Java Platform

From Wikipedia, the free encyclopedia

Java Platforms

Micro Edition (ME)

Standard Edition (SE)

Enterprise Edition (EE)

The Java Platform is  the world's most broadly deployed open source software technology, in use by hundreds of millions of users across the world to create, display, operate and  interact with services on the internet. The Java platform runs on devices as small as the SIM card in your phone, up into nearly 1 billion Java enabled phones, it  runs on myriad set top boxes, hundreds of millions of desktop PC's, and  into a diversity of network devices, from servers and  storage systems, to network devices.

Formally, the Java Platform is  the name for a bundle of related programs, or  platform, from Sun Microsystems which allow for developing and  running programs written in the Java programming language. The platform is  not specific to any one processor or  operating system, but rather, an  execution engine (called a virtual machine) and  a set of standard libraries which provide common functionality are  implemented for various hardware and  operatings systems so that Java programs can run identically on all of them.

The Java Platform (formerly Java 2 Platform[1]), includes the Java Platform Standard Edition or  Java SE (formerly J2SE), the Java Platform Enterprise Edition or  Java EE (formerly J2EE), and  the Java Platform Micro Edition or  Java ME (formerly J2ME). As of 2006, the current version of the Java Platform is  alternatively specified as version 1.5 or  version 5.0 or  version 5 (all refer to the same version), however, version 5 is  preferred. A good overview of the myriad of technologies that makes up the current Java Platform can be found on the JDK Documentation Page.

Contents 1 Java technologies 2 Java Virtual Machine 3 Class libraries 4 Languages 5 Similar platforms 6 See also

[edit] Java technologies

Technically speaking, Java consists of several programs, each of which provides a distinct portion of its overall capabilities. There is  the Java compiler that converts Java source code into Java bytecode (an intermediate language for the Java Virtual Machine a.k.a. JVM) and  provided as part of the Java Development Kit (JDK). There is  a sophisticated Java Runtime Environment (JRE) that usually implements the JVM by means of a Just-In-Time compiler that converts intermediate bytecode into native machine code on the fly. There are  extensive libraries (pre-compiled into Java bytecode) containing reusable code, as well as numerous ways for Java applications to be deployed, including being embedded in a web page as an  applet. Taken together, this entire set of software technologies is  referred to as the 'Java Platform'.

[edit] Java Virtual Machine

Main article: Java Virtual Machine

The heart of the Java Platform is  the concept of a common "virtual" processor that executes Java bytecode programs. This bytecode is  the same no matter what hardware or  operating system the program is  running under. The Java Platform provides a just-in-time (JIT) compiler within the Java Virtual Machine, or  JVM, which handles execution of Java. The JIT compiler translates the Java bytecode into native processor instructions at run-time and  caches the native code in memory during execution.

The use of bytecode as an  intermediate language permits Java programs to run on any platform that has a virtual machine available. The use of a JIT compiler means that Java applications, after a short delay during loading and  once they have  "warmed up" by being all or  mostly JIT-compiled, tend to run about as fast as native programs. Since JRE version 1.2, Sun's JVM implementation has included a just-in-time compiler instead of an  interpreter.

[edit] Class libraries

In most modern operating systems, a large body of reusable code is  provided to simplify the programmer's job. This code is  typically provided as a set of dynamically loadable libraries that applications can call at runtime. Because the Java Platform is  not dependent on any specific operating system, applications cannot rely on any of the existing libraries. Instead, the Java Platform provides a comprehensive set of standard class libraries, containing much of the same reusable functions commonly found in modern operating systems.

The Java class libraries serve three purposes within the Java Platform. Like other standard code libraries, they provide the programmer a well-known set of functions to perform common tasks, such as maintaining lists of items or  performing complex string parsing. In addition, the class libraries provide an  abstract interface to tasks that would normally depend heavily on the hardware and  operating system. Tasks such as network access and  file access are  often heavily dependent on the native capabilities of the platform. The Java java.net and  java.io libraries implement the required native code internally, then provide a standard interface for the Java applications to perform those tasks. Finally, some underlying platforms may not support all of the features a Java application expects. In these cases, the class libraries can either emulate those features using whatever is  available, or  provide a consistent way to check for the presence of a specific feature.

[edit] Languages

See the category JVM programming languages.

The word Java, by itself, usually refers to the Java programming language which was designed for use with the Java Platform. Programming languages are  typically outside of the scope of the phrase "platform", although the Java programming language is  listed as a core part of the Java platform. The language and  runtime are  therefore commonly considered a single unit.

Nevertheless, third parties have  produced a number of compilers or  interpreters which target the JVM. Some of these are  for existing languages, while others are  for extensions to the Java language itself. These include:

• AspectJ, Java with aspect oriented-programming
• Generic Java (GJ), which was incorporated into official Java as of Java SE 5.0
• Groovy
• BeanShell
• Jython, a Python interpreter that include jythonc, a Python-to-Java bytecode compiler
• NetREXX
• Nice
• Pizza
• Scala
• JRuby, a Ruby interpreter
• Sleep, an  interpreter mixing Perl and  Objective-C features
• Rhino, a JavaScript interpreter

[edit] Similar platforms

The success of Java and  its write once, run anywhere concept has led to other similar efforts, notably the Microsoft .NET platform, appearing since 2002, which incorporates many of the successful aspects of Java. However, .NET's goal of making 36+ versions of Windows operating systems alike to a programmer did not include non-Windows operating systems or  non-Intel-compatible processors. .NET's goals did, however, include a strong emphasis on cross-language library usability, and  it has been somewhat more  successful than Java in achieving that (though this is  rapidly changing as of 2006).

.NET includes an  implementation of Java called Visual J# (formerly known as J++) that is  not compatible with the Java specification, and  the associated class library mostly dates to the old JDK 1.1 version of the language; for these reasons, it  is more  a transitional language to switch from Java to the Microsoft .NET platform, than a first class Microsoft .NET language.

[edit] See also

• List of Java APIs
• Java (Sun)
• Java (programming language)

Java (Sun)
Major Technologies:	Java (programming language) | Java Platform | Java Development Kit | Java Virtual Machine | Java Runtime Environment
History:	Java version history | Criticism of Java | Java Community Process | Sun Microsystems
Language Features:	Bytecode | Syntax | Applets | Servlets | JavaServer Pages