The word applet was first used in 1990 in PC Magazine. However, the concept of an applet, or more broadly a small interpreted program downloaded and executed by the user, dates at least to RFC 5 by Jeff Rulifson, which described the Decode-Encode Language, which was designed to allow remote use of the oN-Line System over ARPANET, by downloading small programs to enhance the interaction. This has been specifically credited as a forerunner of Java's downloadable programs in RFC 2555.
Applet as an extension of other software
In some cases, an applet does not run independently. These applets must run either in a container provided by a host program, through a plugin, or a variety of other applications including mobile devices that support the applet programming model.
Web-based Applets
Applets were used to provide interactive features to web applications that historically could not be provided by HTML alone. They could capture mouse input and also had controls like buttons or check boxes. In response to the user action an applet could change the provided graphic content. This made applets well suitable for demonstration, visualization, and teaching. There were online applet collections for studying various subjects, from physics to heart physiology. Applets were also used to create online game collections that allowed players to compete against live opponents in real-time. An applet could also be a text area only, providing, for instance, a cross platform command-line interface to some remote system. If needed, an applet could leave the dedicated area and run as a separate window. However, applets had very little control over web page content outside the applet dedicated area, so they were less useful for improving the site appearance in general. Applets could also play media in formats that are not natively supported by the browser. HTML pages could embed parameters that were passed to the applet. Hence the same applet could appear differently depending on the parameters that were passed. Examples of Web-based Applets include:
3D modeling display applets, used to rotate and zoom a model
Browser games that were applet-based, though some developed into fully functional applications that required installation.
Applet Vs. Subroutine
A larger application distinguishes its applets through several features:
Applets execute only on the "client" platform environment of a system, as contrasted from "servlet". As such, an applet provides functionality or performance beyond the default capabilities of its container.
The container restricts applets' capabilities.
Applets are written in a language different from the scripting or HTML language that invokes it. The applet is written in a compiled language, whereas the scripting language of the container is an interpreted language, hence the greater performance or functionality of the applet. Unlike a subroutine, a complete web component can be implemented as an applet.
A Java applet is a Java program that is launched from HTML and run in a web browser. It can provide web applications with interactive features that cannot be provided by HTML. Since Java's bytecode is platform-independent, Java applets can be executed by browsers running under many platforms, including Windows, Unix, macOS, and Linux. When a Java technology-enabled web browser processes a page that contains an applet, the applet's code is transferred to the client's system and executed by the browser's Java Virtual Machine. An HTML page references an applet either via the deprecated
