Listing 1. Jump.java 
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);
　}
}