java - Why the below program, without a sleep go to deadlock state but with sleep it executes all the three threads and terminates normally? -

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() +" @ 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 role of notifyall(). notifyall() allows waiting thread acquire lock sequentially in random order or 1 thread can acquire lock?

without sleep statement statement obj.exit(); executed before of threads reaching wait status. ie. notifyall call on before @ least 1 of thread in wait status. @ least 1 of threads stuck in wait status waiting other thread notify , wake up. never happen obj.exit() finished.

with sleep statement in place , of threads chance reach wait status , notifyall call after sleep wake them all, order of waking not deterministic , handled thread scheduler.