Each thread is initialized with c=new C() and locks different objects.

class Example{
    public static void main(String arr[]){
        C c = new C();
        ThreadB th1=new ThreadB("th1",c);
        ThreadB th2=new ThreadB("th2",c);
    }
}
class ThreadB implements Runnable{
    C c;
    Thread thread;
    ThreadB(String name,C c){
        //c=new C();
        this.c=c;
        thread=new Thread(this,name);
        thread.start();
    }
    public void run(){
        if(thread.getName().equals("th1")){
            for(int i=0;i<3;i++)c.t1(false);
            c.t1(true);
        }
        if(thread.getName().equals("th2")){
            for(int i=0;i<3;i++)c.t2(false);
            c.t2(true);
        }
        System.out.println("end");
    }
}
class C{
    synchronized void t1(boolean boo){
        if(boo){
            notify();
            return;
        }
        System.out.println("t1");
        notify();
        try{
            wait();
        }catch(InterruptedException exc){System.out.println(exc);}
    }
    synchronized void t2(boolean boo){
        if(boo){
            System.out.println();notify();return;
        }
        System.out.println("t2");
        notify();//notifyAll()也没效果；
    }
}

The wait object C of these two threads is not the same, and they cannot sense the other party’s lock