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

1. MIT D-Lab ICT4D Lab 2: J2ME: Java 2 Micro Edition(Writing Programs for Mobile Phones using Java) Luis F. G. Sarmenta draft 3/13/2008

2. 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 • ability to send/transfer cellphone credits via SMS • leads to cash-less, credit-card less, electronic payment mechanisms

3. Overview

4. 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

5. 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

6. 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 • Commercial deployment • packaged with phone • download from the MNO • download from a software vendor/aggregator’s web site • request by SMS • (all of these usually require network connectivity, but may not charge you traffic cost)

7. J2ME Application Development

8. Book (Highly Recommended!) Li and Knudsen. Beginning J2ME: From Novice to Professional, Third Edition. Published by Apress.(http://www.apress.com/book/view/1590594797) Examples The Sun Wireless Toolkit has many examples! See also http://java.sun.com/javame/reference/ Lectures http://eprom.mit.edu/education.html References

9. Tools • Java • Sun Wireless Toolkit • Eclipse • EclipseME

10. 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!

11. 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

12. Basics from MIT AITI lecture in Kenyaby Mike Gordon (MIT) Summer 2007

13. 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

14. Terminology Soft Buttons Navigation (Arrow) Buttons Select (OK) Button

15. 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);

16. 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

17. Life Cycle of a MIDlet Constructor destroyApp() Paused pauseApp() startApp() destroyApp() Active Destroyed

18. Differences Between J2SE and CLDC/MIDP • No floating point (before CLDC 1.1) • System.out.print/println don’t 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!

19. 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

20. The MIDlet Philosophy • The device’s 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

21. The MIDlet Philosophy Show a Displayable with something on it Wait for input from user Decide what Displayable to show next and what should be on this Displayable. Go to 1.

22. Example Application: ToDoList

23. 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

24. Commands Commands • A command is something the user can invoke • We don’t 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)

25. 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.

26. 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

27. 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;

28. 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); }

29. 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) { }

30. Example Run

31. 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)

32. Forms example • Form form = new Form(“Form Title”); • StringItem strItem = new StringItem(“Label:”, “Value”); • form.append(strItem);

33. 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

34. Example

35. Example: Form and SMS import javax.microedition.lcdui.*; import javax.microedition.midlet.*; publicclass Hello extends MIDlet implements CommandListener { privatestatic Command CMD_EXIT = new Command("Exit", Command.EXIT, 0); privatestatic Command CMD_OK = new Command("OK", Command.OK, 0); private Form form; private TextField textField; public Hello() { } protectedvoid destroyApp(boolean arg0) throws MIDletStateChangeException { } protectedvoid pauseApp() { } protectedvoid startApp() throws MIDletStateChangeException { form = new Form(""); textField = new TextField("Name", "", 20, TextField.ANY); form.append(textField); form.addCommand(CMD_EXIT); form.addCommand(CMD_OK); form.setCommandListener(this); Display.getDisplay(this).setCurrent(form); } publicvoid okPressed() { SMSLibrary.sendShortMessage("Hello " + textField.getString(), "6174606583"); } publicvoid commandAction(Command c, Displayable d) { if (c == CMD_OK) { okPressed(); } elseif (c == CMD_EXIT) { notifyDestroyed(); } } }

36. Some Notes • Don’t 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

37. J2ME Basic GUI Programming from MIT AITI lecture in Kenyaby Mike Gordon (MIT) Summer 2007

38. Graphics

39. Other Features

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

41. 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 from forum.nokia.com • Get NFC tags from Rich Fletcher

42. 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

43. Exercise • Collect user’s input and send it via SMS to server • no need to receive the SMS via J2ME for now

44. J2ME Basic GUI Programming from MIT AITI lecture in Kenyaby Mike Gordon (MIT) Summer 2007

45. J2ME GUI • Idea: Use abstractions to support many different mobile devices, different screen sizes, colors, different input types • Displayables • Alerts • Lists • Form • TextBox

46. 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

47. 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

48. 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

49. Text Box - Flags • Combine flags and constraints with | (or) Displayable d = new TextBox(“Email”,64,TextField.ANY | TextField.PASSWORD);

50. 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?”