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Author

OverRiding???

Naresh Shaan
Greenhorn

Joined: Mar 18, 2006
Posts: 22
Hello All,

Here is a Program,

package myDemo;

public class MyOverRidingDemo {

public MyOverRidingDemo() {
super();
// TODO Auto-generated constructor stub
A obj=new B();

obj.add();
System.out.println("Value Of I : "+obj.i);
}

/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
new MyOverRidingDemo();
}

}
class A {
int i=10;
public void add(){
System.out.println("Add() in Class A");
}
}

class B extends A {
int i=20;
public void add(){
System.out.println("Add() in Class B");
}
}


When i run this program, the out put is as follows :

Add() in Class B
Value Of I : 10


It is pretty clear that B is overriding the add() method of Class A.

When an instance of B is made and assigned to a variable of type A,

obj.add() should refer to add of B

and obj.i should refer to i of B.

but over here..why is it Referring to i Of A???


"The greatest pleasure in life is doing what people say you cannot do." - Walter Bagehot
Amit Biswas
Ranch Hand

Joined: Jun 01, 2006
Posts: 52
Naresh,
Overriding applies to instance methods only. For static methods and instance variables, you can only hide the parent class equivalent in the method. If you add a getter for the 'i' variable in yor super-class and override the same in sub-class, like the following:

class SuperClass
{
public int i = 10;
public int getVal(){
return i;
}
}
class SubClass
{
public int i = 5; //hiding the superclass value
public int getVal() { //overrding the super class method
return i; //returns 5 since it has shadowed the superclass value of 10
}
}
.....
public static void main(String [] args)
{
SuperClass obj1 = new SuperClass();
SuperClass obj2 = new SubClass();
SubClass obj3 = new SubClass();

syout(obj1.i); //will print 10 since the reference type is SuperClass
sysout(obj1.getVal()); //will print 10 since object type is SuperClass

syout(obj2.i);//will print 10 since reference type is SuperClass
sysout(obj2.getVal());//will print 5 since object type is SubClass

syout(obj3.i); //will print 5 since reference type is SubClass
sysout(obj3.getVal()); //will print 5 since object type is SubClass

}


Basically, you redefine an instance variable in a subclass and NOT override them. The same is true for static methods and fields as well.
Amit Biswas
Ranch Hand

Joined: Jun 01, 2006
Posts: 52
A correction: Read
you can only hide the parent class equivalent in the method

as
you can only hide the parent class equivalent in the subclass
 
Don't get me started about those stupid light bulbs.
 
subject: OverRiding???