Java is a programming language from Sun Microsystems. Java is the general term used to denote the software and its components, which include 'Java Runtime Environment' (JRE), and 'Java Virtual Machine' (JVM).

[edit] Overview

Java is intended to be a universal programming language for all platforms. The source is compiled into pseudocode and an interpreter is then written to run it on the target platform. The pseudocode is zipped together into a package and is given a .jar extension. There is a run time package (interpreter) available for each target machine.

In theory the programmer need not worry about the target platform when writing the original code. In practice a full desktop computer can use this model but mobile platforms usually support a subset of the full functionality. Thus standards like MIDP have been developed. Waba is another run time and development project for small portable low powered units. Java Platform, Micro Edition (Java ME, formerly J2ME), is the Java platform for consumer and embedded devices, such as mobile phones, PDAs, TV set-top boxes, and a whole range of other mobile and wireless devices. Java ME is like the Sun Java Runtime Environment (JRE) in that Java ME is built following a standard set of Java platform guidelines, and is developed with the help of leading mobile manufacturers and wireless service providers.

Java ME is the kind of platform that delivers new application power and cutting edge wireless connection benefits to your cellular phone or PDA when you need it. Java ME is now inside millions of devices, and is today's platform of choice for developing consumer tools and features found on cell phones and PDAs everywhere.

[edit] Terms

• Applet: In general, an applet is a software component that performs a narrow function within another program environment, such as a web browser. Java applets provide interactive features in a web browser using a Java Virtual Machine (JVM).

• JRE (Java Runtime environment): It is an implementation of the Java Virtual Machine* which actually executes Java programs.

• Java Runtime Environment (JRE) Cache: A storage area within the Java console, which must sometimes be cleared manually in order to allow the latest Java version to load and install.

• Java Virtual Machine (JVM): In Java, a set of software programs that enable the execution of instructions – usually written in Java bytecode. JVMs are available for all the most common hardware and software platforms.

• JAR: Java software bytecode programs usually have a .jar extension and are compressed using ZIP.

• JDK (Java Development Toolkit): It is a bundle of software that you can use to develop Java based applications.

• JIT (Just in Time): It is a term applied to the compiler that compiles the source on the fly as it is needed.

• JAD is a text base installation file that tells the Java Virtual Machine (JVM) on your phone the name of the executable (JAR) to download and install on your machine.