How do I define multiple implementations for a method?

Question

Just to play around a little, I'm trying to make a turn-based battle game with two players through command line. Each player controls a monster with up to 4 different moves. I have defined Monster and Move classes to define the different monsters and moves. When a player uses a move, I'm thinking I want to call something like a performOn(Monster mon) method in the move to use. In that method I want to define the implementation for what the move does, since not every move will do the same thing. I'm pretty sure Java can do this but I'm not entirely sure how it's done. For both the Monster and Move classes, I have an inner Builder class to avoid big constructor methods. And if anyone has a better idea of how to perform a move, please feel free to share. :)

Thanks!

Example:

// moves is a HashMap<String, Move>
monster1.moves.get("Firebreath").performOn(monster2); // damages monster2
monster2.moves.get("Heal").performOn(monster2); // heals monster2

Answer 1

You can either make a super class for Move and all the special moves can extend it:

public abstract class Move
{
 public abstract void performOn(Monster m);
}

And then extend:

public class FirebreathMove extends Move
{
 public void performOn(Monster m)
 {
 // do something to Monster
 }
}

Or you can create an interface:

public interface Move
{
 public void performOn(Monster m);
}

And your moves can implement it:

public class FirebreathMove implements Move
{
 public void performOn(Monster m)
 {
 // do something to Monster
 }
}

In either case you'd have a reference to a Move that you can call performOn(Monster), but it depends on whether all moves share some kind of common functionality that you want to subclass (first method, with superclass) or if Moves can also be other things and you just need the performOn(Monster) method signature. For example, if you had something like a Weapon, that has a Move:

public class FancyWeapon extends Weapon implements Move
{
}

• lancex: So you're suggesting a class be created for each move?
• Jon Lin: @lancex I don't know how you have everything organized, but where else would you put the functionality to perform a specific move?
• lancex: I was thinking maybe I could just define the implementation for a method and pass it to the Move when I create it by doing something like... Move move = new Move(){ public int perform(Monster m){ ..implementation.. } } Although I'm not entirely sure what something like that actually does...
• Jon Lin: @lancex Using anonymous classes like that is reserved for something done on-the-fly or a use once scenario. If you intend on reusing (as in, monster1 can use Firebreath and later monster2 can use Firebreath), it's better to have that code in a public class, where other classes can reference it publicly. If you want to use a Move in more than one place in your code, anonymous classes is bad way to do it.
• Matt: @lancex What you're describing is creating anonymous inner classes. It's best to have actual classes as described above as they would be re-useable.

Answer 2

I'm not sure if this is what you mean, but an interface could be what you're after?

An interface would look like this: public interface Move() { void performOn(Object o); String getMoveName(); }

That example, you'd then make a series of classes: public class BreatheFire implements Move { @Overrides public void performOn(Object o) { .... } }.

Hope that helps!

Answer 3

You could have a Move parent class(or interface) so it works out similar to this.

public interface Move{
 public void performOn(Monster m);
}
public Firebreath implements Move{
 public void performOn(Monster m)
 {
 m.takeFireDamage(5);
 }
}
public Heal implements Move{
 public void performOn(Monster m)
 {
 m.healDamage(5);
 }
}