- join的作用:
多数情况下,主线程创建并启动子线程,如果子线程中要进行大量的耗时运算,主线程可能早于子线程结束之前结束。倘若子线程处理一个数据,主线程要取得这个数据中的值,就要用到join()方法,它的作用就是等待线程对象的销毁。 - 源码
public final void join() throws InterruptedException {
join(0);
}
public final synchronized void join(long millis)
throws InterruptedException {
long base = System.currentTimeMillis();
long now = 0;
if (millis < 0) {
throw new IllegalArgumentException("timeout value is negative");
}
if (millis == 0) {
while (isAlive()) {//等待该线程被销毁。
wait(0);//
}
} else {
while (isAlive()) {
long delay = millis - now;
if (delay <= 0) {
break;
}
wait(delay);
now = System.currentTimeMillis() - base;
}
}
}
可以看到join()方法的内部是通过wait(long times)方法来实现线程等待的。所以他其实具备wait(long times)方法的特征。
- 简单的例子
/*
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* To change this template file, choose Tools | Templates
* and open the template in the editor.
*/
package Thread;
/**
*
* @author zjq
*/
public class join_1 extends Thread{
@Override
public void run(){
try {
int secondValue = (int)(Math.random()*10000);
System.out.println(secondValue);
Thread.sleep(secondValue);
} catch (Exception e) {
e.printStackTrace();
}
}
public static void main(String[] args) throws InterruptedException {
join_1 threadTest = new join_1();
threadTest.start();
threadTest.join();
System.out.println("threadTest执行完毕后我再执行");
}
}