Java CDC

Java2 Standard Edition

• Java has been through versions 1.0-1.4
• From Java 1.2 onwards, it is also called Java 2
• It was originally designed for set-top boxes, but changed to a general-purpose language due to a project deadline nearly closing the Java project
• There is "cruft" in Java - many obsolete classes
• Java Standard Edition is large
  • The libraries occupy about 5M of disk
  • A typical Java application uses 50M+ of RAM, although much of this is caused by e.g. default stack size settings
• So Java 2 is big and "old" (9 years since public release)

Limiting Java size

• Java is a general purpose language, just like Windows and Linux are general purpose Operating Systems
• Just like Windows and Linux, Java can be reduced in size
• This can be done by
  • Reducing virtual machine size and requirements - the configuration
  • Choosing appropriate application requirements - the profile

Profiles and Configurations

Configurations

• This sets out the different types of virtual machines and their requirments
• The Connected Device Configuration (CDC) is for systems with a reasonable amount of memory: 2M+
• The Connected, Limited Device Configuration (LCDC) is for small devices from 160Kb upwards
• The standard J2SE (Standard Edition) and J2EE (Enterprise Edition) versions remain for large systems such as desktop PCs
• The configurations basically set out the memory constraints of the system
  • CLDC for cellphones, two-way pagers, personal organisers, home appliances, etc
  • CDC for emerging cellphones, point-of-sale terminals, more expensive home appliances, automobile navigation systems, etc

VM classes

Profiles

• The configuration says what the virtual machine can do and needs
• An application needs to do more e.g. use I/O to communicate with the user
• A profile is added on top, to support a class of applications e.g. small screen devices such as phones; wireless connectivity for portable devices; internet connectivity for fixed devices

CDC

The CDC Configuration

This defines what is needed to run a virtual machine in 2M+, supporting all Java 2 language features

• All basic data types: int, float, boolean, etc
• Objects and classes
• Garbage collection
• Threads
• Java 2 security
• Some I/O
• Some networking
• Some internationalisation
• RMI, JNI, reflection, serialisation, JVM debugger interface, weak references

CDC classes

• java.lang - virtual machine classes
• java.util - some
• java.net - UDP, not TCP
• java.io - file I/O
• java.text - minimal I18n, for error messages
• java.security - minimal

CVM

• The CVM is the virtual machine for the CDC configuration
• It is written in C and uses all the techniques learnt in the last 9 years of JVM technology
• It requires about 1/2 the space of a traditional JVM, about 0.5M+
• There is no GUI stuff - the AWT is gone, Swing is not included - why should a JVM need a GUI?

Foundation profile

• The CDC requires a set of classes to run the VM, but not all of of the standard Java classes
• The Foundation profile adds in most of the rest of the contents of the packages for non-gui applications
  • java.lang
  • java.util
  • java.net - adds sockets and HTTP
  • java.io - readers and writers
  • java.text
  • java.security - code signing, certificates
• All of the deprecated classes and methods are gone
  • e.g. the class java.io.LineNumberInputStream is gone
  • e.g. the method java.io.DataInputStream.readLine() is gone
• Note that the AWT is not included, and neither are any of the javax packages

Relation of CDC to J2SE

• There is just a general cleanup of J2SE classes
• All Java 2 language features are present
• A CDC/Foundation application will run under J2SE and J2EE, but maybe not the other way
• GUI classes are missing
• Extension classes are missing (no Swing, either)
• Future application-level profiles may add to these classes
• Currently, there are lots of proposed GUI classes for embedded applications, so standardisation may take a long time

CDC Profiles

There are currently two profiles defined above the Foundation profile

• Personal Basis Profile
  The Personal Basis Profile is for network-connected devices supporting a basic level of graphic presentation. It is suitable for the interactive television market and contains many of the necessary APIs for support of the Multimedia Home Platform (MHP)
• Personal Profile
  The Personal Profile, JSR-62, provides Java APIs for devices requiring a high degree of network connectivity such as applications for the home and office.

Personal Basis profile

• The AWT has
  • general drawing classes and methods e.g. Graphics.drawLine()
  • general event generation and handling e.g. MouseEvent and MouseListener
  • specific widgets such as Button, List
• The Personal Basis Profile has the general classes, but not the specific widgets
• This allows any desired GUI to be built e.g. HAVi GUI objects, Java TV GUI objects, etc

Personal Basis Profile classes

Personal profile

• The Personal Profile replaces the Personal Java specification
• The Personal profile basically adds in the rest of the AWT
• It still leaves out deprecated classes and methods from the J2SE
• It does not include the javax packages