solution of http://wouter.coekaerts.be/2012/puzzle-dreams

Dream.java

package dream;

import sleep.Sleeper;

public class Dream {
    int num = 0;
    public void dream(final Sleeper s) {
        if (num++ < 10) {
            Thread thread = new Thread(new Runnable() {
                public void run() {
                    s.enter(Dream.this);
                }
            });
            thread.start();
            synchronized (s) {
                try {
                    s.wait(100);
                } catch (InterruptedException e) { }
            }
        }
    }
}