I\'m not a native English and so I don\'t understand well the meaning of \'flavor\' may be is it referred to a regex syntax?? and if so how many regex syntax are there?
A "flavor" in this context is a particular syntax, as you have surmised. There are many; counting them would be only an academic endeavor.
To find the ones that are generally used, look at the forms accepted by grep.
grep
Java may use whatever syntax has a Java implementation.