copying subclass object

**spark** · July 22nd, 2012, 01:34 PM

hi all ..
I am trying to copy Subclass object to Super class ..

which is in my code . from Bclass object to Aclass object.. but it is not copied .
the program compiled successfully .

but the value of Aclass object x is still 10 ..
Any help ??
and thanks in advance.

class Aclass{
int x;

Aclass(){
x =10;
}

Aclass(int i ){
x =i;
}

Aclass ( Aclass object)
{
x = object.x;
}
}

class Bclass extends Aclass {
int x;

Bclass ( int i )
{

x = i;
}

Bclass ( Bclass obj){
super( obj);
x= obj.x;
}
}

public class refrencertst {
public static void main ( String arg[]){
Aclass Aobj = new Aclass(6);
Bclass Bobj= new Bclass (5);

Aclass Aobj2 = new Aclass (Bobj);

System.out.print(" member is " + Aobj2.x);

}
}

**spark** · July 22nd, 2012, 02:24 PM

Solved ,,
i put a constructor In Aclass with arguement of Bclass, to when it is called it will copy subclass object ..

Aclass ( Bclass obj){
x = obj.x;
}

Solved .

but is it possible to do this ??

Super class object = subclass object ?

**jps** · July 22nd, 2012, 03:10 PM

So when you have a superclass extended by a subclass, the subclass is a type of the superclass. But this does not mean that you can save the superclass as a type of the subclass.
Consider your sample...

Class B extends Class A. Ok so far so good. Now all objects of class B are also objects of class A. Anywhere you expect to find a class A object in your code, you can throw in an object of class B.

Now consider this...
Class C also extends class A. An object of class C is also class A.

Now compare B to C. Both B and C are of type A, but B and C may not be used for one another, unless the type you expect is type A. If your code wants a B object, you must provide a B object, and if your code requires a C object you must provide a C object.

What you have done is create a superclass (A) dependant on a subclass (B). This limits the superclass to always include the subclass B and therefore really takes away the meaning of extending class B from A to begin with. That makes it seem to me that possible your B class should have been the super class instead. (Maybe... just guessing).
If you want to provide some real class samples of what you are trying to do, I can explain with more details. Basically I am asking what purpose do you have in extending a class, and then using the extended class in the super class? Its like you cut something into two parts, just to glue them back together.

**spark** · July 23rd, 2012, 05:49 PM

thanks for Explanation. and details ..

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