經典線程同步問題之3個線程交替數數

問題描述，3個線程交替數數從1數到75，例如：

線程1： 1 2 3 4 5

線程2：6 7 8 9 10

線程3：11 12 13 14 15

......

用synchronized實現如下：

package com.afeiluo;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

class Counter {
	final int maxNum = 75;
	int currNum = 1;
}

class Task implements Runnable {
	private Counter counter;
	private int id;

	public Task(Counter counter, int id) {
		this.counter = counter;
		this.id = id;
	}

	@Override
	public void run() {
		synchronized (counter) {
			while (counter.currNum <= counter.maxNum) {
				if (counter.currNum / 5 % 3 == id) {
					System.out.print("id:" + id+" ");
					for (int i = 0; i < 5; i++) {
						System.out.print(counter.currNum++ + ",");
					}
					System.out.println();
					counter.notifyAll();
				} else {
					try {
						counter.wait();
					} catch (InterruptedException e) {
						e.printStackTrace();
					}
				}
			}
		}
	}

}

public class MyPrint1to75 {
	public static void main(String[] args) {
		Counter counter = new Counter();
		ExecutorService exec = Executors.newCachedThreadPool();
        for(int i=0;i<3;i++){
        	exec.execute(new Task(counter,i));
        }
        exec.shutdown();
	}
}