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 originally delivered: 3/13/2008draft 2: 4/10/2008

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 • Some MNO’s may not allow this • 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. 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/1590594797) 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/ 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 adapted from MIT AITI lecture to high school students 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 J2MEP • 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. Other Features

38. 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.

39. 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

40. 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

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

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

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

44. 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

45. 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

46. 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

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

48. 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?”

49. 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

50. 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);