Java / Processing attach one class to another

Question

I am writing a 2d game library on processing, and I am currently dealing with the physics side of things. I have a class called Object - which is used to manipulate an image. I want to be able to 'attach' my Physics class to the Object class - so that I can access all of the Physics functions through the Object i.e.:

//Scroll to left to see more of comments
class Object extends Game{ //It's worth pointing out that all of my classes extend a Game class
    Object(String name){ //A way to add an image to my Object and initialise the class fully
        PImage image = loadImage(name);
    }

    void attachPhysics(){ //I want to be able to call this so that I can directly access functions in the Physics class

    }
}


class Physics extends Game {  //My Physics class also extends the Game class

     Physics(){
          //Main initialisation here
     }

     void projectile(int angle, int speed, int drag){
        //Projectile code goes here


     }

}

So if I had these two classes, I would then be able to call on them like so:

//Scroll to left to see more of comments
void setup(){
    Object ball = new Object("ball.gif");
}

void draw(){ //In processing draw is similar to main in java
    ball.attachPhysics(); //I attach Physics

    ball.projectile(40, 5, -1); //I should then be able to access Physics classes via the ball Object which can manipulate the ball Object (call on its functions as well)
}

If anyone could help me out on this I would be grateful, I can post the full code if you like. It's worth noting that processing is just java with some added functions, and this code currently isn't set up as a library, it is just being compiled directly from processing.

Answer 1

The ball and physics instances do not have reference to eachother. Consider doing something like this (in setup or draw, or better in some initialization routine outside both classes):

physics phys = new physics();
ball.attachPhysics(physics);

Then you have a reference to the physics instance in your ball and you can call methods on it. Probably the physics method projectile would need to have a reference to your ball as well, so something like:

projectile(40, 5, -1, this);// this is the refence to the ball instance

Besides that, consider naming conventions of Java

I.e. start with Upper case (and don't call it object).