paintComponent through list of objects

Question

How would I iterate through a list of objects to paint their draw() methods? If I have it set up correctly how do I implement this correctly?

Class I'd like to draw onto:

public class Window extends JPanel implements IObserver, ActionListener{
    private Timer timer = new Timer(5, this);
    public Window(){
        super.setBorder(BorderFactory.createTitledBorder("Window:"));
        timer.start();
    }
    public void update(IObservable o, Object arg){
        GameWorldProxy gwp = (GameWorldProxy) o;
        Iterator gameObjects = gwp.getCollection().getIterator();
        while(gameObjects.hasNext()){
            GameObject gameObj = (GameObject) gameObjects.getNext();
            System.out.println(gameObj);
        }
    }

    public void paintComponent(Graphics g){
        super.paintComponent(g);
    }
    public void actionPerformed(ActionEvent e){
        repaint();
    }
}

Car class:

public class Car extends MoveableObject implements ISteerable, IDrawable{
    public void draw(Graphics g, int x, int y) {
        g.setColor(Color.RED);
        g.fillRect(x, y, 25, 10);
    }

}

So for example, I have a few different classes other than the Car class. It has a draw() method in there and the GameObject class extends from Car From my understanding I should also have a draw() method in GameObject. Say there's 2 listing of Cars under the gameObj, how would I draw them both? I'm not sure I quite understand how to iterate through the list to draw it on the panel.

Answer 1

The solution as intimated in the comments is to iterate through your list of Cars in the paintComponent method, and draw them there using the Graphics object that the JVM has given you. Use a for loop in that method, and in the loop call each Car's drawing method. And as mentioned, a Swing Timer should never be started within a painting method, nor should any of the object's behaviors or states be changed, other than to draw them and that's it.

e.g.,

// don't like class name of Window as this name shadows an important
// core Java Swing class.
public class Window extends JPanel implements IObserver, ActionListener{
    private Timer timer = new Timer(5, this);
    private GameWorldProxy gwp;

    public Window(){
        super.setBorder(BorderFactory.createTitledBorder("Window:"));
        timer.start();
    }
    public void update(IObservable o, Object arg){
        gwp = (GameWorldProxy) o;
    }

    public void paintComponent(Graphics g){
        super.paintComponent(g);
        for (GameObject gameObject : gwp.getCollection()) {
          gameObject.draw(g); // may need x and y here, but not sure where this data is held
        }        
    }
    public void actionPerformed(ActionEvent e){
      // some method to move components here
      repaint();
    }
}

---

Edit
You ask in comment:

you are correct the draw() method needs x and y since I just put that in.

I would not include x and y in the draw method. I'd have a separate setter method for moving constituent objects, and use the draw method for draw and draw only.

Should it also need the length and width?

No idea as this question appears completely orthogonal to the problems at hand in this question. Perhaps you need to ask a different question for this.

Another question is, that for loop should iterate and draw each class how it should appear correct? As long as the draw() method under the classes are correctly setup?

Not sure what you're asking here.