Simple monitor test written in Java

Monitor.java

import java.util.*;

class Monitor{

    private static class SimpleMonitor{
        private static class ConditionVariable{
            boolean lock;
            public ConditionVariable(boolean lock){
                this.lock = lock;
            }
            public void signal(){
                this.lock = false;
            }
            public void hold(){
                try {
                    while(this.lock){ Thread.sleep(5); };
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }
        Queue<ConditionVariable> q = new LinkedList<ConditionVariable>();
        ConditionVariable qlock = new ConditionVariable(false);
        public void acquire(){
            try {
                qlock.hold();
                ConditionVariable c = new ConditionVariable(!q.isEmpty());
                q.add(c);
                qlock.signal();
                c.hold();
            }catch(Exception e){
                e.printStackTrace();
            }
        }
        public void release(){
            qlock.hold();
            q.poll();
            if(!q.isEmpty()){
                q.peek().signal();
            }
            qlock.signal();
        }
    }


    public static int counter = 0;

    public static void main(String[] args) {
        final SimpleMonitor monitor = new SimpleMonitor();
        for(int i = 0; i < 4; i++){
            new Thread(new Runnable() {
                @Override
                public void run() {
                    try {
                        while(true){
                            monitor.acquire();
                            System.out.println("Working...");
                            counter++;
                            Thread.sleep(5 + (int)(Math.random() * 10));
                            if (counter > 1){
                                System.out.println("Oh No! THERE WAS A COLLISION IN THE CRITICAL SECTION!!!!!!!");
                            }
                            counter--;
                            monitor.release();
                        }
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            }).start();
        }
    }
}