java多线程join

目的：程序执行完任务后，再执行其他的任务。
实现原理：
使用Thread类的join()方法时。当一个线程对象的join()方法被调用是，调用它的线程将被挂起，直到这个线程对象完成它的任务。
代码：引用的java7并发编程实战手册示例代码
package com.packtpub.java7.concurrency.chapter1.recipe6.task;

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

/**
* Class that simulates an initialization operation. It sleeps during four seconds
*
*/
public class DataSourcesLoader implements Runnable {

/**
 * Main method of the class
 */
@Override
public void run() {

    // Writes a messsage
    System.out.printf("Begining data sources loading: %s\n",new Date());
    // Sleeps four seconds
    try {
        TimeUnit.SECONDS.sleep(4);
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
    // Writes a message
    System.out.printf("Data sources loading has finished: %s\n",new Date());
}

}

package com.packtpub.java7.concurrency.chapter1.recipe6.task;

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

/**
* Class that simulates an initialization operation. It sleeps during six seconds
*
*/
public class NetworkConnectionsLoader implements Runnable {

/**
 * Main method of the class
 */
@Override
public void run() {
    // Writes a message
    System.out.printf("Begining network connections loading: %s\n",new Date());
    // Sleep six seconds
    try {
        TimeUnit.SECONDS.sleep(6);
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
    // Writes a message
    System.out.printf("Network connections loading has finished: %s\n",new Date());
}

}

package com.packtpub.java7.concurrency.chapter1.recipe6.core;

import java.util.Date;

import com.packtpub.java7.concurrency.chapter1.recipe6.task.DataSourcesLoader;
import com.packtpub.java7.concurrency.chapter1.recipe6.task.NetworkConnectionsLoader;

/**
* Main class of the Example. Create and start two initialization tasks
* and wait for their finish
*
*/
public class Main {

/**
 * Main method of the class. Create and star two initialization tasks
 * and wait for their finish
 * @param args
 */
public static void main(String[] args) {

    // Creates and starts a DataSourceLoader runnable object
    DataSourcesLoader dsLoader = new DataSourcesLoader();
    Thread thread1 = new Thread(dsLoader,"DataSourceThread");
    thread1.start();

    // Creates and starts a NetworkConnectionsLoader runnable object
    NetworkConnectionsLoader ncLoader = new NetworkConnectionsLoader();
    Thread thread2 = new Thread(ncLoader,"NetworkConnectionLoader");
    thread2.start();

    // Wait for the finalization of the two threads
    try {
        thread1.join();
        thread2.join();
    } catch (InterruptedException e) {
        e.printStackTrace();
    }

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

}

扩展：

通过查看源码看到join的重载方法
join():
join(long,int)
本质调用的都是join(long)



通过查看反编译后的源代码，可知道只要线程运行结束（isAlive）或者时间到了之后(delay<=0;break;)，被挂起的线程将再次可以执行。