多线程 -- run()方法和start()方法的区别

来源：互联网发布：手机怎么开通淘宝卖家编辑：程序博客网时间：2024/05/19 05:05

一. 直接调用run()方法

public class Two_Thread implements Runnable {public static void main(String[] args) {// TODO Auto-generated method stubTwo_Thread R = new Two_Thread();R.run(); // 直接调用run()方法， 而不是start()方法启动线程System.out.println(Thread.currentThread().getName()+" back to main");}@Overridepublic void run() {// TODO Auto-generated method stubincreate();}private  void increate() { // TODO Auto-generated method stubfor(int i=0;i<5;i++){System.out.println(Thread.currentThread().getName()+" i = "+i);        try { Thread.sleep(1000); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); }}}}

无论什么时候，打印的log都是以下不变：

main i = 0
main i = 1
main i = 2
main i = 3
main i = 4
main back to main

由log可以看出，run()方法是通过main线程启动的，并且它不不具有任何内在的线程能力（即总是执行完run方法，才打印main back to main）。如果要实现线程行为，必须采用start()方法。

二.添加一个线程t1. 并且去掉线程休眠 Thread.sleep(1000);

public class Two_Thread implements Runnable {public static void main(String[] args) {// TODO Auto-generated method stubTwo_Thread R = new Two_Thread();Thread t1 = new Thread(R,"1"); //用Runnable对象1初始化t1.start(); //通过start()方法启动线程R.run();//调用Runable对象中的run()方法System.out.println(Thread.currentThread().getName()+" back to main");}@Overridepublic void run() {// TODO Auto-generated method stubincreate();}private  void increate() { // TODO Auto-generated method stubfor(int i=0;i<5;i++){System.out.println(Thread.currentThread().getName()+" i = "+i);   }}}

此时打印的log是随机的：但是无论什么时候，这句“main back to main”log，一定是在执行完main i = 4之后才会执行。因为在主线程中，这俩句是顺序执行的。

情况1：

main i = 0
1 i = 0
main i = 1
1 i = 1
main i = 2
1 i = 2
main i = 3
1 i = 3
main i = 4
1 i = 4
main back to main

情况2：

1 i = 0
main i = 0
1 i = 1
main i = 1
1 i = 2
main i = 2
1 i = 3
main i = 3
main i = 4
main back to main
1 i = 4

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