Can I access a subclass method through a base class-typed reference?

Question

Below is the piece of code I am trying to work on but unable to sort out the issue: "Can I really do the below in Java.. If yes please help to know me "How" and if no "Why?" "... Have a look at the code below...

class Base{

      public void func(){

            System.out.println("In Base Class func method !!");         
      };
}

class Derived extends Base{

      public void func(){   // Method Overriding

            System.out.println("In Derived Class func method"); 
      }

      public void func2(){  // How to access this by Base class reference

            System.out.println("In Derived Class func2 method");
      }  
}

class InheritDemo{

      public static void main(String [] args){

            Base B= new Derived();
            B.func2();   // <--- Can I access this ??? This is the issue...
      }
}

Thanks in advance!!!! Waiting for some helpful answers :) ...

If you think that you must do something like this, you need to re-visit your design. — Sergey Kalinichenko, Aug 15 '12 at 18:53

score 4 · Answer 1 · edited Aug 15 '12 at 19:26

4

short and sweet? No you cant.. How must Base know what functions/methods are present in the extended class?

EDIT:

By explict/type casting, this may be achieved, as the compiler takes it you know what you are doing when casting the object Base to Derived:

if (B instanceof Derived) {//make sure it is an instance of the child class before casting
((Derived) B).func2();
}

edited Aug 15 '12 at 19:26

dimo414

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answered Aug 15 '12 at 18:53

David Kroukamp

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score 2 · Answer 2 · answered Aug 15 '12 at 18:52

2

This wont even compile as B is unaware of the func2

answered Aug 15 '12 at 18:52

srikanth yaradla

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thanks for replying.. But that is what i Want to ask .. Can I make B aware of it anyhow ?? As i can using pointers in C++ but how can i do it here in java??? – AnkitChhajed Aug 15 '12 at 18:56
Base class is not aware of the methods specific to Derived.You can only access derived class methods by type casting to Dervied like `((Derived) B).func2();` – srikanth yaradla Aug 15 '12 at 19:00

Razvan · Answer 3 · 2012-08-15T18:59:21.027

2

Since the type of object B is Base and the Base type doesn't have a func2() in its public interface, your code is not going to compile.

You can either define B as Derived or cast the B object to Derived:

   Derived B = new Derived(); B.func2();
   //or
   Base B = new Derived(); ((Derived)B).func2();

edited Aug 15 '12 at 18:59

answered Aug 15 '12 at 18:54

Razvan

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score 1 · Answer 4 · answered Aug 15 '12 at 18:54

1

You can do

((Derived) B).func2();

You can't do

B.func2();

as func2 is not a method of the Base class.

answered Aug 15 '12 at 18:54

Peter Lawrey

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score 0 · Answer 5 · answered Aug 15 '12 at 18:54

0

Like this:

((Derived) B).func2();

answered Aug 15 '12 at 18:54

Gilbert Le Blanc

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Can I access a subclass method through a base class-typed reference?

5 Answers5

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