Java Information

The JAVA language concept

Without being at all a JAVA tutorial, this page gives you the minimum information you should know about this language to be able to use existing JAVA applications.

The JAVA characteristics JAVA is a programming language, developed by Sun Microsystems and first released in 1995 (release 1.0). Since that time, it gained a large popularity mainly due to two caracteristics :
  • A JAVA programme is hardware and operating system independant. If well written (!), the same JAVA programme, compiled once, will run identically on a SUN/solaris workstation, a PC/windows computer or a Macintosh computer. Not mentioning other Unix flavors, including Linux, and every Web browser, with some restrictions described below.
    This universal executability is made possible because a JAVA programme is run through a JAVA Virtual Machine.
  • it is an object oriented language. This feature is mainly of interest for software developers

The JAVA Virtual Machine A JAVA programme is build by a JAVA compiler wich generates its own binary code. This binary code is independant from any hardware and operating system. To be executed, it needs a virtual machine, which is a programme analysing this binary code and executing the instructions it contains.
Of course, this Java Virtual Machine (JVM) is hardware and operating system dependant. Two types of Virtual Machines exist: those included in every Web Browser, and those running as an independant programme, like the Java RunTime Environment (JRE) from Sun Microsystems. These programmes need to be downloaded for your particular platform. As seen in the next paragraph, these two types of Virtual Machines dont behave exactly the same.

Applet and Standalone Application A JVM in a web browser runs a JAVA programme as an Applet. The applet is embedded in a web page and downloaded from a web server like any other HTML page or image when requested.
A independant JVM runs a JAVA programme as a Standalone Application.

Usefull links Information and relevant links about JAVA can be obtained on the web at the Sun java page.

aladin


© UDS/CNRS

Contact