Java 2 Platform,Micro Edition (J2ME)

By Xiaorong Wang

Agenda

IntroductionCLDC and MIDPProgramming with CLDC/MIDPSummary and Resources

JavaTM 2 Platform

Java 2 Enterprise Edition (J2EE)Java 2 Standard Edition (J2SE)Java 2 Micro Edition (J2ME)

What is J2ME?Java 2 Micro Edition (J2ME) is Sun’s version of Java aimed at machines with limited hardware resourcesLimited screen size, memory, and processing powerPDAs, cell phones, other consumer electronic and embedded devices

ConfigurationThe foundation of J2ME is configurationsA configuration defines Java APIs and a specification of a java virtual machineA configuration defines a minimum Java platform for a family of devices

Two Types of Configuration

Connected device configuration (CDC)Connected limited device configuration (CLDC)

The Architecture of J2ME

Profiles

On top of the configurations are the profilesMobile Information Device Profile (MIDP)The foundation configuration is CLDCMIDP is a profile for mobile information

devices, such as: cellular phones, two-way pagers, and PDAs

Agenda

IntroductionCLDC and MIDPProgramming with CLDC/MIDPSummary and Resources

Overview

Native OS & AppsNative Interface

KVM OS Interface

CLDC (Java)KVM (C)

Native C

all

CLDC Interface

J2M

E MIDPMIDP Interface

Memory

Java Application Manager

MIDlet 1 MIDlet 2

Connected, Limited Device Configuration

(CLDC)Targets at devices with160KB to 512KB total memory available

for Java technologyLimited power (often battery)Limited connectivity to a network (often

wireless)Extremely constrained UI, small screens

CLDC Language and VM Compatibility

Full Java Language and Java Virtual Machine Specification compatibilityLanguage-level different: Floating point not supported in CLDC 1.0CLDC libraries are limited

CLDC LibrariesClasses inherited from Java 2 Platform, Standard Edition (J2SE version 1.3) are in packages:java.lang.*java.util.*java.io.*

New classes introduced by CLDC:javax.microedition.*

MIDP: OverviewMobile Information Device Profile (MIDP) coversTimersApplication lifecyclePersistent storageNetworkingUser interface

MIDP: LibrariesClasses inherited from J2SE:java.lang.*: IllegalStateExceptionjava.util.*: Timer, TimerTask

New classes introduced by MIDP:javax.microedition.rms.*javax.microedition.midlet.*javax.microedition.io.*javax.microedition.lcdui.*

Agenda

IntroductionCLDC and MIDPProgramming with CLDC/MIDPSummary and Resources

Steps Flowchart

Edit Source CodeEdit Source Code

Compile and PreverifyCompile and Preverify

EmulatorEmulator

*.java

*.class

ArchiveMIDlet

DownloadTo Device

*.jar*.class

Resources:text, image,…

Manifest File

import javax.microedition.midlet.*;import javax.microedition.lcdui.*;

public class HelloMidlet extends MIDlet implements CommandListener{ // Initialize the Midlet Display variable private Display midletDisplay; // Initialize a variable for the doneCommand private Command doneCommand;

public HelloMidlet() { // Retrieve the display from the static display object midletDisplay = Display.getDisplay(this); // Initialize the doneCommand doneCommand = new Command("DONE", Command.SCREEN, 1); }

public void startApp(){ // Create the TextBox containing the "Hello Midlet World!!" message TextBox textBox = new TextBox("Hello Midlet", "Hello Midlet World!!", 256, 0); // Add the done Command to the TextBox textBox.addCommand(doneCommand); // Set the command listener for the textBox to the current midlet textBox.setCommandListener( (CommandListener) this); // Set the current display of the midlet to the textBox screen midletDisplay.setCurrent(textBox); }public void pauseApp(){}public void destroyApp(boolean unconditional){}

/* The commandAction method is implemented by this * midlet to satisfy the CommandListener interface and * handle the done action. */ public void commandAction(Command command, Displayable screen) { // If the command is the doneCommand if (command == doneCommand) { // Call the destroyApp method destroyApp(false); // Notify the midlet platform that the midlet has completed notifyDestroyed(); } }}

Life Cycle Of Midlet

PausedPaused

ActiveActive

DestroyedDestroyedpauseApp()

startApp()

destroyApp()

destroyApp()

New()

Developing Tools

Java 2 Standard Edition, version 1.3.0 or higher (http://java.sun.com/j2se/1.3)

J2ME Wireless Toolkit (http://java.sun.com/products/j2mewtoolkit)

Using the KToolBar

KToolBar

Building the MIDlet

Compile the Java source filesPreverify the class filesPackage:Jar up the verified class filesJar up the resource files

Running the Midlet

Agenda

IntroductionCLDC and MIDPProgramming with CLDC/MIDPSummary and Resources

SummarySome of the companies that making

J2ME products: Research in Motion (RIM): Blackberry

two-way handhelds Nokia: Mobile phones NEXTEL: Mobile phones – i85s and

i50sx American Express: Java Card for its

Blue credit cards

Resources

http://java.sun.com/j2mehttp://www.javaworld.com