Java中利用反射對類的hidden成員方法和屬性的訪問

java中通過訪問控制符來控制對類成員的訪問,private 成員表示只在類的內部才可以被訪問,但是利用java的反射機制卻可以再類的外部來訪問類的私有成員

下面是個簡單的例子來說明這一點

1. package com.eric.reflect;
3. import java.lang.reflect.Field;
4. import java.lang.reflect.Method;
6. /**
7. *
8. * this class mainly for explain how to access hidden method or field
9. *
10. *
11. *
12. * archive $ProjectName: $
13. *
14. * @author Admin
15. *
16. * @version $Revision: $ $Name: $
17. */
18. public class AccesHiddenElements {
19. public static void main(String[] args) {
20. Inter inter = new InterImpl();
21. inter.f();
22. if (inter instanceof InterImpl) {
23. // use class cast to method that in InterImpl class
24. ((InterImpl) inter).g();
25. // can't access h method
26. // ((InterImpl) inter).h();
27. }
28. // (1)javap -private InterImpl to get all method name eg h()
29. // (2)use reflect to access private method
30. accessMehodByName(inter, "h");
31. accessFieldByName(inter, "name");
32. Inter annousInter = new Inter() {
33. public void f() {
34. System.out.println("f() method in annousInter");
35. }
37. private void g() {
38. System.out.println("g() method in annousInter");
39. }
41. };
42. accessMehodByName(annousInter, "g");
43. }
45. static void accessMehodByName(Object obj, String methodName) {
46. try {
47. Method method = obj.getClass().getDeclaredMethod(methodName);
48. method.setAccessible(true);
49. method.invoke(obj);
50. } catch (Exception e) {
51. e.printStackTrace();
52. }
53. }
55. static void accessFieldByName(Object obj, String methodName) {
56. try {
57. Field field = obj.getClass().getDeclaredField(methodName);
58. field.setAccessible(true);
59. System.out.println(field.getInt(obj));
60. } catch (Exception e) {
61. e.printStackTrace();
62. }
63. }
65. }
67. interface Inter {
68. public void f();
69. }
71. class InterImpl implements Inter {
72. <pre name="code" class="java"> //私有屬性,正常情況下外部類不可以訪問此方法

private int name = 10;public void f() {System.out.println("f() in InterImpl");}public void g() {System.out.println("g() in InterImpl");} //私有方法,正常情況下外部類不可以訪問此方法private void h() {System.out.println("h() in InterImpl");}}/* * * History: * * * * $Log: $ */