Java is a general programming language that can run on Windows, Linux or Mac computers regardless of computer architecture. This versatility is accomplished by converting the Java computer programs into bytecodes that are interpreted by a virtual machine. The Java Virtual Machine (JVM) is a computer program tailored for the specific hardware and operating-system platform. When you download Java software, the package contains the JVM and Java Plug-in software that enables browsers to execute Java Applets.
A Java Applet is a small application written in the Java language and stored as bytecodes. When a browser encounters a web page containing a Java Applet, the browser uses the Java Plug-in to decode the instructions indicated by the applet. The result is usually an interactive web page that the user can use to play a game or perform calculations. Weaknesses in the web browsers can be exploited by malicious Java applets, and for this reason some mobile browsers do not run Java applets at all, or they issue a security warning that asks for confirmation before allowing Java applets to be executed. The warnings may discourage users from using particular web pages even when they pose no danger. It is possible that in the future, browsers will not run Java Applets at all.