Question

Very new to Java.

I have a class called GraphicsObject and a class Bug that extends it.

I have an ArrayList that holds all GraphicsObject in it:

private ArrayList<GraphicsObject> gc = new ArrayList();

Then I have a function that gets called every frame called updateObjects().

public void updateObjects(){
        for(int i = 0; i < gc.size(); i++){
            if(gc.get(i).toString().equals("Bug") ){
                (Bug)gc.get(i).moveNorth();
            }
        }
    }

The typecasting fails and the moveNorth() method never gets recognized because the class GraphicsObject does not have that method, only Bug does.

Any solutions?

Answer 1

there’s a few ways you could go about it:

The most appropriate in this case would be

    for(int i = 0; i < gc.size(); i++){
        if( gc.get(i) instanceof Bug ){
            ((Bug)(gc.get(i)).moveNorth();
        }
    }

Alternatively, you could add a method to graphicsObject and have Bug override it

   abstract public void defaultAction();

and in Bug

    @Override
    public void defaultAction() {
        moveNorth();
    }      

then in your renderer:

    for(GraphicsObject go : gc){
        go.defaultAction();
    }