How can I allow only one word(string) with javax.validation?

Which regular expression can I use for @Pattern()

I'm not looking for matching the word

I want to allow only single word for input with no white space

Possible input: cat, dogs, bird, tree, moon --> they are all one word

Input with more than single word or sentence is not allowed e.g.) a cat, two dogs ---> they are two words so I don't want to allow them as a user input

Please suggest using @Pattern() rather than other method

Thank you