A Java applet is an applet delivered to users in the form of Java bytecode. Java applets can be part of a web page and executed by the Java Virtual Machine (JVM) in a process separate from the web browser, or run in Sun’s AppletViewer, a stand-alone tool for testing applets. Java applets were introduced in the first version of the Java language in 1995, and are written in programming languages that compile to Java bytecode, usually in Java, but also in other languages such as Jython, JRuby, or Eiffel (via SmartEiffel).
Since Java’s bytecode is cross-platform or platform independent, Java applets can be executed by browsers for many platforms, including Microsoft Windows, Unix, OS X and Linux. It is also trivial to run a Java applet as an application software with very little extra code so that it can be run directly from the integrated development environment (IDE).