Programming Mobile and Wireless Devices using J2ME

Molde University College INF 245 Fall 2007 OBø

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Programming Mobile and Wireless Devices

using J2ME

Ola Bø


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Motivation

added nov 2005


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Content

Overview over the J2ME-plattform Close up of technologies for Mobile and

Wireless applications CLDC Connected Limited Device Configuration MIDP Mobile Information Device Profile


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J2ME in the Java landscape

(Source Sun Microsystems Inc.)

Smartphones

Set top boxes


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Problem and solution The problem is device heterogeneity

Memory, Screen, Filesystem, Available storage for libraries, Camera, GPS, ... differs widely

That means the Java Platform can not be the same on all devices

Solution: Different configurations and profiles in different devices Extensions called JSRs

Nightmare Programming an application aimed at a wide selection of

heterogeneous devices is arduous even with J2ME. Making the same application ”native” is probably far worse. Even if a device has a certain functionality (GPS, Camera, MP3

player...), the functionality can only be controlled from a J2ME program through a working JSR library in device firmware. No library – no control


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J2ME Configurations

A configuration sets a standard for the available Java technology on a class of devices CLDC Connected Limited Device Configuration

Limited devices (160-512k RAM total for Java) Mobile phones and PDA’s

CDC Connected Device Configuration Set top boxes High end wireless devices

add material from mikkonen


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J2ME Profiles

MIDP Mobile Information Device Profile Foundation Profile (non gui networked device) Personal basis, Personal and RMI Profiles

add material from mikkonen


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JCP Java Community processJSR Java Specification Requests

JCP organises further standardisation of Java

When new requirements emerges a new JSR is created

Requirement work is driven by people from various industrial companies

JSR makes the extension of Java flexible

Implementation of new JSRs in mobile devices gives steadily increased in the potential functionality of Java devices

The specifications are available at jcp.org


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Four Generations Nokia2003 2005

2002 2004


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Top end devices 2007

Nokia E90 Communicator

Sony Ericsson P1


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J2ME for mobile and wireless devices

Special libraries for mobile and wireless devices: GUI, storage

A subset of the Java libraries adapted to a lowest common denominator for mobile devices

The virtual machine – corresponding to JVM in standard Java


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What does CLDC contain Core java language and library Libraries for i/o and communication Security Internationalization The content is partly inherited from J2SE

java.lang.*, java.util.*, java.io.*and partly new java.microedition.*

And what does CLDC not contain: UI, application life cycle, Persistence, and special

interfaces for the device.


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CLDC is limited

That means some Java language features are missing

CLDC 1.0 No Floating point No Finalization, No Thread Groups, No JNI Limited Error Handling

CLDC 1.1 Floating point INCLUDED


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CLDC based classes need special handlig Preverification and

Package steps are mandatory for classes to be run over CLDC. Supports faster start

up of CLDC based apps.

Preverification and packaging may be done using Command line tools KToolbar in the WTK An IDE

Packaging

Myapp.jar


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CLDC System Properties

Can ask for property to ascertain what profile we have on the device

Can adapt the application to the capabilities of the CLDC and MIDP present in the device java.lang.System.getProperty("microedition.profiles"), will

return "MIDP-1.0" if this is the profile implemented in the phone.

Other possible properties are for example: microedition.platform microedition.encoding microedition.configuration


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MIDP 1.0 MIDP 1.0 covers:

Application Life Cycle Toolkit for user interface – display and input Device independent persistent data storage GCF based networking using HTTP 1.1

New standard MIDP 2.0 released nov. 2002 There will still be an installed base of MIDP 1.0

devices for some time. New possibilities in MIDP 2.0 may be enticing


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MIDP applications AKA midlets

A MIDP application is called a MIDlet Must extend the MIDlet class

A midlet suite is a bundle of midlets. can access same persistent data

Packaging Midlet suites are packaged in JAR files

The preverified class files in the suite Resource files (for example icons,

sounds) A manifest with application properties

Each JAR file corresponds to a JAD file describing its contents for deployment (name, description, version etc.)

JAR File


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Provisioning

Provisioning is getting the application into the device. Several scenarios for download: "Over The Air (OTA) " using HTTP over wireless

protocols By device synchronization software from a

desktop computer using serial, usb, IR or bluetooth

Not standardized in MIDP 1.0, OTA provisioning standardized in MIDP 2.0


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Midlet Application Skeleton

All MIDlets have this common skeleton Constructor called once startApp() called at start or

after pause pauseApp() called at

pause – timer events may be received

destroyApp() called when application is terminated


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Application LifeCycle

Paused

Active

Destroyed

StartApp

DestroyApp

DestroyApp

PauseApp

Initialised and ready to run

Resources acquired, application running

All resources released, All threads stopped


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Application LifeCycle methods(source javadoc for class javax.microedition.MIDlet, consult documentation for details)

Called by device Called by midletstartApp()*

Tells MIDlet it has entered the active state and can start working

resumeRequest()

Tells device midlet want to continue

pauseApp()*

Tells MIDlet it has been paused

notifyPaused()

Tells device midlet wants to pause

destroyApp(boolean)*

Tells MIDlet to release resources and stop threads

notifyDestroyed()

Tells device midlet wants to be destroyed. All resources and threads should already have been released

* abstract methods, to be implemented by programmer when subclassing MIDlet.


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MIDP 1.0 High Level User Interface Windowing not appropriate on limited devices Interface using whole Screens – four kinds

1. Alert - message2. TextBox – Editable or non-editable textbox3. Form4. List Screens have a title Commands can be added to screens

How commands appear is device dependent (Soft key, Menu item, ... )

Commands must be handled by class implementing the CommandListener Interface

(for further details see javax microedition.lcdui.Command)

Show a screen by using display.setCurrent(myForm)


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TextBox, a high level screen

Used to show or edit a text on the whole screen Input constraints specifies content type and other

aspects of the TextBox ANY EMAILADDR NUMERIC PHONENUMBER URL DECIMAL How are these input constraints related to the limited input

capabilities of mobile devices and to the T9 algorithm?

•PASSWORD•UNEDITABLE (MIDP 2.0)•SENSITIVE (MIDP 2.0)•NON_PREDICTIVE(MIDP 2.0)•INITIAL_CAPS_WORD(MIDP 2.0)•INITIAL_CAPS_SENTENCE(MIDP 2.0)


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Texbox CodeTitle Initial text

Command

Soft Key

Maximumtext length

Constraint


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MIDP UI – Alert a high level screen

Used to show a message A timeout can be set An image can be added A gauge can be added showing progress (MIDP

2.0) Is displayed by a special version of

display.setCurrent(Alert,Screen) The second parameter is what to display when alert

screen gone. (display.getCurrent can be used here)


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Alert and CommandListenerCode


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List

Uses the whole screen for a list Three use scenarios depending on

Choice.type1. IMPLICIT selecting invokes command

2. EXCLUSIVE selecting one deselects previous

3. MULTIPLE selecting more than one possible


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Code for Implicit List


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Code for Multiple List


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Code for implicit list

String[] elements = { ... }; //Menu items as List elements

List menuList = new List("Menu", List.IMPLICIT, elements, null);

Command selectCommand = new Command("Open", Command.ITEM, 1);

menuList.setSelectCommand(selectCommand);

menuList.setCommandListener(...);


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Form A form displays a number of Items Items can be:

Texfield for flexible text entry StringItem for text display ImageItem for image display DateField for date display and entry Choicegroup selectable list of text and/or images Gauge a bargraph display of a numeric quantity CustomItem an item you can develop Spacer, a layout assistance item

Commands can be connected to Items Layout is specified both in form and in items

Layout directives are hints only. If form too high for display, it will scroll

What Items where used on the form shown? ImageItem, StringItem and two Textfields

High Level Interface – an Overview

Screen

TextBox

textmaxsizeconstraints

Alert

titletexttypeimage

List

listtType

append()getSelectedIndex()

Displayable

addCommand()addCommandListener()

Form

append()

Item


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Same Form, different devices, different results


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Form Code


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High level UI – Form an overview

ChoiceGroup ImageItem GaugeStringItem Spacer CustomItem

Form

append()

Item

labellayout

TextField

For text entry For text presentation only

Multiple or single choice between texts/images

Display of an image

Often used as a progress indicator

Used for adjusting space between other items

Make your own item


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Guidelines for UI Design HCI on mobile and wireless devices a challenge!

Why? Use simple forms with few Items

Remember: Small screen size, mobile context of use Can you avoid scrolling?

Minimize input, use RMS to store user settings Use static form content

Small screen means small changes not easy to spot Use uniform appearance for easy learning Always provide commands like OK, BACK and EXIT on screen

use uniform command configuration on all forms to ease learning and use

Use soft keys rather than on-screen keys Use Threads and Gauges to avoid UI-blocking during network IO

improves user experience


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Top 10 Usability Guidelines for Enterprise Applications (Nokia 2004) http://www.forum.nokia.com/main/0,,23_56,00.html#tips

Provide a clear navigation model Core features of the application should be available from the main view. Navigation model should be focused on the main tasks. Advanced functionality should be hidden from novice users.

Use familiar language Terminology familiar to target users should be used instead of technical terminology. Terminology should be consistent with the Series 60 UI style. Target users’ native language should be used.

Hide the complexity of connectivity Short network coverage problems should not stop or cause loss of users' work Connection status should be displayed clearly. Synchronization should be automatic but under user control.

Provide useful feedback Let the user know if an action was succesful or not. If processing takes more than 0.5 seconds, indicate that something is happening.

Be consistent with controls Minimize errors and the need for learning by using softkeys as in the Series 60 UI style Build shortcuts for advanced users, use shortcuts similar to other applications.


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More guidelines Provide a simple Options menu

Navigation key default action(s) should also be available in an Options menu. Sort items in the Options menu according to Series 60 UI Style Guide. Main actions should be available without scrolling.

Use tabs wisely The most essential functionality should be provided in the first tab. Underlying tabs can

be used to hide advanced functionality. If more than five tabs are needed, use a list for accessing the tabs (see the Settings

application). Text is preferable to icons in tab titles.

Make entering information easy Instead of text entry, prefer alternative forms of information entry, such as selecting

from a list or capturing images. Offer reasonable default values.

Information presentation Display the most relevant information first. Essential information should not be displayed with icons only. Use colors and symbols for highlighting and grouping items.

Provide Help Context-sensitive help should be provided in the application. More detailed help should be provided on a Web site or in the user guide.


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Low Level UI – CanvasLi and Knudsen Chapter 4

Canvas is a displayable that is completely controlled by program

An application can combine canvases and screens A list to choose racing track A canvas to do the racing

Methods to handle game actions and pointer events A Canvas must be subclassed! paint method for painting must be implemented The paint method provides a Graphics object having

methods for painting


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Canvas methodsEvent delivery methods used to send events to application. Event delivery

methods are called seriallyshowNotify() // called before canvas becomes visible

hideNotify() // called after canvas has been hidden

keyPressed(), keyRepeated(), keyReleased()

pointerPressed(), pointerDragged(), pointerReleased()

(hasPointerEvents() checks if device supports a poiner)

paint() // tells app to paint screen again. (Not to be called by app)

sizeChanged()

Methods used by application to learn the meaning of the key pressedgetKeyCode() (returns KEY_NUM0..KEY_NUM9, KEY_STAR,...)

getGameAction() (returns UP, DOWN,.., FIRE, GAME_A, ..,GAME_D)

getKeyName() (returns a text describing the key)

Methods used by applicationrepaint() requests repaint of whole or partial screen

serviceRepaints() forces pending repaint requests

callSerially()

setFullScreenMode(boolean)


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Graphics MethodsDrawLine

DrawRect

DrawRoundRect

FillRect

drawString

drawArc

FillArc

drawChar

drawChars

drawImage

drawRegion

setFont

setColor

setStrokeStyle

setClip //sets region that will be changed by drawing

translate //sets origin for drawing


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Low Level UI, an overview

Canvas

paint(g : Graphics)showNotify()hideNotify()keyPressed()getGameAction()serviceRepaints()setFullScreenMode()

Command

Graphics

drawLine()drawArc()drawRect()fillRect()drawImage()drawRegion()drawString()drawChars()setColor()setFont()setClip()

Displayable

addCommand()setCommandListener()

0..n0..n

CommandListener

commandAction()

<<Interface>>

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MIDP 1.0 Communication

Device must implement a HTTP 1.1 client interface Transport is not

necessarily over TCP/IP

Source: Bill Day J2ME


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Networking using GCF

Need a more compact solution, than the standard libraries

GCF: General Connection Framework is the answer In GCF all protocols can be specified using an URL-

approach: Connector.open("<protocol>://<address>:<parameters>")

But no network protocol is mandatory in CLDC What protocol can actually be used depend on the device

and the profile ExamplesConnector.open("http://www.sis.pitt.edu/mwap/test.html")

Connector.open("file://pictures/picture12.jpg")

Connector.open("comm://9600:18N")


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SMS-messaging from Java ch11WMA Wireless Messaging Api – JSR 120

Supports sending ordinary SMS App to App communication using SMS over a port

Simple API Connector MessageConnection Message

BinaryMessage TextMessage

MessageListener


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WMA-an overview

Connector

open()

<<Factory>>Message

setAddress()getAddress()getTimestamp()

<<Interface>>

TextMessage

setPayloadText()getPayloadText()

<<Interface>>BinaryMessage

setPayloadData()getPayloadData()

<<Interface>>

MessageConnection

close()newMessage()send()receive()setMessageListener()

<<Interface>>

MessageListener

notifyIncomingMessage()

<<Interface>>


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Persistent storage Li and Knudsen chapter 8 Problem and solution

Device storage mechanisms far from standardized MIDP provides a standardized interface to device storage

called Record Management System – RMS The Device platform – that is the MIDP implementation for

the device is responsible for best effort storing to what media is available.

Atomic, synchronous, serialized record updates guaranteed by implementation (no manual locking)

RMS store data as byte arrays in a named RecordStore. Each byte array is accessible via an integer record number. (A very crude solution indeed – but standardized )


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Persistent storage methods(Source Javadoc for class javax.microedition.rms – consult documetation for details)

static RecordStore openRecordStore(String recordStoreName, boolean createIfNecessary)

Open (and possibly create) a record store associated with the given MIDlet suite.

closeRecordStore()

This method is called when the MIDlet requests to have the record store closed.

static void deleteRecordStore(String recordStoreName)

int addRecord(byte[] data, int offset, int numBytes)

void setRecord(int recordId, byte[] newData, int offset, int numBytes)

byte[] getRecord(int recordId)

RecordEnumeration enumerateRecords(RecordFilter filter, RecordComparator comparator, boolean keepUpdated)

Returns an enumeration for traversing a set of records in the record store in an optionally specified order.


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Transfer from/to record store

A record may be assembled with a DataOutputStreamByteArrayOutputStream baos=new ByteArrayOutputStream(barr);

DataOutputStream dout=new DataOutputStream(baos);

dout.writeUTF(url);

dout.writeInt(qid);

dout.writeLong(timestamp);

dout.flush();

answerStore.addRecord(baos.toByteArray(),0,baos.size());

dout.close();

baos.close();

A Record may be disassebled with a DataInputStreamRecordStore answerStore=RecordStore.openRecordStore(”answer”,true);

ByteArrayInputStream bais=new ByteArrayInputStream(answerStore.getRecord(recordid)):

DataInputStream din=new DataInputStream(bais);

String url=din.readUTF();

int qid=din.readInt();

long timeStamp=din.readLong();

Documents

Programming Mobile and Wireless Devices using J2ME