Passing a class type to a method, then casting to that type?

Question

I'm still pretty new to Java, so I might be missing something obvious here.

I have the following code that I use to pick class types from a list of all my entities:

public Array<?> PickEntities(Class<?> cls) {
    Array<? super SpriteEntity> allEntities = new Array<Object>();
    for (SpriteEntity entity : MyGame.AllEntities) {
        if (entity.getClass() == cls) {
                allEntities.add(entity);
        }
    }
    return allEntities;
}

That works fine, but it means that when calling this method I still need to cast it to the class on the other side. For example:

asteroid = (Asteroid)PickEntities(Asteroid.class);

What I would like to do is use the class I am passing to my PickEntities class (the cls parameter) and then cast the returning array (allEntities) to that type.

Is there a way to do this? Whenever I try it just tells me that 'cls' is not a type and can't be used to cast.

Answer 1

Your method should be generic:

public <T extends SpriteEntity> List<T> pickEntities(Class<T> clazz) {
    List<T> result = new ArrayList<T>();
    for (SpriteEntity entity : MyGame.allEntities) {
        if (entity.getClass() == clazz) {
            result.add((T) entity);
        }
    }
    return result;
}

Note that I used standard collection classes, and standard Java naming conventions.