As java is very new, the makers of it haven't quite got everything right yet.
Applets are perhaps the most familiar face of java.
Applets are tiny programmes that can be embedded into a web page to produce startling effects and interactivity. For example, applets aren't allowed any kind of access to the client's file system, nor can they send any information elsewhere unless they are explicitly allowed to do so. Servlets are a bit like applets except that they run on the server, not the client. In practice this means they are suitable for quite different kinds of operation, and you don't see them on web pages. Beans are not complete programmes at all.