# Java: Regular expression summary

[This text is taken directly from the Java API documentation]

Construct | Matches |
---|---|

Characters | |

x |
The character x |

\\ |
The backslash character |

\0n |
The character with octal value 0n
(0 <= n <= 7) |

\0nn |
The character with octal value 0nn
(0 <= n <= 7) |

\0mnn |
The character with octal value 0mnn
(0 <= m <= 3,
0 <= n <= 7) |

\xhh |
The character with hexadecimal value 0xhh |

\uhhhh |
The character with hexadecimal value 0xhhhh |

\t |
The tab character ('\u0009') |

\n |
The newline (line feed) character ('\u000A') |

\r |
The carriage-return character ('\u000D') |

\f |
The form-feed character ('\u000C') |

\a |
The alert (bell) character ('\u0007') |

\e |
The escape character ('\u001B') |

\cx |
The control character corresponding to x |

Character classes | |

[abc] |
a, b, or c (simple class) |

[^abc] |
Any character except a, b, or c (negation) |

[a-zA-Z] |
a through z
or A through Z, inclusive (range) |

[a-d[m-p]] |
a through d,
or m through p: [a-dm-p] (union) |

[a-z&&[def]] |
d, e, or f (intersection) |

[a-z&&[^bc]] |
a through z,
except for b and c: [ad-z] (subtraction) |

[a-z&&[^m-p]] |
a through z,
and not m through p: [a-lq-z](subtraction) |

Predefined character classes | |

. |
Any character (may or may not match line terminators) |

\d |
A digit: [0-9] |

\D |
A non-digit: [^0-9] |

\s |
A whitespace character: [ \t\n\x0B\f\r] |

\S |
A non-whitespace character: [^\s] |

\w |
A word character: [a-zA-Z_0-9] |

\W |
A non-word character: [^\w] |

POSIX character classes (US-ASCII only) | |

\p{Lower} |
A lower-case alphabetic character: [a-z] |

\p{Upper} |
An upper-case alphabetic character:[A-Z] |

\p{ASCII} |
All ASCII:[\x00-\x7F] |

\p{Alpha} |
An alphabetic character:[\p{Lower}\p{Upper}] |

\p{Digit} |
A decimal digit: [0-9] |

\p{Alnum} |
An alphanumeric character:[\p{Alpha}\p{Digit}] |

\p{Punct} |
Punctuation: One of !"#$%&'()*+,-./:;<=>?@[\]^_`{|}~ |

\p{Graph} |
A visible character: [\p{Alnum}\p{Punct}] |

\p{Print} |
A printable character: [\p{Graph}] |

\p{Blank} |
A space or a tab: [ \t] |

\p{Cntrl} |
A control character: [\x00-\x1F\x7F] |

\p{XDigit} |
A hexadecimal digit: [0-9a-fA-F] |

\p{Space} |
A whitespace character: [ \t\n\x0B\f\r] |

Classes for Unicode blocks and categories | |

\p{InGreek} |
A character in the Greek block (simple block) |

\p{Lu} |
An uppercase letter (simple category) |

\p{Sc} |
A currency symbol |

\P{InGreek} |
Any character except one in the Greek block (negation) |

[\p{L}&&[^\p{Lu}]] |
Any letter except an uppercase letter (subtraction) |

Boundary matchers | |

^ |
The beginning of a line |

$ |
The end of a line |

\b |
A word boundary |

\B |
A non-word boundary |

\A |
The beginning of the input |

\G |
The end of the previous match |

\Z |
The end of the input but for the final terminator, if any |

\z |
The end of the input |

Greedy quantifiers | |

X? |
X, once or not at all |

X* |
X, zero or more times |

X+ |
X, one or more times |

X{n} |
X, exactly n times |

X{n,} |
X, at least n times |

X{n,m} |
X, at least n but not more than m times |

Reluctant quantifiers | |

X?? |
X, once or not at all |

X*? |
X, zero or more times |

X+? |
X, one or more times |

X{n}? |
X, exactly n times |

X{n,}? |
X, at least n times |

X{n,m}? |
X, at least n but not more than m times |

Possessive quantifiers | |

X?+ |
X, once or not at all |

X*+ |
X, zero or more times |

X++ |
X, one or more times |

X{n}+ |
X, exactly n times |

X{n,}+ |
X, at least n times |

X{n,m}+ |
X, at least n but not more than m times |

Logical operators | |

XY |
X followed by Y |

X|Y |
Either X or Y |

Grouping operators | |

(X) |
X. This capturing group is remembered so it can be referenced later. Numbered starting at 1. |

(?:X) |
X. Used purely for grouping, and isn't remembered. |

Back references | |

\n |
Whatever the n^{th}
capturing group matched |

Quotation | |

\ |
Nothing, but quotes the following character |

\Q |
Nothing, but quotes all characters until \E |

\E |
Nothing, but ends quoting started by \Q |

Special constructs (all groupings are non-capturing) | |

(?idmsux-idmsux) |
Nothing, but turns match flags on - off |

(?idmsux-idmsux:X) |
X, as a non-capturing group with the
given flags on - off |

(?=X) |
X, via zero-width positive lookahead |

(?!X) |
X, via zero-width negative lookahead |

(?<=X) |
X, via zero-width positive lookbehind |

(?<!X) |
X, via zero-width negative lookbehind |

(?>X) |
X, as an independent, non-capturing group |