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。

 package com.mianshi.easy;

 public class StartRunTest {

     /**

      * 直接调用run()和用start()启动一个线程的差别

      */

     public static void main(String[] args){

         Thread thread=new ThreadDemo();

         //第一种

         //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

         /*thread.run();

         for(int i=0;i<100;i++){

             System.out.println(i);

         }*/

         //第二种

         //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,

         //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)

         thread.start();

         for(int i=0;i<100;i++){

             System.out.println(i);

         }

         //第三种

         //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

         //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，

         //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

         /*thread.setDaemon(true);

         thread.start();*/

         //第四种

         //用户线程可以被System.exit(0)强制kill掉,所以也只打印出七句

        /* thread.start();

         System.out.println("main thread is over");

         System.exit(1);*/

     }

     public static class ThreadDemo extends Thread{

         @Override

         public void run() {

             for (int i = 0; i < 100; i++) {

                 System.out.println("This is a Thread test"+i);

             }

         }

     }

 }

结果：

0

1

2

3

4

5

6

7

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

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

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

26

27

28

29

30

31

32

33

34

35

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75

76

77

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

79

80

81

82

83

84

85

86

87

88

89

90

91

92

93

94

95

96

97

98

99

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

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。

 package com.mianshi.easy;

 public class StartRunTest {

     /**

      * 直接调用run()和用start()启动一个线程的差别

      */

     public static void main(String[] args){

         Thread thread=new ThreadDemo();

         //第一种

         //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

         thread.run();

         for(int i=0;i<100;i++){

             System.out.println(i);

         }

         //第二种

         //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,

         //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)

         /*thread.start();

         for(int i=0;i<100;i++){

             System.out.println(i);

         }*/

         //第三种

         //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

         //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，

         //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

         /*thread.setDaemon(true);

         thread.start();*/

         //第四种

         //用户线程可以被System.exit(0)强制kill掉,所以也只打印出七句

        /* thread.start();

         System.out.println("main thread is over");

         System.exit(1);*/

     }

     public static class ThreadDemo extends Thread{

         @Override

         public void run() {

             for (int i = 0; i < 100; i++) {

                 System.out.println("This is a Thread test"+i);

             }

         }

     }

 }

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

0

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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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