• Best of JavaWorld
• Editor's Choice

Some reader favorites:

EJB fundamentals and session beans 

Create a scrollable virtual desktop in Swing

HMVC: The layered pattern for client tiers

Double-checked locking: Clever but broken

Wizard API updated!
Tim Boudreau has released a new version of the Swing Wizard library (version 0.997) that fixes the WizardException bug reported in JavaWorld's recent Open Source Java Project profile. The article's examples have been reworked to test out the new, improved WizardException. Thanks, Tim, for this helpful fix!
Open Source Java Projects: The Wizard API

package net.frog_parrot.jump;
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
/**
 * This is the main class of the Tumbleweed game.
 *
 * @author Carol Hamer
 */
   public class Jump extends MIDlet implements CommandListener {
   //---------------------------------------------------------
   // Commands
    /**
    * The command to end the game.
    */
   private Command myExitCommand = new Command("Exit", Command.EXIT, 99);
   /**
    * The command to start moving when the game is paused.
    */
   private Command myGoCommand = new Command("Go", Command.SCREEN, 1);
   
   /**
    * The command to pause the game.
    */
   private Command myPauseCommand = new Command("Pause", Command.SCREEN, 1);
   /**
    * The command to start a new game.
    */
   private Command myNewCommand = new Command("Play Again", Command.SCREEN, 1);
   //---------------------------------------------------------
   // Game object fields
   /**
    * The canvas that all of the game will be drawn on.
    */
   private JumpCanvas myCanvas;
   /**
    * The thread that advances the cowboy.
    */
   private GameThread myGameThread;
   
//-----------------------------------------------------
   // Initialization and game state changes
   /**
    * Initialize the canvas and the commands.
    */
   public Jump() {
      try {
         myCanvas = new JumpCanvas(this);
         myCanvas.addCommand(myExitCommand);
         myCanvas.addCommand(myPauseCommand);
         myCanvas.setCommandListener(this);
      } catch(Exception e) {
         errorMsg(e);
      }
   }
   
   /**
    * Switch the command to the play again command.
    */
   void setNewCommand () {
      myCanvas.removeCommand(myPauseCommand);
      myCanvas.removeCommand(myGoCommand);
      myCanvas.addCommand(myNewCommand);
   }
   
   /**
    * Switch the command to the go command.
    */
   private void setGoCommand() {
      myCanvas.removeCommand(myPauseCommand);
      myCanvas.removeCommand(myNewCommand);
      myCanvas.addCommand(myGoCommand);
   }
   
   /**
    * Switch the command to the pause command.
    */
   private void setPauseCommand () {
      myCanvas.removeCommand(myNewCommand);
      myCanvas.removeCommand(myGoCommand);
      myCanvas.addCommand(myPauseCommand);
   }
   
   //----------------------------------------------------------------
   // Implementation of MIDlet.
   // These methods may be called by the application management
   // software at any time, so you always check fields for null
   // before calling methods on them.
   
   /**
    * Start the application.
    */
   public void startApp() throws MIDletStateChangeException {
      if(myCanvas != null) {
         if(myGameThread == null) {
            myGameThread = new GameThread(myCanvas);
            myCanvas.start();
            myGameThread.start();
         } else {
            myCanvas.removeCommand(myGoCommand);
            myCanvas.addCommand(myPauseCommand);
            myCanvas.flushKeys();
            myGameThread.resumeGame();
         }
      }
   }
   
   /**
   * Stop and throw out the garbage.
   */
   public void destroyApp(boolean unconditional)
         throws MIDletStateChangeException {
      if(myGameThread != null) {
         myGameThread.requestStop();
      }
      myGameThread = null;
      myCanvas = null;
      System.gc();
   }
   
   /**
    * Request the thread to pause.
    */
   public void pauseApp() {
      if(myCanvas != null) {
         setGoCommand();
      }
      If(myGameThread != null) {
         myGameThread.pauseGame();
      }
   }
   
   //----------------------------------------------------------------
   // Implementation of CommandListener
   /*
    * Respond to a command issued on the Canvas.
    * (either reset or exit).
    */
   public void commandAction(Command c, Displayable s) {
      if(c == myGoCommand) {
         myCanvas.removeCommand(myGoCommand);
         myCanvas.addCommand(myPauseCommand);
         myCanvas.flushKeys();
         myGameThread.resumeGame();
      } else if(c == myPauseCommand) {
         myCanvas.removeCommand(myPauseCommand);
         myCanvas.addCommand(myGoCommand);
         myGameThread.pauseGame();
      } else if(c == myNewCommand) {
         myCanvas.removeCommand(myNewCommand);
         myCanvas.addCommand(myPauseCommand);
         myCanvas.reset();
         myGameThread.resumeGame();
      } else if((c == myExitCommand) || (c == Alert.DISMISS_COMMAND)) {
         try {
            destroyApp(false);
            notifyDestroyed();
         } catch (MIDletStateChangeException ex) {
         }
      }
   }
   
   //-------------------------------------------------------
   // Error methods
   
   /**
    * Converts an exception to a message and displays
    * the message.
    */
   void errorMsg(Exception e) {
      if(e.getMessage() == null) {
         errorMsg(e.getClass().getName());
      } else {
         errorMsg(e.getClass().getName() + ":" + e.getMessage());
      }
   }
   
   /**
    * Displays an error message alert if something goes wrong.
    */
   void errorMsg(String msg) {
      Alert errorAlert = new Alert("error", msg, null, AlertType.ERROR);
      errorAlert.setCommandListener(this);
      errorAlert.setTimeout(Alert.FOREVER);
      Display.getDisplay(this).setCurrent(errorAlert);
   }
}