J2ME Tutorials: Java Plateform Micro Edition

Java
ME was designed by Sun Microsystems and is a replacement for a similar
technology, Personal Java. Originally developed under the Java Community
Process as JSR 68, the different flavors of Java ME have evolved in
separate JSRs. Sun provides a reference implementation of the
specification, but has tended not to provide free binary implementations
of its Java ME runtime environment for mobile devices, rather relying on
third parties to provide their own. As of 22 December 2006, the Java ME
source code is licensed under the GNU General Public License, and is
released under the project name phone.

Java
ME has become a popular option for creating games for cell phones, as they
can be emulated on a PC during the development stage and easily uploaded
to the phone. This contrasts with the difficulty of developing, testing,
and loading games for other special gaming platforms such as those made by
Nintendo, Sony, Microsoft, and others, as expensive system-specific
hardware and kits are required.

Usage of Java ME

Java
ME includes flexible user interfaces, robust security, built-in network
protocols, and support for networked and offline applications that can be
downloaded dynamically. Applications based on Java ME are portable across
many devices; yet leverage each device?s native capabilities.

Java
ME device as implement a profile, the most common of these are the Mobile
Information Device Profile aimed at mobile devices, such as cell phones,
and the Personal Profile aimed at consumer products and embedded devices
like Set-top boxes and PDAs.

Developing with Java ME

Writing
a Java ME application uses the same basics programming constructs as used
with Java SE applications. Basically there are two types of configurations
involved in Java ME application development, which are:

CLDC
(Connected Limited Device Configuration)

CDC (Connected
Device Configuration)

Architecture
The Java ME Architecture comprises of three software layers:

The
first layer is the configuration layer that includes the JVM, which
directly interacts with the native OS. The Configuration layer also
handles the interaction between the profile and the JVM.

The second layer is the profile layer, which consists of the minimum set
of application programming interface (API) for the small devices.

The
third layer is the Mobile Information Device profile (MIDP) layer. The
MIDP layer contains java APIs for user network connections, persistence
storage, and the user interface. It also has access to CLDC libraries and
MIDP libraries.

The Java ME Application Development

I.
System Requirements - Hardware

Minimum hardware requirements are:

100
MB hard disk space
128
MB system RAM
800
MHz Pentium III CPU

II.
Minimal Software Requirement

IDE
? Sun ONE Studio 4, Mobile Edition,

(formerly Forte for Java)
GUI
? Sun Java ME Wireless Toolkit 2.5.1 (WTK 2.5.1) for CLDC

For Windows:
Download the Sun Java Wireless Toolkit for CLDC from
http://java.sun.com/products/ s j w t o o l k i t / d o w n l o a d. h t m
l Ensure that you have installed an appropriate

Java SE environment.
Run the installer, sun_java_wireless_toolkit- 2_5_1-windows.exe. Follow
the instructions provided by the installer.

Download the Sun Java Wireless Toolkit for CLDC from
http://java.sun.com/products/ s j w t o o l k i t / d o w n l o a d . h t
m l Ensure that you have installed an appropriate

Java
SE environment

Run the installer, sun_java_wireless_toolkit- 2_5_1-linux.exe. Follow the
instructions provided by the installer.

III. install Sun Java ME Wireless Toolkit 2.5.1 (WTK 2.5.1) on the Windows
platform.

Download
the installer file i.e. netbeans_mobility-5_5_1-win.exe
Double
Click the icon of downloaded exe.

Now we are ready to create an application with Java Platform ME. Lets create a new project with the following steps:

Step 1: Go to Windows start panel and choose" Wireless Toolkit 2.5.1? as: Start > Programs > Sun Java Wireless Toolkit 2.5.1 for CLDC > Wireless Toolkit 2.5.1. The console window appears like this.

Step 2: Now, Click the ?New Project?
on the toolkit menu bar, then a new project box opens. Fill the appropriate Project name and
MIDlet class Name of your choice. After that, click Create Project button.

Step 3: Now, Click the ?New Project?
on the toolkit menu bar, then a new project box opens. Fill the appropriate Project name
(Roseindia)and MIDlet class Name(RoseindiaMID) of your choice. After that, click Create Project button.

Step 4: Then a ?Settings for project? window appears. For default settings, click OK. It is

Step 5: Next appears a window indicating the updated project settings saved in the Console.

Here is the code of this program:

import javax.microedition.lcdui.*;

import javax.microedition.midlet.MIDlet;
public class HelloWorld extends MIDlet implements CommandListener {
public void startApp() {
Display display = Display.getDisplay(this);

Form mainForm = new Form("HelloWorld");

mainForm.append("Welcome to the world of Mobile");

Command exitCommand = new Command("Exit", Command.EXIT, 0);

mainForm.addCommand(exitCommand);

mainForm.setCommandListener(this);

display.setCurrent(mainForm);

}

public void pauseApp () {}

public void destroyApp(boolean unconditional) {}

public void commandAction(Command c, Displayable s) {

if (c.getCommandType() == Command.EXIT)

notifyDestroyed();

}

}

Download source code.

Step 6:

Now we need to develop a simplest "Hello World" program in the directory
structure in src folder.

Step 7:
Now, Click the ?Open Project? on the toolkit menu bar,

Step 8:
Next click the ?Build? button from the toolkit menu bar. This causes the Sun Java Wireless Toolkit for CLDC to compile and preverify the Java source files. The whole build process is shown below.