Web applications are applications that run in a web browser.
Intranet is an internal web page, usually for companies.
Java is a programming language.
If you want to find out the "objective" of those (as in why use a web app instead of a regular .exe installer), there are plenty of books and articles on each subject, just check around the web, this is not the place to re-write articles which is what your question really requires.
Ok, thanks. But can you help me and get project topics related to ( web application + wireless and wired network intranet + java )
You are asking for info for a large chunk of the planet's internet and application base, do a web search, you will get the same info anyone else on the forums will, and you'll be able to put in more detail about exactly what you are looking for.