which method is invoked and why?

[Abhishek Reddy]

class A 
{
protected void meth() 
{
System.out.println("meth() of A called");
}
}
class B extends A
{
protected void meth() 
{
System.out.println("meth() of B called");
}
}
class C extends B
{
public static void main(String args[]) 
{
C c=new C();
A a=(A)c;
a.meth();//------which method is invoked and why-
System.out.println("exited main");
}
}
 

In the above code i typecasted the "c" reference to A type. When i invoke the method meth() on "a" reference method meth() of class B is invoked rather than Class A method..why is that so..
[ September 29, 2006: Message edited by: Barry Gaunt ]

[Ankur Sharma]

Originally posted by Abhishek Reddy Chepyala:
class A
{
protected void meth()
{
System.out.println("meth() of A called");
}
}
class B extends A
{
protected void meth()
{
System.out.println("meth() of B called");
}
}
class C extends B
{
public static void main(String args[])
{
C c=new C();
A a=(A)c;
a.meth();//------which method is invoked and why-
System.out.println("exited main");
}
}

In the above code i typecasted the "c" reference to A type. When i invoke the method meth() on "a" reference method meth() of class B is invoked rather than Class A method..why is that so..

Ok Let me explain,

Please correct me other ranchers If I am wrong,

Prior to explain this I would like to introduce one example

public class Sample extends ABC {
public void add() {
System.out.println(" in child");
}
public static void main(String arg[]) {
ABC a = new Sample();
a.add();
}
}
class ABC {
public void add() {
System.out.println(" in Parent");
}
}

What do you think the output is?

Correct Output is: in child

Anyways now as you see in the your code that C is direct subclass of Class B
So it will search the called method in it body itself but if it failed then it goes into the direct superclass that is B

There it found the method so it executes the method given in Class B

It is the exmple of run Time Binding.
Check this out PolyMorphism-Run Time Binding

[Abhishek Reddy]

public class Sample extends ABC {
public void add() {
System.out.println(" in child");
}
public static void main(String arg[]) {
ABC a = new Sample();
a.add();
}
}
class ABC {
public void add() {
System.out.println(" in Parent");
}
}

At runtime reference "a" is pointing to SampleObject so, the behaviour..its fine....now tell me what happens when we typecast the refrence "a" to ABC type ie ABC a1=(ABC)a;...will it still point to Sample object..

[Ankur Sharma]

Originally posted by Abhishek Reddy Chepyala:
public class Sample extends ABC {
public void add() {
System.out.println(" in child");
}
public static void main(String arg[]) {
ABC a = new Sample();
a.add();
}
}
class ABC {
public void add() {
System.out.println(" in Parent");
}
}

At runtime reference "a" is pointing to SampleObject so, the behaviour..its fine....now tell me what happens when we typecast the refrence "a" to ABC type ie ABC a1=(ABC)a;...will it still point to Sample object..

Yes ofcourse it will still the same Sample Object.
Run this code and then check.

public class Sample extends ABC {
public void add() {
System.out.println(" in child");
}
public static void main(String arg[]) {
ABC a = [B](ABC)[/B]new Sample();[B]//Updated Object[/B]
a.add();
}
}
class ABC {
public void add() {
System.out.println(" in Parent");
}
}

Again the same output is there: in child.

Please let me know if there are any issues.
[ September 29, 2006: Message edited by: Ankur Sharma ]

[Joe Harry]

Hi Ankur,

So casting is applicable only to references and not for actual objects...am I right??Please clarify.

Regards,
Jothi Shankar Kumar. S