Java Tutorial/J2ME/Command

Add Command to MIDlet

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import javax.microedition.lcdui.rumand;
import javax.microedition.lcdui.rumandListener;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.Displayable;
import javax.microedition.lcdui.TextBox;
import javax.microedition.lcdui.TextField;
import javax.microedition.lcdui.Ticker;
import javax.microedition.midlet.MIDlet;
public class TextBoxMIDlet extends MIDlet implements CommandListener {
  private static final int MAX_TEXT_SIZE = 64;
  protected TextBox textBox;
  protected Display display;
  private static final Command EXIT_COMMAND = new Command("Exit", Command.EXIT,0);
  private static final Command OK_COMMAND = new Command("OK", Command.OK, 0);
  private static final Command CLEAR_COMMAND = new Command("Clear",Command.SCREEN, 1);
  private static final Command REVERSE_COMMAND = new Command("Reverse",Command.SCREEN, 1);
  protected void startApp() {
    String str = null;
    try {
      InputStream is = getClass().getResourceAsStream("resources/text.txt");
      InputStreamReader r = new InputStreamReader(is);
      char[] buffer = new char[32];
      StringBuffer sb = new StringBuffer();
      int count;
      while ((count = r.read(buffer, 0, buffer.length)) > -1) {
        sb.append(buffer, 0, count);
      }
      str = sb.toString();
    } catch (IOException ex) {
      str = "Failed to load text";
    }
    textBox = new TextBox("TextBox Example", str, MAX_TEXT_SIZE, TextField.ANY);
    Ticker ticker = new Ticker("This is a ticker...");
    textBox.setTicker(ticker);
    textBox.addCommand(OK_COMMAND);
    textBox.addCommand(EXIT_COMMAND);
    textBox.addCommand(CLEAR_COMMAND);
    textBox.addCommand(REVERSE_COMMAND);
    textBox.setCommandListener(this);
    display = Display.getDisplay(this);
    display.setCurrent(textBox);
  }
  protected void pauseApp() {
  }
  protected void destroyApp(boolean unconditional) {
  }
  public void commandAction(Command c, Displayable d) {
    if (c == EXIT_COMMAND) {
      destroyApp(true);
      notifyDestroyed();
    } else if (c == OK_COMMAND) {
      System.out.println("OK pressed");
    } else if (c == CLEAR_COMMAND) {
      textBox.setString(null);
    } else if (c == REVERSE_COMMAND) {
      String str = textBox.getString();
      if (str != null) {
        StringBuffer sb = new StringBuffer(str);
        textBox.setString(sb.reverse().toString());
      }
    }
  }
}

A MIDlet with simple text and a few commands.

import javax.microedition.lcdui.rumand;
import javax.microedition.lcdui.rumandListener;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.Displayable;
import javax.microedition.lcdui.TextBox;
import javax.microedition.midlet.MIDlet;
public class FewCommandsMIDlet extends MIDlet implements CommandListener {
  private Command exitCommand = new Command("A", Command.SCREEN, 1);
  private Command infoCommand = new Command("B", Command.SCREEN, 2);
  private Command aboutCommand = new Command("C", Command.SCREEN, 2);
  private Display display;
  public FewCommandsMIDlet() {
    display = Display.getDisplay(this);
  }
  public void startApp() {
    TextBox t = new TextBox("sdf", "Welcome to MIDP Programming", 256, 0);
    t.addCommand(infoCommand);
    t.addCommand(exitCommand);
    t.addCommand(aboutCommand);
    t.setCommandListener(this);
    display.setCurrent(t);
  }
  public void pauseApp() {
  }
  public void destroyApp(boolean unconditional) {
  }
  public void commandAction(Command c, Displayable s) {
    if (c == exitCommand) {
      destroyApp(false);
      notifyDestroyed();
    }
  }
}

Exit Command

import javax.microedition.lcdui.rumand;
import javax.microedition.lcdui.rumandListener;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.Displayable;
import javax.microedition.lcdui.Form;
import javax.microedition.lcdui.TextField;
import javax.microedition.midlet.MIDlet;
public class TextFieldMIDlet extends MIDlet implements CommandListener {
  private Command exitCommand = new Command("Exit", Command.EXIT, 1);
  private TextField aTextField = new TextField("Label", "Content", 4, TextField.ANY);
  private Display display = Display.getDisplay(this);
  public TextFieldMIDlet() {
  }
  public void startApp() {
    Form aForm = new Form("TextField");
    aForm.append(aTextField);
    aForm.addCommand(exitCommand);
    aForm.setCommandListener(this);
    display.setCurrent(aForm);
  }
  public void pauseApp() {
  }
  public void destroyApp(boolean unconditional) {
  }
  public void commandAction(Command c, Displayable s) {
    if (c == exitCommand) {
      destroyApp(false);
      notifyDestroyed();
    }
  }
}

Get command label and type

import javax.microedition.lcdui.rumand;
import javax.microedition.lcdui.rumandListener;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.Displayable;
import javax.microedition.lcdui.TextBox;
import javax.microedition.midlet.MIDlet;
public class J2MECommandGetter extends MIDlet implements CommandListener {
  private Command exitCommand = new Command("EXIT", Command.EXIT, 1);
  private Command infoCommand = new Command("info", Command.SCREEN, 1);
  TextBox t= new TextBox("Hello MIDP", "Welcome to MIDP Programming", 256, 0);
  private Display display;
  public J2MECommandGetter() {
    display = Display.getDisplay(this);
  }
  public void startApp() {
    t.addCommand(exitCommand);
    t.addCommand(infoCommand);
    t.setCommandListener(this);
    display.setCurrent(t);
  }
  public void pauseApp() {
  }
  public void destroyApp(boolean unconditional) {
  }
  public void commandAction(Command c, Displayable s) {
    if (c == exitCommand) {
      destroyApp(false);
      notifyDestroyed();
    }
    if (c == infoCommand) {
      ((TextBox) s).setString(infoCommand.getLabel() + " " + infoCommand.getCommandType()
          + infoCommand.getPriority());
    }
  }
}

Help command

import javax.microedition.lcdui.rumand;
import javax.microedition.lcdui.rumandListener;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.Displayable;
import javax.microedition.lcdui.Form;
import javax.microedition.lcdui.TextBox;
import javax.microedition.midlet.MIDlet;
public class J2MEOnlineHelp extends MIDlet implements CommandListener {
  private Display display;
  private Command back = new Command("Back", Command.BACK, 2);
  private Command exit = new Command("Exit", Command.EXIT, 1);
  private Command help = new Command("Help", Command.HELP, 3);
  private Form form = new Form("Online Help Example");
  private TextBox helpMesg;
  public J2MEOnlineHelp() {
    display = Display.getDisplay(this);
    helpMesg = new TextBox("Online Help","Press Back to return .",81, 0);
    helpMesg.addCommand(back);
    form.addCommand(exit);
    form.addCommand(help);
    form.setCommandListener(this);
    helpMesg.setCommandListener(this);
  }
  public void startApp() {
    display.setCurrent(form);
  }
  public void pauseApp() {
  }
  public void destroyApp(boolean unconditional) {
  }
  public void commandAction(Command command, Displayable displayable) {
    if (command == back) {
      display.setCurrent(form);
    } else if (command == exit) {
      destroyApp(false);
      notifyDestroyed();
    } else if (command == help) {
      display.setCurrent(helpMesg);
    }
  }
}

Start the MIDlet by creating a list of items and associating the exit command with it

/* License
 * 
 * Copyright 1994-2004 Sun Microsystems, Inc. All Rights Reserved.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *  
 *  * Redistribution of source code must retain the above copyright notice,
 *      this list of conditions and the following disclaimer.
 * 
 *  * Redistribution in binary form must reproduce the above copyright notice,
 *      this list of conditions and the following disclaimer in the
 *      documentation and/or other materials provided with the distribution.
 * 
 * Neither the name of Sun Microsystems, Inc. or the names of contributors
 * may be used to endorse or promote products derived from this software
 * without specific prior written permission.
 *  
 * This software is provided "AS IS," without a warranty of any kind. ALL
 * EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES, INCLUDING
 * ANY IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE
 * OR NON-INFRINGEMENT, ARE HEREBY EXCLUDED. SUN MICROSYSTEMS, INC. ("SUN")
 * AND ITS LICENSORS SHALL NOT BE LIABLE FOR ANY DAMAGES SUFFERED BY LICENSEE
 * AS A RESULT OF USING, MODIFYING OR DISTRIBUTING THIS SOFTWARE OR ITS
 * DERIVATIVES. IN NO EVENT WILL SUN OR ITS LICENSORS BE LIABLE FOR ANY LOST
 * REVENUE, PROFIT OR DATA, OR FOR DIRECT, INDIRECT, SPECIAL, CONSEQUENTIAL,
 * INCIDENTAL OR PUNITIVE DAMAGES, HOWEVER CAUSED AND REGARDLESS OF THE THEORY
 * OF LIABILITY, ARISING OUT OF THE USE OF OR INABILITY TO USE THIS SOFTWARE,
 * EVEN IF SUN HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
 *  
 * You acknowledge that this software is not designed, licensed or intended
 * for use in the design, construction, operation or maintenance of any
 * nuclear facility. 
 */
import javax.microedition.lcdui.Choice;
import javax.microedition.lcdui.rumand;
import javax.microedition.lcdui.rumandListener;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.Displayable;
import javax.microedition.lcdui.List;
import javax.microedition.lcdui.TextBox;
import javax.microedition.lcdui.TextField;
import javax.microedition.midlet.MIDlet;
import javax.microedition.midlet.MIDletStateChangeException;
public class EventEx1 extends MIDlet implements CommandListener {
  // display manager
  Display display = null;
  // a menu with items
  List menu = null; // main menu
  // textbox
  TextBox input = null;
  // command
  static final Command backCommand = new Command("Back", Command.BACK, 0);
  static final Command mainMenuCommand = new Command("Main", Command.SCREEN, 1);
  static final Command exitCommand = new Command("Exit", Command.STOP, 2);
  String currentMenu = null;
  // constructor.
  public EventEx1() {
  }
  /**
   * Start the MIDlet by creating a list of items and associating the exit
   * command with it.
   */
  public void startApp() throws MIDletStateChangeException {
    display = Display.getDisplay(this);
    menu = new List("Menu Items", Choice.IMPLICIT);
    menu.append("Item1", null);
    menu.append("Item2", null);
    menu.append("Item3", null);
    menu.append("Item4", null);
    menu.addCommand(exitCommand);
    menu.setCommandListener(this);
    mainMenu();
  }
  public void pauseApp() {
    display = null;
    menu = null;
    input = null;
  }
  public void destroyApp(boolean unconditional) {
    notifyDestroyed();
  }
  // main menu
  void mainMenu() {
    display.setCurrent(menu);
    currentMenu = "Main";
  }
  /**
   * a generic method that will be called when selected any of the items on the
   * list.
   */
  public void prepare() {
    input = new TextBox("Enter some text: ", "", 5, TextField.ANY);
    input.addCommand(backCommand);
    input.setCommandListener(this);
    input.setString("");
    display.setCurrent(input);
  }
  /**
   * Test item1.
   */
  public void testItem1() {
    prepare();
    currentMenu = "item1";
  }
  /**
   * Test item2.
   */
  public void testItem2() {
    prepare();
    currentMenu = "item2";
  }
  /**
   * Test item3.
   */
  public void testItem3() {
    prepare();
    currentMenu = "item3";
  }
  /**
   * Test item4.
   */
  public void testItem4() {
    prepare();
    currentMenu = "item4";
  }
  /**
   * Handle events.
   */
  public void commandAction(Command c, Displayable d) {
    String label = c.getLabel();
    if (label.equals("Exit")) {
      destroyApp(true);
    } else if (label.equals("Back")) {
      if (currentMenu.equals("item1") || currentMenu.equals("item2")
          || currentMenu.equals("item3") || currentMenu.equals("item4")) {
        // go back to menu
        mainMenu();
      }
    } else {
      List down = (List) display.getCurrent();
      switch (down.getSelectedIndex()) {
      case 0:
        testItem1();
        break;
      case 1:
        testItem2();
        break;
      case 2:
        testItem3();
        break;
      case 3:
        testItem4();
        break;
      }
    }
  }
}