Pattern (Java Platform SE 6)

java.lang.Object
  
public final class Pattern
extends Object
implements Serializable



A compiled representation of a regular expression.

 
 A regular expression, specified as a string, must first be compiled into
 an instance of this class.  The resulting pattern can then be used to create
 a Matcher object that can match arbitrary character sequences against the regular
 expression.  All of the state involved in performing a match resides in the
 matcher, so many matchers can share the same pattern.

 
 A typical invocation sequence is thus

 
 Pattern p = Pattern.compile("a*b");
 Matcher m = p.matcher("aaaaab");
 boolean b = m.matches();

  A matches method is defined by this class as a
 convenience for when a regular expression is used just once.  This method
 compiles an expression and matches an input sequence against it in a single
 invocation.  The statement

 
 boolean b = Pattern.matches("a*b", "aaaaab");

 is equivalent to the three statements above, though for repeated matches it
 is less efficient since it does not allow the compiled pattern to be reused.

  Instances of this class are immutable and are safe for use by multiple
 concurrent threads.  Instances of the Matcher class are not safe for
 such use.


 
 
 Summary of regular-expression constructs 


 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}\x20]
\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]
 
java.lang.Character classes (simple java character type)
\p{javaLowerCase} Equivalent to java.lang.Character.isLowerCase()
\p{javaUpperCase} Equivalent to java.lang.Character.isUpperCase()
\p{javaWhitespace} Equivalent to java.lang.Character.isWhitespace()
\p{javaMirrored} Equivalent to java.lang.Character.isMirrored()
 
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
(X) X, as a capturing group
 
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 (non-capturing)
(?:X) X, as a non-capturing group
(?idmsux-idmsux)  Nothing, but turns match flags i
 d m s
 u x on - off
(?idmsux-idmsux:X)   X, as a non-capturing group with the
         given flags i d
 m s u
 x 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

 


 
  Backslashes, escapes, and quoting 

  The backslash character ('\') serves to introduce escaped
 constructs, as defined in the table above, as well as to quote characters
 that otherwise would be interpreted as unescaped constructs.  Thus the
 expression \\ matches a single backslash and \{ matches a
 left brace.

 
 It is an error to use a backslash prior to any alphabetic character that
 does not denote an escaped construct; these are reserved for future
 extensions to the regular-expression language.  A backslash may be used
 prior to a non-alphabetic character regardless of whether that character is
 part of an unescaped construct.

 
 Backslashes within string literals in Java source code are interpreted
 as required by the Java Language
 Specification as either Unicode
 escapes or other character
 escapes.  It is therefore necessary to double backslashes in string
 literals that represent regular expressions to protect them from
 interpretation by the Java bytecode compiler.  The string literal
 "\b", for example, matches a single backspace character when
 interpreted as a regular expression, while "\\b" matches a
 word boundary.  The string literal "\(hello\)" is illegal
 and leads to a compile-time error; in order to match the string
 (hello) the string literal "\\(hello\\)"
 must be used.

 
 
 Character Classes 


     Character classes may appear within other character classes, and
    may be composed by the union operator (implicit) and the intersection
    operator (&&).
    The union operator denotes a class that contains every character that is
    in at least one of its operand classes.  The intersection operator
    denotes a class that contains every character that is in both of its
    operand classes.

    
 The precedence of character-class operators is as follows, from
    highest to lowest:

    
1     Literal escape     \x
2     Grouping [...]
3     Range a-z
4     Union [a-e][i-u]
5     Intersection [a-z&&[aeiou]]

     Note that a different set of metacharacters are in effect inside
    a character class than outside a character class. For instance, the
    regular expression . loses its special meaning inside a
    character class, while the expression - becomes a range
    forming metacharacter.

 
 
 Line terminators 


  A line terminator is a one- or two-character sequence that marks
 the end of a line of the input character sequence.  The following are
 recognized as line terminators:

 
 A newline (line feed) character ('\n'),

   
 A carriage-return character followed immediately by a newline
   character ("\r\n"),

   
 A standalone carriage-return character ('\r'),

   
 A next-line character ('\u0085'),

   
 A line-separator character ('\u2028'), or

   
 A paragraph-separator character ('\u2029).

 
 If UNIX_LINES mode is activated, then the only line terminators
 recognized are newline characters.

 
 The regular expression . matches any character except a line
 terminator unless the DOTALL flag is specified.

 
 By default, the regular expressions ^ and $ ignore
 line terminators and only match at the beginning and the end, respectively,
 of the entire input sequence. If MULTILINE mode is activated then
 ^ matches at the beginning of input and after any line terminator
 except at the end of input. When in MULTILINE mode $
 matches just before a line terminator or the end of the input sequence.

 
 
 Groups and capturing 


  Capturing groups are numbered by counting their opening parentheses from
 left to right.  In the expression ((A)(B(C))), for example, there
 are four such groups: 

 1     ((A)(B(C)))
2     (A)
3     (B(C))
4     (C)

  Group zero always stands for the entire expression.

 
 Capturing groups are so named because, during a match, each subsequence
 of the input sequence that matches such a group is saved.  The captured
 subsequence may be used later in the expression, via a back reference, and
 may also be retrieved from the matcher once the match operation is complete.

 
 The captured input associated with a group is always the subsequence
 that the group most recently matched.  If a group is evaluated a second time
 because of quantification then its previously-captured value, if any, will
 be retained if the second evaluation fails.  Matching the string
 "aba" against the expression (a(b)?)+, for example, leaves
 group two set to "b".  All captured input is discarded at the
 beginning of each match.

 
 Groups beginning with (? are pure, non-capturing groups
 that do not capture text and do not count towards the group total.


 
 Unicode support 

  This class is in conformance with Level 1 of Unicode Technical
 Standard #18: Unicode Regular Expression Guidelines, plus RL2.1
 Canonical Equivalents.

 
 Unicode escape sequences such as \u2014 in Java source code
 are processed as described in §3.3
 of the Java Language Specification.  Such escape sequences are also
 implemented directly by the regular-expression parser so that Unicode
 escapes can be used in expressions that are read from files or from the
 keyboard.  Thus the strings "\u2014" and "\\u2014",
 while not equal, compile into the same pattern, which matches the character
 with hexadecimal value 0x2014.

  
Unicode blocks and categories are written with the
 \p and \P constructs as in
 Perl. \p{prop} matches if the input has the
 property prop, while \P{prop} does not match if
 the input has that property.  Blocks are specified with the prefix
 In, as in InMongolian.  Categories may be specified with
 the optional prefix Is: Both \p{L} and \p{IsL}
 denote the category of Unicode letters.  Blocks and categories can be used
 both inside and outside of a character class.

 
 The supported categories are those of
 
 The Unicode Standard in the version specified by the
 Character class. The category names are those
 defined in the Standard, both normative and informative.
 The block names supported by Pattern are the valid block names
 accepted and defined by
 UnicodeBlock.forName.

  
Categories that behave like the java.lang.Character
 boolean ismethodname methods (except for the deprecated ones) are
 available through the same \p{prop} syntax where
 the specified property has the name javamethodname.

 
 Comparison to Perl 5 


 The Pattern engine performs traditional NFA-based matching
 with ordered alternation as occurs in Perl 5.

 
 Perl constructs not supported by this class: 

  The conditional constructs (?{X}) and
    (?(condition)X|Y),
    
 The embedded code constructs (?{code})
    and (??{code}),
 The embedded comment syntax (?#comment), and 
 The preprocessing operations \l \u,
    \L, and \U.  

  Constructs supported by this class but not by Perl: 

 


     Possessive quantifiers, which greedily match as much as they can
    and do not back off, even when doing so would allow the overall match to
    succeed.  
 Character-class union and intersection as described
    above.

  Notable differences from Perl: 

  In Perl, \1 through \9 are always interpreted
    as back references; a backslash-escaped number greater than 9 is
    treated as a back reference if at least that many subexpressions exist,
    otherwise it is interpreted, if possible, as an octal escape.  In this
    class octal escapes must always begin with a zero. In this class,
    \1 through \9 are always interpreted as back
    references, and a larger number is accepted as a back reference if at
    least that many subexpressions exist at that point in the regular
    expression, otherwise the parser will drop digits until the number is
    smaller or equal to the existing number of groups or it is one digit.
    
 Perl uses the g flag to request a match that resumes
    where the last match left off.  This functionality is provided implicitly
    by the Matcher class: Repeated invocations of the find method will resume where the last match left off,
    unless the matcher is reset.  
 In Perl, embedded flags at the top level of an expression affect
    the whole expression.  In this class, embedded flags always take effect
    at the point at which they appear, whether they are at the top level or
    within a group; in the latter case, flags are restored at the end of the
    group just as in Perl.  
 Perl is forgiving about malformed matching constructs, as in the
    expression *a, as well as dangling brackets, as in the
    expression abc], and treats them as literals.  This
    class also accepts dangling brackets but is strict about dangling
    metacharacters like +, ? and *, and will throw a
    PatternSyntaxException if it encounters them. 


  For a more precise description of the behavior of regular expression
 constructs, please see 
 Mastering Regular Expressions, 3nd Edition, Jeffrey E. F. Friedl,
 O'Reilly and Associates, 2006.
 



Since:
1.4
See Also:
String.split(String, int), 
String.split(String), 
Serialized Form







Field Summary

static int CANON_EQ



          Enables canonical equivalence.

static int CASE_INSENSITIVE



          Enables case-insensitive matching.

static int COMMENTS



          Permits whitespace and comments in pattern.

static int DOTALL



          Enables dotall mode.

static int LITERAL



          Enables literal parsing of the pattern.

static int MULTILINE



          Enables multiline mode.

static int UNICODE_CASE



          Enables Unicode-aware case folding.

static int UNIX_LINES



          Enables Unix lines mode.
 




Method Summary

static Pattern compile(String regex)



          Compiles the given regular expression into a pattern.

static Pattern compile(String regex,
        int flags)



          Compiles the given regular expression into a pattern with the given
 flags.

 int flags()



          Returns this pattern's match flags.

 Matcher matcher(CharSequence input)



          Creates a matcher that will match the given input against this pattern.

static boolean matches(String regex,
        CharSequence input)



          Compiles the given regular expression and attempts to match the given
 input against it.

 String pattern()



          Returns the regular expression from which this pattern was compiled.

static String quote(String s)



          Returns a literal pattern String for the specified
 String.

 String[] split(CharSequence input)



          Splits the given input sequence around matches of this pattern.

 String[] split(CharSequence input,
      int limit)



          Splits the given input sequence around matches of this pattern.

 String toString()



          Returns the string representation of this pattern.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
 






Field Detail


UNIX_LINES
public static final int UNIX_LINES
Enables Unix lines mode.

  In this mode, only the '\n' line terminator is recognized
 in the behavior of ., ^, and $.

 
 Unix lines mode can also be enabled via the embedded flag
 expression (?d).

See Also:
Constant Field Values




CASE_INSENSITIVE
public static final int CASE_INSENSITIVE
Enables case-insensitive matching.

  By default, case-insensitive matching assumes that only characters
 in the US-ASCII charset are being matched.  Unicode-aware
 case-insensitive matching can be enabled by specifying the UNICODE_CASE flag in conjunction with this flag.

 
 Case-insensitive matching can also be enabled via the embedded flag
 expression (?i).

 
 Specifying this flag may impose a slight performance penalty.  

See Also:
Constant Field Values




COMMENTS
public static final int COMMENTS
Permits whitespace and comments in pattern.

  In this mode, whitespace is ignored, and embedded comments starting
 with # are ignored until the end of a line.

 
 Comments mode can also be enabled via the embedded flag
 expression (?x).

See Also:
Constant Field Values




MULTILINE
public static final int MULTILINE
Enables multiline mode.

  In multiline mode the expressions ^ and $ match
 just after or just before, respectively, a line terminator or the end of
 the input sequence.  By default these expressions only match at the
 beginning and the end of the entire input sequence.

 
 Multiline mode can also be enabled via the embedded flag
 expression (?m).  

See Also:
Constant Field Values




LITERAL
public static final int LITERAL
Enables literal parsing of the pattern.

  When this flag is specified then the input string that specifies
 the pattern is treated as a sequence of literal characters.
 Metacharacters or escape sequences in the input sequence will be
 given no special meaning.

 
The flags CASE_INSENSITIVE and UNICODE_CASE retain their impact on
 matching when used in conjunction with this flag. The other flags
 become superfluous.

 
 There is no embedded flag character for enabling literal parsing.

Since:
1.5
See Also:
Constant Field Values




DOTALL
public static final int DOTALL
Enables dotall mode.

  In dotall mode, the expression . matches any character,
 including a line terminator.  By default this expression does not match
 line terminators.

 
 Dotall mode can also be enabled via the embedded flag
 expression (?s).  (The s is a mnemonic for
 "single-line" mode, which is what this is called in Perl.)  

See Also:
Constant Field Values




UNICODE_CASE
public static final int UNICODE_CASE
Enables Unicode-aware case folding.

  When this flag is specified then case-insensitive matching, when
 enabled by the CASE_INSENSITIVE flag, is done in a manner
 consistent with the Unicode Standard.  By default, case-insensitive
 matching assumes that only characters in the US-ASCII charset are being
 matched.

 
 Unicode-aware case folding can also be enabled via the embedded flag
 expression (?u).

 
 Specifying this flag may impose a performance penalty.  

See Also:
Constant Field Values




CANON_EQ
public static final int CANON_EQ
Enables canonical equivalence.

  When this flag is specified then two characters will be considered
 to match if, and only if, their full canonical decompositions match.
 The expression "a\u030A", for example, will match the
 string "\u00E5" when this flag is specified.  By default,
 matching does not take canonical equivalence into account.

 
 There is no embedded flag character for enabling canonical
 equivalence.

 
 Specifying this flag may impose a performance penalty.  

See Also:
Constant Field Values






Method Detail


compile
public static Pattern compile(String regex)
Compiles the given regular expression into a pattern.  


Parameters:
regex - The expression to be compiled
Throws:
PatternSyntaxException - If the expression's syntax is invalid




compile
public static Pattern compile(String regex,
                              int flags)
Compiles the given regular expression into a pattern with the given
 flags.  


Parameters:
regex - The expression to be compiled
flags - Match flags, a bit mask that may include
         CASE_INSENSITIVE, MULTILINE, DOTALL,
         UNICODE_CASE, CANON_EQ, UNIX_LINES,
         LITERAL and COMMENTS
Throws:
IllegalArgumentException - If bit values other than those corresponding to the defined
          match flags are set in flags
PatternSyntaxException - If the expression's syntax is invalid




pattern
public String pattern()
Returns the regular expression from which this pattern was compiled.
 


Returns:
The source of this pattern




toString
public String toString()
Returns the string representation of this pattern. This
 is the regular expression from which this pattern was
 compiled.

Overrides:
toString in class Object
Returns:
The string representation of this pattern
Since:
1.5




matcher
public Matcher matcher(CharSequence input)
Creates a matcher that will match the given input against this pattern.
 


Parameters:
input - The character sequence to be matched
Returns:
A new matcher for this pattern




flags
public int flags()
Returns this pattern's match flags.  


Returns:
The match flags specified when this pattern was compiled




matches
public static boolean matches(String regex,
                              CharSequence input)
Compiles the given regular expression and attempts to match the given
 input against it.

  An invocation of this convenience method of the form

 
 Pattern.matches(regex, input);

 behaves in exactly the same way as the expression

  Pattern.compile(regex).matcher(input).matches()

  If a pattern is to be used multiple times, compiling it once and reusing
 it will be more efficient than invoking this method each time.  


Parameters:
regex - The expression to be compiled
input - The character sequence to be matched
Throws:
PatternSyntaxException - If the expression's syntax is invalid




split
public String[] split(CharSequence input,
                      int limit)
Splits the given input sequence around matches of this pattern.

  The array returned by this method contains each substring of the
 input sequence that is terminated by another subsequence that matches
 this pattern or is terminated by the end of the input sequence.  The
 substrings in the array are in the order in which they occur in the
 input.  If this pattern does not match any subsequence of the input then
 the resulting array has just one element, namely the input sequence in
 string form.

 
 The limit parameter controls the number of times the
 pattern is applied and therefore affects the length of the resulting
 array.  If the limit n is greater than zero then the pattern
 will be applied at most n - 1 times, the array's
 length will be no greater than n, and the array's last entry
 will contain all input beyond the last matched delimiter.  If n
 is non-positive then the pattern will be applied as many times as
 possible and the array can have any length.  If n is zero then
 the pattern will be applied as many times as possible, the array can
 have any length, and trailing empty strings will be discarded.

 
 The input "boo:and:foo", for example, yields the following
 results with these parameters:

 
Regex     Limit     Result    
: 2 { "boo", "and:foo" }
: 5 { "boo", "and", "foo" }
: -2 { "boo", "and", "foo" }
o 5 { "b", "", ":and:f", "", "" }
o -2 { "b", "", ":and:f", "", "" }
o 0 { "b", "", ":and:f" }


Parameters:
input - The character sequence to be split
limit - The result threshold, as described above
Returns:
The array of strings computed by splitting the input
          around matches of this pattern




split
public String[] split(CharSequence input)
Splits the given input sequence around matches of this pattern.

  This method works as if by invoking the two-argument split method with the given input
 sequence and a limit argument of zero.  Trailing empty strings are
 therefore not included in the resulting array. 

  The input "boo:and:foo", for example, yields the following
 results with these expressions:

 
Regex     Result
: { "boo", "and", "foo" }
o { "b", "", ":and:f" }


Parameters:
input - The character sequence to be split
Returns:
The array of strings computed by splitting the input
          around matches of this pattern




quote
public static String quote(String s)
Returns a literal pattern String for the specified
 String.

 This method produces a String that can be used to
 create a Pattern that would match the string
 s as if it were a literal pattern. Metacharacters
 or escape sequences in the input sequence will be given no special
 meaning.


Parameters:
s - The string to be literalized
Returns:
A literal string replacement
Since:
1.5










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Construct	Matches

Characters
x	The character x
`\\`	The backslash character
`\0`n	The character with octal value `0`n (0 `<=` n `<=` 7)
`\0`nn	The character with octal value `0`nn (0 `<=` n `<=` 7)
`\0`mnn	The character with octal value `0`mnn (0 `<=` m `<=` 3, 0 `<=` n `<=` 7)
`\x`hh	The character with hexadecimal value `0x`hh
`\u`hhhh	The character with hexadecimal value `0x`hhhh
`\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'`)
`\c`x	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}\x20]`
`\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]`

java.lang.Character classes (simple java character type)
`\p{javaLowerCase}`	Equivalent to java.lang.Character.isLowerCase()
`\p{javaUpperCase}`	Equivalent to java.lang.Character.isUpperCase()
`\p{javaWhitespace}`	Equivalent to java.lang.Character.isWhitespace()
`\p{javaMirrored}`	Equivalent to java.lang.Character.isMirrored()

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
`(`X`)`	X, as a capturing group

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 (non-capturing)
`(?:`X`)`	X, as a non-capturing group
`(?idmsux-idmsux)`	Nothing, but turns match flags i d m s u x on - off
`(?idmsux-idmsux:`X`)`	X, as a non-capturing group with the given flags i d m s u x 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

1	`((A)(B(C)))`
2	`(A)`
3	`(B(C))`
4	`(C)`

Field Summary
`static int`	`CANON_EQ` Enables canonical equivalence.
`static int`	`CASE_INSENSITIVE` Enables case-insensitive matching.
`static int`	`COMMENTS` Permits whitespace and comments in pattern.
`static int`	`DOTALL` Enables dotall mode.
`static int`	`LITERAL` Enables literal parsing of the pattern.
`static int`	`MULTILINE` Enables multiline mode.
`static int`	`UNICODE_CASE` Enables Unicode-aware case folding.
`static int`	`UNIX_LINES` Enables Unix lines mode.

Method Summary
`static Pattern`	`compile(String regex)` Compiles the given regular expression into a pattern.
`static Pattern`	`compile(String regex, int flags)` Compiles the given regular expression into a pattern with the given flags.
`int`	`flags()` Returns this pattern's match flags.
`Matcher`	`matcher(CharSequence input)` Creates a matcher that will match the given input against this pattern.
`static boolean`	`matches(String regex, CharSequence input)` Compiles the given regular expression and attempts to match the given input against it.
`String`	`pattern()` Returns the regular expression from which this pattern was compiled.
`static String`	`quote(String s)` Returns a literal pattern `String` for the specified `String`.
`String[]`	`split(CharSequence input)` Splits the given input sequence around matches of this pattern.
`String[]`	`split(CharSequence input, int limit)` Splits the given input sequence around matches of this pattern.
`String`	`toString()` Returns the string representation of this pattern.

Regex	Limit	Result
:	2	`{ "boo", "and:foo" }`
:	5	`{ "boo", "and", "foo" }`
:	-2	`{ "boo", "and", "foo" }`
o	5	`{ "b", "", ":and:f", "", "" }`
o	-2	`{ "b", "", ":and:f", "", "" }`
o	0	`{ "b", "", ":and:f" }`

1	Literal escape	`\x`
2	Grouping	`[...]`
3	Range	`a-z`
4	Union	`[a-e][i-u]`
5	Intersection	`[a-z&&[aeiou]]`

Jay Taylor's notes

Pattern (Java Platform SE 6)

java.util.regex Class Pattern

Summary of regular-expression constructs

Backslashes, escapes, and quoting

Character Classes

Line terminators

Groups and capturing

Unicode support

Comparison to Perl 5

UNIX_LINES

CASE_INSENSITIVE

COMMENTS

MULTILINE

LITERAL

DOTALL

UNICODE_CASE

CANON_EQ

compile

compile

pattern

toString

matcher

flags

matches

split

split

quote

java.util.regex
Class Pattern