Class 32: Lab: Animation

import java.awt.Color;     // Yes, we care about colors
import java.awt.Frame;     // The window that holds our baloon
import java.awt.Graphics;  // Our handy-dandy paintbrush
import java.awt.Rectangle; // For the bounds

/**
 * A simple application that animates an expanding circle.
 *
 * @author Samuel A. Rebelsky
 * @version 1.0 of March 2000
 */
public class Balloon
  extends Frame
  implements Runnable
{

  // +--------+--------------------------------------------------
  // | Fields |
  // +--------+

  /**
   * The color of the balloon.
   */
  protected Color color;

  /**
   * The radius of the balloon.
   */
  protected int radius;

  /**
   * The x coordinate of the center of the balloon.
   */
  protected int xcoord;

  /**
   * The y coordinate of the center of the balloon.
   */
  protected int ycoord;

  /**
   * The amount to change the radius by.
   */
  protected int deltaRadius;

  /**
   * The thread of computation associated with this object.
   */
  protected Thread thread;

  // +--------------+--------------------------------------------
  // | Constructors |
  // +--------------+

  public Balloon(Color initialColor) {
    this.color = initialColor;
    this.radius = 10;
    this.deltaRadius = 5;
    this.xcoord = 50;
    this.ycoord = 300;
    this.setSize(400,400);
    this.show();
    this.thread = new Thread(this);
    this.thread.setPriority(Thread.MIN_PRIORITY);
    this.thread.start();
  } // Balloon

  // +-----------+-----------------------------------------------
  // | Modifiers |
  // +-----------+

  /**
   * Update the balloon.
   */
  public void update() {
    this.radius = this.radius + this.deltaRadius;
    this.xcoord = this.xcoord + 1;
    this.ycoord = this.ycoord - 2;
  } // update()

  // +-------------------------+---------------------------------
  // | Overriden Frame Methods |
  // +-------------------------+

  /**
   * Paint the current version of the balloon.
   */
  public void paint(Graphics paintBrush) {
    // System.err.println("Painting ...");
    Rectangle bounds = this.getBounds();
    if (this.radius < 10) {
      this.deltaRadius = 5;
    }
    else if (2*this.radius > bounds.width) {
      this.deltaRadius = -5;
    }
    // Paint the balloon
    paintBrush.setColor(this.color);
    paintBrush.fillOval(this.xcoord-this.radius, 
                        this.ycoord-this.radius,
                        this.radius*2,
                        this.radius*2);
  } // paint(Graphics)

  // +------------------+----------------------------------------
  // | Runnable Methods |
  // +------------------+
  
  public void run() {
    while (true) {
      try { this.thread.sleep(200); }
      catch (InterruptedException e) { }
      update();
      repaint();
    } // while
  } // run()

  // +------+----------------------------------------------------
  // | Main |
  // +------+

  public static void main(String[] args) {
    new Balloon(Color.red);
  }
} // class Balloon