RegEx Cheatsheet

Character classes

Pattern	Matches
.	any character except newline
\w \d \s	word, digit, whitespace
\W \D \S	not word, digit, whitespace
[abc]	any of a, b, or c
[^abc]	not a, b, or c
[a-g]	character between a & g

Anchors

Pattern	Matches
^abc$	start / end of string
\b \B	word / not-word boundary

Escaped characters

Pattern	Matches
\. \* \\	escaped special characters
\t \n \r	tab, linefeed, carriage return

Groups & lookaround

Pattern	Meaning
(abc)	capture group
\1	backreference to group #1
(?:abc)	non-capturing group
(?=abc)	positive lookahead
(?!abc)	negative lookahead

Quantifiers & alternation

Pattern	Meaning
a* a+ a?	0+, 1+, 0 or 1
a{5} a{2,}	exactly 5, two or more
a{1,3}	between one & three
a+? a{2,}?	lazy — match as few as possible
ab|cd	match ab or cd

Java notes

• Escape backslashes in string literals: "\\d+". Use Pattern/Matcher, or String.matches/replaceAll/split.
• Prefer pre-compiled Pattern for reuse; matches() anchors the whole input implicitly.