ArrayList and Bouncing Balls

[jamie23]

My program is suppose to ask the user how many balls bouncing they would like to have then store the random values of the ball including random color in an ArrayList. I believe that I am having an issue with the paintComponent, the program with pop up the GUI window just fine but the background isn't black and there are no balls bouncing. I was hoping that someone could suggest how to fix this problem. I attached the code.
Thank you

[Fubarable]

Your code for all to see, comments removed:

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.GraphicsEnvironment;
import java.awt.Point;
import javax.swing.*;
import java.util.ArrayList;
import java.util.Scanner;

/**
 * Frame to hold a bouncing ball panel, implemented in the BallPanel class.
 * Controls the animation of the ball via pauses and calls to BallPanel's move
 * and paintComponent methods.
 * 
 * @author Michael Peterson
 */
public class BallTest extends JFrame {
   private static final int WINDOW_WIDTH = 500;
   private static final int WINDOW_HEIGHT = 300;
   private BallPanel ballPanel;

   public static void pause() {
      try {
         Thread.sleep(20);
      } catch (Exception e) {
         System.out.println(e);
         e.printStackTrace();
      }
   }

   public BallTest(ArrayList<Ball> ballList, int numberOfBalls) {
      super("Bouncing Ball");
      setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      setSize(WINDOW_WIDTH, WINDOW_HEIGHT);
      setLayout(new BorderLayout());
      ballPanel = new BallPanel(ballList, numberOfBalls);
      add(ballPanel);
      center(this);
      setVisible(true);
      while (true) {
         pause();
         ballPanel.move(WINDOW_WIDTH, WINDOW_HEIGHT, ballList, numberOfBalls);
         ballPanel.repaint();
      }
   }

   public static void center(JFrame frame) {
      GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment(); 
      Point center = ge.getCenterPoint();
      int w = frame.getWidth();
      int h = frame.getHeight();
      int x = center.x - w / 2, y = center.y - h / 2;
      frame.setBounds(x, y, w, h);
      frame.validate();
   }

   public static void main(String[] args) {
      Scanner keyboard = new Scanner(System.in);
      ArrayList<Ball> ballList = new ArrayList<Ball>();
      String response = JOptionPane.showInputDialog(null, "How many balls do you want boucning",
               "Bouncing Balls", JOptionPane.QUESTION_MESSAGE);
      int numberOfBalls = Integer.parseInt(response);
      System.out.println("number" + numberOfBalls);
      BallTest t = new BallTest(ballList, numberOfBalls);
   }
}

class Ball {
   int bxCoord;
   int byCoord;
   int bHeight;
   int bWidth;
   int bRise;
   int bRun;
   Color bColor;
   BallPanel ballPanel;

   public Ball() {
      bxCoord = 0;
      byCoord = 0;
      bHeight = 0;
      bWidth = 0;
      bRise = 0;
      bRun = 0;
      bColor = Color.red;
   }

   public void initialize() {
      this.bxCoord = getBxCoord();
      this.byCoord = getByCoord();
      this.bHeight = getBHeight();
      this.bWidth = getBWidth();
      this.bRise = getBRise();
      this.bRun = getBRun();
      this.bColor = getBColor();
   }

   public int getBxCoord() {
      setBxCoord();
      System.out.println(bxCoord);
      return bxCoord;
   }

   public int getByCoord() {
      setByCoord();
      System.out.println(byCoord);
      return byCoord;
   }

   public int getBHeight() {
      setBHeight();
      System.out.println(bHeight);
      return bHeight;
   }

   public int getBWidth() {
      setBWidth();
      System.out.println(bWidth);
      return bWidth;
   }

   public int getBRise() {
      setBRise();
      System.out.println(bRise);
      return bRise;
   }

   public int getBRun() {
      setBRun();
      System.out.println(bRun);
      return bRun;
   }

   public Color getBColor() {
      setBColor();
      System.out.println(bColor);
      return bColor;
   }

   public void setBxCoord() {
      bxCoord = (int) (Math.random() * 50);
   }

   public void setByCoord() {
      byCoord = (int) (Math.random() * 50);
   }

   public void setBHeight() {
      bHeight = (int) (Math.random() * 10) + 11;
   }

   public void setBWidth() {
      bWidth = (int) (Math.random() * 10) + 11;
   }

   public void setBRise() {
      bRise = (int) (Math.random() * 10);
   }

   public void setBRun() {
      bRun = (int) (Math.random() * 10);
   }

   public void setBColor() {
      int red = (int) (Math.random() * 255);
      int green = (int) (Math.random() * 255);
      int blue = (int) (Math.random() * 255);
      Color randomColor = new Color(red, green, blue);
      bColor = randomColor;
   }

   public void paintComponent(Graphics g) {
      g.setColor(this.bColor);
      g.fillOval(this.bxCoord, this.byCoord, this.bWidth, this.bHeight);
   }

   public void move(int WINDOW_WIDTH, int WINDOW_HEIGHT) {
      if (this.bxCoord < (0 - this.bRun) || this.bxCoord > (WINDOW_WIDTH - this.bWidth)) {
         this.bRun = -this.bRun;
      }
      if (this.byCoord < (0 - this.bRise) || this.byCoord > (WINDOW_HEIGHT - this.bHeight)) {
         this.bRise = -this.bRise;
      }
      this.bxCoord += this.bRun;
      this.byCoord += this.bRise;
   }
}

class BallPanel extends JPanel {
   Ball ball;

   public BallPanel(ArrayList<Ball> ballList, int numberOfBalls) {
      for (int i = 0; i < numberOfBalls; i++) {
         ball = new Ball();
         ball.initialize();
         ballList.add(ball);
      }
   }

   public void paintComponent(Graphics g, ArrayList<Ball> ballList, int numberOfBalls) {
      super.paintComponent(g);
      g.setColor(Color.black);
      g.fillRect(0, 0, getWidth(), getHeight());
      for (int i = 0; i < numberOfBalls; i++) {
         ballList.get(i).paintComponent(g);
      }
   }

   public void move(int WINDOW_WIDTH, int WINDOW_HEIGHT, ArrayList<Ball> ballList, int numberOfBalls) {
      for (int i = 0; i < numberOfBalls; i++) {
         ballList.get(i).move(WINDOW_WIDTH, WINDOW_HEIGHT);
      }
   }
}

You'll want to read up on Concurrency in Swing and why doing Thread.sleep(...) and while (true) is not a good idea on the main Swing thread, the EDT.

Next, you'll want to read the tutorial on and use a Swing Timer