Passing A Graphics Object To 3 Other Classes?

Basically I am making a paddleball game, like i'm sure everyone does in learning Java. I'm supposed to use different classes for each component, i.e. one for the ball, one for the paddle, and one for the display, then finally one as a 'controller' to implement mouselistener and stuff.

However, I can't quite grasp how to implement the paintComponent method. I know I can only have it in one class extended from JPanel, and I have the syntax for creating an object which I understand is something like this:

public void paintComponent(Graphics g){ //this is the rectangle my game will be played on,
super.paintComponent(g); //a gray background to define boundaries for the ball
g.setColor(Color.GRAY);
g.drawRect(0, 0, Frame.getHeight(), Frame.getWidth());

However what I don't understand is, how do I then pass this graphics object to the ball and paddle to let them draw themselves? I found something that described it like this here

class GamePanel extends JPanel {
Entity e=new Entity;
@Override
protected paintComponent(Graphics g) {
super.paintComponent(g);

[Code] .....

What I don't get is, if I use this, where would I put the drawRect and stuff to make the other shapes I need? in their class, under the entity.Draw(g) method? or in the display class where it calls the graphic object in the first place?

Last, how can I have my controller class refresh the displays of each of these with the timer I have implemented? Is there a simple way to call one refresh command and have it refresh the drawing of both the paddle and ball simultaneously, or would I need to call a separate refresh command for each object?