Java Thread and runnable

java中可有两种方式实现多线程，

一种是继承Thread类，(Thread本身实现了Runnable接口，就是说需要写void run 方法，来执行相关操作)

一种是实现Runnable接口

start, 和主线程一起执行，执行的顺序不确定

join，线程们 先执行，当所有的子线程执行完毕后，主线程才执行操作（文章最下面的例子）

// 1 Provide a Runnable object, the Thread class itself implements Runnable
//~~~ 1.1
Thread t1 = new Thread(new Runnable() {
    @Override
    public void run() {
        output("t1");
    }
});
t1.start();

//~~~ 1.2 is more general
public class HelloRunnable implements Runnable {
    public void run() {
        System.out.println("Hello from a thread!");
    }
}
(new Thread(new HelloRunnable())).start();

// 2 Subclass Thread (in simple applications)  The Thread class itself implements Runnable
public class HelloThread extends Thread {
    public void run() {
        System.out.println("Hello from a thread!");
    }
}
 (new HelloThread()).start();

// thread.join
t1.start()
t2.start()
outputresult // 如果想要等到 两个线程t1, t2 都执行完成，再通过outputresult，在主线程输出结果，需要t1.join(), t2.join()

t1.start()
t2.start()
t1.join()
t2.join()
outputresult