Toggling Function Behavior Over Time

I have two classes LightController & Circle. I am trying to create a method to do the following.

1.Grows the diameter of the circle referenced by the receiver's instance variable light, to the argument size.

2. The diameter is incremented in steps of 2, the xPos and yPos are decremented in steps of 1 until the diameter reaches the value given by size.

3. Between each step there is a random colour change. The message delay(anInt) is used to slow down tthe graphical interface, as required.

How can I write the method to do this? I have been fiddling around for ages and just had no luck.

The method is called public void grow(int size) and is in the Light Controller class.

Both classes can be seen below.

import ou.*;
import java.util.*;
/**
* Class LightController
* This class uses the Circle class, and the Shapes window to simulate a disco light, that grows and shrinks and changes colour.
*
*/

public class LightController {
/* instance variables */
private Circle light; // simulates a circular disco light in the Shapes window
private Random randomNumberGenerator;

[Code] ....