Java 2D Game Polymorphism

Question

I am developing a simple 2D game in Java and I'm stuck.

All my game objects( Enemy , Player , Item , Wall , ...) are extending Entity .

Entity is an abstract class containing some abstract methods like update() .

I have made an interface called Drawable which contains a draw() method.

Some game objects like Item should be an Entity but also be Drawable while others, like Wall, should just be an Entity (not connected to a tile, just x and y coordinates)

It all looks something like this:

List<Entity> entities;

In constructor i do this:

entities = tileMapReader.getEntities();

My question is: How should i draw my Drawable s?

I want to be able to do something like this:

for (Entity entity : entities) {
    entity.draw(g);
}

But since all Entities don't have the draw() method I can't do that. And i don't think if (entity instanceof Drawable) is such a good idea.

Answer 1

You can test whether an Entity implements Drawable using the instanceof operator:

for (Entity entity : entities) {
    if (entity instanceof Drawable) {
        ((Drawable) entity).draw(g);
    }
}

Answer 2

Keep an additional collection of Drawables. That way you can limit to drawing those, and do all the other things to all Entities.

Answer 3

First, your walls are invisible? Second, I like the other two answers: You can either keep a collection of Drawables, or check to see if that one implements Drawable.

A third option would be to have all entities implement drawable and leave the Wall's implementation blank.