Q from JQplus

[Wesley Liu]

Given the following classes and declarations, which of these statements are true?
class A
{
private int i = 10;
public void f( ) { }
public void g( ) { }
}
class B extends A
{
public int i = 20;
public void g( ) {}
}
A a = new A( );
A b = new B( );
A.System.out.println(b.i); will print out 20
B.System.out.println(b.i); will print out 10
C.None of above
the answer is C, but I donot understand why it is not 20.
[This message has been edited by Wesley Liu (edited May 21, 2001).]

[Gaurav Mantro]

Hi.
Can you recompile your question with full code as I think in your answers section you have three A options. I assume that they are part of code, so wanted to be sure that you didn't missed anything else in code while putting down the question.
regards
Gaurav Mantro.
------------------
http://www.mantrotech.com

[Wesley Liu]

Originally posted by Wesley Liu:
Given the following classes and declarations, which of these statements are true?
class A
{
private int i = 10;
public void f( ) { }
public void g( ) { }
}
class B extends A
{
public int i = 20;
public void g( ) {}
}
A a = new A( );
A b = new B( );
Options:
A.System.out.println(b.i); will print out 20
B.System.out.println(b.i); will print out 10
C.None of above
the answer is C, but I donot understand why it is not 20.
[This message has been edited by Wesley Liu (edited May 21, 2001).]

[SRV Gopal]

Hi,
I have some very basic doubts ...
===========================================================
class A
{
private int i = 10;
public void f( ) { }
public void g( ) { }
}
class B extends A
{
public int i = 20;
public void g( ) {}
}
A a = new A( );
A b = new B( );
Options:
A.System.out.println(b.i); will print out 20
B.System.out.println(b.i); will print out 10
=========================================================
Are the last two lines valid? Can you refer System.out.println() with a user defined reference type such as A or B as above?
-Thanks

[SRV Gopal]

Hi,
Sorry Guys ... that was stupid on my part. Really sorry about the earlier mail

[James Du]

Hi Wesley Liu,
when you use a variable but a method, It is the compile-time type rather than the run-time type of the reference determines the version of the variable it uses. it involves no dynamic binding.
Therefore, in the code you provided, since b is declared type A, the A's version of i was used. It could be determined in the compile time.
Hope it helps
James

[sona gold]

[B]Given the following classes and declarations, which of these statements are true?
class A
{
private int i = 10;
public void f( ) { }
public void g( ) { }
}
class B extends A
{
public int i = 20;
public void g( ) {}
}
A a = new A( );
A b = new B( );
A.System.out.println(b.i); will print out 20
B.System.out.println(b.i); will print out 10
C.None of above
the answer is C, but I donot understand why it is not 20.

(b.i) --- here the reference type is A and object is of type B
now the variables of the reference type are picked up and the methods of object type.
now when u say b.i , the control is transferred to the class A to fetch the value of i.
but i is declared private in class A and so it is not accessible outside A.
if u declare i as public in A, the answer will be 10.
hope it is clear now

[Ravindra Mohan]

Hi Folks,
I agree with Sona Nagee.
When you create an object by a reference of the super class,
the method calls are decided by the type of the object , in this case, B Class's method, overrides the A class's method. Whereas, in case of variables, they are hidden and the variables are refferred by the type of reference in the problem in context it's A Class's variable. But, the real trick in the question
is the accessbility modifier of the variable "i" in the Base class A (its private), so you can inherrit it , nor can you access it outside the class A. So the answer is (C), it should be COMPILER ERROR, "Variable i class A not accessible in class B" .
Hope the issue is clear now.
Ravindra Mohan.

[This message has been edited by Ravindra Mohan (edited May 22, 2001).]