A Java applet is an application that can be embedded in a web page, similar to the way an image or video can be displayed in a web page. Since applets are computer programs, they can be interactive and perform complex functions, such as games, interactive maps, and drawing programs. Java applets are written in the Java programming language.
The first version of the Java programming language, released in 1995, included applets.
Java applets allow web developers to include interactive content within a web page. Applets are client-side applications, meaning they run in the browser on the web site visitor's computer. Applets run using the Java Virtual Machine (JVM) installed on the client computer.
Java applets are platform independent, and can run on any computer that has the JVM and an applet-capable web browser. Standard "unsigned" applets are relatively secure because they run in a isolated sandbox that prevents them from accessing computer files and other sensitive information. Because applets are written in Java, the applet developer can use the full capabilities of the Java programming language, including complex features such as video acceleration, image processing, and database connectivity. Java and many Java development tools are free.
While Java applets have better computer platform support than similar client-side application technologies, there's more overhead in loading an applet. Many developers prefer to use faster, lighter technologies, such as Flash or Silverlight, because they load in the browser faster, require less computer resources, and offer a better range of graphical elements.
There is a strong movement in the Java developer community to abandon applets in favor of the Java WebStart (JWS) technology. JWS applications launch from the web, but do not run in the browser, and behave more like a standard desktop application.
Signed applets contain a signature used to verify the source of applet, indicating that the applet can be trusted if the source is trustworthy. Signed applets are granted additional permissions on the client computer, such as the ability to read and write files to the local file system. Only signed applets from trusted sources should be accepted.
Applets require the JVM and an applet-capable browser, which are available for the most popular computer platforms, but may not be available for older and less popular platforms. It is not uncommon for the JVM to be outdated or not installed on a computer system, causing the applet to fail to run properly if it runs at all.
- Photo Credit Image by Flickr.com, courtesy of moonstar909
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