Question

I am working on porting a Roguelike dungeon adventure game to the Android.
http://tyrant.sourceforge.net

When I start my program, I initialize the world and all it’s objects first. I have a class that contains 3 million(!) HashMap entries. When I try to initialize that class, it takes 5+ minutes to run on my Android, which is a very unacceptable length of time. Once the class is is initialized, the game runs great and is quite fun.

So I thought I could serialize this object and reload it at runtime. I serialize it, and pack it in the .APK file, it’s over 5MB in size. Android just chokes and gives me an OutOfMemory error.

I can deserialize part of the class(800KB), and then dynamically create the rest of entries. That still takes quite a few minutes to finish too, it still has to create 3 million entries from the serialized data. But I do know that my serialization code works fine.

How can I store this very large class file on the Android and load it later? What are some options I can explore? Making my user wait 5 minutes for the app to start is not very good at all.

Here is the troubling class in the original source code:
http://tyrant.cvs.sourceforge.net/viewvc/tyrant/tyrant/mikera/engine/Lib.java?view=markup

and the troubling field is:

private transient Map types;

(I’m aware it’s transient)

it ends up storing over 3 million entries!

Answer 1

Well part of the problem is what is in the types map.

From what I can make out, it is effectively a Map<String, Map<Integer, List>>, where the 2nd level maps are really non-sparse arrays. If you chose a better data structure it would occupy less space and you could build it much faster. (I think you are right not to serialize it … since it looks like it might not be changed during game play.)

A HashMap<Integer, Object> takes a LOT more space than an Object[].

---

A better data structure would be Map<String, LevelMap> where LevelMap is something like this:

public class LevelMap {
    private static final ArrayList<String> EMPTY = Collections.emptyList();

    private ArrayList<String>[] levels;
    private int firstLevel;

    public LevelMap(int firstLevel, int lastLevel) {
        this.firstLevel = firstLevel;
        levels = new ArrayList<String>[lastLevel - firstLevel + 1];
    }

    public static void addToTypeMap(String key, String value, 
            int firstLevel, int lastLevel) {
        LevelMap l = types.get(key);
        if (l == null) {
            l = new LevelMap(firstLevel, lastLevel);
            types.put(key, l);
        } 
        l.add(value, firstLevel, lastLevel);
    }

    public void add(String value, int firstLevel, int lastLevel) {
        ensure(firstLevel, lastLevel);
        for (int i = firstLevel; i <= lastLevel; i++) {
            j = i - this.firstLevel;
            if (levels[j] == null) {
                levels[j] == new ArrayList<String>();
            }
            levels[j].add(value);
        }
    }

    private void ensure(int firstLevel, int lastLevel) {
        // Make sure that these levels are in the levelmap
        // If necessary, reallocate this.levels and adjust this.firstLevel
    }

    public String get(int level) {
        if (level < this.firstLevel ||
            level >= this.firstLevel + levels.length ||
            levels[level - this.firstLevel] == null) {
            return EMPTY;
        } else {
            return levels[level - this.firstLevel];
        }
    }
}