Array or Hashmap

Question

I'm planning on loading all of my data from a separate thread into a single variable. This variable needs to hold 18 character models 8 terrains and random objects. I was originally planning on separating these two categories into Hashmaps and then the put the two hashmaps into a single hashmap so that I may call them by name. I then decided to buy them into ArrayLists instead of hashmaps. Similar to all games i'm looking for the best performance I dropped the ArrayLists but wanted to know if I would get better performance from an dimensional Array, An Array of 2 arrays or Hashmap?
Edited by: Bonechilla on Aug 23, 2009 9:54 AM

Answer 1

For such a small number of items, it will be very difficult (and pointless) to measure a difference in performance between different implementations.
But in answer to your question, I would advise building an interface for this collection describing how you want them to be stored and retrieved. i.e.
public interface Models
    public abstract void add(String name, Model model);
    public abstract Model get(String name);
    public abstract int size();
}Why? because then you can produce all these implementations and try them all out.
For example using a HashMap:public class HashMapModels extends HashMap<String, Model>
        implements Models
}or two ArrayLists:public class ArrayModels implements Models
    private ArrayList<String> names;
    private ArrayList<Model> models;
    public ArrayModels()
        names = new ArrayList<String>();
        models = new ArrayList<Model>();
    public void add(String name, Model model)
        names.add( name );
        models.add( model );
    public Model get(String keyName)
        int index = 0;
        for (String name : names) {
            if (name.equals( keyName )) {
                return models.get( index );
            } else {
                index++;
        return null;
    public int size()
        return models.size();
}Out of the two above, the HashMap should be the fastest and be the easiest to maintain. But what will really aid you in performance is if the models are stored in separate collections; one for terrains, one for characters and another for random models.
Perhaps:public class ModelStore
    private Models terrains;
    private Models characters;
    private Models objects;
    public Model getTerrain(String name)
        return terrains.get( name );
    public Model getCharacter(String name)
        return characters.get( name );
    public Model getObject(String name)
        return objects.get( name );
}Now if you want to retrieve a terrain model you should only search through the 8 terrains and so skip the characters and random objects.
You should also be thinking about what type of characteristics your collection needs. Presumably once it's loaded you will not be adding new elements to the collection, you will never insert models randomly into it (only adding to the end) and you will be performing lots of random access. If you can search by the models index (i.e. using an int) rather then it's name, then an array will easily be the fastest and all models could be stored in one big array. If your searching by name (or some other object used to identify the model) then I would recommend a TreeMap. Once all the items are added I'd guess it would give the best performance at searching for Models.
But without profiling different ideas with real data, all of this is purely guesswork.