Question: I am starting with Java now.. Could you point me some simple tool that can check for:
-unused methods, class usage, check my style...

Answer: Checkstyle - development tool to help programmers write Java code that adheres to a coding standard. It automates the process of checking Java code to spare humans of this boring (but important) task. This makes it ideal for projects that want to enforce a coding standard.
The things that Checkstyle can check for are:

Unused or duplicate import statements.
Javadoc comments are defined for class, interface, variable
and method declarations. Note: This can be made to check
only public and protected declarations.
Javadoc tags for a method match the actual code.
Detect instantiations of classes that should not be instantiated
(e.g. java.lang.Boolean).
Content of try, catch and finally blocks.
Enforce line wrapping on operators.
Presence of to-do comments.
And much more....
http://checkstyle.sourceforge.net/

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You can take evolutional copy here (fully functional):
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