Java Introduction
Java is a programming language for writing programs that can not only be run on machines that support Java (Java applications), but can also be embedded in web pages (Java applets). Programs can work as applets and/or applications. Embedding executable code in a web page allows the page to be interactive, with animations, games and interactive transaction processing. There are security considerations to embedding, however, which Java tries to address. Java is designed to be machine independent. Java is object-oriented. Java applications may be console applications, only supporting character output to your computer screen, or windowed Java applications. The latter use graphical user interface (GUI) mechanisms and create and manage multiple windows, like other Windows applications.
Java can run on lots of computers and operating systems. It does not execute directly on your computer, but on the Java virtual machine - a standardised hypothetical computer that is emulated inside the computer by a program. Your Java source code is compiled to create a binary program consisting of bytecodes - machine instructions for the Java virtual machine. When you execute the program, the bytecodes are checked for tampering, interpreted, and executed within the Java virtual machine. A Java interpreter may have been incorporated in your web browser. The bytecodes are machine-independent.
One drawback is that Java runs about one tenth as fast as native code, but this is not noticeable with most kinds of programs. You can get around this by using a just in time (JIT) compiler, a program that converts and caches Java programs to native machine instructions as they are loaded. This slows down the loading, however.
Sun provide a Java Development Kit (JDK) for free from http://www.javasoft.com. There are different versions this for different hardware platforms and operating systems. Use the JDK to create and edit source code, then compile and debug. Other companies supply other products to do the job.
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