abstract class and protected member behaviour

[M Rama]

From the code

  
package abstract1.pck1;
 
abstract public class A {

protected int x= 9; //1

protected abstract void foo();
 
}
 

package abstract1.pck2;
 
import abstract1.pck1.*;
 
 public class B extends A {
 
 protected String x = "10"; //2

 protected void foo(){System.out.println(x);}
}
 

The inherited member x is int. However, I am redeclaring it as String while subclassing. Is this allowed?

Also, if I make line 1 as public, I am able to change line 2 as private. Compiler doesn't complain that the member has become less accessible. Is that ok as well?

[ankur rathi]

variables doesn't take part in the process of inheritance ...

[M Rama]

Rathi Ji,
If I comment line 2, the answer prints 9. Shouldn't that mean that it gets inherited?

[Animesh Shrivastava]

Variables are not inherited, they are hidden.
It means the there are two varaibles in sub class, one is variable x present in Class A and other is x in Class B.
So here as u r accessing x, the JVM will first search if that variable is present in ur class, if the varaible is defined in ur class, if not it searches its super class and finally comes up with the result.
I hope thats ok with u

Thanks

[Raghu Shree]

Hi,
Members are not overriding. If you declared the member in subclass i.e,. available in superclass that memeber will be shadowing. This is also called as instance memeber hiding.

[Parameswaran Thangavel]

hi i had two questions

1)Though it is shadowing can i say it is possible to access the superclass variable using the Fully qualified Name.
(i.e)SuperClassName.variablename

is there anyother way to access it.

2) The protected variable of the super class which resides in different package will become a private member in the subclass.
is it okay..

[Raghu Shree]

Hi Paramesh,

1)Though it is shadowing can i say it is possible to access the superclass variable using the Fully qualified Name.
(i.e)SuperClassName.variablename

If it is static memebers it is possible. just walk through the below code. If any doubt post again.

class superClass
{
   int x=100;
   public void showX()
   {
      System.out.println("X value in super class " + x);
    }
 }
 
 class subClass extends superClass
 {
    int x=200;
    public void showX()
    {
       System.out.println("X value in sup class " + x);
     }
  }
 
  class instanceHiding
  {
     public static void main(String args[])
     {
        subClass subC = new subClass();
        superClass supC = new superClass();
 

        // instance variables are access from objects
        System.out.println ("Instance Variables Access From class objects ");
        System.out.println("Subclass X " + subC.x);
        System.out.println("Superclass X " + supC.x);
        supC.showX();
        subC.showX();
 
        supC=subC; // SuperClass object supC has subclass reference
 
System.out.println ("Instance Variables Access From Dynamic method Dispatch");
        System.out.println("Subclass X " + subC.x);
        System.out.println("Superclass X " + supC.x); // It also prints 100
        System.out.println("Superclass X " );
        supC.showX(); // It prints 200 because superclass object supC has subclass reference
 
        subC=(subClass)supC;
 
System.out.println("Subclass X " + subC.x);
System.out.println("Superclass X " + supC.x); // It also prints 100
System.out.println("Superclass X " );
        subC.showX(); // It prints 200 because superclass object supC has subclass reference
 
     }
  }

[Mark Spritzler]

"M"-
Welcome to the JavaRanch! Please adjust your displayed name to meet the

JavaRanch Naming Policy.

You can change it

here.

Thanks! and welcome to the JavaRanch!

Mark

[M Rama]

Mark,
I guess you are refering to my name here. The naming policy in javaranch does say that I could use initial for first name.

[M Rama]

Thanks for the answer guys. I need to read more on this topic to get a good idea.