Polymorphism ...how to deal with variables

[sudip Kumar]

I think I am missing something basic over here...please help...
Please look at the below code:

class Parent {
	int i=10;
	void show(){
		System.out.println("in Parent class");
	}
}

public class Child extends Parent{
	
	int i=293;
	void show(){
		System.out.println("in child class");
	}
	public static void main(String a[]){
		Parent obj = new Child();
		obj.show();
		System.out.println(obj.i);
	}
	
}

The output in this case is
in child class
10

The parent reference invokes the method in the child class because of dynamic polymorphism....but should'nt it do the same thing for the variable also.
I mean obj.i actually calls the variable of the parent class and not of the object type ( child). But for methods it does call the method of the object type.

Please help.

[Rob Spoor]

Polymorphism only applies to non-static methods. Static methods and fields instead hide or shadow the method / field from the super class. The reference type (here it's Parent) decides which version to use, unlike the actual type for non-static methods.

[sudip Kumar]

Hello Rob,

Did you reply to this problem...the thread shows that there is 1 reply from you...but on cliking there is nothing...

[Matthew Brown]

You still missing Rob's reply? Because I can see it OK.

[sudip Kumar]

Thanks Rob

Was able to see your reply finally...

Static methods and fields instead hide or shadow the method / field from the super class. The reference type (here it's Parent) decides which version to use, unlike the actual type for non-static methods.

Do you mean that static methods and static variables only or even instance variables...

Here the case is with the instance variable which is being invoked in a static way as the parent reference calls the parent class'es variable....

[Jeff Verdegan]

sudip Kumar wrote:
Do you mean that static methods and static variables only or even instance variables...

Runtime polymorphism in Java applies only to non-private, non-static, non-final methods. It does not apply to anything that is static, private, or final, and it does not apply to any member variables.

So, if we have

class Parent {
  ...
}

class Child extends Parent {
  ...
}

...

Parent p = new Child();

and then we refer to p.X, then if X is a member variable, or if it's private, static, or final, it is determined at compile time that we will get the X from whatever type reference "p" is declared to be--in this case, Parent. Only if X is a non-private, non-static, non-final method will we get X from the actual object that p refers to at runtime.

[sudip Kumar]

Thaks Jeff for that wonderful reply...really helps....

[Jeff Verdegan]

You're welcome! And welcome to the Ranch!