J2ME_Introduction

8/7/2019 J2ME_Introduction

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Introduction to J2ME

ESPRIT Saif [email protected]


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Java 2 Platform Micro Edition

(J2ME)Java platform for small devices

A subset of J2SE

Released mid June 1999

Target devices:

-

2Introduction to J2ME

Mobile phones, smart phones

PDAs (inc PocketPCs)

TVs, VCRs, CD playersAlmost every mobile phone support J2ME

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J2ME Phones

3Introduction to [email protected]


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J2ME Phones (Up to 15 Jan 2008)http://developers.sun.com/mobility/device/pub/device/list.do?sort=manufacturer&filterIds=61&page=1



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3 Java Platforms

Java 2 Platform


Standard Edition

(J2SE)

Enterprise Edition

(J2EE)

Micro Edition

(J2ME)

Standard desktop &

Workstation Applications

Heavy duty server

systems

Small & memory

Constrained devices

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J2ME ArchitectureTo increase the flexibility of design, the J2MEconsists of two distinct layers:

Configurations and Profiles

Configuration


range of devices with similar capabilities

Profile

Provides capabilities, on top of configuration, for aspecific device type

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J2ME Architecture

Two types of J2MEconfigurations

1. Connected DeviceConfiguration

2. Connected Limited

J2ME

Profile

Profile


Device ConfigurationJ2ME

Libraries

JavaVirtual Machine

Configuration

CDC, orCLDC

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CLDC vs CDCCLDC

160 Kbytes to 512 Kbytes of total memoryavailable16-bit or 32-bit processorLow power consumption and often operatingwith battery power


Connectivity with limited bandwidth.CDC

2Mbytes or more memory for Java platform

32-bit processorHigh bandwidth network connection, mostoften using TCP/IP

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CLDC



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Mobile Information Device Profile

(MIDP)Is a set of APIs that allow developers to controlmobile device-specific problems

i.e. user interfaces, local storage and clientapplication lifecycles etc.MIDlets minimum requirements


two-way wireless network input device (i.e. keypad) 128 KB for CLDC/MIDP class and another 32 KB

for the KVMMidlets are the most important and popularapplications in the J2ME family.

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MIDP



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Building J2ME Apps- ToolWe will use Sun Java Wireless Toolkit 2.x forCLDC (The newest version is 2.5.2 in Jan 2008)which can be downloaded fromhttp://java.sun.com/j2me/download.html



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J2ME Wireless Toolkit DemoLaunch the Wireless Toolkit: Start > Programs > Sun Java(TM) Wireless Toolkit

2.5.2 for CLDC


WTK already includes a set of demo programs readyto run.

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J2ME Wireless Toolkit DemoSelect menu item

File > Open Project ...Select UIDemo andclick Open Project .


The projects can be used as the templates of yourapplications.

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J2ME Wireless Toolkit DemoClick the Build and then the Run buttons.



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J2ME Wireless Toolkit DemoThe main menu screen is shown up. You can choosea program and select Launch to start the program.



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MIDlet ProgrammingAny MIDP application must extends MIDlet

This is the MIDP equivalent of an applet, wherestarting/stopping is under the control of theenvironment

Like Java applets, MIDlets have an application lifec cle while runnin on a mobile device.


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MIDlet Transition StatesSpecifically, a MIDlet can be in one of three states asshown:


Why do we needa Paused state?

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

public class MyApp extends MIDlet {

public void startApp() {// start up code

}

Note that startApp(), pauseApp()and destroyApp() are abstractmethods.

You Midlet program mustoverride these 3 methods eventhough you are not do anythingin it.


// we aren't showing any more

}

public void destroyApp(boolean unconditional) {// clean up

}}

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Two Level APIThere are two areas the API which you should beconcerned with - the high and low-level API.

High-Level Provides input elements such as, text fields, choices, and form

Low-level is for drawing on Canvases and capturing


keyed eventsAll MIDlet applications need to import the necessarymidlet and lcdui packages: import javax.microedition.midlet.*; import javax.microedition.lcdui.*;

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Displaying ObjectsHigh-level Screens have a base class calledDisplayable .

To show something on a MIDP device, you need toobtain the devices display javax.microedition.lcdui.Display class.


manager for each active MIDlet and providesinformation about the devices display capability.

Subclassed Displayable classes will fill the whole

screen

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Displaying ObjectsTo show a Displable object you must use thesetCurrent() method on the Display object.Form mainForm = new Form ("First Program ");Display display = Display.getDisplay(this);

display .setCurrent (mainForm);


Note that Form is a Displayable subclass.

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First Example - HelloWorldimport javax.microedition.midlet.*;import javax.microedition.lcdui.*;

public class HelloWorld extends MIDlet {

public HelloWorld() {}

public void startApp() {


Form form = new Form( "First Program" );form.append( "Hello World" );Display.getDisplay(this).setCurrent ( form );

}

public void pauseApp() {}

public void destroyApp( boolean unconditional ) {

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Building the MIDletRun the program KToolbarStart >Programs >J2ME Wireless Toolkit 2.x >KToolbar

Click on New Project and enter the Project name andclass name as shown below



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Building the MIDletAfter pressing the Create Project Button, a directorytree will be created for the project:



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Building the MIDletUse TextPad to create a source file HelloWorld.javaand save it under the directory src .



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Building and Run the MIDletClick the Build and then the Run buttons.



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How can the program exit?The program can not exit unless you close theemulator.

To provide a way to exit the program, you need touse Commands.A command is like a button, it has a title, like "OK" or"Cancel," and our a lication can res ond


appropriately when the user invokes the command.

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Event Handling with CommandsDisplayable, the parent of all screen displays,supports Commands .

The device determines how the commands areshown on the screen or invoked by user.

Every Displayable keeps a list of its Commands. You


can a an remove omman s us ng e o ow ngmethods:

public void addCommand(Command cmd)

public void removeCommand(Command cmd)

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Command ObjectsIn J2ME, commands are commonly represented withsoft-buttons on the device. The following diagramshows two Command objects, one with the label"Exit" and one with label "View."


soft-buttons

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Command ObjectsIf there are too many commands to be shown on thedisplay, a device will create a menu to hold multiplecommands. The following diagram shows how this

might look.



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Use Command objectsThe basic steps to process events with a Commandobject are as follows:

1. Create a Command object.

2. Add the Command to a Form (or other GUIobjects TextBox, List, or Canvas).


. .

Upon detection of an event, the listener will call themethod commandAction().

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Create a CommandTo create a Command, you need to supply a label, atype, and a priority.

The type is used to signify a commonly used

command. It helps device to arrange the commands.Command Meaning

BACK returns to the previous screen.


CANCEL standard negative answer to a dialogEXIT for exiting from the application.

HELP a request for on-line help.

ITEM specific to the items of the Screen or the elements of aChoice.

OK standard positive answer to a dialog

SCREEN an application-defined command

STOP A command that will stop some currently runningprocess, operation, etc.

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Create a CommandTo create a standard OK command, for example, youwould do this:Command c = new Command("OK", Command.OK, 0);

labeltype priority


To create a command specific to your application,you might do this:Command c = new Command(

"Launch", Command.SCREEN, 0);

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Priority and Long LabelEvery command has a priority.

Lower numbers indicate a higher priority.

If you add a command with priority 0, then severalmore with priority 1, the priority 0 command will showup on the screen directly. The other commands willmost likel end u in a secondar menu.


MIDP also supports for long labels on commands.You can create a command with a short and longlabel like this:

Command c = new Command("Run", "Run simulation" ,Command.SCREEN, 0);

The device decides which label it will use based onthe available screen space and the size of the labels.

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Responding to CommandsCommands show up on the screen, but nothinghappens automatically when a user invokes acommand.

You need to write an object called a listener whichwill be called when the user invokes any command ina Displayable.


The listener is an object that implements theCommandListener interface.To register the listener with a Displayable, use thefollowing method:

public void setListener (CommandListener l)Note it is one Listener per Displayable, NOT oneListener per one Command.

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

public class Commander extends MIDlet implements CommandListener {public void startApp() {

Displayable d = new Form( "Test Command" );Command c = new Command("Exit", Command.EXIT, 0);d.addCommand(c);d.setCommandListener(this);


Display.getDisplay(this).setCurrent(d);}

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

public void commandAction (Command c, Displayable s) {notifyDestroyed();}

} Abstract method of CommandListener. Willbe called when any command in the Form isselected.

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Another Command Example


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Another Command Example

(Two Forms)Launch

Exit


Exit

2nd Form

Go to First Form

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Another Command Example (Two


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

public class Commander2 extends MIDlet implements CommandListener {Display display = null;Form f1 = null;Form f2 = null;


// commandCommand firstFormCommand =

new Command("1st Form", "Go to First Form", Command.SCREEN, 0);Command secondFormCommand =

new Command("2nd Form", "Go to Second Form", Command.SCREEN, 0);Command exitCommand =new Command("Exit", Command.EXIT, 1);

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Forms)public void startApp() {display = Display.getDisplay(this);

f1 = new Form( "Form 1" );

f1.append( "This is Form No. 1" );f1.addCommand(secondFormCommand);f1.addCommand(exitCommand);f1.setCommandListener(this);


f2 = new Form( "Form 2" );f2.append( "This is Form No. 2" );f2.addCommand(firstFormCommand);f2.addCommand(exitCommand);f2.setCommandListener(this);

display.setCurrent( f1 );}

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Forms)public void pauseApp() {}

public void destroyApp(boolean unconditional) {

}

public void commandAction(Command c, Displayable d) {String label = c.getLabel();


a e .equa s " x t"notifyDestroyed();

} else if (label.equals("1st Form")) {Display.getDisplay(this).setCurrent( f1 );

} else {Display.getDisplay(this).setCurrent( f2 );

}}

}


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Simple DebuggingSystem.out.print and System.out.println can be usedfor debugging.

When run in the simulator, the output is put on theconsole, not the phone.

public void commandAction(Command c, Displayable d) {


.

if (label.equals("Exit")) {notifyDestroyed();} else if (label.equals("1st Form")) {

System.out.println("1st Form is called");display.setCurrent( f1 );

} else {System.out.println("2nd Form is called");display.setCurrent( f2 );

}

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J2ME_Introduction