API：
join
public final void join()
throws InterruptedException
- 等待该线程终止。
-
- 抛出：
InterruptedException– 假设不论什么线程中断了当前线程。当抛出该异常时，当前线程的中断状态 被清除。
join
public final void join(long millis)
throws InterruptedException
- 等待该线程终止的时间最长为
millis毫秒。超时为0意味着要一直等下去。 -
- 參数：
millis– 以毫秒为单位的等待时间。- 抛出：
InterruptedException– 假设不论什么线程中断了当前线程。当抛出该异常时，当前线程的中断状态 被清除。
join
public final void join(long millis,
int nanos)
throws InterruptedException
- 等待该线程终止的时间最长为
millis毫秒 +nanos纳秒。 -
- 參数：
millis– 以毫秒为单位的等待时间。nanos– 要等待的 0-999999 附加纳秒。- 抛出：
IllegalArgumentException– 假设 millis 值为负，则 nanos 的值不在 0-999999 范围内。InterruptedException– 假设不论什么线程中断了当前线程。当抛出该异常时。当前线程的中断状态 被清除。
解析：
Thread.join()。是用来指定当前主线程等待其它线程运行完成后。再来继续运行Thread.join()后面的代码。
例1：
package com.example;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());
}public static void main(String[] args){
DataSourcesLoader dsLoader = new DataSourcesLoader();
Thread thread1 = new Thread(dsLoader,"DataSourceThread"); thread1.start(); try {
thread1.join();
} catch (InterruptedException e) {
e.printStackTrace();
} System.out.printf("Main: Configuration has been loaded: %s\n",new Date());
}}
运行结果：
Beginning data sources loading: Fri Nov 14 14:27:31 CST 2014
Data sources loading has finished: Fri Nov 14 14:27:35 CST 2014
Main: Configuration has been loaded: Fri Nov 14 14:27:35 CST 2014
假设去掉thread1.join()，运行的结果例如以下：
Main: Configuration has been loaded: Fri Nov 14 14:28:33 CST 2014
Beginning data sources loading: Fri Nov 14 14:28:33 CST 2014
Data sources loading has finished: Fri Nov 14 14:28:37 CST 2014
通过结果。就能够非常明显的说明上面红字的部分：“再来继续运行Thread.join()后面的代码”
例2：
package com.example;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());
}public static void main(String[] args){
DataSourcesLoader dsLoader = new DataSourcesLoader();
Thread thread1 = new Thread(dsLoader,"DataSourceThread"); thread1.start(); try {
thread1.join(3000);
} catch (InterruptedException e) {
e.printStackTrace();
} System.out.printf("Main: Configuration has been loaded: %s\n",new Date());
}}
这里使用的是：
thread1.join(3000);
这句话的意思是，仅仅要满足以下2个条件中的一个时，主线程就会继续运行thread.join()后面的代码：
条件1：thread1 运行完成。
条件2：已经等待 thread1 运行了3000ms.
样例中。thread1 自身的运行时间是4s。而设置的等待时间是3s，所以得到的运行结果例如以下。thread1还没有运行完，主线程就開始运行后面的代码。由于 thread1 等待的时间已经超时了：
Beginning data sources loading: Fri Nov 14 14:35:45 CST 2014
Main: Configuration has been loaded: Fri Nov 14 14:35:48 CST 2014
Data sources loading has finished: Fri Nov 14 14:35:49 CST 2014
那么结合上面的2个样例。我们能够判断出以下代码的运行结果了：
例3：
package com.example;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 com.example;import java.util.Date;
import java.util.concurrent.TimeUnit;public class NetworkConnectionsLoader implements Runnable{@Override
public void run() {
System.out.printf("Beginning network connect loading: %s\n",new Date());
try {
TimeUnit.SECONDS.sleep(6);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.printf("Network connect loading has finished: %s\n",new Date());}public static void main(String[] args){
DataSourcesLoader dsLoader = new DataSourcesLoader();
Thread thread1 = new Thread(dsLoader,"DataSourceThread"); NetworkConnectionsLoader ncLoader = new NetworkConnectionsLoader();
Thread thread2 = new Thread(ncLoader,"NetworkConnectionLoader"); thread1.start();
thread2.start(); try {
thread1.join();
thread2.join(1900);
} catch (InterruptedException e) {
e.printStackTrace();
} System.out.printf("Main: Configuration has been loaded: %s\n",new Date());
}}
运行结果：
Beginning data sources loading: Fri Nov 14 14:39:20 CST 2014
Beginning network connect loading: Fri Nov 14 14:39:20 CST 2014
Data sources loading has finished: Fri Nov 14 14:39:24 CST 2014
Main: Configuration has been loaded: Fri Nov 14 14:39:26 CST 2014
Network connect loading has finished: Fri Nov 14 14:39:26 CST 2014
注意：假设把例3的 thread2.join(1900) 部分改动为：
thread2.join(3000);
结果会和上面的一样吗？
依据我最開始指出的“Thread.join()。是用来指定当前主线程等待其它线程运行完成后，再来继续运行Thread.join()后面的代码。”
我们能够看到，运行结果会有区别：
Beginning data sources loading: Fri Nov 14 14:41:21 CST 2014
Beginning network connect loading: Fri Nov 14 14:41:21 CST 2014
Data sources loading has finished: Fri Nov 14 14:41:25 CST 2014
Network connect loading has finished: Fri Nov 14 14:41:27 CST 2014
Main: Configuration has been loaded: Fri Nov 14 14:41:27 CST 2014</span>
至于为什么会有这个区别，我上面也已经说明了，我想这个应该不难理解。
PS：代码部分截取来自《Java 7 Concurrency Cookbook》
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