    }
}

TestMyThread.java:

class TestMyThread{
    public static void main(String[] args){
        MyThread myThread = new MyThread();
        Thread t1 = new Thread(myThread);
        Thread t2 = new Thread(myThread);
        Thread t3 = new Thread(myThread);
        Thread t4 = new Thread(myThread);
        t1.setName("线程1");
        t2.setName("线程2");
        t3.setName("线程3");
        t4.setName("线程4");
        t1.start();
        t2.start();
        t3.start();
        t4.start();
        try{
            Thread.sleep(1000);
        }catch(Exception e){
            e.printStackTrace();
        }
        System.out.println(myThread.i);//加锁时为0，不加锁为0到-3
    }
}