java - wait()，notify(),notifyAll() T2 start! T2 end! T1 start! 为什么会阻塞

public class Thread04 {
   final Object object = new Object();
Runnable rb4 = new Runnable() {
    public void run(){
        synchronized (object){

                System.out.println("T1 start!");
                try {
                    object.wait();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                object.notify();
                System.out.println("T1 end!");
            }
        }
};
Runnable rb5 = new Runnable() {
    public void run(){
        synchronized (object){
            System.out.println("T2 start!");
            object.notify();
            System.out.println("T2 end!");
            }
        }
};
public static void main(String[] args) {
        Thread04 th = new Thread04();
        new Thread(th.rb4).start();
        new Thread(th.rb5).start();
     }
 }