J2ME Introduction

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J2ME - Introduction
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What is J2ME?

• NEITHER a specific piece of software /
  specification
• A collection of Java classes, interfaces
  dedicated to small, mobile devices

http//java.sun.com/j2me/docs/index.html
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Advantages of J2ME

• Easy to learn
• Learning J2ME is like learning Java programs
• Platform independent
• WAP applications are highly device dependent
  (need a WAP-enabled phone including components
  for supporting the WAE and communication
  protocols)
• The layering architecture of the J2ME programming
  model allows MIDlets (applications for mobile
  devices) to run on different mobile devices (Java
  systems). Build on top of an operating system and
  all lower levels components are hided by the OS
• Integration with other Java components
• Can build complex mobile applications using with
  least effort by integration with other Java
  components
• Good for security-oriented applications, which
  use cryptographic classes
• Can build wireless Internet applications

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J2ME System Model

• J2ME framework is divided into Configurations and
  Profiles

http//java.sun.com/j2me/docs/index.html
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Scope of J2ME

• J2ME defines
• A series of Java virtual machines each for use on
  different types of small devices
• A group of libraries and APIs that can be run
  under each of the virtual machines
• Various tools for deployment and device
  configuration
• Configuration
• Mobile devices have different capabilities
  (limitations). J2ME defines configurations for a
  horizontal grouping of devices based on
  availability of memory and processing power of
  the devices
• Profiles
• defines a set of APIs that reside on top of a
  configuration that offers the program access to
  device-specific capabilities

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Scope of J2ME

• MIDP (mobile information device profile) is
  designed to be used with the configuration
  (CLDC), and provides a set of APIs for use by
  limited resources devices, i.e., mobile phones

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J2ME System Model Configurations

• Designed for a specific kind of device based on
  memory constraints and processor power (i.e.
  defines a minimum Java platform for a family of
  devices)
• Usually specifies a JVM that can be easily ported
  to devices supporting the configuration (called
  KVM)
• Specifies the characteristics and features of
  virtual machine present, minimum Java libraries
  that are supported and minimum set of features
  for a category of devices
• Major Configurations in current specification
  include
• Connected Device Configuration (CDC)
• Connected, Limited Device Configuration (CLDC)

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Connected Device Configuration (CDC)

• Device requirements A connected device (CD) has
  a minimum 512KB of ROM, 256KB of RAM, 32-bit
  processors, and some network connection with
  limited bandwidth
• CDC is designed for "more powerful" wireless
  devices like TV set-top boxes, car navigation
  systems, and high-end PDAs.
• CDC specifies that a full-featured Java Virtual
  Machine (JVM) (defined in J2EE) is supported

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Connected, Limited Device Configuration (CLDC)

• Covers mobile devices like mobile phones, PDAs,
  pagers, and other "tiny" wireless devices
• For smaller devices than CDC, with limited
  capacity and network connection (e.g., lt 9.6Kbps
  for mobile phones)
• For devices with 160KB to 512 KB of memory
  available for Java platform
• For devices with limited power supply
• Built on "scale-down" version of JVM called KVM
  (Sun 'K Virtual Machine, with size in tens of
  kilobytes, rather than JVM with tens of
  megabytes)

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MIDP Requirements

• A Mobile Information Device (MID) has the
  following characteristics
• 128KB of non-volatile memory for MIDP
  implementation
• 32KB of volatile memory for runtime heap
• 8KB of non-volatile memory for persistent data
• A screen of a least 96 x 54 pixels
• Some capacity for input, either by keypad,
  keyboard, or touch screen
• Two-way network connection, possible
  intermittent
• Detail information about MIDP (Mobile Information
  Device Profile) can be found in
  http//java.sun.com/products/midp/

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MIDP Targets and MIDlets

• MIDP enables application development with mobile,
  wireless-connected devices like cellular phones
  and two-way pagers
• Main features of the supported devices
• small displays
• limited input devices
• limited local storage
• limited battery life
• limited CPU power
• MIDlets
• Small applications that run under the MIDP are
  called MIDlets
• A MIDlet is a Java application that uses the MIDP
  and the CLDC
• In a mobile phone, application management
  software (AMS) controls start, stop and execute
  MIDlet (controls the entire lifecycle)
• Device manufacturer provides the AMS Software

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MIDP Implementation Model

• The APIs available to MIDP application are
  provided by the packages in CLDC and MIDP

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MIDP Implementation Model

• CLDC
• Defines the "core" of MIDP APIs (mainly came from
  the J2SE world)
• Includes fundamental language classes in
  java.lang, stream classes from java.io, and
  utility APIs from java.util
• Specifies a generalized wireless network API in
  javax.microedition.io

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MIDP Implementation Model

• MIDP
• javax.microedition.lcdui
• Provides a set of features for implementation of
  user interfaces (UI)
• The central abstraction of the MIDP's UI is that
  of a screen
• A screen is an object that encapsulates
  device-specific graphics rendering user input.
  The user can traverse through the items on that
  screen
• The screen takes care of all events that occur as
  the user navigates in the screen, with only
  higher-level events being passed on to the
  application

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MIDP Implementation Model

• MIDP
• javax.microedition.midlet
• Defines MIDP applications, as well as the
  interactions between the application and the
  environment
• Core API of MIDP
• An application of the Mobile Information Device
  Profile is called a MIDlet
• javax.microedition.rms
• Provides a mechanism for MIDlets to persistently
  store data and later retrieve it
• Modeled after a simple record oriented database
• Called the Record Management System

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MIDlet State Model

• MIDlets transition to different states during
  their lifetime
• The following diagram shows a state transition
  diagram that represents these MIDlet states and
  the events that cause transition from one state
  to another

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Installation Sequences

• Install J2SE SDK (version 1.4 - J2SE v
  1.4.2_11  SDK) from
• http//java.sun.com/j2se/1.4.2/download.html
• Install J2ME Wireless Toolkit (version 2.2 ) from
  
• http//java.sun.com/products/sjwtoolkit/download-
  2_2.html
• Install J2ME Patch (Patch 200511 ) from
• http//java.sun.com/products/sjwtoolkit/download-
  2_2.html

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J2ME Default Directory

• C\WTK22
• All projects are stored at
• C\WTK22\apps\ltprjNamegt
• All programs within a project are stored at
• C\WTK22\apps\ltprjNamegt\src
• MIDlets document is stored at
• C\WTK22\docs\api\midp\index.html

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J2ME Interface

• C\WTK22\bin\ktoolbar.bat

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J2ME Interface
package cs4289.j2me2_2 - first statement within
helloMidlet.java public class helloMidlet extends
MIDlet
Try demo01_howToCompile project
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MIDlet states
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MIDlet states

• Paused
• When MIDlet has just been started new
  ltmidletObjgt()
• As a result of pauseApp() and then notifyPaused()
• Active
• MIDlet is running
• As a result of startApp() and then
  resumeRequest()
• Destroyed
• MIDlet will terminate and release resources
• As a result of destroyApp(boolean unconditional)
  and then notifyDestroyed()

true terminate immediately false can not
terminate (throw MIDletStateChangeException )
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MIDlet states

• notifyPaused(), resumeRequest(),
  notifyDestroyed()
• AMS (Application Management Software) / JAM (Java
  Application Manager) download, execute and
  remove MODlet suite
• Request AMS to change state
• AMS may have chance to refuse these requests

Try demo02_showLifeCycle
Try demo03_JAMMIDletComm
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MIDlet states

• In Paused state, AMS is free to execute other
  thread

Interface Runnable

• public void run()
• extends MIDlet implements Runnable

Try demo04_threadMIDlet
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How to get information from MIDlet suite

• javax.microedition.midlet.MIDlet
• String getAppProperty(String key)

Try demo06_midletResource
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MIDlet User Interface
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Display class

• public static Display getDisplay(MIDlet m)
• Gets the Display object that is unique to this
  MIDlet
• Display display_scr
• display_scr Display.getDisplay(this)

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Display class

• public void setCurrent(Displayable
  nextDisplayable)
• Requests that a different Displayable object be
  made visible on the display
• display_scr.setCurrent(xxx)
• xxx Displayable object
• Such as Screen, List, Alert, TextBox, Form

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Interface CommandListener

• Used by MIDlet to receive high-level events
• xxxx implements CommandListener
• void commandAction(Command c, Displayable d)
• Indicates that a command event has occurred on
  Displayable d

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Command class

• Command(String label, int commandType, int
  priority)
• Creates a new command object with the given short
  label, type, and priority.
• The defined types are BACK, CANCEL, EXIT, HELP,
  ITEM, OK, SCREEN, and STOP.

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Command class

• javax.microedition.lcdui.Displayable
• public void addCommand(Command cmd)
• tbl_msg.addCommand(cmd_exit)

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Displayable class

• public void setTicker(Ticker ticker)
• Sets a ticker for use with this Displayable
• public void setTitle(String s)
• Sets the title of the Displayable
• public void setCommandListener(CommandListener l)
• Sets a listener for Commands to this Displayable

Running Text
Title
Content
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Ticker class

• Ticker(String str)
• Constructs a new Ticker object, given its initial
  contents string

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Form class

• Form(String title)
• Creates a new, empty Form
• public int append(Item item)
• Adds an Item into the Form. The newly added Item
  becomes the last Item in the Form, and the size
  of the Form grows by one