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The Java platform is the name for a computing environment, or platform, from Sun Microsystems which can run applications developed using the Java programming language and set of development tools. In this case, the platform is not a specific hardware or operating system, but rather an execution engine called a virtual machine, and a set of standard libraries which provide common functionality. The platform is properly called the Java Platform (formerly Java 2 Platform*), and 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 .
Java technologies The Java Platform consists of a wide array of technologies, each of which provides a distinct portion of the overall development or Java Runtime Environment. For example, end-users typically interface with the Java Virtual Machine and the standard set of class libraries. In addition, there are numerous ways for Java applications to be deployed, including being embedded into a web page. Lastly, developers who are creating applications for the platform use a set of development tools called the Java Development Kit. 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 the same application to be 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. 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. Languages See the category . 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: Similar platforms The success of Java and its write once, run anywhere concept has also led to other similar efforts. The most notable of these is the Microsoft .NET platform, which copies many of the concepts and innovations of Java. In fact, it has an implementation of Java called Visual J# (formerly known as J++). It must be noted that this implementation 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. See also | ||||||||
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