j2me
TRANSCRIPT
Java 2 Platform, Micro Edition (J2ME)Abhijit Raut Archana
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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!!!J2ME 2
IntroductionPersonalized 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.J2ME 7
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.J2ME 8
Java EditionsJava 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. J2EE J2ME-based devices have J2SE fewer classes.J2ME
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PersonalJava and EmbeddedJava J2ME
is not the first attempt at adapting Java for constrained environments. PersonalJavaUses 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 Addresses specific needs of a certain device family
J2ME Profile
Profile
J2ME Libraries Java Language Java Virtual Machine
Optional PackagesHost Operating SystemJ2ME 13
J2ME Core ConceptsJ2ME is based on 3 core concepts: Configurations Profiles Optional packages
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ConfigurationsA
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.J2ME 15
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
Configuration CLDCConnected Limited Device Configuration
CDCConnected 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
The CDC supports a complete, fullfeatured Java 2 virtual machine
Change in classfile verification preverificationJ2ME 19
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
The CDC includes 17 packages Includes more classes even in the shared packages
Only selected classes from each package are included
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CLDC vs. CDC J2SE Subset
J2SE
CDC
CLDC
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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.J2ME 23
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 - exampleimport 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. }J2ME 25
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.J2ME 26
J2ME Core ConceptsJ2ME 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.J2ME 28
Profiles
Profile MI PMobile Information Device Profile
P
P
FPFoundation Profile
PBPPersonal Basis Profile
PPPersonal Profile
Personal Digital Assistant 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 ConceptsJ2ME 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.J2ME 37
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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.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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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.J2ME 42
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.J2ME 43
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 MIDletExtends MIDlet Implements CommandListener
public class HelloMIDlet extends MIDlet implements CommandListener {
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Creating a MIDletCreating 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 Form Command
Base class
CommandListener ItemCommandListener
Item
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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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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
int append(Item item) public Item get(int itemNum) public
Layout public
void setItemStateListener(ItemState Listener iListener)J2ME 53
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.J2ME 55
Command class Command Command
label public String getLabel()
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)J2ME 58
Sample classes API MIDlet Form Command
CommandListener ItemCommandListener
Item
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Item classA
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(ItemCom mandListener listener) public void notifyStateChanged() public int getPreferredWidth()J2ME 61
Getting Started 1st
step: Download suns 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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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} J2ME/apps/{proj}/bin J2ME/apps/{proj}/lib J2ME/apps/{proj}/res J2ME/apps/{proj}/src J2ME/apps/lib source, resource, and binary files JAR, JAD, unpacked manifest files. external class libraries, (JAR or ZIP) for a specific project resource files source files external class libraries, (JAR or ZIP) for all KToolbar projects.J2ME 66
And then what?
Choose the target platform JTWI - conforms to Write your code Java Technology for the Wireless Industry (JSR-185). Save MIDP1.0 - includes MIDP 1.0 and CLDC 1.0 Custom - user defined settings, you can select project Build configurations and various APIs. profile, (Compile + Preverify) Run
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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/ Fun!!!
Have
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