Lab 2: J2ME: Java 2 Micro Edition (Writing Programs for Mobile Phones using Java)

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Lab 2 J2ME Java 2 Micro Edition(Writing
Programs for Mobile Phones using Java)
MIT D-Lab ICT4D

• Luis F. G. Sarmenta
• originally delivered 3/13/2008draft 2 4/10/2008

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Recap Mobile Phone Capabilities, Apps

• SMS (Text Messaging) based services
• send text commands, receive info
• receive alerts and subscriptions
• MMS (Multimedia Messaging) based services
• send and receive multimedia to/from server
• J2ME (Java 2 Micro Edition) applications
• programs running on the phone
• e.g., games
• Internet/Web services
• via WAP (limited) and/or GPRS (dialup-speed
  connection)
• via 3G (broadband speed connection)
• Location-based services
• services that make use of location of users
• Micropayment applications

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Overview
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What is J2ME for?

• Writing Programs that run on the phone
• no need to be connected online
• uses processor and interface of phone
• Applications
• Games
• for fun, but can be educational
• Calculation / Computation tools
• e.g., medical calculators, etc.
• Provide a better user interface to a service
• e.g., Maps for mobile (Google, Microsoft, et al)
• can be useful for data forms

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What J2ME lets you do

• Computation / logic
• general-purpose language
• limited only by processor speed and memory
• Graphics
• including 3D on new phones
• Connectivity
• SMS, MMS, Bluetooth, HTTP
• Other Features
• NFC/RFID, Location, etc.
• Write Once Run Anywhere
• IF you write your program well, AND your
  device supports all optional features you use

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Deployment and Business Model

• Development or Free Use
• via Bluetooth, cable, or infrared
• free download over the web via GPRS/3G
• download the jad file first, which makes phone
  download the jar file
• Note you may pay traffic cost
• Some MNOs may not allow this
• Commercial deployment
• packaged with phone
• download from the MNO
• download from a software vendor/aggregators web
  site
• request by SMS
• (all of these usually require network
  connectivity, but may not charge you traffic
  cost)

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J2ME Application Development
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References

• Note Our lab sessions for this class are only
  meant to jump-start you and get you on your way.
  You should read further on your own!
• Book (Highly Recommended!)
• Li and Knudsen. Beginning J2ME From Novice to
  Professional, Third Edition. Published by
  Apress.(http//www.apress.com/book/view/159059479
  7)
• Examples
• The Sun Wireless Toolkit has many examples!
• See also http//java.sun.com/javame/reference/
• See also source code download available from
  Apress
• Some Lecture Notes by Others
• http//eprom.mit.edu/education.html
• http//web.mit.edu/21w.780/www/spring2007/

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Tools

• Java
• Sun Wireless Toolkit
• Eclipse
• EclipseME

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Mobile Phone for Our Labs(Thanks to Nokia
Research Center Cambridge!)

• N82 and N95
• camera, 3G, GPS, TV out
• E61i
• QWERTY keyboard
• 6131 NFC
• mid-range phone with NFC (contactless RFID)
  reader
• N810
• Internet tablet (not a phone)
• hi-res screen, GPS, camera, QWERTY, etc.
• 2610
• low-end phone
• only 9.99 for an official refurb unit, no
  contract!

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Why High-End Phones?

• You can always simulate a low-end phone with a
  high-end phone but not the other way around
• For some projects, using high-end phones is OK,
  since only a few people (e.g., health workers)
  need to have these
• Also prices will inevitably go down in the
  future
• In any case, we will encourage designing
  solutions that have the broadest impact
• e.g., SMS-based services and platform-independent
  J2ME

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Basics

• adapted from MIT AITI lecture to high school
  students in Kenyaby Mike Gordon (MIT)
• Summer 2007

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Compilation for J2ME

• Extra steps versus desktop Java
• Compilation using Java compiler
• Must include the J2ME Java libraries
• Pre-verification of bytecode
• Package the classes application for deployment
• Create a jar archive of the class files
• All this is done for you in the Java Wireless
  Toolkit

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Terminology
Soft Buttons
Navigation (Arrow) Buttons
Select (OK) Button
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CLDC/MIDP Applications

• All cell phone applications inherit from the
  MIDlet class
• javax.microedition.midlet.MIDlet
• The MIDlet class defines 3 abstract methods that
  the cell phone app must override
• protected abstract void startApp()
• protected abstract void pauseApp()
• protected abstract void destroyApp(boolean
  unconditional)

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MIDlets

• These methods are called by the J2ME runtime
  system (interpreter) on your phone.
• startApp(), when application is started
• pauseApp(), when application is paused
• destroyApp(boolean) when application is exited

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Life Cycle of a MIDlet
Constructor
destroyApp()
Paused
pauseApp()
startApp()
destroyApp()
Active
Destroyed
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Differences Between J2SE and J2MEP

• No floating point (before CLDC 1.1)
• System.out.print/println dont do anything on
  real phone
• Subset of java.lang
• Limited implementation of many classes
• Very limited java.util / java.io
• Make sure you are reading the JavaDoc for the
  J2ME MIDP when you are developing!

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The MIDlet Philosophy

• Abstraction
• Specify the user interface in abstract terms
• Just specify the components to add
• A limited set of predefined components
• Let the MIDP implementation decide on the
  placement and appearance
• Example
• add a Done command somewhere on the screen

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The MIDlet Philosophy

• The devices display is represented by an object
  of the Display class
• Think of it as an easel
• Objects that can be added to a Display are
  subclasses of Displayable
• Canvas on the easel
• MIDlets change the display by calling
  setCurrent(Displayable) in Display

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The MIDlet Philosophy

1. Show a Displayable with something on it
2. Wait for input from user
3. Decide what Displayable to show next and what
   should be on this Displayable.
4. Go to 1.

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Example Application ToDoList
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The Displayable Hierarchy
Displayable
Canvas
Screen
Alert
List
Form
TextBox

• The Screen sub-classes are abstract, meaning it
  is up the MIDP implementation to decided on their
  appearance
• All these classes are defined in
  javax.microedition.lcdui

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Commands

• A command is something the user can invoke
• We dont really care how it is shown on the
  screen
• Example
• Command c new Command(OK, Command.OK, 0)
  
• You can add commands to a Displayable using
• public void addCommand(Command)

Commands
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Responding to Command Events

• When a Command is invoked by the user, a method
  is called to service the command
• The exact method is
• public void commandAction( Command c,
  Displayable d)
• c is the Command invoked and d is the Displayable
  the Command was added to.

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Responding to Command Events

• We need to tell the Displayable the object in
  which to call commandAction()
• Two Steps
• The class of the object must implement the
  interface CommandListener
• CommandListener defines commandAction()
• You tell the Displayable which object by calling
  setCommandListener(CommandListener) on the
  Displayable

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Example

• import javax.microedition.lcdui.
• import javax.microedition.midlet.MIDlet
• public class HelloWorld extends MIDlet implements
  CommandListener
• private static Command CMD_EXIT new
  Command("Exit", Command.EXIT, 0)
• private static Command CMD_NEXT new
  Command("Next", Command.OK, 0)
• private TextBox textBox1
• private TextBox textBox2

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Example

• public void startApp()
• textBox1 new TextBox("TextBox1",
• "The first Displayable", 30, TextField.ANY)
• textBox1.addCommand(CMD_NEXT)
• textBox1.setCommandListener(this)
• textBox2 new TextBox("TextBox2",
• "The second Displayable", 30, TextField.ANY)
• textBox2.addCommand(CMD_EXIT)
• textBox2.setCommandListener(this)
• Display.getDisplay(this).setCurrent(textBox1)

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Example

• public void commandAction(Command c, Displayable
  d)
• if (d textBox1 c CMD_NEXT)
• Display.getDisplay(this).setCurrent(textBox2)
  
• else if (d textBox2 c CMD_EXIT)
• notifyDestroyed()
• public void pauseApp()
• public void destroyApp(boolean u)

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Example Run
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Forms

• A form includes collection of UI controls called
  Items
• public Form(String title)
• public Form(String title,Item items)
• public int append()
• public void set(int index,Item item)
• public void delete(int index)
• public void deleteAll()
• public int size()
• public Item get(int index)

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Forms example

• Form form new Form(Form Title)
• StringItem strItem new StringItem(Label,
  Value)
• form.append(strItem)

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Forms - Items

• String , textfield, image Items, datefield
• Choice Group similar to Lists before
• events and item changes as well
• Can create custom items to use on your own and
  now you can build up almost any type of UI
  component to make your needs

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Example
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Example Form and SMS

• import javax.microedition.lcdui.
• import javax.microedition.midlet.
• public class Hello extends MIDlet implements
  CommandListener
• private static Command CMD_EXIT new
  Command("Exit", Command.EXIT, 0)
• private static Command CMD_OK new
  Command("OK", Command.OK, 0)
• private Form form
• private TextField textField
• public Hello()
• protected void destroyApp(boolean arg0)
  throws MIDletStateChangeException
• protected void pauseApp()
• protected void startApp() throws
  MIDletStateChangeException
• form new Form("")

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Some Notes

• Dont forget to add the Midlet class file to the
  list of Midlets in the jad
• Make sure Java Compiler is set to generate 1.1
  code

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Other Features
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SMS and Messaging API

• For simple sending, just use the SMSLibrary class
  we provide for you
• See Knudsen book for more details and more
  advanced features
• receiving SMS
• sending and receiving MMS
• binary SMS
• etc.

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NFC (Contactless)

• NFC Near Field Communications
• communicate with contactless / RFID devices
• Supported by Nokia 6131 NFC phone and a few
  others
• Reading Unique ID is simple
• You can also send more complex commands to the
  NFC
• Download Nokia 6131 NFC SDK from forum.nokia.com
• Get NFC tags from Rich Fletcher

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Other Features

• GUI Controls and Graphics
• Location
• Security
• Bluetooth
• Web
• etc.
• See Knudsen book for Bluetooth and Web access
• See Sun Wireless Toolkit Examples for other
  examples

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Exercise

• Collect users input and send it via SMS to
  server
• no need to receive the SMS via J2ME for now

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J2ME Basic GUI Programming

• from MIT AITI lecture in Kenyaby Mike Gordon
  (MIT)
• Summer 2007

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J2ME GUI

• Idea Use abstractions to support many different
  mobile devices, different screen sizes, colors,
  different input types
• Displayables
• Alerts
• Lists
• Form
• TextBox

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Textbox

• allows the user to enter a String
  (zipcode,name,password)
• depending on input may be a tedious process

• public TextBox(String title, String text, int
  maxSize, int constraints)
• title screen title
• text initial text on screen
• maxSize maximum size of text box
• constraints restrict input

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TextBox - Constraints

• Constrain the input characters
• TextField.ANY allows any type of input
  supported by the device
• TextField.NUMERIC restricts to only integers
• TextField.DECIMAL allows numbers with fractional
  parts
• TextField.PHONENUMBER requires a telephone
  number
• TextField.EMAILADDR requires an email address
• TextField.URL requires a web address

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Text Box - Flags

• Flags define behaviour, opposed to restricting it
• TextField.PASSWORD
• TextField.UNEDITABLE
• TextField.SENSITIVE
• TextField.NON_PREDICTIVE
• TextField.INITIAL_CAPS_WORD
• TextField.INTIAL_CAPS_SENTENCE
• No Validation than use TextField.ANY and 0 for
  constraints parameter

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Text Box - Flags

• Combine flags and constraints with (or)
• Displayable d
• new TextBox(Email,64,TextField.ANY
  TextField.PASSWORD)

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Alerts

• alert types ALARM, CONFIRMATION,ERROR,INFO, and
  WARNING

• timed certain amount of time Your
  transaction complete
• modal until user dismisses it are you sure
  you want to quit? exit without saving?

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Alerts

• public Alert() or
• public Alert(String title, String alertText,
  Image alertImg, AlertType alertType)
• any or all parameters can be null

• default timeout , but can change timeout length
• Forever timeout means that it is modal

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Alerts

• You can create an alert with
• Alert alt new Alert(Sorry, I Am sorry Dave,
  null, null)
• Set the timeout to 5 seconds by
• alt.setTimeout(5000)
• Make it a modal alert by
• alt.setTimeout(FOREVER)

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Lists

• users select items (called elements) from choices
• Exclusive -Single Selection ex. radio buttons
• Multiple Multiple Selection ex. check list
• Text String or image is used to represent each
  element

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Lists
Exclusive Multiple
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Creating Lists

• public List(String title, int type)
• public List(String title, int type,String
  stringElements, Image imageElements)

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Modifying Lists

• public void set(int elementNum, String
  stringPart, Image imagePart)
• public void insert(int elementNum, String
  stringPart, Image imagePart)
• public int append(String stringPart, Image
  imagePart)

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Modifying Lists

• public String getString(int elementNum)
• public String getImage(int elementNum)
• public void delete(int elementNum)
• public void deleteAll()
• public boolean isSelected(int index)
• public int getSelectedIndex()
• public void setSelectedIndex(int index, boolean
  selected)

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Forms

• A form includes collection of UI controls called
  Items
• public Form(String title)
• public Form(String title,Item items)
• public int append()
• public void set(int index,Item item)
• public void delete(int index)
• public void deleteAll()
• public int size()
• public Item get(int index)

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Forms example

• Form form new Form(Form Title)
• StringItem strItem new StringItem(Label,
  Value)
• form.append(strItem)

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Forms - Items

• String , textfield, image Items, datefield
• Choice Group similar to Lists before
• events and item changes as well
• Can create custom items to use on your own and
  now you can build up almost any type of UI
  component to make your needs

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Form Layout

• Left to right, rows top to bottom
• items have labels, and can also have commands
• set size
• set layouts for individual items
• setLayout() getLayout()
• LAYOUT_LEFT, LAYOUT_CENTER....

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Commands
To Create a command, you need a name, type and
also a priority. Ex
Command c new Command(OK, Command.OK, 0)
public void addCommand(Command cmd) public void
removeCommand(Command cmd)
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Command Types
There are different types of commands available
for you to use
Command.OK Confirms a selction Command.CANCEL
Cancels pending changes Command.BACK Moves
the user back to a previous screen Command.STOP
Stop a running operation Command.HELP Shows
application Instructions Command.SCREEN
indicates generic type for specific application
commands
Command c new Command("Launch", Command.SCREEN,
0)
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J2ME GUI Resources

• Knudsen and Li. Beginning J2ME From Novice to
  Professional, Third Edition. Apress.
  (http//www.apress.com/book/view/1590594797)
• http//www.onjava.com/pub/a/onjava/excerpt/wireles
  sjava_ch5/index1.html
• http//developers.sun.com/mobility/midp/articles/u
  i/ - Sun's J2ME GUI tutorial
• http//www.j2mepolish.org/
• A powerful dual-license open-source GUI Designer
  which may be useful for your own projects beyond
  this course