Re: Accessing grandparent's overridden methods.

From:
Patricia Shanahan <pats@acm.org>
Newsgroups:
comp.lang.java.programmer
Date:
Tue, 01 Jan 2008 16:27:22 -0800
Message-ID:
<flelpo$1pck$1@ihnp4.ucsd.edu>
Mark Rafn wrote:

[ B extends A, C extends B, each implements/overrides showMe() ]

Kira Yamato <kirakun@earthlink.net> wrote:

Question: how can I [in class C] access class A's showMe()?
I'm suspecting this cannot be done without modifying codes
outside of class C.


1) if you need to do this, you've probably got a broken object model. You
shouldn't know or care about it's implementation beyond what method signatures
are available to you.


Strongly agree. Either C should not be calling A's method, or B's
version does not do the same job as A's method, and should have a
different name.

2) If you really need it, you could use reflection.
  this.getClass().getSuperclass().getSuperclass().getMethod("showMe", null)
will get you the Method you want to call.


This does not seem to work. However, to be fair, I was not really
expecting it to work so I may have missed something. Please review. I get:

Direct showMe call
C
Super call
B
Refection call
C

when I run the following. Note that I would only throw "Exception" in a
test program, where I want any problem in the reflection, no matter what
it is, to flow to the top and crash the program.

public class ReflectionTest {

   public static void main(String[] args)
   throws Exception {
     new C().test();
   }

   static class A {
     public void showMe() {
       System.out.println("A");
     }
   }

   static class B extends A {
     public void showMe() {
       System.out.println("B");
     }
   }

   static class C extends B {
     public void showMe() {
       System.out.println("C");
     }

     public void test() throws Exception {
       System.out.println("Direct showMe call");
       showMe(); // prints C
       System.out.println("Super call");
       super.showMe(); // prints B
       System.out.println("Refection call");
       Method grandparentMethod =
         getClass().getSuperclass().getSuperclass()
           .getMethod("showMe", (Class[]) null);
       grandparentMethod.invoke(this, new Object[0]);
     }
   }

}

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