How to invoke a java method based on a subclass type?

Question

I'm trying to dispatch objects to separate method according to their subclass.

For instance, consider those 2 objects

class A extends I {}
class B extends I {}

and the method

void dispatch(I i) {}

in dispatch(), I'd like to invoke a method according to the type of i. Hence if i is actually of type A, the handlerA(A a) method will be called. If it's of type B, handlerB(B b) will be called, and so on ... I tried with method overloading but I guess it doesn't work this way

what is the best way to achieve this ? I'd like to avoid using if/else statement ...

Thanks in advance,

edit: I can't modify any of those classes.

Answer 1

Use the Visitor Pattern.

In short, have I declare an accept(Visitor<T> ...) method, and have Visitor expose onA(A ...), onB(B ...), etc. methods. Your implementations of the I interface will call the appropriate method on the passed in Visitor<T>.

Its probably not worth it (due to boilerplate) if you only have 2 concrete classes, but somewhere around 3 or 4 it starts being worth it - if just to avoid duplicated if-else constructs.

Answer 2

So in I you declare the handler() method, and implement it appropriately (i.e. differently) in both A and B.

This is Polymorphism :)