单个线程唤醒多个线程的经典例子（加入了注释）

原文出处：http://zhangjunhd.blog.51cto.com/113473/71387

比赛类：

package deng;

import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;

/*
 * 模拟线程之间的协作。
 * Game类有2个同步方法prepare()和go()。
 * 标志位start用于判断当前线程是否需要wait()。
 * Game类的实例首先启动所有的Athele类实例，使其进入wait()状态，
 * 在一段时间后，改变标志位并notifyAll()所有处于wait状态的Athele线程。
 */
public class Game implements Runnable {
    private Set<Athlete> players = new HashSet<Athlete>();
    private boolean start = false;
    
    //添加运动员
    public void addPlayer(Athlete one) {
      players.add(one);
    }
    //删除运动员
    public void removePlayer(Athlete one) {
      players.remove(one);
    }
    
    //获得所有参赛的运动员
    public Collection<Athlete> getPlayers() {
      return Collections.unmodifiableSet(players);
    }
    /*
     * start为false即比赛没有开始，
     * 运动员进入就绪状态
     */
    public void prepare(Athlete athlete) throws InterruptedException {
      System.out.println(athlete.toString() + " ready!");
      synchronized (this) {
        while (!start)
        	wait();//NotifyAll时，start已经为true，即比赛已经开始
        if (start)//各运动员开始比赛
          System.out.println(athlete + " go!");
      }
    }

    public synchronized void go() {
      notifyAll();
    }
    /*
     * 开启Iterator中所有运动员线程
     * 让所有的运动员进入就绪待跑状态
     */
    public void ready() {
      Iterator<Athlete> iter = getPlayers().iterator();
      while (iter.hasNext())
        new Thread(iter.next()).start();
    }

    public void run() {
      start = false;
      System.out.println("Ready......");
      System.out.println("Ready......");
      System.out.println("Ready......");
      //让所有运动员准备就绪
      ready();
      start = true;
      System.out.println("Go!");
      go();
    }

    public static void main(String[] args) {
      Game game = new Game();
      //准备10个运动员线程
      for (int i = 0; i < 10; i++)
        game.addPlayer(new Athlete(i, game));
      //开始比赛
      new Thread(game).start();
    }
}

运动员类：

package deng;

import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;

class Athlete implements Runnable {
    private final int id;
    private Game game;

    public Athlete(int id, Game game) {
      this.id = id;
      this.game = game;
    }

    public boolean equals(Object o) {
      if (!(o instanceof Athlete))
        return false;
      Athlete athlete = (Athlete) o;
      return id == athlete.id;
    }

    public String toString() {
      return "Athlete<" + id + ">";
    }

    public int hashCode() {
      return new Integer(id).hashCode();
    }

    public void run() {
      try {
        game.prepare(this);
      } catch (InterruptedException e) {
        System.out.println(this + " quit the game");
      }
    }
  }