Java applet

Java applets are small applications written in the Java programming language, or another programming language that compiles to Java bytecode, and delivered to users in the form of Java bytecode.

At the time of their introduction, the intended use was for the user to launch the applet from a web page, and for the applet to then execute within a Java virtual machine (JVM) in a process separate from the web browser itself. A Java applet could appear in a frame of the web page, a new application window, a program from Sun called appletviewer, or a stand-alone tool for testing applets.^{[clarification needed]}

Java applets were introduced in the first version of the Java language, which was released in 1995. Beginning in 2013, major web browsers began to phase out support for NPAPI, the underlying technology applets used to run. with applets becoming completely unable to be run by 2015–2017. Java applets were deprecated by Java 9 in 2017. Java applets were deprecated for removal by Java 17 in 2021. Java applets are targeted to be removed by Java 26 in 2026.

Java applets were usually written in Java, but other languages such as Jython, JRuby, Pascal, Scala, NetRexx, or Eiffel (via SmartEiffel) could be used as well.

Unlike early versions of JavaScript, Java applets had access to 3D hardware acceleration, making them well-suited for non-trivial, computation-intensive visualizations. Since applets' introduction, JavaScript has gained support for hardware-accelerated graphics via canvas technology (or specifically WebGL, then later WebGPU in the case of 3D graphics), as well as just-in-time compilation.

Since Java bytecode is cross-platform (or platform independent), Java applets could be executed by clients for many platforms, including Microsoft Windows, FreeBSD, Unix, macOS and Linux. They could not be run on mobile devices, which do not support running standard Oracle JVM bytecode. Android devices can run code written in Java compiled for the Android Runtime.

The applets are used to provide interactive features to web applications that cannot be provided by HTML alone. They can capture mouse input and also have controls like buttons or check boxes. In response to user actions, an applet can change the provided graphic content. This makes applets well-suited for demonstration, visualization, and teaching. There are online applet collections for studying various subjects, from physics to heart physiology.

An applet can also be a text area only; providing, for instance, a cross-platform command-line interface 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's dedicated area, so they are less useful for improving the site appearance in general, unlike other types of browser extensions (while applets like news tickers or WYSIWYG editors are also known). Applets can also play media in formats that are not natively supported by the browser.