Java Implementable Class Creation?

Question

So I want to make a game engine, and I instantly realized that stuff has to be "auto-imported". For example, when you implements Runnable, you get an error because it HAS to have the run() method in the class.

How do you do this? How would i have a class, when implemented, FORCE a method, and then automatically run this method?

An example, usable when answering:

I have a Frame class. This frame class will, when implemented, ALWAYS use a method, in the class that implemented it, named draw(), and will HAVE to be implemented to use the frame class. Example code:

public class test implements HFrame {
    // constructor
    public test() {

    }

    // method called when test is run
    public static void init() {
        HFrame f = new HFrame(WIDTH, HEIGHT);
        f.display(); // makes the frame visible
    }

    // method that frame will always call when it is implemented
    public void draw() {
        // stuff to draw
        new Circle(0, 0, 50, 50);
    }
}

using the comments, how would i get this to work?

thanks for the help, and i apologize if this isnt worded the best...

Answer 1

In order to "force" a class to implement certain methods you use an interface, an example of which is below

public interface GameEngineInterface {
    void init();
    void draw();
    Vector3d annotherMethod(Object object);
}

Any class that is going to be used by your Game engine would implement the GameEngineInterface engine.

GameEngine methods would work as such

public Object someMethod(GameEngineInterface anyObjectThatImplementsGameEngineInterface){
    //method body
}

The GameEngine then doesn't care about the specifics of the implimenting methods, just that it can call those methods.

Answer 2

Create an interface with the methods that you want to run. All the classes that will be used must implement that interface. This is exactly how Runnable works: Runnable is an interface with one method void run() that the Thread can call to execute the runnable.

Answer 3

Looks like you need to implement the Template Method design pattern. In your example, run would call draw(), which must be implemented in the concrete class.