Question

So in java the way to initialise an interface, such as a collection or list, is to create an instance of a class that implements it, eg:

Collection<Object> moo = new ArrayList();

If I wanted to specify an implementation at a later time in my code, I was thinking of doing this by creating another class like:

class ListList extends ArrayList{

}

and then initialise the variable with

Collection<Object> moo = new ListList();

And then all that’s required if I want to change the implementation later on is to change what ListList extends.

So, here’s the question.. is there a better way of doing this (I still feel as though I’m inexperienced with this type of thing).

Answer 1

is there a better way of doing this

Yes: use a factory method:

public static Collection<Object> createCollection() {
    return new ArrayList<Object>(); // change this later, if need be
}

Then, invoke the factory rather than instantiating:

Collection<Object> moo = createCollection();

Your suggestion of using a “dummy” subclass might appear attractive, but such abuses of inheritance invariably lead to pain and suffering later on. You really don’t want to do that.