In computing

Computing

Computing is usually defined as the activity of using and improving computer hardware and software. It is the computer-specific part of information technology...

, an applet is any small application that performs one specific task that runs within the scope of a larger program, often as a plug-in. An applet typically also refers to Java applet

Java applet

A Java applet is an applet delivered to users in the form of Java bytecode. Java applets can run in a Web browser using a Java Virtual Machine , or in Sun's AppletViewer, a stand-alone tool for testing applets...

s, i.e., programs written in the Java

Java (programming language)

Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities...

 programming language that are included in a web page

Web page

A web page or webpage is a document or information resource that is suitable for the World Wide Web and can be accessed through a web browser and displayed on a monitor or mobile device. This information is usually in HTML or XHTML format, and may provide navigation to other web pages via hypertext...

. The word Applet was first used in 1990 in PC Magazine.

Applet as a standalone application

Provided that an applet is hosted by an operating system

Operating system

An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...

, it can function as any other normal software application but is small in size and performs only a small set of tasks. Examples of applications often classified as applets are all of the accessories bundled in Microsoft Windows

Microsoft Windows

Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...

 (such as Windows Notepad or Microsoft Paint

Microsoft Paint

Paint is a simple graphics painting program that has been included with all versions of Microsoft Windows. It is often referred to as MS Paint or Microsoft Paint...

). Applets are not full-featured application programs.

Applet as an extension of other software

In some cases, an applet does not run independently. These applets must run either in a container

Container (data structure)

In computer science, a container is a class, a data structure, or an abstract data type whose instances are collections of other objects. In other words; they are used for storing objects in an organized way following specific access rules...

 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 are used to provide interactive features to web applications that cannot be provided by HTML

HTML

HyperText Markup Language is the predominant markup language for web pages. HTML elements are the basic building-blocks of webpages....

 alone. They can capture mouse input

Mouse (computing)

In computing, a mouse is a pointing device that functions by detecting two-dimensional motion relative to its supporting surface. Physically, a mouse consists of an object held under one of the user's hands, with one or more buttons...

 and also have controls like buttons

Button (computing)

In computing, a button is a user interface element that provides the user a simple way to trigger an event, like searching for a query at a search engine, or to interact with dialog boxes, like confirming an action.-Description:A typical button is a rectangle or rounded rectangle, wider than it is...

 or check box

Check box

In computing, a checkbox is a graphical user interface element that permits the user to make multiple selections from a number of options or to have the user answer yes or no on a simple yes/no question.Normally, checkboxes are shown on...

es. In response to the user action an applet can change the provided graphic content. This makes applets well suitable for demonstration, visualization, and teaching. There are online applet collections for studying various subjects, from physics to heart physiology. Applets are also used to create online game collections that allow players to compete against live opponents in real-time.

An applet can also be a text area only, providing, for instance, a cross platform command-line interface

Command-line interface

A command-line interface is a mechanism for interacting with a computer operating system or software by typing commands to perform specific tasks...

 to some remote system. If needed, an applet can leave the dedicated area and run as a separate window. However, applets have very little control over web page content outside the applet dedicated area, so they are less useful for improving the site appearance in general (while applets like news ticker

News ticker

A news ticker resides in the lower third of the television screen space on television news networks dedicated to presenting headlines or minor pieces of news. It may also refer to a long, thin scoreboard-style display seen around the front of some offices or public buildings...

s or WYSIWYG

WYSIWYG

WYSIWYG is an acronym for What You See Is What You Get. The term is used in computing to describe a system in which content displayed onscreen during editing appears in a form closely corresponding to its appearance when printed or displayed as a finished product...

 editors are also known). Applets can also play media in formats that are not natively supported by the browser

HTML pages may embed parameters that are passed to the applet. Hence the same applet may appear differently depending on the parameters that were passed.

Examples of Web-based Applets include:

• QuickTime movies
  QuickTime
  QuickTime is an extensible proprietary multimedia framework developed by Apple Inc., capable of handling various formats of digital video, picture, sound, panoramic images, and interactivity. The classic version of QuickTime is available for Windows XP and later, as well as Mac OS X Leopard and...
  
  
• Flash movies
  SWF
  SWF is an Adobe Flash file format used for multimedia, vector graphics and ActionScript. Originating with FutureWave Software, then transferred to Macromedia, and then coming under the control of Adobe, SWF files can contain animations or applets of varying degrees of interactivity and function.,...
  
  
• Windows Media Player
  Windows Media Player
  Windows Media Player is a media player and media library application developed by Microsoft that is used for playing audio, video and viewing images on personal computers running the Microsoft Windows operating system, as well as on Pocket PC and Windows Mobile-based devices...
  
   applets, used to display embedded video files in Internet Explorer
  Internet Explorer
  Windows Internet Explorer is a series of graphical web browsers developed by Microsoft and included as part of the Microsoft Windows line of operating systems, starting in 1995. It was first released as part of the add-on package Plus! for Windows 95 that year...
  
   (and other browsers
  Web browser
  A web browser is a software application for retrieving, presenting, and traversing information resources on the World Wide Web. An information resource is identified by a Uniform Resource Identifier and may be a web page, image, video, or other piece of content...
  
   that support the plugin)
• 3D modeling
  3D modeling
  In 3D computer graphics, 3D modeling is the process of developing a mathematical representation of any three-dimensional surface of object via specialized software. The product is called a 3D model...
  
   display applets, used to rotate and zoom a model
• Browser game
  Browser game
  A browser game is a computer game that is played over the Internet using a web browser. Browser games can be created and run using standard web technologies or browser plug-ins. Browser games include all video game genres and can be single-player or multiplayer...
  
  s can be applet-based, though some may develop into fully functional applications that require 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
  Java Servlet
  A servlet is a Java programming language class used to extend the capabilities of servers that host applications accessed via a request-response programming model. Although servlets can respond to any type of request, they are commonly used to extend the applications hosted by Web servers...
  
  ". As such, an applet provides functionality or performance beyond the default capabilities of its container (the browser).
• The container restricts applets' capabilities.
• Applets are written in a language different from the scripting or HTML
  HTML
  HyperText Markup Language is the predominant markup language for web pages. HTML elements are the basic building-blocks of webpages....
  
   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.

Java Applet

Java Applets can provide web applications with interactive features that cannot be provided by HTML

HTML

HyperText Markup Language is the predominant markup language for web pages. HTML elements are the basic building-blocks of webpages....

. Since Java's bytecode

Bytecode

Bytecode, also known as p-code , is a term which has been used to denote various forms of instruction sets designed for efficient execution by a software interpreter as well as being suitable for further compilation into machine code...

 is platform-independent, Java applets can be executed by browsers running under many platforms, including Windows

Microsoft Windows

Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...

, Unix

Unix

Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...

, Mac OS

Mac OS

Mac OS is a series of graphical user interface-based operating systems developed by Apple Inc. for their Macintosh line of computer systems. The Macintosh user experience is credited with popularizing the graphical user interface...

, and Linux

Linux

Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...

. When a Java technology-enabled web browser

Web browser

A web browser is a software application for retrieving, presenting, and traversing information resources on the World Wide Web. An information resource is identified by a Uniform Resource Identifier and may be a web page, image, video, or other piece of content...

 processes a page that contains an applet, the applet's code

Code

A code is a rule for converting a piece of information into another form or representation , not necessarily of the same type....

 is transferred to the client's system and executed by the browser's Java Virtual Machine

Java Virtual Machine

A Java virtual machine is a virtual machine capable of executing Java bytecode. It is the code execution component of the Java software platform. Sun Microsystems stated that there are over 4.5 billion JVM-enabled devices.-Overview:...

 (JVM). An HTML page references an applet either via the deprecated tag or via its replacement, the