关于反射小总结

我之前总结的关于反射的另一篇文章:

http://www.cnblogs.com/DreamDrive/p/4217130.html

项目结构图:

CC类和SuperCC类是一种继承关系.想通过CC对象访问SuperCC中的方法.而建立一个DD客户端类.

//===============================分隔线一====================================================

CC.java

package c;

public class CC extends SuperCC {

}

SuperCC.java

package c;

public class SuperCC {

    public void test() {
        System.out.println("This is SuperCC");
    }
}

DD.java

import java.lang.reflect.Method;

import c.CC;
import c.SuperCC;

public class DD {

    public static void main(String[] args) {
        // CC对象访问SuperCC中的方法
        // 方式一:
        CC cc = new CC();
        cc.test();

        // 方式二:
        try {
            // Method declaredTestMethod = cc.getClass().getDeclaredMethod("test"); 出现异常 java.lang.NoSuchMethodException:c.CC.test()
            Method declaredTestMethod = SuperCC.class.getDeclaredMethod("test"); // 正常打印出"This is SuperCC"
            declaredTestMethod.setAccessible(true);
            declaredTestMethod.invoke(cc);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

 解释一下为什么在第一种情况下

cc.getClass().getDeclaredMethod("test");

会出现异常呢?
cc.getClaass 获取的值是 class c.CC
SuperCC.class 获取的值是 class c.SuperCC


如果在CC类中重写SuperCC中的test()方法.
C.java

package c;

public class CC extends SuperCC {

    @Override
    public void test() {
        System.out.println("This is CC");
    }
}

DD.java

import java.lang.reflect.Method;

import c.CC;
import c.SuperCC;

public class DD {

    public static void main(String[] args) {
        // CC对象访问SuperCC中的方法
        // 方式一:
        CC cc = new CC();
        cc.test();

        // 方式二:
        try {
            //Method declaredTestMethod = cc.getClass().getDeclaredMethod("test"); // 正常打印出"This is CC" 
            Method declaredTestMethod = SuperCC.class.getDeclaredMethod("test"); // 正常打印出"This is CC" 
            declaredTestMethod.setAccessible(true);
            declaredTestMethod.invoke(cc);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

 这两种方式都会正常打印出"This is CC".

  

 //===============================分隔线二====================================================

再用一下toString()方法

C.java

package c;

/**
 * created by kongxiaohan on Jul 21, 2015 Detailled comment
 *
 */
public class CC extends SuperCC {

    @Override
    public String toString() {
        System.out.println("This is CC toString");
        return "CC [toString()=" + super.toString() + "]";
    }
}

SuperCC.java

package c;

public class SuperCC {

    @Override
    public String toString() {
        System.out.println("This is SuperCC toString");
        return "SuperCC [toString()=" + super.toString() + "]";
    }

}

DD.java

package d;

import java.lang.reflect.Method;

import c.CC;
import c.SuperCC;

public class DD {

    public static void main(String[] args) {
        CC cc = new CC();
        try {
            // Method declaredTestMethod = Object.class.getDeclaredMethod("toString"); //正常 但是什么都不打印(也是正常的)
            // Method declaredTestMethod = cc.getClass().getDeclaredMethod("toString"); // 正常 分别打印 This is CC toString  This is SuperCC toString
             Method declaredTestMethod = SuperCC.class.getDeclaredMethod("toString"); // 正常 分别打印 This is CC toString  This is SuperCC toString
            // java.lang.NoSuchMethodException: c.SuperCC.toString()
            declaredTestMethod.setAccessible(true);
            declaredTestMethod.invoke(cc);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

同样如果以上CC.java中不重写toString()方法.

Method declaredTestMethod = cc.getClass().getDeclaredMethod("toString");是会报java.lang.NoSuchMethodException: c.CC.toString()
Method declaredTestMethod = SuperCC.class.getDeclaredMethod("toString");是正常打印的 This is SuperCC toString

//========================================================分割线三====================================================================