public class Lock {

    private boolean used;

    public Lock(){
        this.used = false;
    }

    public Lock(boolean used){
        this.used = used;
    }

    /*
      Try to take the lock (non-blocking).
    */
    public synchronized boolean tryTake(){
	if( used ){
	    return false;
	}
	used = true;
	return true;
    }

    /*
      Take the lock (blocking).
    */
    public synchronized void take() {
	while( used ){
	    try {
	        wait();
	    } catch(InterruptedException e) {};
	}
	used = true;
    }

    /*
      Leave the critical section.
     */
    public synchronized void release(){
	if( !used ){
	    throw new RuntimeException("trying to release the lock while free");
	}
	used = false;
	notify();
    }

}