Java并发学习之六——等待线程的终结

本文是学习网络上的文章时的总结，感谢大家无私的分享。

1、在某些情况下，我们需要等待线程的终结。例如，我们可能会遇到程序在执行前需要初始化资源。在执行剩下的代码之前，我们需要等待线程完成初始化任务。为了达到此目的，我们使用Thread类的join()方法。当前线程调用某个线程的这个方法时，它会暂停当前线程，直到被调用线程执行完成。

2、Java提供2种形式的join（）方法：

Join(longmilliseconds)

Join(long milliseconds,long nanos)

第一种join方法，让调用线程等待特定的毫秒数。例如，如果thread1对象使用代码thread2.join(1000),那么线程thread1暂停运行，直到
以下其中一个条件发生：

Thread2结束运行

1000毫秒过去了

当其中一个条件为真时，join()方法返回。

第二个版本的join方法和第一个很像，只不过它接收一个毫秒数和一个纳秒数作为参数。

举例

package chapter;

import java.util.Date;
import java.util.concurrent.TimeUnit;

public class DataSourcesLoader implements Runnable{

	@Override
	public void run() {
		System.out.printf("Beginning data sources loading : %s\n", new Date());
		try {
			TimeUnit.SECONDS.sleep(4);
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
		System.out.printf("Data sources loading has finished :%s\n",new Date());

	}
}

package chapter;

import java.util.Date;
import java.util.concurrent.TimeUnit;

public class NetwworkConnectionsLoader implements Runnable{

	@Override
	public void run() {
		System.out.printf("Beginning Net sources loading : %s\n", new Date());
		try {
			TimeUnit.SECONDS.sleep(6);
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
		System.out.printf("Net sources loading has finished :%s\n",new Date());

	}
}

package chapter;

import java.util.Date;

public class Main6 {

	/**
	 * <p>
	 * </p>
	 * @author zhangjunshuai
	 * @date 2014-8-14 下午4:40:58
	 * @param args
	 * @throws InterruptedException
	 */
	public static void main(String[] args) throws InterruptedException {

		DataSourcesLoader dsLoader = new DataSourcesLoader();
		Thread thread1 = new Thread(dsLoader,"DataSourcesLoader" +
				"");
		NetwworkConnectionsLoader ncLoader = new NetwworkConnectionsLoader();
		Thread thread2 = new Thread(ncLoader,"NetwworkConnectionsLoader");

		thread1.start();
		thread2.start();

		thread1.join();
		thread2.join();

		System.out.printf("Main: Configuration has been loaded: %s\n",new Date());
	}

}

运行结果

以上为书本示例，我在网上找了一个示例。

package mytest;
class Thread1 extends Thread
{
	public Thread1(String threadName)
	{
		super(threadName);
	}

	public void run()
	{
		System.out.println(getName() + "is running");
		try
		{
			sleep(2000);
		}
		catch (InterruptedException e)
		{
			e.printStackTrace();
		}
		System.out.println("thread1 is over");
	}
}

package mytest;
class Thread2 extends Thread
{
	private Thread1 thread1;

	public Thread2(String threadName, Thread1 thread1)
	{
		super(threadName);
		this.thread1 = thread1;
	}

	public void run()
	{
		System.out.println(getName() +  "is running");
		try
		{
			thread1.start();
			thread1.join();
		}
		catch (InterruptedException e)
		{
			e.printStackTrace();
		}
		System.out.println("thread2 is over");
	}
}

package mytest;
public class JoinTest
{
    public static void main(String[] args)
    {
        Thread1 thread1 = new Thread1("Thread1");
        Thread2 thread2 = new Thread2("Thread2", thread1);
        thread2.start();
    }
}

运行结果

如果去除join方法

Java并发学习之六——等待线程的终结