• 1. Thread
• 2. Runnable
• 3. start() 和 run()

我们先来看一下，使用Thread如何创建线程：

public class ThreadDemo extends Thread {

    @Override

    public void run() {

        System.out.println("Current thread name is: " + Thread.currentThread().getName());

    }

    public static void main(String[] args) {

        for (int i = 0; i < 10; i++) {

            Thread thread = new ThreadDemo();

            thread.start();

        }

    }

}

Current thread name is: Thread-0

Current thread name is: Thread-2

Current thread name is: Thread-1

Current thread name is: Thread-3

Current thread name is: Thread-5

Current thread name is: Thread-4

Current thread name is: Thread-6

Current thread name is: Thread-7

Current thread name is: Thread-8

Current thread name is: Thread-9

可以看到，我们创建来10个线程，但是执行的顺序是不确定的。可以设置优先级，默认是5，最大是10，最小是1.但是即使设置来优先级，顺序也是不能保证。

public static void main(String[] args) {

    for (int i = 0; i < 10; i++) {

        Thread thread = new ThreadDemo();

        thread.setPriority(i + 1);

        thread.start();

    }

}

优先级逐渐上升，但执行但结果还是一样。

我们再来使用Runnable创建线程：

public class RunnableDemo implements Runnable {

    @Override

    public void run() {

        System.out.println("Current runnable thread name is: " + Thread.currentThread().getName());

    }

    public static void main(String[] args) {

        for (int i = 0; i < 10; i++) {

            Thread thread = new Thread(new RunnableDemo());

            thread.start();

        }

    }

}

Current runnable thread name is: Thread-0

Current runnable thread name is: Thread-3

Current runnable thread name is: Thread-2

Current runnable thread name is: Thread-5

Current runnable thread name is: Thread-1

Current runnable thread name is: Thread-6

Current runnable thread name is: Thread-7

Current runnable thread name is: Thread-4

Current runnable thread name is: Thread-8

Current runnable thread name is: Thread-9

可以看出，实现Runnable接口接口之后但RunnableDemo类但实例还是无法直接运行的，它必须将实例对象传入Thread类，然后，才能调用Thread对象中的start()进行启动。

我们接下来来看一下start() 和 run()的区别：
当我们中定义新的线程类的时候，唯一覆写的方法就是run()。那么，我们能不能直接调用run()方法呢？
答案是肯定的。
我们将start()替换为run()再试一下：

public static void main(String[] args) {

    for (int i = 0; i < 10; i++) {

        Thread thread = new Thread(new RunnableDemo());

        thread.run();

    }

}

Current runnable thread name is: main

Current runnable thread name is: main

Current runnable thread name is: main

Current runnable thread name is: main

Current runnable thread name is: main

Current runnable thread name is: main

Current runnable thread name is: main

Current runnable thread name is: main

Current runnable thread name is: main

Current runnable thread name is: main

结果全是主线程在运行，也就是说根据就没有新的线程启动运行。所以，使用run()方法调用时，就和一般的函数调用一样，是由当前线程进行调用的，并不会启动新的线程，然后在新的线程中运行这个run()方法。只有使用start()方法去调用，才会启动新的线程，然后，在新的线程中运行run()方法。