一道多线程题目的解决方案

在iteye上看到的一道多线程的题目，参考了一下网友的实现，那Eclipse调试通过，算是对JAVA5的并发库有个大致的了解，分享出来，欢迎园里的同学拍砖。

题目：

要求用三个线程，按顺序打印1,2,3,4,5.... 71,72,73,74, 75.

线程1先打印1,2,3,4,5, 然后是线程2打印6,7,8,9,10, 然后是线程3打印11,12,13,14,15. 接着再由线程1打印16,17,18,19,20....以此类推, 直到线程3打印到75。

分析：感觉出题人是要考察一下你是否能够很好的控制多线程，让他们有序的进行。

1、线程池：3个线程，需要使用并发库的线程池

2、锁（lcok）：在打印的时候，只允许一个线程进入，其他的线程等待

下面的主要的代码：

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class NumberPrinter {

	private Lock lock = new ReentrantLock();

	private Condition c1 = lock.newCondition();
	private Condition c2 = lock.newCondition();
	private Condition c3 = lock.newCondition();

	private Map<Integer, Condition> condtionContext = 
		new HashMap<Integer, Condition>();

	public NumberPrinter() {
		condtionContext.put(Integer.valueOf(0), c1);
		condtionContext.put(Integer.valueOf(1), c2);
		condtionContext.put(Integer.valueOf(2), c3);
	}
	
	private int count = 0;   
	
	public void print(int id) {
		lock.lock();
		try {
			while(count*5 < 75) {
				int curID = calcID();
				if (id == curID) {
					for (int i = 1; i<=5; i++) {
						System.out.print(count*5 +i+ ",");
					}
					System.out.println();
					count++;
					int nextID = calcID();
					Condition nextCondition = condtionContext.get(
							Integer.valueOf(nextID));
					//通知下一线程
					nextCondition.signal();
				} else {
					Condition condition = condtionContext.get(
							Integer.valueOf(id));
					condition.await();
				}
			}
			//通知线程结束
			for(Condition c : condtionContext.values()) {
				c.signal();
			}
		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			lock.unlock();
		}
	}

	
	private int calcID() {
		// TODO Auto-generated method stub
		return count % 3;
	}


	/**
	 * @param args
	 */
	public static void main(String[] args) {
		ExecutorService executor = Executors.newFixedThreadPool(3);
		final CountDownLatch latch = new CountDownLatch(1);   
		final NumberPrinter printer = new NumberPrinter(); 
		for (int i = 0; i < 3; i++) {   
			final int id = i;
			executor.submit(new Runnable() {
				@Override
				public void run() {
					// TODO Auto-generated method stub
					try {
						latch.await();
					} catch (InterruptedException e) {
						// TODO Auto-generated catch block
						e.printStackTrace();
					}
					
					printer.print(id);
				}
				
			});
		}
		
		System.out.println("三个任务开始顺序打印数字。。。。。。"); 
		latch.countDown();
		executor.shutdown();
	}

}