Why can the wait() method be called without the notify() method when using the thread class object as a lock?

public class WaitMain {
    public volatile static int i = 0;
    public static void main(String[] args) throws InterruptedException {
        Thread t1 = new Thread(){
            public void run(){
                for (i = 0; i < 1000000; i++);
            }
        };
        t1.start();
        synchronized (t1){
            t1.wait();
        }
        System.out.println(i);
    }
}

In the above code, I didn't call any notify or notifyAll methods, but the main thread still woke up and executed normally. I want to know why. Thanks.

The description for this is a bit hidden in the documentation of Thread.join() :

> As a thread terminates the this.notifyAll method is invoked. It is recommended that applications not use wait, notify, or notifyAll on Thread instances.

What happens is this:

• the main method creates a new Thread t1 and starts it
• it then calls t1.wait()
• the Thread t1 some time later terminates and implicitly calls t1.notifyAll() as per the documentation
• this wakes up the main thread