Regular expression languages also have character classes. : Introduction « Regular Expressions « Java Tutorial

Character classes specify a list of possible characters that can match any single character in the string you want to match.

1. Using the expression [^012], any single digit except for 0, 1, and 2 is matched.
2. You can specify character ranges using the dash.
3. The character class [a–z] matches any single lowercase letter.
4. [^a–z] matches any character except a lowercase letter.
5. [0–9] to match a single digit.
6. [0–3] to match a 0, 1, 2, or 3.
7. [a–zA–Z] to match any single letter.