java – 为什么下面的程序,没有睡眠会进入死锁状态,但是在睡眠状

public class ThreadTest {
public static void main(String[] args) throws InterruptedException {
    ExampleTest obj = new ExampleTest();
    Thread t1 = new Thread(new Runn(obj));
    Thread t2 = new Thread(new Runn(obj));
    Thread t3 = new Thread(new Runn(obj));
    t1.start();
    t2.start();
    t3.start();

    //Thread.sleep(1);

    obj.exit();

}

}

class ExampleTest {
public synchronized void enter() {
    try {
        System.out.println("printed " +Thread.currentThread().getName() +" inside wait");
        this.wait();
        System.out.println("printed " +Thread.currentThread().getName() +" exit wait");
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
    System.out.println("printed " +Thread.currentThread().getName() +" at time: "+System.currentTimeMillis());
}

public synchronized void exit() {
    this.notifyAll();
}

}

class Runn implements Runnable {
ExampleTest obj;

public Runn(ExampleTest obj) {
    this.obj = obj;
}

@Override
public void run() {
    obj.enter();
}

}

what is the role of notifyAll(). Will notifyAll() allows all the waiting thread to acquire lock sequentially in random order or only one thread can acquire the lock?