Using ClassLoader for custumize an application

Question

Customize an application that has thousands of classes may be an hard adventure
in java.
If we need to cistomize a class (e.g. Account) used by several classes of the application,
the operation seems to be easy with an OO language: we have simply to inherit the class
Account into a new class Account2 and with delegation and so on we have reached the
target.
But all other classes of application refers to Account class (the base class) and not to
Account2 (the inherit class)
So we have to inherit all classes that instantiates Account and all classes that instantiate
those classes and so on: a real nuclear explosion!!
Is needed to inherit a good part of my application.
Obviusly modifing all vase sources may be a solution, but is needed to ship all sources
to customers and is not so a good idea.
I have already tried several ways, such defining my own classloader and so on but I have
no found a real solution.
Does someone has an idea?
Every help will be really appreciate.
All the best.

Answer 1

But all other classes of application refers to Account
class (the base class) and not to
Account2 (the inherit class)
So we have to inherit all classes that instantiates
Account and all classes that instantiate
those classes and so on: a real nuclear explosion!!Which is why people use interfaces and abstraction
for such things.
Maybe these will help:
Object Oriented concepts
Why extends is evil - Improve your code by replacing concrete base classes with interfaces
Object-oriented language basics, Part 6 - Use interfaces for safe multiple inheritance and a great deal more