1. import java.util.Random;
   
2. 
   
3. /*
   
4. * 当有多个数据时，将其封装成对象，
   
5. * 存放的是对象，而不再是单个数据。
   
6. */
   
7. public class ThreadScopeShareDate1 {
   
8. 
   
9. public static void main(String [] args)
   
10. {
    
11. for(int x=0;x<2;x++)
    
12. {
    
13. new Thread(new Runnable(){
    
14. public void run()
    
15. {
    
16. int data = new Random().nextInt();
    
17. System.out.println(Thread.currentThread()
    
18. .getName()+" has put "+ data);
    
19. MyThreadLocal mtl = MyThreadLocal.getInstance();
    
20. mtl.setAge(data);
    
21. mtl.setName("name"+ data);
    
22. new A().get();
    
23. new B().get();
    
24. }
    
25. }).start();
    
26. }
    
27. }
    
28. static class A{
    
29. public void get()
    
30. {
    
31. MyThreadLocal mtl = MyThreadLocal.getInstance();
    
32. System.out.println("A form "+Thread.currentThread().getName()+
    
33. " " + mtl.getAge()+" "+mtl.getName());
    
34. }
    
35. }
    
36. static class B{
    
37. public void get()
    
38. {
    
39. MyThreadLocal mtl = MyThreadLocal.getInstance();
    
40. System.out.println("B from "+Thread.currentThread().getName()+
    
41. " " + mtl.getAge()+" "+mtl.getName());
    
42. }
    
43. }
    
44. }
    
45. 
    
46. class MyThreadLocal{
    
47. private String name;
    
48. private int age;
    
49. 
    
50. private static ThreadLocal<MyThreadLocal> tl = new ThreadLocal<MyThreadLocal>();
    
51. private static MyThreadLocal instance =null;
    
52. private MyThreadLocal(){}
    
53. public static MyThreadLocal getInstance()
    
54. {
    
55. instance = tl.get();
    
56. if(instance == null)
    
57. {
    
58. instance = new MyThreadLocal();
    
59. tl.set(instance);
    
60. }
    
61. return instance;
    
62. }
    
63. 
    
64. public String getName() {
    
65. return name;
    
66. }
    
67. public void setName(String name) {
    
68. this.name = name;
    
69. }
    
70. public int getAge() {
    
71. return age;
    
72. }
    
73. public void setAge(int age) {
    
74. this.age = age;
    
75. }
    
76. 
    
77. }
    

复制代码

为什么打印的是这样的结果：
Thread-0 has put -1622789957
Thread-1 has put -1010639133
A form Thread-0  0   null
A form Thread-1  -1010639133   name-1010639133
B from Thread-0  0   null
B from Thread-1  -1010639133   name-1010639133

打印出来的竟然有0 和null ，而张老师讲课时运行多次都不会有0 和 null 的结果，有知道的请分析一下哪里出错了，错误的原因是什么？

站位。等回复。

1. private static ThreadLocal<MyThreadLocal> tl = new ThreadLocal<MyThreadLocal>();
   
2. [color=Red]private static MyThreadLocal instance =null; //关键是这句话引起的错误，你想过没有，你把返回值设置为静态的，在内存中就只有一份，你用的ThreadLocal根本就起不了作用。多线程可以同时访问，同时修改，所以结果不会出现互斥的现象，也没有实现数据共享[/color]
   
3. private MyThreadLocal(){}
   
4. public static MyThreadLocal getInstance()
   
5. {
   
6. instance = tl.get();
   
7. if(instance == null)
   
8. {
   
9. instance = new MyThreadLocal();
   
10. tl.set(instance);
    
11. }
    
12. return instance;
    
13. }

复制代码

这样改就行了：
private static ThreadLocal<MyThreadLocal> tl = new ThreadLocal<MyThreadLocal>();
//private static MyThreadLocal instance =null;
private MyThreadLocal(){}
public static MyThreadLocal getInstance()
{
MyThreadLocal instance = tl.get();
if(instance == null)
{
instance = new MyThreadLocal();
tl.set(instance);
}
return instance;
}

忘记加上结果了：
Thread-0 has put -1824922109
A form Thread-0 -1824922109 name-1824922109
B from Thread-0 -1824922109 name-1824922109
Thread-1 has put -625868128
A form Thread-1 -625868128 name-625868128
B from Thread-1 -625868128 name-625868128

hello_world！ 发表于 2012-10-21 16:31
忘记加上结果了：
Thread-0 has put -1824922109
A form Thread-0 -1824922109 name-1824922109

看明白了你所说的，谢谢啦