Hiding methods and attributes while inheriting

Question

Hello All,
This is kinda urgent. While making a subclass I want to block access to methods and attributes of super class when anone creates an object of sub-class. In my particular situation I cannot override the methods.
Let me explain it with an example:
I have a class A which contains an attribute of type Object. All the methods accept Object type parameters and act accordingly. Now I want to create a sub-class B which acts on Strings only. I can create a wrapper to class A but I want to add some behavior which is specific to strings and use rest of the behavior as in class A. I cannot override the methods of class A because they take Objects as parameters whereas in class B the same methods take string as parameters.
I hope you have understood the problem. Please reply ASAP.
Thanks in advance

Answer 1

Sorry the diagram turned out wrong. ObjectClass and StringClass are both supposed to be derived
from the AbstractBaseClass.
This method is one way to achieve what you want. You make an AbstractBaseList class that has only
protected methods that take objects.
To implement a generic Object version of this class you extend it and override the protected methods in
the AbstractBaseList class to make them public.
To implement a String list you extend the AbstractBaseList class and override the protected methods to
make them public (but change the type of the parameters).
The only problem with this approach is that the return types of the methods cannot be changed. Therefore
I recommend the AbstractBaseList implement a method called
protected Object getByIndex(int i) {
// do list type stuff in here
Then the ObjectList can implement
public Object get(int i) {
return super.getByIndex(i);
and the StringList can implement
public String get(int i) {
return (String) super.getByIndex(i);
In effect all you need to do is to implement wrapper classes that enforce type casting on the Object based
set/get values.
Another option is to use JDK1.5 with its generics classes. These effectivly allow you to specify which type of
object an instance of a class accepts.
Another question. What is the matter with the Collections classes provided in the JDK?
matfud