Java多个子类，但类型不同

Question

Say I have a base class Base and it's subclasses SubA and SubB .

public class Base(){

    public (static?) Animation anim;

    public Base(Frame[] frames){

        CpuIntensiveAnimationCreation(frames);

        // I need only one 'instance' of Animation Per subclass.
        // Every different TYPE of subclass needs it's own Animation instance.
        // A subclass can share one Animation, among multiple subclass-instances. (static?)

    }

See, I don't want to initialize a new Animation instance for every instance of a subclass I make, since it takes quite some time. I do however need every subclass to have it's own Animation.
I could ofcourse have a static Animation per subclass and not use a superclass, but that would require a lot of redundant/copied code.

How should I get to this?

Answer 1

Don't make it part of the class/subclass. It would be a lot easier to have a

Map<Class<? extends Base>, Animation>

Create an animation registry as its own class and have it contain a mapping of classes to their animations.

Answer 2

My suggestion would be to have an abstract method getAnimation() in the base class.

Subclasses could then override this method to return a static Animation per subclass.

Answer 3

So, you need a static field in your subclass to hold the animation you describe.

Now, you don't want to duplicate code, so you can put the method to generate that Animation in a static method on the Base class.

Does that answer your question?

Answer 4

How about in Base :

You create a constructor that gets an instance of Subclass and instead of normal construction checks if it has an animation property and if not called the function initializing it statically for the class? It can inherit it from an abstract method in Base

That inverts the responsibility and causes the Base class to again be in charge the animation is there.

Answer 5

1. Create a abstract method for getting Animation like getAnim() in Base class.

2. Lets make Animation static in every Subclass , so all the instances of a Single subclass will share the same Animation instance . So by doing this every class will have its own Animation.