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标题: ThreadLocal问题 [打印本页]
作者: 汪小照    时间: 2012-10-21 15:26
标题: ThreadLocal问题
本帖最后由 汪小照 于 2012-10-22 10:32 编辑
  1. import java.util.Random;

  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 {

  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. }

  46. class MyThreadLocal{
  47. private String name;
  48. private int age;

  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. }

  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. }

  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？
作者: 给生活加点料    时间: 2012-10-21 15:47
站位。等回复。
作者: hello_world！    时间: 2012-10-21 16:30
  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;
}
作者: hello_world！    时间: 2012-10-21 16:31
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
作者: 汪小照    时间: 2012-10-21 20:00
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



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