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Java ME

Introduction

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Java Editions

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Differences J2SE / Java ME (MIDP)

Java ME is mainly a subset of J2SE

But different UI-and event handling functionality

Less utility classes (only Vector and Hashtable, noLinkedLists, )

Code runs on both platforms?

general algorithms: yes

But the whole application needs porting

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Java ME Core Concepts

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Configuration

Defines Java Platform for different device

classes:

A configuration specifies the minimum set offeatures and Java class libraries that the

associated Java virtual machine (JVM)

should support.

J2ME offers two configurations Connected Limited Device Configuration (CLDC)

Connected Device Configuration (CDC).

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Configuration

CLDC Limited user interface

Low computing power (usually with a battery)

Network with low bandwidth

CDC

Network connection with high bandwidth,possibly persistent

Larger memory requirements

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CLDC CLDC is the J2ME configuration for

devices with less than 512 KB memory

footprint.

CLDC is for the kilo VM (KVM), which is

a highly optimized JVM meant for lower-

end, network-connected, battery-operateddevices based on 16-bit or 32-bit

microprocessors.

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CDC This configuration targets larger devices with

more capacity and with a network-connection,

like high-end personal digital assistants, andset-top boxes.

On the CDC configuration there are three different

defined profiles:

The Foundation Profile (JSR 219) The Personal Basis Profile (JSR 217) and

The Personal Profile (JSR 216)

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J2SE-CDC-CLDC

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Profiles

Extension and more detailed specificationfor a configuration

Contains APIsfor UI, event handling, datastorage, networks, timers,

Minimum requirements for devices (screen

size, input possibilities, ...) For mobile phones:Mobile Information

Device Profile (MIDP)

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Profiles

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Sample Architecture of a Phone

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Java ME Examples

Motorola/MOTORAZR V3

CLDC 1.0

MIDP 2.0 Nokia N70

CLDC 1.1

MIDP 2.0

SonyEricssonP990i CLDC 1.1

MIDP 2.0

CDC 1.0

Personal Profile

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Java ME Examples

Nokia N86 8MP

CLDC 1.1

MIDP 2.1

MSA (Subset)

Amazon Kindle 2

CDC

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MIDlet MIDP does not support the running of

applications that use a static main method as

their entry point, nor calling the System.exit

method in order to terminate.

Instead, we use a MIDlet, which is a MID

Profile application.

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MIDlet Every application must extend

javax.microedition.midlet.MIDletclass to

allow the application management software

to:

control the MIDlet

be able to retrieve properties from theapplication descriptor

notify and request state changes

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MIDlet The extending class is the main class of the

application.

The MIDlet class defines abstract methods

that the main class implements (for

example: startApp(), destroyApp(),

notifyDestroyed()).

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MIDlet Suite One or more MIDlets are packaged together

into aMIDlet suite, composed of:

JAR (Java archive) file

JAD (Java Application Descriptor) file

All the user-defined classes and resources

required by the suite's MIDlets must be inthe JAR file.

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Creating a MIDlet import javax.microedition.midlet.*;

import javax.microedition.lcdui.*;

public class HelloMidlet extends MIDlet {private Display display;TextBox box = null;public HelloMidlet() {}public void startApp() {

display = Display.getDisplay(this);box = new TextBox("Simple Example", "Hello World", 20, 0);display.setCurrent(box);

}

public void pauseApp() {}public void destroyApp(boolean unconditional) {}

}

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Event Handling

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Listener Implement the Listener-Interface to get

informed:

CommandListener: commandAction()Notificationwhen e.g. a menu item has been selected

ItemCommandListener: commandAction()Used for

events for individual items

ItemStateListener: itemStateChanged()When an UIelement has been changed

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Command-Types

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Command-Exit Class HelloWorldMIDlet:

implements CommandListener

Define new command (member variable):

private Command cmdExit;

Create it in the constructor:

cmdExit= new Command(Exit, Command.EXIT, 1);frmMain.addCommand(cmdExit);

frmMain.setCommandListener(this);

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Command Handling Method defined in the base class CommandListener:

public void commandAction(Commandc,

Displayable d){

if (c == cmdExit)

{destroyApp(true);

notifyDestroyed();

}

}

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Discussion

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