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标题: final 反射问题 谁能解释一下 [打印本页]
作者: lzw123451    时间: 2013-3-14 17:03
标题: final 反射问题 谁能解释一下
本帖最后由 李志卫 于 2013-3-16 23:52 编辑
  1. import java.lang.reflect.Field;

  3. public class Test9{

  5. public final int x = 100;

  7. public int Method(Test9 t1,Test9 t2) throws Exception{

  9. int i = t1.x;

  11. System.out.println("i's value is "+i);

  13. changeX(t1);
  14. System.out.println("i2's value is "+t1.x);

  16. int j = t2.x;

  18. System.out.println("j's value is "+j);

  20. return j - i;

  22. }

  24. public static void changeX(Test9 t1) throws Exception{

  26. Class clazz = t1.getClass();

  28. Field fieldX = clazz.getDeclaredField("x");

  30. fieldX.setAccessible(true);

  32. fieldX.setInt(t1, 300);

  34. System.out.println("fieldX's vlaue is "+fieldX.getInt(t1));

  36. }

  38. public int test() throws Exception{

  40. return Method(this,this);

  42. }

  44. public static void main(String[] args) throws Exception{

  46. Test9 t1 = new Test9();

  48. System.out.println(t1.test());

  50. }

  52. }
复制代码
结果是
i's value is 100
fieldX's vlaue is 300
i2's value is 100
j's value is 100
0
  1. import java.lang.reflect.Field;

  3. public class Test9{

  5. public final int x;
  6. public Test9()
  7. {
  8. x = 100;
  9. }

  11. public int Method(Test9 t1,Test9 t2) throws Exception{

  13. int i = t1.x;

  15. System.out.println("i's value is "+i);

  17. changeX(t1);
  18. System.out.println("i2's value is "+t1.x);

  20. int j = t2.x;

  22. System.out.println("j's value is "+j);

  24. return j - i;

  26. }

  28. public static void changeX(Test9 t1) throws Exception{

  30. Class clazz = t1.getClass();

  32. Field fieldX = clazz.getDeclaredField("x");

  34. fieldX.setAccessible(true);

  36. fieldX.setInt(t1, 300);

  38. System.out.println("fieldX's vlaue is "+fieldX.getInt(t1));

  40. }

  42. public int test() throws Exception{

  44. return Method(this,this);

  46. }

  48. public static void main(String[] args) throws Exception{

  50. Test9 t1 = new Test9();

  52. System.out.println(t1.test());



  56. }

  58. }


复制代码
结果是
i's value is 100
fieldX's vlaue is 300
i2's value is 300
j's value is 300
200


为什么两种情况不一样？
作者: 沈文杰    时间: 2013-3-14 17:35
难道是用记事本打的？头都看昏了，麻烦你排下版。。。这太不规范了。
作者: tianyun    时间: 2013-3-14 18:08
import java.lang.reflect.*;
public class Test9{

public final int x;

public Test9()

{

x = 100;

}
//输出两对象相减的结果

public int Method(Test9 t1,Test9 t2) throws Exception{

int i = t1.x;
//此时i为100
System.out.println("i's value is "+i);

changeX(t1); //调用方法后t1.x为300

System.out.println("i2's value is "+t1.x);

int j = t2.x;//j为300,this代表t1

System.out.println("j's value is "+j);

return j - i; //300-100

}
//更改对象属性值
public static void changeX(Test9 t1) throws Exception{

Class clazz = t1.getClass();

Field fieldX = clazz.getDeclaredField("x");

fieldX.setAccessible(true);

fieldX.setInt(t1, 300);

System.out.println("fieldX's vlaue is "+fieldX.getInt(t1));

}

public int test() throws Exception{

return Method(this,this);

}

public static void main(String[] args) throws Exception{

Test9 t1 = new Test9();

System.out.println(t1.test());

}

}


/*运行结果是：

i's value is 100

fieldX's vlaue is 300

i2's value is 300

j's value is 300

200*/
//this代表同一对象
作者: tianyun    时间: 2013-3-14 18:09
参照这思路解决第二个！
作者: lzw123451    时间: 2013-3-14 18:22
tianyun 发表于 2013-3-14 18:09
参照这思路解决第二个！

???？
第一种情况 用反射最终没改变x的值
第二种情况 却改变成功了
为什么
作者: lzw123451    时间: 2013-3-15 12:38
{:soso_e127:}还没人回答问题呢。上面的答案莫名奇妙，乱写一通



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