一、extends Thread 编写类并extends Thead类，Override run() 实例化编写的类，执行方法 start() 开启线程  

public class Main {
    public static void main(String[] args) {
        Thread t = new MyThread();
        t.start(); // 启动新线程
    }
}

class MyThread extends Thread {
    @Override
    public void run() {
        System.out.println("start new thread!");
    }
}

二、implements Runnable 编写类并implements Runnable接口，Override run() 实例化并执行方法 start() 开启线程 与上一方法区别是无需继承Thread类  

public class Main {
    public static void main(String[] args) {
        Thread t = new Thread(new MyRunnable());
        t.start(); // 启动新线程
    }
}

class MyRunnable implements Runnable {
    @Override
    public void run() {
        System.out.println("start new thread!");
    }
}