如何在Java中通过反射访问父类的父类的私有字段? [英] How to access a private field of the super class of the super class with reflection in Java?

问题描述

在一个正在使用的API中，我有一个抽象类( A类)，该类具有私有字段( A.privateField ). B类 扩展了API中的A类.我需要扩展B类及其实现，即 C类，但是我需要A类的privateField.我应该使用反射:如何访问超超类的私有字段?

In one API I am using I have an Abstract Class (Class A) that has a private field (A.privateField). Class B extends Class A within the API. I need to extend Class B with my implementation of it, Class C, but I need privateField of class A. I should use reflection: How can I access a private field of a super super class?

Class A
    - privateField
Class B extends A
Class C extends B
    + method use A.privateField

推荐答案

您需要这样做的事实表明设计存在缺陷.

The fact that you need to do this points to a flawed design.

但是，可以按照以下步骤进行操作:

However, it can be done as follows:

class A
{
  private int privateField = 3;
}

class B extends A
{}

class C extends B
{
   void m() throws NoSuchFieldException, IllegalAccessException
   {
      Field f = getClass().getSuperclass().getSuperclass().getDeclaredField("privateField");
      f.setAccessible(true); // enables access to private variables
      System.out.println(f.get(this));
   }
}

致电:

new C().m();

Andrzej Doyle所说的遍历类层次结构" 的一种方法如下:

One way to do the 'walking up the class hierarchy' that Andrzej Doyle was talking about is as follows:

Class c = getClass();
Field f = null;
while (f == null && c != null) // stop when we got field or reached top of class hierarchy
{
   try
   {
     f = c.getDeclaredField("privateField");
   }
   catch (NoSuchFieldException e)
   {
     // only get super-class when we couldn't find field
     c = c.getSuperclass();
   }
}
if (f == null) // walked to the top of class hierarchy without finding field
{
   System.out.println("No such field found!");
}
else
{
   f.setAccessible(true);
   System.out.println(f.get(this));
}

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