浅析Thread类run()和start()的区别

1.先看看jdk文档

void    run()
If this thread was constructed using a separate Runnable run object, then that Runnable object's run method is called; otherwise, this method does nothing and returns.

void    start()
Causes this thread to begin execution; the Java Virtual Machine calls the run method of this thread.

线程调用run()方法是直接执行其run方法（正常情况）。

线程调用start()方法后进入准备状态，等待CPU的调度，当切换到该线程时，线程进入运行状态，执行run()方法。

既然都是执行线程的run方法，为什么不直接调用run方法？

2.再看代码

public class Main {

    public static void main(String[] args) {
        Mythread t = new Mythread();
        Thread thread1 = new Thread(t);
        Thread thread2 = new Thread(t);
        System.out.println("begin = " + System.currentTimeMillis());
        thread1.setName("我是线程1");
        thread2.setName("我是线程2");
        thread1.run();
        thread2.start();
        System.out.println("end = " + System.currentTimeMillis());
    }
}

class Mythread extends Thread{
    public void run() {
        try {
            System.out.println("threadName: "+this.currentThread().getName()+" begin");
            Thread.sleep(1000);
            System.out.println("threadName: "+this.currentThread().getName()+" end");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

运行结果：

可以发现直接调用run方法时是被主线程当做普通的方法调用，并不是真正的多线程。