Need some help with Java!!

import java.awt.*;
import java.awt.geom.*;

/**
* A circle that can be manipulated and that draws itself on a canvas.
*
* @author Eric Lund
* @version 9/29/11
*/

public class Circle
{
private int diameter;
private int xPosition;
private int yPosition;
private String color;
private boolean isVisible;

/**
* Create a new circle at default position with default color.
*/
public Circle()
{
diameter = 30;
xPosition = 20;
yPosition = 60;
color = "blue";
isVisible = false;
}

/**
* Create a new circle with specified diameter.
*/
public Circle(int size)
{
diameter = size;
xPosition = 20;
yPosition = 60;
color = "blue";
isVisible = false;
}

/**
* An accessor for returning the diameter.
*/
public int getDiameter()
{
return diameter;
}

/**
* Make this circle visible. If it was already visible, do nothing.
*/
public void makeVisible()
{
isVisible = true;
draw();
}

/**
* Make this circle invisible. If it was already invisible, do nothing.
*/
public void makeInvisible()
{
erase();
isVisible = false;
}

/**
* Move the circle a few pixels to the right.
*/
public void moveRight()
{
moveHorizontal(20);
}

/**
* Move the circle a few pixels to the left.
*/
public void moveLeft()
{
moveHorizontal(-20);
}

/**
* Move the circle a few pixels up.
*/
public void moveUp()
{
moveVertical(-20);
}

/**
* Move the circle a few pixels down.
*/
public void moveDown()
{
moveVertical(20);
}

/**
* Move the circle horizontally by 'distance' pixels.
*/
public void moveHorizontal(int distance)
{
erase();
xPosition += distance;
draw();
}

/**
* Move the circle vertically by 'distance' pixels.
*/
public void moveVertical(int distance)
{
erase();
yPosition += distance;
draw();
}

/**
* Slowly move the circle horizontally by 'distance' pixels.
*/
public void slowMoveHorizontal(int distance)
{
int delta;

if(distance < 0)
{
delta = -1;
distance = -distance;
}
else
{
delta = 1;
}

for(int i = 0; i < distance; i++)
{
xPosition += delta;
draw();
}
}

/**
* Slowly move the circle vertically by 'distance' pixels.
*/
public void slowMoveVertical(int distance)
{
int delta;

if(distance < 0)
{
delta = -1;
distance = -distance;
}
else
{
delta = 1;
}

for(int i = 0; i < distance; i++)
{
yPosition += delta;
draw();
}
}

/**
* Change the size to the new size (in pixels). Size must be >= 0.
*/
public void changeSize(int newDiameter)
{
erase();
diameter = newDiameter;
draw();
}

/**
* Change the color. Valid colors are "red", "yellow", "blue", "green",
* "magenta" and "black".
*/
public void changeColor(String newColor)
{
color = newColor;
draw();
}

/*
* Draw the circle with current specifications on screen.
*/
private void draw()
{
if(isVisible) {
Canvas canvas = Canvas.getCanvas();
canvas.draw(this, color, new Ellipse2D.Double(xPosition, yPosition,
diameter, diameter));
canvas.wait(10);
}
}

/*
* Erase the circle on screen.
*/
private void erase()
{
if(isVisible) {
Canvas canvas = Canvas.getCanvas();
canvas.erase(this);
}
}
}

import java.util.ArrayList;

/**
* SuperCircleDrawer is an arraylist for circles. In order to add circles into the
* list you must create instances of circles and then add them to SuperCircleDrawer
* by the storeCircle method. Once circles have been added, one can perform the
* following methods. drawCircles, eraseCircles, moveAllHorizontal, MoveAllVetical,
* doubleAllDaimeters, drawLargeCircles, and finally drawLargestCircle.
*
* In depth detail of the methods can be viewed in the comments above the method.
*
* @author Eric Lund
* @version 9/29/11
*/
public class SuperCircleDrawer
{
private ArrayList<Circle> circleCollection; //declares a field called "circleCollection" that references an ArrayList of Circles.
private int counter;

/**
* Creates a new constructor that creates a new array list of circles.
*/
public SuperCircleDrawer()
{
circleCollection = new ArrayList<Circle>(); //makes an empty arraylist to hold the individual Cicrles.
}

/**
* Add a circle to the ArrayList
*
* @param Adds the specified circle into the arraylist.
*/
public void storeCircle (Circle addcircle)
{
circleCollection.add(addcircle);
}

/**
* The method causes all of the circles in the list to become visible.
*/
public void drawCircles()
{
for (Circle circles : circleCollection)
{
circles.makeVisible();
}
}

/**
* The method causes all of the circles in the list to become invisible.
*/
public void eraseCircles()
{
for (Circle circles : circleCollection)
{
circles.makeInvisible();
}
}

/**
* Moves all of the circles horzontailly by the specified amount in pixles. If
* the specified amount is a negitive number it will result in a leftwards
* horizontal shift, where as a postivie number will result in rightward horizontal
* shift.
*
* @param Horizontally moves all the circles left or right by the specified number.
*/
public void moveAllHorizontal(int distance)
{
for (Circle circles : circleCollection)
{
circles.moveHorizontal(distance);
}
}

/**
* Moves all of the circles vertically by the specified amount in pixles. If
* the specified amount is a negitive number it will result in a upwards
* vertical shift, where as a postivie number will result in downwards vertical
* shift.
*
* @param vertically moves all the circles up or down by the specified number.
*/
public void moveAllVertical(int distance)
{
for (Circle circles : circleCollection)
{
circles.moveVertical(distance);
}
}

/**
* doubles the size of all the circles.
*/
public void doubleAllDiameters()
{
for (Circle circles : circleCollection)
{
circles.changeSize(circles.getDiameter()*2);
}
}

/**
* Draws circles with a diameter larger the 30. Circles with a diameter of 30 or less
* will become invisivle.
*/
public void drawLargeCircle()
{
for (Circle circles : circleCollection)
{
if(circles.getDiameter() > 30)
{
circles.makeVisible();
}
else
{
circles.makeInvisible();
}
}
}

/**
* Draws the biggest circle in the arraylist
*/
public void drawLargestCircle()
{
}




}