1. Java 2 Platform, Micro Edition
( (J2ME
J2ME 1

2. Contents
 What’sJ2ME?
 J2ME core concepts
 Configurations (CLDC, CDC(
 Profiles (MIDP(
 MIDlet, MIDlet Suite
 Basic classes API
 Installation and using the Toolkit
 Demos!!!
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3. Introduction
 Personalized and intelligent information appliances
are necessities in our life today.
 Such appliances can be:
 cellphones
 two-way pagers
 smart cards
 personal organizers
 palmtops
 These appliances tend to be special-purpose,
limited-resource, network-connected devices.
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4. 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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5. ?So – what’s 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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6. J2ME 6

7. Java Editions
 Differentdevices 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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8. 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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9. Java Editions
Java 2 Platform
Java2 Java2 Java2
Standard Edition Enterprise Edition Micro Edition
(J2SE™) (J2EE™) (J2ME™)
Standard desktop & Heavy duty server Small & memory
workstation applications systems constrained devices
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10. 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 J2EE
fewer classes. J2SE
J2ME
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11. 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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12. 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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13. J2ME Core Concepts
 Configuration
Profiles
J2ME
 Minimum platform Profile
required for a
group of devices
J2ME
 Profile Libraries
Configuration
 Addresses specific Java Language
needs of a certain
device family Java Virtual Machine
 Optional Packages
Host Operating System
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14. J2ME Core Concepts
J2ME is based on 3 core concepts:
 Configurations
 Profiles
 Optional packages
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15. 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
 Touse a configuration, a device must
meet certain minimum requirements.
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16. 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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17. Configurations
Configuration
Configuration
CLDC
CLDC CDC
CDC
Connected Limited Connected Device
Device Configuration Configuration
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18. CLDC vs. CDC
 CLDC  CDC
 For very constrained  2 MB or more
devices memory for Java
 160 - 512 KB of total platform
memory  32-bit processor
 16-bit or 32-bit  High bandwidth
processor network connection,
 Low power most often using
consumption and TCP/IP
often operating with
battery power
 Connectivity with
limited bandwidth
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19. CLDC vs. CDC - VM
 Features
missing in  The CDC supports a
the CLDC VM: complete, full-
featured Java 2
 Floating point types virtual machine
 Object finalization
 JNI or reflection
 Thread groups or
daemon threads
 User Class loaders
 Change in classfile
verification  preverification
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20. 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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21. CLDC vs. CDC – J2SE Subset
 TheCLDC includes  The CDC includes
classes from: 17 packages
 java.lang  Includes more
 java.io classes even in the
 java.util shared packages
 Onlyselected
classes from each
package are
included
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22. CLDC vs. CDC – J2SE Subset
J2SE CDC CLDC
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23. 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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24. 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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25. GCF - example
import java.io.*;
import javax.microedition.io.*;
StreamConnection conn = null;
InputStream is = null;
String url = "socket://somewhere.com:8909";
try {
conn = (StreamConnection) Connector.open( url );
is = conn.openInputStream();
.... // etc. etc.
}…
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26. 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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27. J2ME Core Concepts
J2ME is based on 3 core concepts:
 Configurations
 Profiles
 Optional packages
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28. 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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29. Profiles
Profile
Profile
MIDP
MIDP PDAP
PDAP FP
FP PBP
PBP PP
PP
Mobile Personal Foundation Personal Personal
Information Digital Profile Basis Profile Profile
Device Assistant
Profile Profile
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30. 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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31. 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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32. 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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33. MIDP - Specification
 TheMIDP 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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34. 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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35. J2ME Core Concepts
J2ME is based on 3 core concepts:
 Configurations
 Profiles
 Optional packages
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36. 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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37. 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 don’t 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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38. J2ME 38

39. …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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40. …MIDlets – The heart of J2ME
 Every application must extend
javax.microedition.midlet.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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41. …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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42. MIDlet Suite
 One or more MIDlets are packaged
together into a MIDlet suite, composed
of:
 JAR (Java archive) file
 JAD (Java Application Descriptor) file
 Allthe user-defined classes and
resources required by the suite's MIDlets
must be in the JAR file.
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43. 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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44. Creating a MIDlet
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45. Creating a MIDlet Importing MIDP
specific
packages
import javax.microedition.lcdui.*;
import javax.microedition.midlet.*;
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46. Creating a MIDlet
Extends MIDlet
Implements
CommandListener
public class HelloMIDlet
extends MIDlet
implements CommandListener {
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47. 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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48. Sample MIDP classes API
 MIDlet
 Form
 Command
 CommandListener
 ItemCommandListener
 Item
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49. Sample classes API
MIDlet – Base class
 Form
 Command
 CommandListener
 ItemCommandListener
 Item
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50. MIDlet class API
 protected abstract void startApp()
 protected abstract void pauseApp()
 protected abstract void
destroyApp(boolean unconditional)
 public final String
getAppProperty(String key)
 public final void notifyDestroyed()
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51. Sample classes API
 MIDlet
Form
 Command
 CommandListener
 ItemCommandListener
 Item
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52. 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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53. Form class API
Item management
public int append(Item item)
public Item get(int itemNum)
Layout
 publicvoid
setItemStateListener(ItemState
Listener iListener)
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54. Sample classes API
 MIDlet
 Form
Command
 CommandListener
 ItemCommadListener
 Item
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55. 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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56. Command class
 Command label
public String getLabel()
 Command type
public int getCommandType()
 Command priority
public int getPriority()
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57. CommandListener class API
 Thisobject is a listener for Commands
that are attached to a Displayable.
 public void
commandAction(Command c,
Displayable d)
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58. 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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59. Sample classes API
 MIDlet
 Form
 Command
 CommandListener
 ItemCommandListener
Item
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60. Item class
A superclass for components that can be
added to a Form.
 All Item objects have a label field
 Choose the Item’s layout, size, and
appearance
 Attach Commands
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61. Item class API
 public void
setDefaultCommand(Command cmd)
 public void
setItemCommandListener(ItemCom
mandListener listener)
 public void
notifyStateChanged()
 public int getPreferredWidth()
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62. …Getting Started
1st
step: Download sun’s J2ME
Wireless Toolkit from:
http://java.sun.com/products/j2mewtoolkit/d
ownload-2_1.html
2nd step: Make sure you have J2SE
SDK installed
3rd step: Install the J2ME Toolkit.
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63. ….After the installation
 Shortcuts are available from the start menu.
 New directories
created
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64. Using KToolbar
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65. Creating a new Application
 Press “New Project”.
 Enter the project’s name and the MIDlet’s
class name.
 New directories will automatically be created.
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66. 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
external class libraries, (JAR or
J2ME/apps/lib ZIP) for all KToolbar projects.
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67. And then what?
 Choose the target platform
 Write your code Java Technology for the Wireless
JTWI - conforms to
Industry (JSR-185).
 Save
MIDP1.0 - includes MIDP 1.0 and CLDC 1.0
Custom - user defined settings, you can select project
 Build
profile, configurations and various APIs.
(Compile + Preverify)
 Run
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68. 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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69. Some other issues
 OTA provisioning
 Using Servlets
 Working with EclipseME
 Web services
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70. !The END
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