Method overloading using derived types as parameters in Java

Question

Let\'s say I have existing code which I want to extend but also to avoid changing it as much as possible.

Somewhere around this code there is a method that receives

Answer 1

Write this:

class Engine {
    public static void method(Base argument) {
        if (argument instanceof Derived) {
            // ...
        }
        else {
            // ...
        }
    }
}

But probably, you should extend your Engine class to allow for more polymorphism, e.g. do something like this:

interface Engine {
    void method(T argument);
}

And have implementations for Base and Derived like this:

class BaseEngine implements Engine {
    @Override
    public void method(Base argument) { ... }
}

class DerivedEngine implements Engine {
    @Override
    public void method(Derived argument) { ... }
}