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。