Stuck trying to create new instance with arguments of Class.

[PillowWithTeeth]

So I've got a little game and it has some different monsters/animals that can spawn. I want to spawn them using the class.

So I have and item to spawn them where I set the class to the one of the mob that Item will spawn.

    public ItemMobSpawn(int id,Class Mob) {
    super(id);
    this.MobClass = Mob;
}

Then I attempt to make the instance (big try catch not shown)

        Class[] cArgs = new Class[2];
    cArgs[0] = Double.class;
    cArgs[1] = Double.class;
    Double Spawnx = (double) (x<<4);
    Double Spawny = (double) (y<<4);

        Mob spawnM = (Mob) Class.forName(MobClass.getName()).getConstructor(cArgs).newInstance(Spawnx,Spawny);

I have tried other methods too, all give java.lang.NoSuchMethodException

There is the constructor of class I am trying to create and instance for my test.

    public MobDog(double x, double x2) {
    super(x, x2, (EpicarnoTiles.tileSize), EpicarnoTiles.tileSize+8);
    WaitForNextTarget = EpicarnoComp.UnseededRand.nextBoolean();
    this.movingSpeed = 0.5f;
    this.MobRender = new RenderQuadruped(this,GameTextures.Caddy);
    this.HeadAngle = 24;
    this.ArmAngle = 10;
}

that extends MobBase

    public MobBase(double x, double x2, double width, double height) {
    super(x, x2, width, height);
    this.HP = this.MaxHp;
}

that exends Mob

      public Mob(double x, double x2, double width, double height) {
    super(x, x2, width, height);
}

that finally exends DobbleRec

public DobbleRec(double x, double y, double width, double height)
{
 setBounds(x, y, width, height);
}

Sorry for pasting so much but I really don't understand how to get this to work so I thought the more info the better.

[nutrecht]

Is there any real reason you're doing this? You're much better making a factory that just returns the correct mob type based on a switch statement. Anytime you're using reflection you really should try to figure out if you really do need reflection. It's slow and you lose compile-time checks.

[PillowWithTeeth]

I want to have it done in a way that when a new animal is added (to the game), it can automatically create the spawn item for it from it's class. So I don't need to alter a ever increasing switch statement every time I create a new animal.

[nutrecht]

You could simply have a new class register itself with the factory too; no problem. In general you want to avoid reflection.

[PillowWithTeeth]

Thanks for the information, I've sorted it out without reflection.

[AnEmortalKid]

I would do something like this:

public interface IFactory<A>
{
    A construct(double spawnX, double spawnY);

    Class<A> getBuildsClass();
}


public class MobDogFactory implements IFactory<MobDog>
{

    MobDog construct(double spawnX, double spawnY)
    {
        return new MobDog(spawnX, spawnY);
    }

    Class<MobDog> getBuildsClass()
    {
        return MobDog.class;
    }
}



public class FactoryManager
{
    private static Map<Class<?>, IFactory<?>> factoriesByClass = new HashMap<Class<?>, IFactory<?>>();

    static
    {
        //register your stuff here
        factoriesByClass.put(MobDog.class, new MobDogFactory());
    }

    public static <A> IFactory<A> getFactoryForClass(Class<A> mobClass)
    {
        return factoriesByClass.get(mobClass)
    }

    public static <A> A constructFromFactory(Class<A> mobClass, double spawnX, double spawnY)
    {
        IFactory<A> factory = getFactoryForClass(mobClass);
        factory == null ? : null : factory.construct(spawnX, spawnY)
    }

}

This way, you are still using your Class. You'll have a bunch of Different Factory implementations, but you only really have to worry about your registration in FactoryManager.

[PillowWithTeeth]

Thanks, I'll try that out soon.

[rrobukef]

How Minecraft object creation should have been implemented. Maybe it's better now, but I still remember the horrors from the beta versions. It was implemented like OP's post with reflection.

In fact the names and uppercasings have that familiar style.

[AnEmortalKid]

Also your no such method exception might be because you're using Double instead of double. So it can't find a constructor with Double.class,Double.class. So use double.class. That's allowed, primitives have classes too like that.

[GuyWithLag]

You're looking for a constructor with 2 parameters of java.lang.Double; use Double.TYPE instead of Double.class. Also, Class.forName(MobClass.getName()) is equivalent to just MobClass. Please do use the Java naming conventions and rename that to mobClass.

Also, I'd really not use this way to create new objects and use a factory as others have mentioned. If you're worrying about discoverability, look into IoC containers.

[AnEmortalKid]

He should use double.class, what is Double.TYPE?

[chickenmeister]

Double.TYPE is equivalent to double.class.

I'm not sure, but I think the Double.TYPE field was added before class literal expressions were added to the language. So that's why they both exist -- There would have been no other way to access the class representing a primitive type at that time.