An applet is a small program that uses the resources of a
larger program and usually provides customization or addi-
tional features. The term first appeared in the early 1990s
in connection with Apple’s AppleScript scripting language
for the Macintosh operating system. Today Java applets rep-
resent the most widespread use of this idea in Web develop-
ment.
Java applets are compiled to an intermediate repre-
sentation called bytecode, and generally are run in a Web
browser. Applets thus represent one
of several alternatives for interacting with users of Web
pages beyond what can be accomplished using simple text
markup.
An applet can be invoked by inserting a reference to
its program code in the text of the Web page, using the
HTML applet element or the now-preferred object element.
Although the distinction between applets and scripting
code (such as in PHP) is somewhat vague, applets usually
run in their own window or otherwise provide their own
interface, while scripting code is generally used to tailor
the behavior of separately created objects. Applets are also rather like plug-ins, but the latter are generally used to
provide a particular capability (such as the ability to read
or play a particular kind of media file), and have a stan-
dardized facility for their installation and management.
Some common uses for applets include animations of
scientific or programming concepts for Web pages support-
ing class curricula and for games designed to be played
using Web browsers. Animation tools such as Flash and
Shockwave are often used for creating graphic applets.
To prevent badly or maliciously written applets from
affecting user files, applets such as Java applets are gen-
erally run within a restricted or “sandbox” environment
where, for example, they are not allowed to write or change
files on disk.
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