Unfortunately this isn't a Servlets question. We have forums specific to APIs, tools, Certifications etc. This way you can go to the direct forum and get the best answer possible from the experts in those arenas.
I am going to move this to the Java In General (Beginner) forum, there should be a link near the top left of this thread that will take you to that forum.
Primitive are most certainly not implemented as classes. There are Class objects available which represent the types "int", "char", "byte", etc, but an int is not an instance of that class; the special Class object is just used as a placeholder.
To answer Sampathkumar's question:
First, Welcome to JavaRanch!
Second: ints and chars aren't objects, and Java simply isn't a "pure O-O" language. There aren't many languages that are "pure" in this sense: Smalltalk, Ruby, and Eiffel are perhaps the best known ones. But Java and its cousin C++ are "multiparadigm" languages.
Is this a "violation" of anything? No, of course not, because there's no law that says a languge has to be "pure O-O" (or pure anything.)
Finally, about assert: it's a language keyword introduced in JDK version 1.4. It's not anywhere in the API, as it's not a method: it's described in an article that comes with the JDK 1.4 documentation.