Title: Programming Mobile and Wireless Devices using J2ME
1Programming Mobile and Wireless Devices using J2ME
2Motivation
added nov 2005
3Content
- Overview over the J2ME-plattform
- Close up of technologies for Mobile and Wireless
applications - CLDC Connected Limited Device Configuration
- MIDP Mobile Information Device Profile
4J2ME in the Java landscape
Set top boxes
Smartphones
(Source Sun Microsystems Inc.)
5Problem 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
6J2ME Configurations
- add material from mikkonen
- 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 PDAs
- CDC Connected Device Configuration
- Set top boxes
- High end wireless devices
7J2ME Profiles
- add material from mikkonen
- MIDP Mobile Information Device Profile
- Foundation Profile (non gui networked device)
- Personal basis, Personal and RMI Profiles
8JCP 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
9Four Generations Nokia
10Top end devices 2007
11J2ME 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
12What 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.
13CLDC 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
14CLDC 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
Myapp.jar
Packaging
15CLDC 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.profile
s"), 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
16MIDP 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
17MIDP 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.)
18Provisioning
- 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
19Midlet 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
20Application LifeCycle
Initialised and ready to run
Resources acquired, application running
All resources released, All threads stopped
21Application LifeCycle methods(source javadoc for
class javax.microedition.MIDlet, consult
documentation for details)
Called by device Called by midlet
startApp() 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.
22MIDP 1.0 High Level User Interface
- Windowing not appropriate on limited devices
- Interface using whole Screens four kinds
- Alert - message
- TextBox Editable or non-editable textbox
- Form
- 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)
23TextBox, 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)
24Texbox Code
Initial text
Title
Command
Constraint
Maximum text length
Soft Key
25MIDP 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)
26Alert and CommandListenerCode
27List
- Uses the whole screen for a list
- Three use scenarios depending on Choice.type
- IMPLICIT selecting invokes command
- EXCLUSIVE selecting one deselects previous
- MULTIPLE selecting more than one possible
28Code for Implicit List
29Code for Multiple List
30Code 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(...)
31Form
- 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
32High Level Interface an Overview
33Same Form, different devices, different results
34Form Code
35High level UI Form an overview
36Guidelines 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
37Top 10 Usability Guidelines for Enterprise
Applications (Nokia 2004) http//www.forum.nokia.
com/main/0,,23_56,00.htmltips
- 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.
38 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.
39Low 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
40Canvas methods
- Event delivery methods used to send events to
application. Event delivery methods are called
serially - showNotify() // 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 pressed - getKeyCode() (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 application
- repaint() requests repaint of whole or partial
screen - serviceRepaints() forces pending repaint requests
- callSerially()
- setFullScreenMode(boolean)
41Graphics Methods
- DrawLine
- 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
42Low Level UI, an overview
43MIDP 1.0 Communication
- Device must implement a HTTP 1.1 client interface
- Transport is not necessarily over TCP/IP
Source Bill Day J2ME
44Networking 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("ltprotocolgt//ltaddres
sgtltparametersgt") - But no network protocol is mandatory in CLDC
- What protocol can actually be used depend on the
device and the profile - Examples
- Connector.open("http//www.sis.pitt.edu/mwap/test.
html") - Connector.open("file//pictures/picture12.jpg")
- Connector.open("comm//960018N")
45SMS-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
46WMA-an overview
47Persistent 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 )
48Persistent 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.
49Transfer from/to record store
- A record may be assembled with a DataOutputStream
- ByteArrayOutputStream baosnew ByteArrayOutputStre
am(barr) - DataOutputStream doutnew DataOutputStream(baos)
- dout.writeUTF(url)
- dout.writeInt(qid)
- dout.writeLong(timestamp)
- dout.flush()
- answerStore.addRecord(baos.toByteArray(),0,baos.si
ze()) - dout.close()
- baos.close()
- A Record may be disassebled with a
DataInputStream - RecordStore answerStoreRecordStore.openRecordStor
e(answer,true) - ByteArrayInputStream baisnew ByteArrayInputStream
(answerStore.getRecord(recordid)) - DataInputStream dinnew DataInputStream(bais)
- String urldin.readUTF()
- int qiddin.readInt()
- long timeStampdin.readLong()