An engine that performs match operations on a java.lang.character sequence by interpreting a Pattern.

 A matcher is created from a pattern by invoking the pattern's matcher method.  Once created, a matcher can be used to
perform three different kinds of match operations:



   The matches method attempts to match the entire
  input sequence against the pattern.

   The lookingAt method attempts to match the
  input sequence, starting at the beginning, against the pattern.

   The find method scans the input sequence looking for
  the next subsequence that matches the pattern.



 Each of these methods returns a boolean indicating success or failure.
More information about a successful match can be obtained by querying the
state of the matcher.

 A matcher finds matches in a subset of its input called the
region. By default, the region contains all of the matcher's input.
The region can be modified via theregion method and queried
via the regionStart and regionEnd
methods. The way that the region boundaries interact with some pattern
constructs can be changed. See useAnchoringBounds and useTransparentBounds
for more details.

 This class also defines methods for replacing matched subsequences with
new strings whose contents can, if desired, be computed from the match
result.  The appendReplacement and appendTail methods can be used in tandem in order to collect
the result into an existing string buffer, or the more convenient replaceAll method can be used to create a string in which every
matching subsequence in the input sequence is replaced.

 The explicit state of a matcher includes the start and end indices of
the most recent successful match.  It also includes the start and end
indices of the input subsequence captured by each capturing group in the pattern as well as a total
count of such subsequences.  As a convenience, methods are also provided for
returning these captured subsequences in string form.

 The explicit state of a matcher is initially undefined; attempting to
query any part of it before a successful match will cause an IllegalStateException to be thrown.  The explicit state of a matcher is
recomputed by every match operation.

 The implicit state of a matcher includes the input character sequence as
well as the append position, which is initially zero and is updated
by the appendReplacement method.

 A matcher may be reset explicitly by invoking its reset()
method or, if a new input sequence is desired, its reset(CharSequence) method.  Resetting a
matcher discards its explicit state information and sets the append position
to zero.

 Instances of this class are not safe for use by multiple concurrent
threads.

The result of a match operation.

This interface contains query methods used to determine the
results of a match against a regular expression. The match boundaries,
groups and group boundaries can be seen but not modified through
a MatchResult.

Character classes may appear within other character classes, and

The precedence of character-class operators is as follows, from

 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

Predefined character classes (Unicode character)

The backreference constructs, \g{n} for

The named character construct, \N{name}

The conditional constructs

The embedded code constructs (?{code})

The embedded comment syntax (?#comment), and

The preprocessing operations \l \u,

Character-class union and intersection as described

In Perl, \1 through \9 are always interpreted

Perl uses the g flag to request a match that resumes

In Perl, embedded flags at the top level of an expression affect

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 java.lang.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
\x{h...h}
    The character with hexadecimal value 0xh...h
        (Character.MIN_CODE_POINT
         <= 0xh...h <=
         Character.MAX_CODE_POINT)
\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]
\h
    A horizontal whitespace character:
    [ \t\xA0\u1680\u180e\u2000-\u200a\u202f\u205f\u3000]
\H
    A non-horizontal whitespace character: [^\h]
\s
    A whitespace character: [ \t\n\x0B\f\r]
\S
    A non-whitespace character: [^\s]
\v
    A vertical whitespace character: [\n\x0B\f\r\x85\u2028\u2029]

\V
    A non-vertical whitespace character: [^\v]
\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 !"#$%&'()*+,-./:;<=>?@[\]^_`{|}~
     <code>[\!"#\$%&amp;'\(\)\*\+,\-\./:;\&lt;=\&gt;\?@\[\\\]\^_`\{\|\}~]</code>
         <code>[\X21-\X2F\X31-\X40\X5B-\X60\X7B-\X7E]</code>
\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 scripts, blocks, categories and binary properties
\p{IsLatin}
    A Latin script character (script)
\p{InGreek}
    A character in the Greek block (block)
\p{Lu}
    An uppercase letter (category)
\p{IsAlphabetic}
    An alphabetic character (binary property)
\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


Linebreak matcher
\R
    Any Unicode linebreak sequence, is equivalent to
    \u000D\u000A|[\u000A\u000B\u000C\u000D\u0085\u2028\u2029]



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 nth
    capturing group matched

\k<name>
    Whatever the
    named-capturing group "name" matched


Quotation

\
    Nothing, but quotes the following character
\Q
    Nothing, but quotes all characters until \E
\E
    Nothing, but ends quoting started by \Q
     Metachars: !$()*+.<>?[\]^{|}


Special constructs (named-capturing and non-capturing)

(?<name>X)
    X, as a named-capturing group
(?:X)
    X, as a non-capturing group
(?idmsuxU-idmsuxU)
    Nothing, but turns match flags i
d m s
u x U
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 (section 3.3) or other character escapes (section 3.10.6)
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

Group number
 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.

Group name
A capturing group can also be assigned a "name", a named-capturing group,
and then be back-referenced later by the "name". Group names are composed of
the following characters. The first character must be a letter.


   The uppercase letters 'A' through 'Z'
       ('\u0041' through '\u005a'),
   The lowercase letters 'a' through 'z'
       ('\u0061' through '\u007a'),
   The digits '0' through '9'
       ('\u0030' through '\u0039'),


 A named-capturing group is still numbered as described in
Group number.

 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 either pure, non-capturing groups
that do not capture text and do not count towards the group total, or
named-capturing group.

 Unicode support

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

Unicode escape sequences such as \u2014 in Java source code
are processed as described in section 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.

A Unicode character can also be represented in a regular-expression by
using its Hex notation(hexadecimal code point value) directly as described in construct
\x{...}, for example a supplementary character U+2011F
can be specified as \x{2011F}, instead of two consecutive
Unicode escape sequences of the surrogate pair
\uD840\uDD1F.

Unicode scripts, blocks, categories and binary properties 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.

Scripts, blocks, categories and binary properties can be used both inside
and outside of a character class.


Scripts are specified either with the prefix Is, as in
IsHiragana, or by using  the script keyword (or its short
form sc)as in script=Hiragana or sc=Hiragana.

The script names supported by Pattern are the valid script names
accepted and defined by
UnicodeScript.forName.


Blocks are specified with the prefix In, as in
InMongolian, or by using the keyword block (or its short
form blk) as in block=Mongolian or blk=Mongolian.

The block names supported by Pattern are the valid block names
accepted and defined by
UnicodeBlock.forName.


Categories may be specified with the optional prefix Is:
Both \p{L} and \p{IsL} denote the category of Unicode
letters. Same as scripts and blocks, categories can also be specified
by using the keyword general_category (or its short form
gc) as in general_category=Lu or gc=Lu.

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.


Binary properties are specified with the prefix Is, as in
IsAlphabetic. The supported binary properties by Pattern
are

   Alphabetic
   Ideographic
   Letter
   Lowercase
   Uppercase
   Titlecase
   Punctuation
   Control
   White_Space
   Digit
   Hex_Digit
   Join_Control
   Noncharacter_Code_Point
   Assigned


The following Predefined Character classes and POSIX character classes
are in conformance with the recommendation of Annex C: Compatibility Properties
of Unicode Regular Expression
, when UNICODE_CHARACTER_CLASS flag is specified.



Classes
Matches

\p{Lower}
    A lowercase character:\p{IsLowercase}
\p{Upper}
    An uppercase character:\p{IsUppercase}
\p{ASCII}
    All ASCII:[\x00-\x7F]
\p{Alpha}
    An alphabetic character:\p{IsAlphabetic}
\p{Digit}
    A decimal digit character:p{IsDigit}
\p{Alnum}
    An alphanumeric character:[\p{IsAlphabetic}\p{IsDigit}]
\p{Punct}
    A punctuation character:p{IsPunctuation}
\p{Graph}
    A visible character: [^\p{IsWhite_Space}\p{gc=Cc}\p{gc=Cs}\p{gc=Cn}]
\p{Print}
    A printable character: [\p{Graph}\p{Blank}&&[^\p{Cntrl}]]
\p{Blank}
    A space or a tab: [\p{IsWhite_Space}&&[^\p{gc=Zl}\p{gc=Zp}\x0a\x0b\x0c\x0d\x85]]
\p{Cntrl}
    A control character: \p{gc=Cc}
\p{XDigit}
    A hexadecimal digit: [\p{gc=Nd}\p{IsHex_Digit}]
\p{Space}
    A whitespace character:\p{IsWhite_Space}
\d
    A digit: \p{IsDigit}
\D
    A non-digit: [^\d]
\s
    A whitespace character: \p{IsWhite_Space}
\S
    A non-whitespace character: [^\s]
\w
    A word character: [\p{Alpha}\p{gc=Mn}\p{gc=Me}\p{gc=Mc}\p{Digit}\p{gc=Pc}\p{IsJoin_Control}]
\W
    A non-word character: [^\w]



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:


    Predefined character classes (Unicode character)
   \X    Match Unicode

   extended grapheme cluster


    The backreference constructs, \g{n} for
   the nthcapturing group and
   \g{name} for
   named-capturing group.


    The named character construct, \N{name}
   for a Unicode character by its name.


    The conditional constructs
   (?(condition)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:



    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.




 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.

Unchecked exception thrown to indicate a syntax error in a
regular-expression pattern.