C is not OOP - neither is C++ really, C uses structured concepts
and C++ does use OOP but is a multi-purpose language, allowing
the programmer to write in procedural or OOP way. Objective-C
is more of a OOP language.
Anyway to your actual question - it is absolutely fine to learn from
Head First Java - as all concepts covered are also in Java 6, 7 and 8.
Very few additional Java features are added to each revision of the
language, and the ones that are will not really effect the standard
core of the language syntax. However, anything below standard 4
is considered outdated by today's standard.
Most textbooks available today are mostly up to date and support
Java 6, 7 and or 8. Your overall knowledge will expand as you delve
deeper into the language and learn about new and exciting concepts.
You can never have too much knowledge in a language, and I do not
believe James Gosling would be able to remember the entire language
off the top of his head without a reference book
Keep working hard and Good luck
Wishes Ada xx