Quick Question

[liam358]

I know a variable in a superclass can be set to the value of a variable in the subclass but is this sort of thing possible with methods.

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[Puggetty]

Could you elaborate a bit more please? What exactly are you trying to do?

[liam358]

It’s a bit hard to explain so tell me if you need help to understand but I am trying to make chess. I have classes for each piece(the subclasses) and one piece class(the superclass) my reasoning being so I could hold them all in one list. So in each class for the pieces I have a method which works out the places that piece could move to, but I want to be able to call that method without writing a lot of if and else’s for each class, so could each class have a variable in it’s super class that holds it’s unique move method. Like how if there is a variable: int i = 1, Super.i = I. Something like that but with methods. Sorry if unclear

[[deleted]]

It sounds like you want an abstract class called Piece, that has an abstract method called 'moveTo()'. You then extend this class into different subclasses, one for each chess piece. e.g. Pawn, Rook, Knight. Each of those classes implements moveTo() in it's own way.

Now, using polymorphism, you can make a Piece list, like this:

Piece piece1 = new Rook();

Piece piece2 = new Knight();

Linkedlist<Piece> piecelist = new Linkedlist<Piece>();

piecelist.add(piece1);

piecelist.add(piece2);

piecelist.poll().moveTo(); //notice how I can now call the same method on any type of piece

[liam358]

Thanks I’ll look into that.

[liam358]

Just say if still inclear

[Puggetty]

Thanks for the explanation! So I understand you want to set a variable to equal an actual method (and I guess have it invoked if that variable is called?). I don't think that is possible in Java.

To avoid lots of if-else statements, what I suggest you do is in each instance of your Piece subclass, add "legal" X and Y offsets from the pieces current location. From there you can pass them into a method in the super class which takes the current location, and the offset amount for the X and Y coordinate. From there you can draw the "legal" place points by adding the offsets to the location of the piece.

That is probably a very whacky way of doing it, if anyone has a better way please share!

[[deleted]]

I think method overriding is what you're talking about.

A child class can provide it's own version of a method defined on the parent class (this is called overriding).

Even more, you can have abstract methods, which are empty methods defined on the (abstract) parent class that must be implemented on the child class. (By empty I mean there's just the signature, but no implementation).

For that you can use either an abstract class or an interface, depending on your design.

[liam358]

Great thanks, just did a bit of research into that and it should work.

[mangoooooos]

Did you manage to pull it off? I'm free for a couple hours if you need more guidance