Lesson02-Getting Started

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Getting Started with

Mobile Programming

1 Objectives

In this section, we will be delving into writing, building, using the emulator andpackaging J2ME applications. The Integrated Programming Environment that we will useis Netbeans 4.1 (www.netbeans.org) with Mobility Pack.

After finishing this lesson, the student should be able to:

Create a simple MIDlet

Create a Project in Netbeans

Create a MIDlet in Netbeans

Run a MIDlet on the emulator

2 Introduction

An IDE (Integrated Development Environment) is a programming environment with aGUI builder, a text or code editor, a compiler and/or interpreter and a debugger. In ourcase, Netbeans also comes with a device emulator. This lets you see how your programwould look like in an actual device.

3 "Hello, world!" MIDlet

We have studied in the previous section the MIDlet's life cycle. A MIDlet's life starts whenit is created by the Application Management System (AMS) of the device. Initially, it is inthe "paused" state.

To be able to create a MIDlet, we must create a subclass of the MIDlet class fromjavax.microedition.midlet package. We must also override or implement the methods:startApp(), destroyApp() and pauseApp(). These are the methods expected by the AMSfor running and controlling our MIDlet.

Mobile Application Development 1


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Unlike a typical Java program where the main() method is only entered once in theprogram's life, the startApp() method may be called more than once during the MIDlet'slife cycle. So you must not put one time initialization codes in the startApp() method.Instead, you can create a MIDlet constructor and do your initializations there.

Here is the code of our first MIDP program:

/*

* HelloMidlet.java

*

* Created on July 8, 2000, 9:00 AM

*/

import javax.microedition.midlet.*;

import javax.microedition.lcdui.*;

/**

*

* @author JEDI Apprentice

* @version

*/

public class HelloMidlet extends MIDlet implements CommandListener {


Active

Paused

Destroyed

destroyApp()

destroyApp()

startApp()

pauseApp()

new


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Display display;

Command exitCommand = new Command("Exit", Command.EXIT, 1);

Alert helloAlert;

public HelloMidlet(){

helloAlert = new Alert(

"Hello MIDlet", "Hello, world!",

null, AlertType.INFO

);

helloAlert.setTimeout(Alert.FOREVER);

helloAlert.addCommand(exitCommand);

helloAlert.setCommandListener(this);

}

public void startApp() {

if (display == null){

display = Display.getDisplay(this);

}

display.setCurrent(helloAlert);

}

public void pauseApp() {

}

public void destroyApp(boolean unconditional) {

}

public void commandAction(Command c, Displayable d){

if (c == exitCommand){

destroyApp(true);

notifyDestroyed(); // Exit

}

}

}

Next, we would dissect our first MIDlet, focusing on every significant line of code:



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As we have said before, we should create a subclass of MIDlet to create our MIDPprogram. In this line, we did created a subclass of MIDlet by extending it and naming itHelloMIdlet.

Display display;

Command exitCommand = new Command("Exit", Command.EXIT, 1);

Alert helloAlert;

These are the variable properties of our MIDlet. We would need the Display object (these

is only one display associated per MIDlet) in order to do some drawing on the screen.The exitCommand is a command we would put in our screen so that we can quit theprogram. If we would not put any exit command, there would be no way to exit ourMIDlet gracefully.

public HelloMidlet(){

helloAlert = new Alert(

"Hello MIDlet", "Hello, world!",

null, AlertType.INFO

);

helloAlert.setTimeout(Alert.FOREVER);

helloAlert.addCommand(exitCommand);

helloAlert.setCommandListener(this);

}

The constructor initializes our Alert object. We would be discussing more of the Alertclass in the next sections. The addCommand() method on the Alert object puts an "Exit"command on the screen. The setCommandListener() method tells the system to pass allcommand events to our MIDlet.


The "implements CommandListener" code is for command/key presses, so that ourprogram would be able to handle "command" events. If we implement aCommandListener, we must create a commandAction() method.

public void commandAction(Command c, Displayable d){

if (c == exitCommand){



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destroyApp(true);

notifyDestroyed(); // Exit

}

}

Our commandAction() only handles request for the "Exit" command. It would terminateour program using notifyDestroyed() if the "Exit" command is issued or pressed.

public void startApp() {if (display == null){

display = Display.getDisplay(this);

}

display.setCurrent(helloAlert);

}

This is the entry point of our program once it is ready to be displayed by the AMS.Remember that the startApp() may be entered more than once in the MIDlet's life cycle.If a MIDlet is paused, say by an incoming phone call, it would enter the paused state(pauseApp). If after the call the AMS wants to bring back our program, it would call thestartApp() method again. The display.setCurrent() method tells the system that we wantour Alert object to be displayed on the screen. We can get the display object by callingthe static Display.getDisplay() method.

Netbeans automatically creates a Java Application Descriptor (JAD) for your program.Netbeans put the JAD file in the "dist" folder under the project's folder. Here a sampleJAD file created by Netbeans:

MIDlet-1: HelloMidlet, , HelloMidletMIDlet-Jar-Size: 1415MIDlet-Jar-URL: ProjectHello.jarMIDlet-Name: ProjectHelloMIDlet-Vendor: VendorMIDlet-Version: 1.0

MicroEdition-Configuration: CLDC-1.1MicroEdition-Profile: MIDP-2.0

Now we're ready to compile, package and run our first MIDlet.



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4 Compilation and Packaging MIDlets

Before we use any of the integrated tools for compiling and automatically packaging ourMIDlet suites, we'll try to do this using the command line tools.

The MIDlet suite is usually packed into a single file called the JAR file. This is acompressed file, much like a ZIP file. In fact, you can open a JAR file using a ZIPdecompressor program.

The MIDlet suite consists of:

The JAR file

The Java Application Descriptor (JAD) file

The JAR file contains:

The class files

Manifest file describing the contents of the archive

resources: images/icons, video, data, etc. used by the suite

The Manifest file, manifest.mf is like the JAD file. It is used by the application manager ofthe device. The required fields of the manifest file are:

MIDlet-Name

MIDlet-Version

MIDlet-Vendor

MIDlet- (where n is a number from 1, for each MIDlet in the JAR file)

MicroEdition-Profile

MicroEdition-Configuration

First we compile the java source files:

javac -bootclasspath C:\WTK23\lib\cldcapi11.jar;C:\WTK23\lib\midpapi20.jar*.java



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The Java Compiler program, "javac", should be on your path. If you see an error like,"cannot find file" or "not an executable", please consult the installation guide for your

Java development kit distribution on how to put in your executable PATH the location ofthe java tools.

Next, we pre-verify the class file(s):

preverify

-classpath C:\WTK23\lib\cldcapi11.jar;C:\WTK23\lib\midpapi20.jar;.

-d . HelloMidlet

preverify is included in the wireless toolkit from java.sun.com. Enter this command in asingle line.

The final step is to create the JAR itself:

jar cvfm HelloMidlet.jar manifest.txt HelloMidlet.class

The jar program is included in the Java Development Kit, and its location should beincluded in your executable path. This command will create the JAR file with filenameHelloMidlet.jar. The manifest.txt would be renamed to manifest.mf in the JAR file.



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5 Using the Sun Wireless Toolkit

We'll now use the Sun Wireless Toolkit to compile and package our MIDlet suite(containing a single MIDlet).

Open ktoolbar (from the Wireless Toolkit distribution):

C reate a new project:



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On this Settings window, you can customize the a very comprehensive selection ofsettings for your project. You can select what configuration to use, what packages/APIs

to include, Push Registry settings and more. For our purposes, we will use the defaultproject settings. Click "OK" to finish creating the project.



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Copy HelloMidlet.java into the project's "src directory: In Window, this is under thedirectory: C:\WTK23\apps\HelloMidlet\src (where C:\WTK23 is where you installed the

wireless toolkit). Click "Build" and "Run":



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6 Using Netbeans and Mobility Pack

As a pre-requisite for this section, Netbeans 4.1 and Mobility Pack should be installed onyour computer.

Step 1: Start creating a new Project



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Step 2: Select the "Mobile" Category

Step 3: Select "Mobile Application"



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Step 4: Name the Project and specify its location

(Uncheck "Create Hello MIDlet, we would be creating our own MIDlet later)

Step 5: Select the Platform (optional)



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Figure 1: Newly Created Mobile Project (NetBeans)


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Step 6: Start creating a new MIDlet



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Step 7: Choose MIDP "Category" and MIDlet "File Type"



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Step 8: Create a Name for the MIDlet



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Figure 2: Creating a new MIDlet automatically creates required MIDlet methods


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Step 10: Replace the automatically created code with our program's code.



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Step 11: Compile and Run the MIDlet in the Emulator



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Step 12: Launch our MIDlet on the Emulator



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Figure 3: Hello World MIDlet in action


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7 Exercises

7.1 Multiple MIDlets in one MIDlet suite

Add a new MIDlet to our project "ProjectHello". Take note that Netbeans automaticallyadds the new MIDlet in the the applications JAD file when you use the "New File..."Wizard.

7.2 Multiple MIDlets in one MIDlet suite using the WirelessToolkit

Use the Sun Wireless Toolkit to add a new MIDlet into your MIDlet suite.


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