Deadlocks are caused by threads waiting for each other

/**
 * Deadlock Case
 */
public class TestDeadLock {

    public void run() {
        MyThread mt = new MyThread();
        new Thread(mt, "Zhang San").start();
        new Thread(mt, "Li Si").start();
    }

    class MyThread implements Runnable {
        private final Object o1 = new Object();
        private final Object o2 = new Object();
        private boolean flag = true;

        @Override
        public void run() {
            if (flag) {
                flag = false;
                synchronized (o1) {
                    System.out.println(Thread.currentThread().getName() + " have o1");
                    try {
                        Thread.sleep(100);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    synchronized (o2) {
                        System.out.println(Thread.currentThread().getName() + " have o2");
                    }
                }
            } else {
                flag = true;
                synchronized (o2) {
                    System.out.println(Thread.currentThread().getName() + " have o2");
                    try {
                        Thread.sleep(100);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    synchronized (o1) {
                        System.out.println(Thread.currentThread().getName() + " have o1");
                    }
                }
            }
        }
    }

    public static void main(String[] args) {
        new TestDeadLock().run();
    }
}

explain

• When a thread 1 enters the running state first, flag = true, obtains the o1 object, and then sleeps (without releasing the lock)
• At this time, when another thread 2 enters the running state, flag = true. Since thread 1 is in sleep and state, and has not yet acquired the o2 object, thread 2 can acquire the o2 object at this time. Then go to sleep (do not release lock)
• Now both threads have finished sleeping. If we get the resources owned by each other and wait for each other, there will be a deadlock.