Brikowski Brikowski - 2 years ago 95
Java Question

Java - store objects in a hierarchy that follows their class inheritance

I need to store lots of objects that belong to different classes:

ClassA {...}
ClassA1 extends ClassA {...}
ClassA2 extends ClassA {...}
ClassA2a extends ClassA2 {...}
ClassB {...}

Now I need to find a way to store all these objects in a way that allows me to efficiently get all objects that belong to a particular class and its inherited child classes. For example, this imaginary code


would return a list of all stored objects that belong to ClassA2 or ClassA2a.

I believe a tree collection of some sort would be suitable, but I can't think of any way to implement it. Any ideas?

(Background: I am creating a simple java game, in which there's number of sprites that I need to manage, while some of those sprites share similar properties. When I check events like collisions, I need to get all objects that extend EnemySprite and compare their coordinates with the player's sprite.)

Answer Source

Mifeet seems to have literally answered your question, but I suspect you shouldn't be trying to do what you're proposing to do. Why not just have a master list of all objects that might collide, then filter it as needed using instanceof?

This is conceptually a lot easier than what you're proposing to do, and the efficiency impact probably isn't that big. (In general, you will probably hear or have heard the mantra: Don't try to optimize too early.)

To be honest, I'm not sure you realize that filtering for EnemySprite will get you all object instances of its subclasses as well.

public class CollisionChecker(){

   private List colliders;

   public CollisionChecker(){    
       colliders = new ArrayList<Object>();    

   public void addCollider(Object o){

   public List<EnemySprite> getEnemySprites(){
       List<EnemySprite> enemies = new ArrayList<EnemySprite>();
       for (Object o : colliders)
           if (o instanceof EnemySprite)
       return enemies;        
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