A Java class file is a file (with the filename extension) containing Java bytecode that can be executed on the Java Virtual Machine (JVM). A Java class file is usually produced by a Java compiler from Java programming language source files ( files) containing Java classes (alternatively, other JVM languages can also be used to create class files).

<programming, language, portability> (After the Indonesian island, a source of programming fluid) A simple, object-oriented, distributed, interpreted, robust, secure, architecture-neutral, portable, multithreaded, dynamic, buzzword-compliant, general-purpose programming language developed by Sun Microsystems in the early 1990's (initially for set-top television controllers), and released to the public in 1995. Java first became popular by being the earliest portable dynamic client-side content for the World-Wide Web in the form of platform-independent Java "applets". In the late 1990's and into the 2000's it has also become very popular on the server side, where an entire set of APIs defines the J2EE. Java is both a set of public specifications (controlled by Sun Microsystems through the JCP) and a series of implementations of those specifications. Java is syntactially similar to C++ without user-definable operator overloading, (though it does have method overloading), without multiple inheritance, and extensive automatic coercions. It has automatic garbage collection. Java extends C++'s object-oriented facilities with those of Objective C for dynamic method resolution. Whereas programs in C++ and similar languages are compiled and linked to platform-specific binary executables, Java programs are typically compiled to portable architecture-neutral bytecode or ".class" files, which are run using a {Java Virtual Machine}. The JVM is also called an interpreter, though it is more correct to say that it uses {Just-In-Time Compilation} to convert the bytecode into native {machine code}, yielding greater efficiency than most interpreted languages, rivalling C++ for many long-running, non-GUI applications. The run-time system is typically written in POSIX-compliant ANSI C or C++. Some implementations allow Java class files to be translated into native machine code during or after compilation. The Java compiler and linker both enforce {strong type checking} - procedures must be explicitly typed. Java supports the creation of virus-free, tamper-free systems with authentication based on public-key encryption. Java has an extensive library of routines for all kinds of programming tasks, rivalling that of other languages. For example, the "java.net} package supports TCP/IP protocols like HTTP and FTP. Java applications can access objects across the Internet via URLs almost as easily as on the local file system. There are also capabilities for several types of distributed applications. The Java GUI libraries provide portable interfaces. For example, there is an abstract Window class and implementations of it for Unix, Microsoft Windows and the Macintosh. The "java.awt" and "javax.swing" classes can be used either in Web-based "Applets" or in client-side or "desktop" applications. There are also packages for developing XML applications, web services, servlets and other web applications, security, date and time calculations and I/O formatting, database (JDBC), and many others. Java is not directly related to JavaScript despite the name. http://java.sun.com/. Usenet newsgroup: news:comp.lang.java. (2005-01-21)