Session2-J2ME development-environment

1Introduction to J2ME

Outline MIDP Building J2ME Apps- Tool J2ME Wireless Toolkit Demo MIDlet Programming

-- MIDlet Transition States

-- Midlet Skeleton

-- Two Level API

-- Displaying Objects

-- First Example – HelloWorld

-- Event Handling with Commands

-- Command Example


Mobile Information Device Profile (MIDP) Is a set of APIs that allow developers to control

mobile device-specific problems

– i.e. user interfaces, local storage and client application lifecycles etc.

MIDlets minimum requirements

– 96 x 54 pixels mono screen

– two-way wireless network

– input device (i.e. keypad)

– 128 KB ROM for CLDC/MIDP class and another 32 KB RAM for the KVM

Midlets are the most important and popular applications in the J2ME family.


MIDP


Building J2ME Apps- Tool Sun Java Wireless Toolkit 2.x for CLDC (The

newest version is 2.5.2 in Jan 2008) which can be downloaded from

http://java.sun.com/j2me/download.html


J2ME Wireless Toolkit Demo Launch the Wireless Toolkit:

– Start > Programs > Sun Java(TM) Wireless Toolkit 2.5.2 for CLDC

WTK already includes a set of demo programs ready to run.


J2ME Wireless Toolkit Demo Select menu item

File > Open Project ... Select UIDemo and

click Open Project.

The projects can be used as the templates of your applications.


J2ME Wireless Toolkit Demo Click the Build and then the Run buttons.


J2ME Wireless Toolkit Demo The main menu screen is shown up. You can choose

a program and select Launch to start the program.


MIDlet Programming Any MIDP application must extends MIDlet This is the MIDP equivalent of an applet, where

starting/stopping is under the control of the environment

Like Java applets, MIDlets have an application life cycle while running on a mobile device.


MIDlet Transition States Specifically, a MIDlet can be in one of three states as

shown:

Why do we need a Paused state?


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

public class MyApp extends MIDlet { public void startApp() { // start up code } public void pauseApp() { // we aren't showing any more }

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

Note that startApp(), pauseApp() and destroyApp() are abstract methods.

Midlet program must override these 3 methods even if not used.


Two Level API There are two areas of the API which you should be

concerned 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 events

All MIDlet applications need to import the necessary midlet and lcdui packages:

– import javax.microedition.midlet.*;

– import javax.microedition.lcdui.*;


Displaying Objects High-level Screens have a base class called

Displayable. To show something on a MIDP device, you need to

obtain the device’s display

– javax.microedition.lcdui.Display This Display class is the one and only display

manager for each active MIDlet and provides information about the device’s display capability.

Subclassed Displayable classes will fill the whole screen


Displaying Objects To show a Displayable object you must use the

setCurrent() 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.


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 ) {}}


Building the MIDlet Run the program KToolbar

Start>Programs>J2ME Wireless Toolkit 2.x>KToolbar

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


Building the MIDlet After pressing the Create Project Button, a directory

tree will be created for the project:


Building the MIDlet Use TextPad to create a source file HelloWorld.java

and save it under the directory src.


Building and Run the MIDlet Click the Build and then the Run buttons.


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

emulator. To provide a way to exit the program, you need to

use Commands. A command is like a button, it has a title, like "OK" or

"Cancel," and your application can respond appropriately when the user invokes the command.


Event Handling with Commands Displayable, the parent of all screen displays,

supports Commands.

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

Every Displayable keeps a list of its Commands. You can add and remove Commands using the following methods:

– public void addCommand(Command cmd)

– public void removeCommand(Command cmd)


Command Objects In J2ME, commands are commonly represented with

soft-buttons on the device. The following diagram shows two Command objects, one with the label "Exit" and one with label "View."

soft-buttons


Command Objects If there are too many commands to be shown on the

display, a device will create a menu to hold multiple commands. The following diagram shows how this might look.


Use Command objects The basic steps to process events with a Command

object are as follows:

1. Create a Command object.

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

3. Create and set a listener for the Form. Upon detection of an event, the listener will call the

method commandAction().


Create a Command To create a Command, you need to supply a label, a

type, 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 dialog

EXIT for exiting from the application.

HELP a request for on-line help.

ITEM specific to the items of the Screen or the elements of a Choice.

OK standard positive answer to a dialog

SCREEN an application-defined command

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


Create a Command To create a standard OK command, for example, you

would do this:

Command c = new Command("OK", Command.OK, 0);

To create a command specific to your application, you might do this:

Command c = new Command(

"Launch", Command.SCREEN, 0);

labeltype priority


Priority and Long Label Every command has a priority. Lower numbers indicate a higher priority. If you add a command with priority 0, then several more

with priority 1, the priority 0 command will show up on the screen directly. The other commands will most likely end up in a secondary menu.

MIDP also supports for long labels on commands. You can create a command with a short and long label

like this:

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

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


Responding to Commands Commands show up on the screen, but nothing

happens automatically when a user invokes a command.

You need to write an object called a listener which will be called when the user invokes any command in a Displayable.

The listener is an object that implements the CommandListener interface.

To register the listener with a Displayable, use the following method:

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

Listener per one Command.


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. Will

be called when any command in the Form is selected.



Another Command Example (Two Forms)

Launch

Exit

Exit

2nd Form

Go to First Form


Another Command Example (Two 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;

Command 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);


Another Command Example (Two 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 ); }


Another Command Example (Two Forms) public void pauseApp() { }

public void destroyApp(boolean unconditional) { }

public void commandAction(Command c, Displayable d) { if (c==exitCommand)

notifyDestroyed(); else if (c==firstFormCommand)

Display.getDisplay(this).setCurrent( f1 ); else

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


Simple Debugging System.out.print and System.out.println can be used

for debugging.

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

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

public void commandAction(Command c, Displayable d) { if (c==exitCommand)

notifyDestroyed(); else if (c==firstFormCommand) {

Display.getDisplay(this).setCurrent( f1 ); System.out.println(“1st Form is called");

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

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

}}

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Session2-J2ME development-environment

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