Java 2 Platform, Micro Edition (J2ME)

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Java 2 Platform, Micro Edition (J2ME)

• Masha Gutkhen
• Keren Gazit

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Contents

• Whats J2ME?
• J2ME core concepts
• Configurations (CLDC, CDC)
• Profiles (MIDP)
• MIDlet, MIDlet Suite
• Basic classes API
• Installation and using the Toolkit
• Demos!!!

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Introduction

• Personalized and intelligent information
  appliances are necessities in our life today.
• Such appliances can be
• cell phones
• two-way pagers
• smart cards
• personal organizers
• palmtops
• These appliances tend to be special-purpose,
  limited-resource, network-connected devices.

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Environment requirements

• We need an environment which is adapted for
  constrained devices - devices that have
  limitations on what they can do when compared to
  standard desktop or server computers.
• The constraints are
• extremely limited memory
• small screen sizes
• alternative input methods
• slow processors

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So whats the solution?

• Because of the vast need, Sun has decided to
  develop a special edition of Java - J2ME (Java
  2 Micro Edition).

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Java Editions

• Different devices have different requirements and
  different expectations of Java.
• One platform (solution) cannot address all the
  market segments (web server, video games etc.)
• Users/developers want flexibility. They want to
  choose what they want to use and what they do
  not.

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Java Editions

• The Java 2 Platform is split into three editions.
• Each edition provides a complete environment for
  running Java-based applications, including the
  Java virtual machine (VM) and runtime classes.
• The three editions target different kinds of
  applications running on different kinds of
  devices.

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Java Editions
Java 2 Platform
Java2 Standard Edition (J2SE)
Java2 Enterprise Edition (J2EE)
Java2 Micro Edition (J2ME)
Standard desktop workstation applications
Heavy duty server systems
Small memory constrained devices
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Java Editions

• Each edition defines different sets of class
  libraries.
• There are thousands of core J2SE runtime classes,
  taking up to 10-20 megabytes of space.
• J2ME-based devices have fewer classes.

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PersonalJava and EmbeddedJava

• J2ME is not the first attempt at adapting Java
  for constrained environments.
• PersonalJava
• Uses the basic Java 1.1 runtime classes with a
  few features from Java 2.
• Implementation still requires a couple of
  megabytes of memory and a fast processor to run.

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PersonalJava and EmbeddedJava

• EmbeddedJava
• Makes every behavior of the JVM and the runtime
  classes optional - the implementor can choose
  exactly which classes and methods are required.
• The limitation "write once, run anywhere".

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J2ME Core Concepts

• Configuration
• Minimum platform required for a group of devices
• Profile
• Addresses specific needs of a certain device
  family
• Optional Packages

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J2ME Core Concepts

• J2ME is based on 3 core concepts
• Configurations
• Profiles
• Optional packages

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Configurations

• A configuration is a complete Java runtime
  environment, consisting of
• Java virtual machine (VM) to execute Java
  bytecode
• Native code to interface to the underlying system
• Set of core Java runtime classes
• To use a configuration, a device must meet
  certain minimum requirements.

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Configurations

• The set of core classes is normally quite small
  and must be enhanced with additional classes
  supplied by J2ME profiles or by configuration
  implementor.
• Configurations do not define any user interface
  classes.

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Configurations
Connected Limited Device Configuration
Connected Device Configuration
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CLDC vs. CDC

• CLDC
• For very constrained devices
• 160 - 512 KB of total memory
• 16-bit or 32-bit processor
• Low power consumption and often operating with
  battery power
• Connectivity with limited bandwidth

• CDC
• 2 MB or more memory for Java platform
• 32-bit processor
• High bandwidth network connection, most often
  using TCP/IP

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CLDC vs. CDC - VM

• Features missing in the CLDC VM
• Floating point types
• Object finalization
• JNI or reflection
• Thread groups or daemon threads
• User Class loaders
• Change in classfile verification ?
  preverification

• The CDC supports a complete, full-featured Java 2
  virtual machine

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The KVM and CVM

• KVM - Java virtual machines for the CLDC
• CVM - Java virtual machines for the CDC
• Written specifically to work in the constrained
  environment of a handheld or embedded device and
  to be easily ported to different platforms.
• CLDC and CDC specifications do not require the
  use of the KVM or the CVM.

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CLDC vs. CDC J2SE Subset

• The CLDC includes classes from
• java.lang
• java.io
• java.util
• Only selected classes from each package are
  included

• The CDC includes 17 packages
• Includes more classes even in the shared packages

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CLDC vs. CDC J2SE Subset
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Handling I/O

• J2SE includes many classes for performing input
  and output.
• There are a large number of I/O classes and they
  tend to encapsulate I/O models that are not
  necessarily found on all devices.
• For example, some handheld devices do not have
  file systems. Socket support is not universal,
  either.

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Handling I/O in CLDC

• The CLDC has define a new set of APIs for I/O
  called the Generic Connection Framework.
• The GCF, part of the new javax.microedition.io
  package, defines interfaces for the different
  kinds of I/O that are possible.
• The CLDC does not actually define any I/O
  implementations these are left to the profiles
  and/or the device vendor to define.

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GCF - example

• import java.io.
• import javax.microedition.io.
• StreamConnection conn null
• InputStream is null
• String url "socket//somewhere.com8909"
• try
• conn (StreamConnection) Connector.open( url
  )
• is conn.openInputStream()
• .... // etc. etc.

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Handling I/O in CDC

• Since the CDC is a superset of the CLDC, it
  includes the GCF.
• CDC also requires GCF support for two specific
  connection types files and datagrams.
• The reason CDC includes the relevant classes
  from java.io and java.net packages.

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J2ME Core Concepts

• J2ME is based on 3 core concepts
• Configurations
• Profiles
• Optional packages

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Profiles

• Adds domain-specific classes to a configuration
• To fill in missing functionality
• To support specific uses of a device
• Most profiles define user interface classes for
  building interactive applications.
• To use a profile, the device must meet the
  minimum requirements of the underlying
  configuration and of the profile.

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Profiles
Mobile Information Device Profile
Personal Digital Assistant Profile
Foundation Profile
Personal Basis Profile
Personal Profile
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MIDP MID Profile

• MIDP is targeted at a class of devices known as
  mobile information devices (MIDs).
• Minimal characteristics of MIDs
• Enough memory to run MIDP applications
• Display of at least 96 X 56 pixels, either
  monochrome or color
• A keypad, keyboard, or touch screen
• Two-way wireless networking capability

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MIDP - Specification

• There are two versions of the MIDP
• MIDP 1.0 - released in September 2000. Many
  devices currently on the market support it.
• MIDP 2.0 - currently in proposed final draft
  form. No devices yet support it.

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MIDP - Specification

• The MIDP adds APIs to the basic APIs defined by
  the CLDC. The new features include
• Support for application lifecycle management
  similar to the way applets are defined in J2SE.
• Persistent storage of data.
• HTTP-based network connectivity based on the
  CLDC's GCF.
• Simple user interface support, with enough
  flexibility to build games or business
  applications.

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MIDP - Specification

• The MIDP specification is silent about a number
  of things
• No standard way to interface to the device's
  phonebook, in order to initiate voice calls.
• How MIDP applications are loaded onto a device
  and how they are activated or deactivated.

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MIDP Applications restrictions

• Memory is a particularly scarce resource.
• The early Motorola J2ME-enabled phones limited
  the size of an application to 50K. Some Nokia
  phones limit them to even less, about 30K.
• MIDP 1.0 applications cannot share classes.
• Placing part of the application in a web or
  application server (as a servlet, typically) that
  the MIDP application calls is almost a
  requirement for anything serious.

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J2ME Core Concepts

• J2ME is based on 3 core concepts
• Configurations
• Profiles
• Optional packages

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Optional Packages

• Set of APIs in support of additional, common
  behaviors.
• Have specific dependencies on a particular
  configuration and/or one or more profiles.
• Examples of optional packages
• RMI Optional Package
• Bluetooth Optional Package
• JDBC Optional Package

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What it all means

• "J2ME application" is an ambiguous term.
• Configuration, profile and optional packages
  should be chosen.
• CDC-based profiles make development simpler due
  to J2SE-like APIs, but dont suit the low-end
  devices.
• CLDC-based profiles makes the development task
  harder, especially when trying to shrink the size
  of the application to run on many of the small
  devices.

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Start working...
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MIDlets The heart of J2ME

• MIDP does not support the running of applications
  that use a static main method as their entry
  point, nor calling the System.exit method in
  order to terminate.
• Instead, we use a MIDlet, which is a MID Profile
  application.

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MIDlets The heart of J2ME

• Every application must extend javax.microedition.m
  idlet.MIDlet class to allow the application
  management software to
• control the MIDlet
• be able to retrieve properties from the
  application descriptor
• notify and request state changes

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MIDlets The heart of J2ME

• The extending class is the main class of the
  application.
• The MIDlet class defines abstract methods that
  the main class implements (for example
  startApp(), destroyApp(), notifyDestroyed()).

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MIDlet Suite

• One or more MIDlets are packaged together into a
  MIDlet suite, composed of
• JAR (Java archive) file
• JAD (Java Application Descriptor) file
• All the user-defined classes and resources
  required by the suite's MIDlets must be in the
  JAR file.

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MIDlet Suite

• The JAR file must also include a manifest that
  describe the MIDlets in the suite.
• The application descriptor (JAD) contains similar
  information, and is used by devices to obtain
  information about a MIDlet suite without having
  to download and install the MIDlet suite first.

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Creating a MIDlet
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Creating a MIDlet
Importing MIDP specific packages
import javax.microedition.lcdui. import
javax.microedition.midlet.
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Creating a MIDlet
Extends MIDlet Implements CommandListener
public class HelloMIDlet extends MIDlet
implements CommandListener
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Creating a MIDlet
Creating the form, adding the Commands
public HelloMIDlet() mMainForm new
Form("HelloMIDlet") mMainForm.append(new
StringItem(null, "Hello, Seminar Software
Design!")) mMainForm.addCommand(new
Command("Exit", Command.EXIT, 0))
mMainForm.setCommandListener(this)
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Sample MIDP classes API

• MIDlet
• Form
• Command
• CommandListener
• ItemCommandListener
• Item

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Sample classes API

• MIDlet Base class
• Form
• Command
• CommandListener
• ItemCommandListener
• Item

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MIDlet class API

• protected abstract void startApp()
• protected abstract void pauseApp()
• protected abstract void destroyApp(boolean uncondi
  tional)
• public final String getAppProperty(String key)
• public final void notifyDestroyed()

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Sample classes API

• MIDlet
• Form
• Command
• CommandListener
• ItemCommandListener
• Item

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Form class

• A Form is a Screen that contains an arbitrary
  mixture of items images, read-only text fields,
  editable text fields, editable date fields,
  gauges, choice groups, and custom items.
• In general, any subclass of the Item class may be
  contained within a form.
• The implementation handles layout, traversal, and
  scrolling.

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Form class API

• Item management
• public int append(Item item)
• public Item get(int itemNum)
• Layout
• public void setItemStateListener(ItemStateListener
   iListener)

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Sample classes API

• MIDlet
• Form
• Command
• CommandListener
• ItemCommadListener
• Item

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Command class

• The Command class represents the semantic meaning
  of an action. Command objects are presented in
  the user interface.
• The action itself is implemented in a
  CommandListener object.
• The CommandListener is associated with a
  Displayable or an Item.
• Once the Command is called the CommandListener
  is invoked, and the action is performed.

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Command class

• Command label
• public String getLabel()
• Command type
• public int getCommandType()
• Command priority
• public int getPriority()

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CommandListener class API

• This object is a listener for Commands that are
  attached to a Displayable.
• public void commandAction(Command c,
  Displayable d)

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ItemCommandListener class API

• When a command (attached to an Item) is invoked,
  the application is notified by having the
  commandAction() method called on the
  ItemCommandListener that had been set on the
  Item.
• public void commandAction(Command c, Item item)

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Sample classes API

• MIDlet
• Form
• Command
• CommandListener
• ItemCommandListener
• Item

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Item class

• A superclass for components that can be added to
  a Form.
• All Item objects have a label field
• Choose the Items layout, size, and appearance
• Attach Commands

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Item class API

• public void setDefaultCommand(Command cmd)
• public void setItemCommandListener(ItemCommandList
  ener listener)
• public void notifyStateChanged()
• public int getPreferredWidth()

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Getting Started

• 1st step Download suns J2ME Wireless Toolkit
  from http//java.sun.com/products/j2mewtoolkit/do
  wnload-2_1.html
• 2nd step Make sure you have J2SE SDK installed
• 3rd step Install the J2ME Toolkit.

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After the installation.

• Shortcuts are available from the start menu.
• New directories created

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Using KToolbar
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Creating a new Application

• Press New Project.
• Enter the projects name and the MIDlets class
  name.
• New directories will automatically be created.

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Where to place your files?
J2ME/apps/proj source, resource, and binary files
J2ME/apps/proj/bin JAR, JAD, unpacked manifest files.
J2ME/apps/proj/lib external class libraries, (JAR or ZIP) for a specific project
J2ME/apps/proj/res resource files
J2ME/apps/proj/src source files
J2ME/apps/lib external class libraries, (JAR or ZIP) for all KToolbar projects.
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And then what?

• Choose the target platform
• Write your code
• Save
• Build (Compile Preverify)
• Run

JTWI - conforms to Java Technology for the
Wireless Industry (JSR-185). MIDP1.0 - includes
MIDP 1.0 and CLDC 1.0 Custom - user defined
settings, you can select project profile,
configurations and various APIs.
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Distribution to actual devices

• Create a package
• Place your code somewhere on the net.
• Update .jad file
• Download the application to your mobile
• Start playing ?

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Some other issues

• OTA provisioning
• Using Servlets
• Working with EclipseME
• Web services

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The END!

• You can download all the demos JARs from
  www.cs.huji.ac.il/kerengaz/j2me/
• Have Fun!!!