jb11.0 threads tick tock 1.0, Java

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//'main' method must be in a class 'Rextester'.
//Compiler version 1.8.0_111

import java.util.*;
import java.lang.*;

class Rextester
{  
    public static void main(String args[])
    {
        System.out.println("Hello, World!");
        Clock c = new Clock();
        c.start();
        c.stop();
    }
}

class Clock{
    ClockState _state;
    boolean _stop = true;
    TickTock _tick, _tock;
    
    public void start(){
        _stop = false;
        _tick.start();
        _tock.start();
    }
    
    public void stop(){
        _stop = true;
    }
    
    public ClockState getState(){
        return _state;
    }
    
    public synchronized void setState(ClockState state){
        _state = state;
        notify();
        if(_stop) return;
        while(_state == state){
            try{
                wait();
            }catch(InterruptedException e){
                System.out.println(e);
            }
        }
    }
    
    public boolean isRun(){
        return !_stop;
    }
    
    Clock(){
        _tick = new TickTock(ClockState.TICK, this);
        _tock = new TickTock(ClockState.TOCK, this);
    }
    
    class TickTock implements Runnable{
        ClockState _role;
        Clock _clock;
        Thread _thr;
        
        public void run(){
            while(_clock.isRun()){
                if(_clock.getState() != _role){
                    _clock.setState(_role);
                    System.out.print(_role);
                }
            }
        }
        private TickTock(ClockState role, Clock clock){
            _role = role;
            _clock = clock;
            _thr = new Thread(this, "Thread " + _role);
        }
        
        public void start(){
            _thr.start();
        }
        
        public void joinThr(){
            try{
                _thr.join();
            }catch(InterruptedException e){
                System.out.println(_thr.getName() + " " + e);
            }
        }
        
    }
    
    
}

enum ClockState {
        TICK(""), TOCK("\n");
    private String _end;
    
    @Override
    public String toString(){
        return super.toString()+_end;
    }
    
    ClockState(String end){
        _end = end;
    }
    }

[ + ] Show input
Compilation time: 0.73 sec, absolute running time: 10.06 sec, cpu time: 0 sec, memory peak: 0 Mb, absolute service time: 10,81 sec