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

public class BlinkingObjectsApplet extends Applet {

  Vector objects = new Vector();
    // double buffering to avoid flashing
  Dimension offDimension;
  Image offImage;
  Graphics offGraphics;
  

  public void init() {
    add(new Button("new object"));
    newObject(this);
  }

  public void start() {
    Enumeration e = objects.elements(); 
    Blinkable obj;
    while (e.hasMoreElements()) { // step through all vector elements
      obj = (Blinkable) e.nextElement();
      obj.startBlinking();
    }
  }

  public void stop() {
    Enumeration e = objects.elements();
    Blinkable obj; 
    while (e.hasMoreElements()) { // step through all vector elements
      obj = (Blinkable) e.nextElement();
      obj.stopBlinking();
    }
  }

  public boolean action(Event e, Object arg) {
    newObject(this);
    repaint(); 
    return(true);
  }

  public void paint(Graphics g) {
    update(g);
  }

  public void update(Graphics g) {
    Dimension d = size();
    if ( (offGraphics == null)
         || (d.width != offDimension.width)
         || (d.height != offDimension.height) ) {
       offDimension = d;
       offImage = createImage(d.width,d.height);
       offGraphics = offImage.getGraphics();
    }
    //Erase the previous image.
    offGraphics.setColor(getBackground());
    offGraphics.fillRect(0, 0, d.width, d.height);
    //Rebuild the image.
    offGraphics.setColor(Color.black);
    Enumeration e = objects.elements(); 
    Blinkable obj;
    while (e.hasMoreElements()) { // step through all vector elements
       obj = (Blinkable) e.nextElement();
       obj.draw(offGraphics);
    } 
    //Paint the image onto the screen.
    g.drawImage(offImage, 0, 0, this);
  }

  void newObject(Applet applet) {
    BlinkingCharacter c;
    BlinkingShape s;
    if (0 == (int) Math.round(Math.random())) {
    // character
      if (0 == (int) Math.round(Math.random())) {
        c = new BlinkingLetter(applet);
      }
      else {
        c = new BlinkingDigit(applet);
      }
      c.randomize(); // choose random properties of  character
      c.startBlinking();
      objects.addElement(c);
    }
    else {
    // shape
      if (0 == (int) Math.round(Math.random())) {
        s = new BlinkingOval(applet);
      }
      else {
        s = new BlinkingRectangle(applet);
      }
      s.randomize(); // choose random properties of  character
      s.startBlinking();
      objects.addElement(s);
    }
  }   
}