Automatic Downcasting

Question

I'm making a framework in Java and have a method in my abstract class, BasicPhase, called processAction (snippet below). It takes two abstract classes as parameters since the user should implement them in child classes. However, it results in the user being required to constantly downcast every time they override the method. How can this be avoided?

BasicPhase.java

public class BasicPhase {
    ...
    public BasicGameState processAction(BasicAction action, BasicGameState state);
    ...
}

Example User Class

MyPhase.java

public class MyPhase extends BasicPhase {
    @Override
    public BasicGameState processAction(BasicAction basicAction, BasicGameState basicState)  {
        MyGameState state = (MyGameState) basicState; //undesired
        MyAction action = (MyAction) basicAction; //undesired

        //Game Logic Here
    }
}

Answer 1

processAction clearly cannot work on the base action and state types, so you need to make the types that need to be passed as parameters specifically the types that processAction can work with. To make the parameter types definable by your derived classes, you need to make the base class generic such that the generic parameters are the types of action and game state the phase accepts.

Do this by making BasicPhase a

public class BasicPhase<TAction extends BasicAction, TState extends BasicGameState>

and the processAction a processAction(TAction action, TState state) then your MyPhase would derive as:

public class MyPhase extends BasicPhase<MyAction, MyGameState> {

Answer 2

If MyPhase.progressAction would exclusively call methods available in BasicAction or BasicGameState, then there would be no need for any downcast. Those methods might be ordinary methods or methods overridden in MyAction and/or MyGameState. So you should consider to change the design of BasicAction, BasicGameState and/or progressAction to make this possible.

Note, as @ErikEidt correctly stated in his comment, that this may not be the best or most sensible solution for your case, since you gave us not enough information to allow any better advice.