run() 和 start() 的区别

1） start：

用start方法来启动线程，真正实现了多线程运行，这时无需等待run方法体代码执行完毕而直接继续执行下面（指主线程下面）的代码。通过调用Thread类的start()方法来启动一个线程，这时此线程处于就绪（可运行）状态，并没有运行，一旦得到cpu时间片，就开始执行run()方法，这里方法run()称为线程体，它包含了要执行的这个线程的内容，Run方法运行结束，此线程随即终止。

 1 package com.mianshi.easy;
 2 public class StartRunTest {
 3     /**
 4      * 直接调用run()和用start()启动一个线程的差别 
 5      */
 6         
 7     public static void main(String[] args){
 8         Thread thread=new ThreadDemo();
 9         //第一种
10         //表明: run()和其他方法的调用没任何不同,main方法按顺序执行了它,并打印出最后一句
11         /*thread.run();
12         for(int i=0;i<100;i++){
13             System.out.println(i);
14         }*/
15         
16         //第二种
17         //表明: start()方法重新创建了一个线程,在main方法执行结束后,由于start()方法创建的线程没有运行结束,
18         //因此主线程未能退出,直到线程thread也执行完毕.这里要注意,默认创建的线程是用户线程(非守护线程)
19         thread.start();
20         for(int i=0;i<100;i++){
21             System.out.println(i);
22         }
23         
24         //第三种
25         //1、为什么没有打印出100句呢?因为我们将thread线程设置为了daemon(守护)线程,程序中只有守护线程存在的时候,是可以退出的,所以只打印了七句便退出了
26         //2、当java虚拟机中有守护线程在运行的时候，java虚拟机会关闭。当所有常规线程运行完毕以后，
27         //守护线程不管运行到哪里，虚拟机都会退出运行。所以你的守护线程最好不要写一些会影响程序的业务逻辑。否则无法预料程序到底会出现什么问题
28         /*thread.setDaemon(true);
29         thread.start();*/
30         
31         //第四种
32         //用户线程可以被System.exit(0)强制kill掉,所以也只打印出七句
33        /* thread.start();
34         System.out.println("main thread is over");
35         System.exit(1);*/
36     }
37     
38     public static class ThreadDemo extends Thread{
39         @Override
40         public void run() {
41             for (int i = 0; i < 100; i++) {
42                 System.out.println("This is a Thread test"+i);
43             }
44         }
45     }
46 }
View Code

结果：

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This is a Thread test0
This is a Thread test1
This is a Thread test2
This is a Thread test3
This is a Thread test4
8
This is a Thread test5
This is a Thread test6
This is a Thread test7
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This is a Thread test8
This is a Thread test9
This is a Thread test10
This is a Thread test11
This is a Thread test12
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This is a Thread test13
78
This is a Thread test14
This is a Thread test15
This is a Thread test16
This is a Thread test17
This is a Thread test18
This is a Thread test19
This is a Thread test20
This is a Thread test21
This is a Thread test22
This is a Thread test23
This is a Thread test24
This is a Thread test25
This is a Thread test26
This is a Thread test27
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This is a Thread test28
This is a Thread test29
This is a Thread test30
This is a Thread test31
This is a Thread test32
This is a Thread test33
This is a Thread test34
This is a Thread test35
This is a Thread test36
This is a Thread test37
This is a Thread test38
This is a Thread test39
This is a Thread test40
This is a Thread test41
This is a Thread test42
This is a Thread test43
This is a Thread test44
This is a Thread test45
This is a Thread test46
This is a Thread test47
This is a Thread test48
This is a Thread test49
This is a Thread test50
This is a Thread test51
This is a Thread test52
This is a Thread test53
This is a Thread test54
This is a Thread test55
This is a Thread test56
This is a Thread test57
This is a Thread test58
This is a Thread test59
This is a Thread test60
This is a Thread test61
This is a Thread test62
This is a Thread test63
This is a Thread test64
This is a Thread test65
This is a Thread test66
This is a Thread test67
This is a Thread test68
This is a Thread test69
This is a Thread test70
This is a Thread test71
This is a Thread test72
This is a Thread test73
This is a Thread test74
This is a Thread test75
This is a Thread test76
This is a Thread test77
This is a Thread test78
This is a Thread test79
This is a Thread test80
This is a Thread test81
This is a Thread test82
This is a Thread test83
This is a Thread test84
This is a Thread test85
This is a Thread test86
This is a Thread test87
This is a Thread test88
This is a Thread test89
This is a Thread test90
This is a Thread test91
This is a Thread test92
This is a Thread test93
This is a Thread test94
This is a Thread test95
This is a Thread test96
This is a Thread test97
This is a Thread test98
This is a Thread test99
View Code

子线程成功创建，主线程的代码也在继续运行，而且证明了子线程短暂等待CPU时间片的过程，此过程中主线程没有停止。

2） run：

run()方法只是类的一个普通方法而已，如果直接调用Run方法，程序中依然只有主线程这一个线程，其程序执行路径还是只有一条，还是要顺序执行，还是要等待run方法体执行完毕后才可继续执行下面的代码，这样就没有达到写线程的目的。

 1 package com.mianshi.easy;
 2 public class StartRunTest {
 3     /**
 4      * 直接调用run()和用start()启动一个线程的差别 
 5      */
 6         
 7     public static void main(String[] args){
 8         Thread thread=new ThreadDemo();
 9         //第一种
10         //表明: run()和其他方法的调用没任何不同,main方法按顺序执行了它,并打印出最后一句
11         thread.run();
12         for(int i=0;i<100;i++){
13             System.out.println(i);
14         }
15         
16         //第二种
17         //表明: start()方法重新创建了一个线程,在main方法执行结束后,由于start()方法创建的线程没有运行结束,
18         //因此主线程未能退出,直到线程thread也执行完毕.这里要注意,默认创建的线程是用户线程(非守护线程)
19         /*thread.start();
20         for(int i=0;i<100;i++){
21             System.out.println(i);
22         }*/
23         
24         //第三种
25         //1、为什么没有打印出100句呢?因为我们将thread线程设置为了daemon(守护)线程,程序中只有守护线程存在的时候,是可以退出的,所以只打印了七句便退出了
26         //2、当java虚拟机中有守护线程在运行的时候，java虚拟机会关闭。当所有常规线程运行完毕以后，
27         //守护线程不管运行到哪里，虚拟机都会退出运行。所以你的守护线程最好不要写一些会影响程序的业务逻辑。否则无法预料程序到底会出现什么问题
28         /*thread.setDaemon(true);
29         thread.start();*/
30         
31         //第四种
32         //用户线程可以被System.exit(0)强制kill掉,所以也只打印出七句
33        /* thread.start();
34         System.out.println("main thread is over");
35         System.exit(1);*/
36     }
37     
38     public static class ThreadDemo extends Thread{
39         @Override
40         public void run() {
41             for (int i = 0; i < 100; i++) {
42                 System.out.println("This is a Thread test"+i);
43             }
44         }
45     }
46 }
View Code

结果：

This is a Thread test0
This is a Thread test1
This is a Thread test2
This is a Thread test3
This is a Thread test4
This is a Thread test5
This is a Thread test6
This is a Thread test7
This is a Thread test8
This is a Thread test9
This is a Thread test10
This is a Thread test11
This is a Thread test12
This is a Thread test13
This is a Thread test14
This is a Thread test15
This is a Thread test16
This is a Thread test17
This is a Thread test18
This is a Thread test19
This is a Thread test20
This is a Thread test21
This is a Thread test22
This is a Thread test23
This is a Thread test24
This is a Thread test25
This is a Thread test26
This is a Thread test27
This is a Thread test28
This is a Thread test29
This is a Thread test30
This is a Thread test31
This is a Thread test32
This is a Thread test33
This is a Thread test34
This is a Thread test35
This is a Thread test36
This is a Thread test37
This is a Thread test38
This is a Thread test39
This is a Thread test40
This is a Thread test41
This is a Thread test42
This is a Thread test43
This is a Thread test44
This is a Thread test45
This is a Thread test46
This is a Thread test47
This is a Thread test48
This is a Thread test49
This is a Thread test50
This is a Thread test51
This is a Thread test52
This is a Thread test53
This is a Thread test54
This is a Thread test55
This is a Thread test56
This is a Thread test57
This is a Thread test58
This is a Thread test59
This is a Thread test60
This is a Thread test61
This is a Thread test62
This is a Thread test63
This is a Thread test64
This is a Thread test65
This is a Thread test66
This is a Thread test67
This is a Thread test68
This is a Thread test69
This is a Thread test70
This is a Thread test71
This is a Thread test72
This is a Thread test73
This is a Thread test74
This is a Thread test75
This is a Thread test76
This is a Thread test77
This is a Thread test78
This is a Thread test79
This is a Thread test80
This is a Thread test81
This is a Thread test82
This is a Thread test83
This is a Thread test84
This is a Thread test85
This is a Thread test86
This is a Thread test87
This is a Thread test88
This is a Thread test89
This is a Thread test90
This is a Thread test91
This is a Thread test92
This is a Thread test93
This is a Thread test94
This is a Thread test95
This is a Thread test96
This is a Thread test97
This is a Thread test98
This is a Thread test99
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View Code

并没有产生子线程，而是普通的方法调用，只有等调用方法执行完后，主线程才能继续执行处后面的代码。

总结：调用start方法方可启动线程，而run方法只是thread的一个普通方法调用，还是在主线程里执行。

参考：http://visionsky.blog.51cto.com/733317/431397

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原文地址：https://www.cnblogs.com/gongxing/p/4654469.html