Loading a class based on a level/stage?

I have come across a bit of a problem. I have a class called "GameScreen" which will know what level and stage has been selected. From that I can build a string to suggest something like "level1_1" or "level1_2". The problem is how do I load this class now?

I was going to use Class.forname(string) however each level is a different class so how do I pass the new operator to the class?

I am tryin开发者_开发技巧g to achieve something like this... world = new World(worldListener); where "World" is the class such as "level1_1".

Hope that makes sense.

Aside from the fact that there are much better ways to implement this (see the other answers, for example), this should work (not tested, ignores exceptions, may cause abdominal distention, etc.):

public World createWorld(String levelClassName, WorldListener listener) throws Exception
{
    Class<?> clazz = Class.forName(name);
    Constructor<World> ctor = (Constructor<World>) clazz.getConstructor(WorldListener.class);
    World world = ctor.newInstance(listener);

    return world;
}

You must use reflection (java.lang.reflect)

First, even if the class for each level is different, all of them should extend/implement a common superclass/interface so basic operations are available (v.g. a constructor, a startLevel() method, and so on).

With reflection, you can chose the class related to your level, instantiate it, and pass it to your engine so it invokes your class.

As a side note, I find the architecture strange. Unless there is some other reason to do this, I would suggest using a unique class for levels and loading the configuration for each level from files. It may not be suited if gameplay changes between level, though.

See the Factory Pattern. For your case you could implement a CreateLevel(String level) method which does a simple case-statement to determine which class to create or use reflection.

Um... there's 101 better ways of doing that.

Update For example:

public abstract class Level {
    // or whatever your interface is
    abstract public void createWorld(WorldListener worldListener);
    abstract public void nextWorld();
}

public class Level1 extends Level {
    public void createLevel(WorldListener worldListener) {
        /** do it **/
    }
    public Level nextLevel() { return new Level2(); }
}

Then somewhere else:

Level cur = new Level1();
do {
    cur.createLevel(worldListener);
    ...
    cur = cur.nextLevel();
} while (cur != null);

Original For example:

public abstract class Level {
    final public int number;
    public Level(int num) { this.number = num; levels[num-1] = this;/* set up level */ }

    // adjust 10 to number of levels
    static private Level[] = new Level[10];
    static public getLevel(int num) { return levels[num-1]; }

    // or whatever your interface is
    abstract public void createWorld(WorldListener worldListener);
}

public class Level1 extends Level {
    public Level1() { super(0); }
    public void createWorld(WorldListener worldListener) {
        /** do it **/
    }
}

Then somewhere else:

Level.getLevel(1).createWorld();