浅谈Java多线程中的join方法

先上代码

新建一个Thread,代码如下:

package com.thread.test;

public class MyThread extends Thread {
    private String name;
    public MyThread(String name) {
        this.name = name;
    }
    @Override
    public void run() {
        for (int i = 0; i < 100; i++) {
            System.out.println(name+"["+i+"]");
        }
        super.run();
    }
}

之后新建测试类,代码如下:

package com.thread.test;
/*
 * 0-50执行的是主线程,50-100执行的是A线程,并且将A线程完全执行完后才继续执行主线程
 */
public class ThreadDemo{
    public static void main(String[] args) {
        MyThread t = new MyThread("A");
        t.start();
        for (int i = 0; i < 100; i++) {
            if (i>50) {
                try {
                    t.join();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            System.out.println("主线程"+"["+i+"]");
        }
    }
}

下面是Java Platform SE8 API中对Thread中Join方法的解释:

public final void join(long millis)
                throws InterruptedExceptionWaits at most millis milliseconds for this thread to die. A timeout of 0 means to wait forever. 
This implementation uses a loop of this.wait calls conditioned on this.isAlive. As a thread terminates the this.notifyAll method is invoked. It is recommended that applications not use wait, notify, or notifyAll on Thread instances.

Parameters: 
millis - the time to wait in milliseconds 
Throws: 
IllegalArgumentException - if the value of millis is negative 
InterruptedException - if any thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.

先上代码

新建一个Thread,代码如下:

package com.thread.test;

public class MyThread extends Thread {
    private String name;
    public MyThread(String name) {
        this.name = name;
    }
    @Override
    public void run() {
        for (int i = 0; i < 100; i++) {
            System.out.println(name+"["+i+"]");
        }
        super.run();
    }
}

之后新建测试类,代码如下:

package com.thread.test;
/*
 * 0-50执行的是主线程,50-100执行的是A线程,并且将A线程完全执行完后才继续执行主线程
 */
public class ThreadDemo{
    public static void main(String[] args) {
        MyThread t = new MyThread("A");
        t.start();
        for (int i = 0; i < 100; i++) {
            if (i>50) {
                try {
                    t.join();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            System.out.println("主线程"+"["+i+"]");
        }
    }
}

下面是Java Platform SE8 API中对Thread中Join方法的解释:

public final void join(long millis)
                throws InterruptedExceptionWaits at most millis milliseconds for this thread to die. A timeout of 0 means to wait forever. 
This implementation uses a loop of this.wait calls conditioned on this.isAlive. As a thread terminates the this.notifyAll method is invoked. It is recommended that applications not use wait, notify, or notifyAll on Thread instances.

Parameters: 
millis - the time to wait in milliseconds 
Throws: 
IllegalArgumentException - if the value of millis is negative 
InterruptedException - if any thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.

 我自己的理解就是会强行进入使用join方法的线程，其他线程等待该线程完全执行完后才会进来。