introduction to j2me

Introduction to J2ME

2Introduction to J2ME

Java 2 Platform Micro Edition (J2ME) Java platform for small devices A subset of J2SE Released mid June 1999 Target devices:

– Two-way pagers

– Mobile phones, smart phones

– PDAs (inc PocketPCs)

– TVs, VCRs, CD players Almost every mobile phone support J2ME

J2ME Phones

3 Java Platforms

Java2 Standard Edition

(J2SE)

Java2 Enterprise Edition

(J2EE)

Java2 Micro Edition

(J2ME)

Java 2 Platform

Standard desktop &Workstation Applications

Heavy duty serversystems

Small & memory Constrained devices

J2ME Architecture To increase the flexibility of design, the J2ME

consists of two distinct layers:

Configurations and Profiles

Configuration

– Defines the minimum Java technology for a broad range of devices with similar capabilities

Profile

– Provides capabilities, on top of configuration, for a specific device type

J2ME Architecture

Two types of J2ME configurations

1. Connected Device Configuration

2. Connected Limited Device Configuration

J2ME Profile

J2ME Libraries

JavaVirtual Machine

Profile

Configuration

CDC, orCLDC

CLDC vs CDC CLDC

160 Kbytes to 512 Kbytes of total memory available

16-bit or 32-bit processor

Low power consumption and often operating with battery power

Connectivity with limited bandwidth. CDC

2Mbytes or more memory for Java platform

32-bit processor

High bandwidth network connection, most often using TCP/IP

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 for CLDC/MIDP class and another 32 KB for the KVM

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

Building J2ME Apps- Tool We will use 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 extend 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.

You Midlet program must override these 3 methods even though you are not doing anything in it.

Two Level API There are two levels of the API

– 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 class. 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 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

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 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) { String label = c.getLabel(); if (label.equals("Exit")) { notifyDestroyed(); } else if (label.equals("1st Form")) { 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 commandAction(Command c, Displayable d) { String label = c.getLabel(); 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 ); }

J2ME User Interface I

Major classes in the lcdui package

To be discussed in this lecture

TextBox The simplest type of screen is the TextBox. TextBox allows the user to enter a string. Text input is a difficult task on mobile phones. Many

devices only have a numeric keypad, so entering a single character is a matter of one, two, three or four button presses.

A good MIDlet requires minimal user input.

an email TextBox

TextBox A TextBox is created by specifying four parameters:

public TextBox(String title, String text, int maxSize, int constraints)

The title is used as the screen title The text and maxSize determine the initial text and maximum

size of the text box. The constraints are used to restrict the user's input.

– ANY : allows any type of input.

– NUMERIC : restricts the input to integers.

– DECIMAL : allows numbers with fractional parts.

– PHONENUMBER : requires a telephone number.

– EMAILADDR : input must be an e-mail address.

– URL : input must be a web address.

TextBox Constraints The devices don't allow invalid input; for example, a NUMERIC

TextBox doesn't allow you to enter alphabetic characters. Constraints may be combined with the flags listed below. Constraints limit the behavior of users, while flags define the

behavior of the TextBox. The available flags are:

PASSWORD : characters are not shown when entered; generally, they are represented by asterisks.

UNEDITABLE : indicates text that cannot be edited.

TextBox FlagsSENSITIVE : indicates that text should not be stored. Some input

schemes store input from the user for later use in autocompletion. This flag indicates that the text should not be saved or cached.

NON_PREDICTIVE : indicates that you are expecting the user to enter text that any text-predicting input scheme will probably not be able to guess. For example, if you're expecting the user to enter an order number like Z51002S, you would use this flag to tell the input scheme to not bother trying to predict the input.

INITIAL_CAPS_WORD : is used for input where each word should be capitalized.

INITIAL_CAPS_SENTENCE indicates input where the first character of each sentence should be capitalized.

NOT all of these settings may be functional in all devices.

TextBox Flags The flags may be combined with any of the other

constraints using the OR operator ( | ). For example, to create a TextBox that asks the user

to enter a number password, you would do something like this:

Displayable d = new TextBox( "PIN", "", 8, TextField.NUMERIC | TextField.PASSWORD);

Password Be careful in using PASSWORD. For every character you enter, the password field

shows an asterisk or some other symbol. On mobile phones and other small devices, security

is less of a concern because the screens are smaller and much more difficult to read than a typical desktop monitor.

Example: Accept a string from TextBox and echo it

One TextBoxTwo Commands - Exit and GreetOne CommandListener

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

public class TextBoxTest extends MIDlet implements CommandListener {

private Display display; private TextBox tbClip; private Command cmExit; private Command cmGreet;

public TextBoxTest() { cmExit = new Command("Exit", Command.EXIT, 0); cmGreet = new Command("Greet", Command.SCREEN, 1);

tbClip = new TextBox("Textbox Test", "", 20, TextField.ANY); tbClip.addCommand(cmExit); tbClip.addCommand(cmGreet); tbClip.setCommandListener(this); }

Example public void startApp() { display = Display.getDisplay(this); display.setCurrent(tbClip); }

public void destroyApp(boolean unconditional) { }

public void commandAction(Command c, Displayable s) { if (c == cmExit) notifyDestroyed(); else if (c == cmGreet) System.out.println("Hello " + tbClip.getString()); }}

Alerts An Alert is essentially a simple dialog box. There are

two types of Alert:

– modal, which displays the dialog until acknowledged by the user, and

– timed, which is displayed for a specified number of seconds.

The constructors for an Alert are shown below:

Alert(String title)

Alert(String title, String alertText, Image alertImage, AlertType alertType)

Alerts The AlertType class provides five types: ALARM,

CONFIRMATION, ERROR, INFO, and WARNING.

The AlertType component uses sound, rather than an image, to notify the user of an event.

By default, timed Alerts are created using a default timeout value; you can find out the default value by calling getDefaultTimeout().

To set the timeout value to five seconds, you could do this:

alert.setTimeout(5000);

If you want a modal alert, use the special value FOREVER:

alert.setTimeout(Alert.FOREVER);

Example Five Alerts The following example, FiveAlerts, shows all types of alert. The display has six commands (5 Alerts + 1 Exit).

The default timeout value is 2000ms = 2 seconds. i.e. The Alert screen will dismiss after 2 seconds.

Example - Five Alerts The Error Alert will stay until the user dismiss it. The Info Alert will stay for on the screen for 4

seconds. After the alert dismisses, the display will return to the

previous screen public void setCurrent(Alert alert)

or go to next screen if the following setCurrent is used:

public void setCurrent(Alert alert, Displayable nextDisplayable)

Example - Five Alertsimport javax.microedition.midlet.*;import javax.microedition.lcdui.*;

public class FiveAlerts extends MIDlet implements CommandListener { private Display disp;

private Form f; private Alert alarm; private Alert confirm; private Alert error; private Alert info; private Alert warning; private Command alarmCommand, confCommand, errCommand, infoCommand, warnCommand, exitCommand; public FiveAlerts() { alarmCommand = new Command("Alarm", Command.SCREEN, 1); confCommand = new Command("Confirm", Command.SCREEN, 1); errCommand = new Command("Error", Command.SCREEN, 1); infoCommand = new Command("Info", Command.SCREEN, 1); warnCommand = new Command("Warning", Command.SCREEN, 1); exitCommand = new Command("Exit", Command.EXIT, 0);

f = new Form("Five Alerts"); f.addCommand(alarmCommand); f.addCommand(confCommand); f.addCommand(errCommand); f.addCommand(infoCommand); f.addCommand(warnCommand); f.addCommand(exitCommand); f.setCommandListener(this);

alarm = new Alert("Alarm", "Your payment is due today.", null, AlertType.ALARM); confirm = new Alert("Confirmation", "Do you want to proceed?", null, AlertType.CONFIRMATION); error = new Alert("Network error", "A network error occurred. Please try again.", null, AlertType.ERROR);

info = new Alert("About", "This program is used to demonstrate use of Alert." + " It will displayed for 4 seconds", null, AlertType.INFO); warning = new Alert("Warning", "Memory is low.", null, AlertType.WARNING);

System.out.println("DefultTimeout = " + alarm.getDefaultTimeout());

error.setTimeout(Alert.FOREVER); info.setTimeout(4000); // display for 4 seconds }

public void startApp() { disp = Display.getDisplay(this); disp.setCurrent(f); }

public void destroyApp(boolean unconditional) {}

public void commandAction(Command c, Displayable s) { if (c == alarmCommand) disp.setCurrent(alarm); else if (c == confCommand) disp.setCurrent(confirm); else if (c == errCommand) disp.setCurrent(error, f); else if (c == infoCommand) disp.setCurrent(info, f); else if (c == warnCommand) disp.setCurrent(warning, f); else if (c == exitCommand) notifyDestroyed(); }}

DISMISS_COMMAND - Done MIDP implementation automatically supply a DISMISS_COMMAND to

dismiss a modal alert. For example, the Sun's emulator provides a Done command mapped

to a soft button.

You can replace the default DISMISS_COMMAND by using the addCommand() method.

When the application first adds a command to an Alert, DISMISS_COMMAND is implicitly removed.

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