Answer by vic for What is a word boundary in regex?

when you use \\b(\\w+)+\\b that means exact match with a word containing only word characters ([a-zA-Z0-9])

in your case for example setting \\b at the begining of regex will accept -12(with space) but again it won't accept -12(without space)

for reference to support my words: https://docs.oracle.com/javase/tutorial/essential/regex/bounds.html