Asperger Asperger - 25 days ago 4
Java Question

Create child class from instantiated base class?

I know this sounds weird but is it possible to create a child class that inherits from an already instantiated base class? I know I can use DI but im just wondering.

Edit: I know this is more a feature of prototype based languages such as javascript. Either way im wondering if this is even worth considering if something like this is possible.

Lets assume I have the following:

public class Parent {
protected id;

public Base(int id) { = id;

public class Child extends Parent {
public void getID() {
return id;

So then in my main I would do something like this:

Parent x = new Parent(1900);
// How to make a child of this particular base?
// x child = new Child();


How to make a child of this particular base?

You can't. The closest you can come is if Parent implements a copy constructor and Child uses it in a constructor, which would let you create a Child that copied that particular parent's state...

...which isn't really all that close. As you say, what you're looking for there is prototypical inheritance, which Java just doesn't have.