一个线程可以在其它线程之上调用join()方法，其效果是等待一段时间直到第二个线程结束才继续执行。如果某个线程在另一个线程t上调用t.join()，此线程将被挂起，直到目标线程t结束才恢复(即t.isAlive()返回假)。
也可以在调用join()方法时带上一个超时参数（单位可以试毫秒，或者毫秒和纳秒），这样如果目标线程在这段时间到期时还没有结束的话，join()方法总能返回。
对join()方法的调用可以被中断，做法是在调用线程上调用interrupted()方法，这时需要用到try-catch子句。
class Sleeper extends Thread{
private int duration;
public Sleeper(String name,int sleepTime) {
super(name);
duration=sleepTime;
start();
}
public void run() {
try {
sleep(duration);
}catch(InterruptedException e) {
System.out.println(getName()+" was interrupted. "+" is interrupted: "+isInterrupted());
return;
}
System.out.println(getName()+" has awakened");
}
}
class Joiner extends Thread{
private Sleeper sleeper;
public Joiner(String name,Sleeper sleeper) {
super(name);
this.sleeper=sleeper;
start();
}
public void run() {
try {
sleeper.join();
}catch(InterruptedException e) {
System.out.println("Interrupted");
}
System.out.println(getName()+" join completed");
}
}
public class Joining {
public static void main(String[] args) {
// TODO Auto-generated method stub
Sleeper sleepy=new Sleeper("Sleepy",1500),
grumpy=new Sleeper("grumpy",1500);
Joiner dopey=new Joiner("Dopey",sleepy),
doc=new Joiner("Doc",grumpy);
grumpy.interrupt();
}
}
/*
grumpy was interrupted. is interrupted: false
Doc join completed
Sleepy has awakened
Dopey join completed
*/