Apple Developer Connection Student Program/ADC Tools Sampler CD Disk 3 1999.iso/Documentation/Books/Learn Java on the Macintosh/Learn Java Projects/15.01 - threads/SimpleDraw.java

Text File | 1996-04-24 | 5KB | 188 lines

/* -------------------------------------------------------------
This applet paints a circle or square of the color you've chosen
wherever you click. Every second, it blinks the shape to yellow.
All shapes blink independently of each other.

This applet keeps a list of the shapes you've drawn
and paints all the shapes in the list when it repaints.

Java's classes: Applet    (applet)
                Event     (awt)     user-generated action
                Graphics  (awt)     used for drawing
                Color     (awt)     defines colors
                Choice    (awt)     shape and color selection choices
                Vector    (util)    list of shapes
                Thread    (lang)

Custom classes: SimpleDraw
                Circle              defines and draws circles
                Square              defines and draws squares
                Shape                a common ancestor for circles and squares
                BlinkThread         controls drawing for a shape

------------------------------------------------------------- */

import java.applet.Applet;
import java.util.*;
import java.awt.*;

public class SimpleDraw extends Applet {
   Vector  threads;
   Choice  shapeChoice;
   Choice  colorChoice;

   /** Create the GUI. */
   public void init() {
      threads = new Vector();

      shapeChoice = new Choice();
      shapeChoice.addItem("Circle");
      shapeChoice.addItem("Square");
      add(shapeChoice);

      colorChoice = new Choice();
      colorChoice.addItem("Red");
      colorChoice.addItem("Green");
      colorChoice.addItem("Blue");
      add(colorChoice);

      BlinkThread.g = getGraphics(); // Get the graphics object for the applet
   }

   /** Create a new shape. */
   public boolean mouseUp(Event e, int x, int y) {

      BlinkThread t;
      Shape s;  // This shape will be either a circle or a square.

      String shapeString = shapeChoice.getSelectedItem();
      String colorString = colorChoice.getSelectedItem();

      if (shapeString.equals("Circle"))
         s = new Circle();
      else
         s = new Square();

      if (colorString.equals("Red"))
         s.color = Color.red;
      else if (colorString.equals("Green"))
         s.color = Color.green;
      else
         s.color = Color.blue;

      s.x = x;
      s.y = y;

      t = new BlinkThread(s);
      t.start();
      threads.addElement(t);

      return true;
   }

   /** Resume all the threads when the applet starts. */
   public void start() {
      BlinkThread t;
      int         numThreads;

      numThreads = threads.size();
      for (int i = 0; i < numThreads; i++) {

         t = (BlinkThread)threads.elementAt(i);
         t.resume();
      }
   }

   /** Suspend all the threads when the applet stops. */
   public void stop() {
      BlinkThread t;
      int         numThreads;

      numThreads = threads.size();
      for (int i = 0; i < numThreads; i++) {

         t = (BlinkThread)threads.elementAt(i);
         t.suspend();
      }
   }

   /** Stop all the threads when the applet goes away. */
   public void destroy() {
      BlinkThread t;
      int         numThreads;

      numThreads = threads.size();
      for (int i = 0; i < numThreads; i++) {

         t = (BlinkThread)threads.elementAt(i);
         t.stop();
      }
   }
}

/** Shapes provide common characteristics for the circle and square. */
abstract class Shape {
   static public final int shapeRadius = 20;

   Color color;
   int x;
   int y;

   abstract void draw(Graphics g);
   abstract void drawBlink(Graphics g);
}

/** Draws and maintains circle information. */
class Circle extends Shape {
   void drawBlink(Graphics g) {
      g.setColor(Color.yellow);
      g.fillOval(this.x - shapeRadius, this.y - shapeRadius, shapeRadius * 2, shapeRadius * 2);
   }

   void draw(Graphics g) {
      g.setColor(this.color);
      g.fillOval(this.x - shapeRadius, this.y - shapeRadius, shapeRadius * 2, shapeRadius * 2);
   }
}

/** Draws and maintains square information. */
class Square extends Shape{
   void drawBlink(Graphics g) {
      g.setColor(Color.yellow);
      g.fillRect(this.x - shapeRadius, this.y - shapeRadius, shapeRadius * 2, shapeRadius * 2);
   }

   void draw(Graphics g) {
      g.setColor(this.color);
      g.fillRect(this.x - shapeRadius, this.y - shapeRadius, shapeRadius * 2, shapeRadius * 2);
   }
}

/** Thread to control when to blink a shape. */
class BlinkThread extends Thread {
   static Graphics g;
   Shape s;

   BlinkThread(Shape s) {
      this.s = s;
   }

   public void run() {

      // don't ever exit the thread
      while(true) {

         try {
            s.drawBlink(g);
            sleep(250);  // Go to sleep for a 1/4 of a second (250 milliseconds)

            s.draw(g);
            sleep(1000); // Go to sleep for 1 second (1000 milliseconds)

         } catch (Exception e) {
         }

      }
   }
}