Transcript J2ME - Omieno Kelvin

Java 2 Platform, Micro Edition
(J2ME)
Masha Gutkhen
Keren Gazit
J2ME
1
Contents
What’s J2ME?
 J2ME core concepts



Configurations (CLDC, CDC)
Profiles (MIDP)

MIDlet, MIDlet Suite

Basic classes API

Installation and using the Toolkit

Demos!!!
J2ME
2
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.
J2ME
3
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
J2ME
4
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).
J2ME
5
J2ME
6
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 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
J2ME
9
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
J2ME
10
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.

J2ME
11
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".

J2ME
12
J2ME Core Concepts

Configuration


Minimum platform
required for a
group of devices
J2ME
Libraries
Profile


J2ME
Profile
Addresses specific
needs of a certain
device family
Java Language
Java Virtual Machine
Optional Packages
Host Operating System
J2ME
13
J2ME Core Concepts
J2ME is based on 3 core concepts:
 Configurations
 Profiles
 Optional packages
J2ME
14
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.
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.

J2ME
16
Configurations
Configuration
CLDC
CDC
Connected Limited
Device Configuration
Connected Device
Configuration
J2ME
17
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

J2ME
CDC
 2 MB or more
memory for Java
platform
 32-bit processor
 High bandwidth
network connection,
most often using
TCP/IP
18
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  preverification
J2ME
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.
J2ME
20
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
J2ME
21
CLDC vs. CDC – J2SE Subset
J2SE
CDC
J2ME
CLDC
22
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.
J2ME
24
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.
}…
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 Concepts
J2ME is based on 3 core concepts:
 Configurations
 Profiles
 Optional packages
J2ME
27
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
MIDP
Mobile
Information
Device
Profile
PDAP
Personal
Digital
Assistant
Profile
FP
Foundation
Profile
J2ME
PBP
PP
Personal
Basis Profile
Personal
Profile
29
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

J2ME
30
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.
J2ME
31
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.
J2ME
32
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.

J2ME
33
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.
J2ME
34
J2ME Core Concepts
J2ME is based on 3 core concepts:
 Configurations
 Profiles
 Optional packages
J2ME
35
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

J2ME
36
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.
J2ME
37
J2ME
38
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.

J2ME
39
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

J2ME
40
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()).

J2ME
41
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
J2ME
44
Creating a MIDlet
Importing MIDP
specific
packages
import javax.microedition.lcdui.*;
import javax.microedition.midlet.*;
J2ME
45
Creating a MIDlet
Extends MIDlet
Implements
CommandListener
public class HelloMIDlet
extends MIDlet
implements CommandListener {
J2ME
46
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);
}
J2ME
47
Sample MIDP classes API
MIDlet
 Form
 Command

CommandListener
 ItemCommandListener


Item
J2ME
48
Sample classes API
 MIDlet
– Base class
Form
 Command

CommandListener
 ItemCommandListener


Item
J2ME
49
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()
J2ME
50
Sample classes API

MIDlet
 Form

Command
CommandListener
 ItemCommandListener


Item
J2ME
51
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.
J2ME
52
Form class API
 Item
management
 public
int append(Item item)
 public Item get(int itemNum)
 Layout

public void
setItemStateListener(ItemState
Listener iListener)
J2ME
53
Sample classes API
MIDlet
 Form

 Command
 CommandListener
 ItemCommadListener

Item
J2ME
54
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 label
 public String getLabel()
Command type
 public int getCommandType()
 Command priority
 public int getPriority()

J2ME
56
CommandListener class API
This object is a listener for Commands
that are attached to a Displayable.
 public void
commandAction(Command c,
Displayable d)

J2ME
57
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
J2ME
59
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

J2ME
60
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 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.
J2ME
62
After the installation….

Shortcuts are available from the start menu.

New directories
created
J2ME
63
Using KToolbar
J2ME
64
Creating a new Application
Press “New Project”.
 Enter the project’s name and the MIDlet’s
class name.
 New directories will automatically be created.

J2ME
65
Where to place your files?
J2ME/apps/{proj}
J2ME/apps/{proj}/res
source, resource, and binary
files
JAR, JAD, unpacked manifest
files.
external class libraries, (JAR or
ZIP) for a specific project
resource files
J2ME/apps/{proj}/src
source files
J2ME/apps/lib
external class libraries, (JAR or
ZIP) for all KToolbar projects.
J2ME/apps/{proj}/bin
J2ME/apps/{proj}/lib
J2ME
66
And then what?





Choose the target platform
JTWI
- conforms
to Java Technology for the Wireless
Write
your
code
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
J2ME
67
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… 

J2ME
68
Some other issues
OTA provisioning
 Using Servlets
 Working with EclipseME
 Web services

J2ME
69
The END!

You can download all the demos
JARs from:
www.cs.huji.ac.il/~kerengaz/j2me/

Have Fun!!!
J2ME
70