Java Thread join 方法可以当前的线程暂停至你声明的另一个线程完全结束，总共有3种重载方法。
Java Thread join
public final void join(); 这个方法会使当前调用的线程进行等待，直至调用的这个方法结束。如果线程被中断会抛出InterruptedException。
public final synchronized void join(long millis); 这个方法会使当调用的线程结束或者等待你声明的时长。等待的时间由操作系统决定。并不能保证当前的线程等待时间是确定的。
public final synchronized void join(long millis, int nanos); 同上，时间细化至毫微秒。
这面这个例子展示了Thread join 的用方法。这段代码的主要目的是确保main线程最后一个执行完，且第三个线程启必须等第一个线程执行完。
package com.journaldev.threads;
public class ThreadJoinExample {
public static void main(String[] args) {
Thread t1 = new Thread(new MyRunnable(), "t1");
Thread t2 = new Thread(new MyRunnable(), "t2");
Thread t3 = new Thread(new MyRunnable(), "t3");
t1.start();
//start second thread after waiting for 2 seconds or if it's dead
try {
t1.join(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
t2.start();
//start third thread only when first thread is dead
try {
t1.join();
} catch (InterruptedException e) {
e.printStackTrace();
}
t3.start();
//let all threads finish execution before finishing main thread
try {
t1.join();
t2.join();
t3.join();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println("All threads are dead, exiting main thread");
}
}
class MyRunnable implements Runnable{
@Override
public void run() {
System.out.println("Thread started:::"+Thread.currentThread().getName());
try {
Thread.sleep(4000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("Thread ended:::"+Thread.currentThread().getName());
}
}
上述代码执行完，结果如下：
Thread started:::t1
Thread started:::t2
Thread ended:::t1
Thread started:::t3
Thread ended:::t2
Thread ended:::t3
All threads are dead, exiting main thread
