What is Java technology?

Java technology is both a high-level, object-oriented programming language and a platform. Java technology is based on the concept of a single Java Virtual Machine (JVM) -- a translator between the language and the underlying software and hardware. All implementations of the programming language must emulate the JVM, enabling Java programs to run on any system that has a version of the JVM.

The Java programming language is unusual because Java programs are both compiled (translated into an intermediate language called Java bytecode) and interpreted (bytecode parsed and run by the JVM). Compilation occurs once, and interpretation happens each time the program runs. Compiled bytecode is a form of optimized machine code for the JVM; the interpreter is an implementation of the JVM.

The Java platform is a software-only platform that runs on top of various hardware-based platforms. It comes in three versions. It consists of the JVM and the Java Application Programming Interface (API), a large collection of ready-made software components (classes) that ease the development and deployment of applets and applications, including robust, secure, and interoperable enterprise applications. It spans everything from basic objects to networking and security and XML generation and Web services. The Java API is grouped into libraries of related classes and interfaces; the libraries are known as packages.

Along with the Java API, every full implementation of the Java platform includes:

• Development tools for compiling, running, monitoring, debugging, and documenting applications.
• Standard mechanisms for deploying applications to users.
• User interface toolkits that make it possible to create sophisticated graphical user interfaces (GUIs).
• Integration libraries that enable database access and manipulation of remote objects.

Java technology was developed by Sun Microsystems. The Java Community Process (JCP), an open organization of international Java developers and licensees, develops and revises Java technology specifications, reference implementations, and technology compatibility kits. In 2007, Sun made the bulk of its core Java technology available as open-source software under the GNU general public license version 2 (GPLv2).

The main benefit of the Java language is the portability of Java applications across hardware platforms and operating systems -- possible because the JVM installed on each platform understands the same bytecode.

The Java language and platform are impressively scalable. At the low end, existing applications can easily be adapted for devices with limited-memory resources. Scaling up, the language is an ideal framework for server-side Web programming. Because it was designed to run in a secure manner over networks, it affords this level of security when operating over the Internet. In essence, Java technology extends a user's computing power from the desktop to the resources of the Web. Web components are supported by runtime platforms called Web containers, whose services include request dispatching, security, concurrency, life-cycle management, and access to APIs such as naming, transactions, and e-mail. At the high end, Java application servers serve as Web containers for Java components, XML, and Web services that can interact with databases and provide dynamic Web content; they also provide an application-deployment environment for enterprise applications, with capabilities for transaction management, security, clustering, performance, availability, connectivity, and scalability.

The Java language was one of the first technologies to support open standards in the enterprise, opening the door to using XML and Web services to help share information and applications across business lines.

Multiple editions of the Java platform

Three editions of the Java platform make it easier for software developers, service providers, and device manufacturers to target specific markets:

• Java SE (Java Platform, Standard Edition). Formerly called J2SE, Java SE lets you develop and deploy Java applications on desktops and servers, as well as embedded and real-time environments. Java SE includes classes that support the development of Java Web services and provides the foundation for Java Platform, Enterprise Edition (Java EE). Java SE 6 ("Mustang") is the current major release of the Java SE platform. Many Java developers use Java SE 5, also known as Java 5.0 or "Tiger."
  
• Java EE (Java Platform, Enterprise Edition). Formerly called J2EE, the enterprise version assists in the development and deployment of portable, robust, scalable, and secure server-side Java applications. Building on the foundation of Java SE, Java EE provides Web services, component-model, management, and communications APIs for implementing enterprise class SOA and Web 2.0 applications.
  
• Java ME (Java Platform, Micro Edition). Formerly called J2ME, Java ME provides a robust, flexible environment for applications running on a broad range of mobile and embedded devices, such as mobile phones, PDAs, TV set-top boxes, and printers. The Java ME platform includes flexible user interfaces, a robust security model, a broad range of built-in network protocols, and extensive support for networked and offline applications that can be downloaded dynamically. Applications based on Java ME specifications are written once for a wide range of devices yet exploit each device's native capabilities.