Question about inheritance...

[Andres Gonzalez]

class A {
  String s1 = "A.s1";
  String s2 = "A.s2";
}
class B extends A {
  String s1 = "B.s1";
  public static void main(String args[]) {
    B x = new B();
    A y = (A)x;
    System.out.println(x.s1+" "+x.s2+" "+y.s1+" "+y.s2);
  }
}

it prints : B.s1 A.s2 A.s1 A.s2
I thought it printed: B.s1 A.s2 B.s1 A.s2
why?
Is variable s1 in class B hiding s1 in class A? how's the procedure to figure this out.. when you extend a class are you inheriting all non-private members (instance variables, methods)?

[G Nadeem]

hi Andres,

Is variable s1 in class B hiding s1 in class A

yes it is.

when you extend a class are you inheriting all non-private members

yes. except those which have hided any super class members.

how's the procedure to figure this out..

only instance methods are overriden.
Super s = new Sub();
s.m(); // will call sub's m IF it is overriden.
on the other hand feilds are shadowed. feilds are accessed using the reference variable type.
Super s = new Sub();// ref var is Super
s.aField; // will access S's aField
Sub s = new Sub();
Super sup = (Sup)s;
sup.aField; // will still access S's aField because the variable 'sup' reference type is Sup and not Sub.
In order to access Super's hidden feilds through Sub refernece, u can 'cast' to Super.
Sub s = new Sub();
int aField = ((Sup)s).aField;// now will access Sup's even if it is shadowed in Sub.
hope it helps.
[ June 07, 2003: Message edited by: G Nadeem ]

[Alexan Kahkejian]

Hi
You can refer to JLS 8.3.3.1
And no need for cast to refer to the hidden field,just use "super." prefix (from non-static method).
Alexan
[ June 07, 2003: Message edited by: Alexan Kahkejian ]

[Alton Hernandez]

Is variable s1 in class B hiding s1 in class A?

Well, technically speaking, the term should be shadowing.

how's the procedure to figure this out..

For shadowed variables, you look at the reference, not the object pointed to by the reference.

when you extend a class are you inheriting all non-private members (instance variables, methods)?

yes

[G Nadeem]

Hi Alton,

Well, technically speaking, the term should be shadowing.

If a class declares a field with a certain name , then the declaration of that field is said to hide any and all accessible declarations of fields with the same name in super classes,and superinterfaces of the class

JLS 2Ed 8.3 pp153-154

A declaration d of a type named n shadows the declarations of any other types named n that are in scope at the point where d occures throughout the scope of d

JLS 2Ed 6.3.1 p86.
so i think in above case is that of hiding and not shadowing. am i making any mistake here?..

[Alton Hernandez]

Originally posted by G Nadeem:
so i think in above case is that of hiding and not shadowing. am i making any mistake here?..

Yes, you're right, its hiding. My mistake

(JLS 6.3.1)
Hiding, in the technical sense defined in this specification, applies only to members which would otherwise be inherited but are not because of a declaration in a subclass.