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Two forms of Java programs — Applications and applets

Most computer programming is concerned with the production of applications. An application, as mentioned in Unit 01, supports the user in tasks not directly related to the computer system. Examples of applications include word processors, we browsers and spreadsheets. Application programs run on their own, as a separate software object of an operating system such as Windows 95 or NT.

Another form of program is called an applet. An applet is a "mini-program", one that relies on other software to support it. The term is usually -- but not always -- used to refer to programs that are embedded in Web pages. The Java programming language can be used to produce both applications and applets. 

Java is not, on the whole, used for the development of system software (i.e. software for doing tasks on the computer system, such as virus checkers, backup programs, operating systems etc.). This is because Java is intended to be platform independent (i.e., to work on any computer) and system programs by their very nature need to know about the intimate details of the particular computer the system program runs on.

Most textbooks on Java are concerned very much with applet programming. This is rather strange in a way, because application programming is so much more common and more useful. However, the programming techniques required to produce an application are the same in most ways to those used in applets. In this module we will mostly be concerned with applet programming.

In the figures below, the first is a bouncing ball application , while the second is a bouncing ball applet running inside a page being viewed with a web browser.

Applications and applets: Summary

    An application is an independent program, with a useful function unrelated to the software system. 
    An applet is a program that is embedded inside another. 
    A Java applet is usually part of a Web page. 
    Programming principles are the same -- both are computer programs.

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