Transcript J2ME

Introduction
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Personalized and intelligent information appliances
are necessities in our life today.
Such appliances can be:
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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
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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:
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extremely limited memory
small screen sizes
alternative input methods
slow processors
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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
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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.
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J2ME Core Concepts
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Configuration
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Minimum platform
required for a
group of devices
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Libraries
Profile
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J2ME
Profile
Addresses specific
needs of a certain
device family
Java Language
Java Virtual Machine
Optional Packages
Host Operating System
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J2ME Core Concepts
J2ME is based on 3 core concepts:
 Configurations
 Profiles
 Optional packages
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Configurations
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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
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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
Configuration
CLDC
CDC
Connected Limited
Device Configuration
Connected Device
Configuration
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CLDC vs. CDC
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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
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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
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Features missing in
the CLDC VM:
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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
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The KVM and CVM
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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
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The CLDC includes
classes from:
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java.lang
java.io
java.util
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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
J2ME
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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
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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.com:8909";
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
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Adds domain-specific classes to a
configuration:
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To fill in missing functionality
To support specific uses of a device
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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
Profile
MIDP
Mobile
Information
Device
Profile
PDAP
Personal
Digital
Assistant
Profile
FP
Foundation
Profile
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PBP
PP
Personal
Basis Profile
Personal
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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:
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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
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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
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The MIDP adds APIs to the basic APIs defined
by the CLDC. The new features include:
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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
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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
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Memory is a particularly scarce resource.
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The early Motorola J2ME-enabled phones limited
the size of an application to 50K. Some Nokia
phones limit them to even less, about 30K.
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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 :
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RMI Optional Package
 Bluetooth Optional Package
 JDBC Optional Package
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What it all means
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"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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The END!
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You can download all the demos
JARs from:
www.cs.huji.ac.il/~kerengaz/j2me/
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Have Fun!!!
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