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java.util.regex
public final class: Pattern [javadoc | source]
java.lang.Object
   java.util.regex.Pattern

All Implemented Interfaces:
    java$io$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
\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]
\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 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
 
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
 
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 {@code Is}, as in {@code IsHiragana}, or by using the {@code script} keyword (or its short form {@code sc})as in {@code script=Hiragana} or {@code 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 {@code In}, as in {@code InMongolian}, or by using the keyword {@code block} (or its short form {@code blk}) as in {@code block=Mongolian} or {@code 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 {@code Is}: Both {@code \p{L}} and {@code \p{IsL}} denote the category of Unicode letters. Same as scripts and blocks, categories can also be specified by using the keyword {@code general_category} (or its short form {@code gc}) as in {@code general_category=Lu} or {@code 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 {@code Is}, as in {@code IsAlphabetic}. The supported binary properties by Pattern are

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}]
\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:

Constructs supported by this class but not by Perl:

Notable differences from 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.

Nested Class Summary:
static final class  Pattern.TreeInfo  Used to accumulate information about a subtree of the object graph so that optimizations can be applied to the subtree. 
static class  Pattern.Node  Base class for all node classes. Subclasses should override the match() method as appropriate. This class is an accepting node, so its match() always returns true. 
static class  Pattern.LastNode   
static class  Pattern.Start  Used for REs that can start anywhere within the input string. This basically tries to match repeatedly at each spot in the input string, moving forward after each try. An anchored search or a BnM will bypass this node completely. 
static final class  Pattern.StartS   
static final class  Pattern.Begin  Node to anchor at the beginning of input. This object implements the match for a \A sequence, and the caret anchor will use this if not in multiline mode. 
static final class  Pattern.End  Node to anchor at the end of input. This is the absolute end, so this should not match at the last newline before the end as $ will. 
static final class  Pattern.Caret  Node to anchor at the beginning of a line. This is essentially the object to match for the multiline ^. 
static final class  Pattern.UnixCaret  Node to anchor at the beginning of a line when in unixdot mode. 
static final class  Pattern.LastMatch  Node to match the location where the last match ended. This is used for the \G construct. 
static final class  Pattern.Dollar  Node to anchor at the end of a line or the end of input based on the multiline mode. When not in multiline mode, the $ can only match at the very end of the input, unless the input ends in a line terminator in which it matches right before the last line terminator. Note that \r\n is considered an atomic line terminator. Like ^ the $ operator matches at a position, it does not match the line terminators themselves. 
static final class  Pattern.UnixDollar  Node to anchor at the end of a line or the end of input based on the multiline mode when in unix lines mode. 
static final class  Pattern.SingleS  Node class that matches a Supplementary Unicode character 
static final class  Pattern.Single  Optimization -- matches a given BMP character 
static final class  Pattern.SingleI  Case insensitive matches a given BMP character 
static final class  Pattern.SingleU  Unicode case insensitive matches a given Unicode character 
static final class  Pattern.Block  Node class that matches a Unicode block. 
static final class  Pattern.Script  Node class that matches a Unicode script 
static final class  Pattern.Category  Node class that matches a Unicode category. 
static final class  Pattern.Utype  Node class that matches a Unicode "type" 
static final class  Pattern.Ctype  Node class that matches a POSIX type. 
static class  Pattern.SliceNode  Base class for all Slice nodes 
static final class  Pattern.Slice  Node class for a case sensitive/BMP-only sequence of literal characters. 
static class  Pattern.SliceI  Node class for a case_insensitive/BMP-only sequence of literal characters. 
static final class  Pattern.SliceU  Node class for a unicode_case_insensitive/BMP-only sequence of literal characters. Uses unicode case folding. 
static final class  Pattern.SliceS  Node class for a case sensitive sequence of literal characters including supplementary characters. 
static class  Pattern.SliceIS  Node class for a case insensitive sequence of literal characters including supplementary characters. 
static final class  Pattern.SliceUS  Node class for a case insensitive sequence of literal characters. Uses unicode case folding. 
static final class  Pattern.All  Implements the Unicode category ALL and the dot metacharacter when in dotall mode. 
static final class  Pattern.Dot  Node class for the dot metacharacter when dotall is not enabled. 
static final class  Pattern.UnixDot  Node class for the dot metacharacter when dotall is not enabled but UNIX_LINES is enabled. 
static final class  Pattern.Ques  The 0 or 1 quantifier. This one class implements all three types. 
static final class  Pattern.Curly  Handles the curly-brace style repetition with a specified minimum and maximum occurrences. The * quantifier is handled as a special case. This class handles the three types. 
static final class  Pattern.GroupCurly  Handles the curly-brace style repetition with a specified minimum and maximum occurrences in deterministic cases. This is an iterative optimization over the Prolog and Loop system which would handle this in a recursive way. The * quantifier is handled as a special case. If capture is true then this class saves group settings and ensures that groups are unset when backing off of a group match. 
static final class  Pattern.BranchConn  A Guard node at the end of each atom node in a Branch. It serves the purpose of chaining the "match" operation to "next" but not the "study", so we can collect the TreeInfo of each atom node without including the TreeInfo of the "next". 
static final class  Pattern.Branch  Handles the branching of alternations. Note this is also used for the ? quantifier to branch between the case where it matches once and where it does not occur. 
static final class  Pattern.GroupHead  The GroupHead saves the location where the group begins in the locals and restores them when the match is done. The matchRef is used when a reference to this group is accessed later in the expression. The locals will have a negative value in them to indicate that we do not want to unset the group if the reference doesn't match. 
static final class  Pattern.GroupRef  Recursive reference to a group in the regular expression. It calls matchRef because if the reference fails to match we would not unset the group. 
static final class  Pattern.GroupTail  The GroupTail handles the setting of group beginning and ending locations when groups are successfully matched. It must also be able to unset groups that have to be backed off of. The GroupTail node is also used when a previous group is referenced, and in that case no group information needs to be set. 
static final class  Pattern.Prolog  This sets up a loop to handle a recursive quantifier structure. 
static class  Pattern.Loop  Handles the repetition count for a greedy Curly. The matchInit is called from the Prolog to save the index of where the group beginning is stored. A zero length group check occurs in the normal match but is skipped in the matchInit. 
static final class  Pattern.LazyLoop  Handles the repetition count for a reluctant Curly. The matchInit is called from the Prolog to save the index of where the group beginning is stored. A zero length group check occurs in the normal match but is skipped in the matchInit. 
static class  Pattern.BackRef  Refers to a group in the regular expression. Attempts to match whatever the group referred to last matched. 
static class  Pattern.CIBackRef   
static final class  Pattern.First  Searches until the next instance of its atom. This is useful for finding the atom efficiently without passing an instance of it (greedy problem) and without a lot of wasted search time (reluctant problem). 
static final class  Pattern.Conditional   
static final class  Pattern.Pos  Zero width positive lookahead. 
static final class  Pattern.Neg  Zero width negative lookahead. 
static class  Pattern.Behind  Zero width positive lookbehind. 
static final class  Pattern.BehindS  Zero width positive lookbehind, including supplementary characters or unpaired surrogates. 
static class  Pattern.NotBehind  Zero width negative lookbehind. 
static final class  Pattern.NotBehindS  Zero width negative lookbehind, including supplementary characters or unpaired surrogates. 
static final class  Pattern.Bound  Handles word boundaries. Includes a field to allow this one class to deal with the different types of word boundaries we can match. The word characters include underscores, letters, and digits. Non spacing marks can are also part of a word if they have a base character, otherwise they are ignored for purposes of finding word boundaries. 
static class  Pattern.BnM  Attempts to match a slice in the input using the Boyer-Moore string matching algorithm. The algorithm is based on the idea that the pattern can be shifted farther ahead in the search text if it is matched right to left.

The pattern is compared to the input one character at a time, from the rightmost character in the pattern to the left. If the characters all match the pattern has been found. If a character does not match, the pattern is shifted right a distance that is the maximum of two functions, the bad character shift and the good suffix shift. This shift moves the attempted match position through the input more quickly than a naive one position at a time check.

The bad character shift is based on the character from the text that did not match. If the character does not appear in the pattern, the pattern can be shifted completely beyond the bad character. If the character does occur in the pattern, the pattern can be shifted to line the pattern up with the next occurrence of that character.

The good suffix shift is based on the idea that some subset on the right side of the pattern has matched. When a bad character is found, the pattern can be shifted right by the pattern length if the subset does not occur again in pattern, or by the amount of distance to the next occurrence of the subset in the pattern. Boyer-Moore search methods adapted from code by Amy Yu. 

static final class  Pattern.BnMS  Supplementary support version of BnM(). Unpaired surrogates are also handled by this class. 
Field Summary
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)

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.

 
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)

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).

 
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 -
 
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.)

 
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.

 
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.

 
public static final  int UNICODE_CHARACTER_CLASS    Enables the Unicode version of Predefined character classes and POSIX character classes.

When this flag is specified then the (US-ASCII only) Predefined character classes and POSIX character classes are in conformance with Unicode Technical Standard #18: Unicode Regular Expression Annex C: Compatibility Properties.

The UNICODE_CHARACTER_CLASS mode can also be enabled via the embedded flag expression (?U).

The flag implies UNICODE_CASE, that is, it enables Unicode-aware case folding.

Specifying this flag may impose a performance penalty.

    since: 1.7 -
 
transient  Node root    The starting point of state machine for the find operation. This allows a match to start anywhere in the input. 
transient  Node matchRoot    The root of object tree for a match operation. The pattern is matched at the beginning. This may include a find that uses BnM or a First node. 
transient  int[] buffer    Temporary storage used by parsing pattern slice. 
transient volatile  Map<String, Integer> namedGroups    Map the "name" of the "named capturing group" to its group id node. 
transient  GroupHead[] groupNodes    Temporary storage used while parsing group references. 
transient  int capturingGroupCount    The number of capturing groups in this Pattern. Used by matchers to allocate storage needed to perform a match. 
transient  int localCount    The local variable count used by parsing tree. Used by matchers to allocate storage needed to perform a match. 
static final  int MAX_REPS     
static final  int GREEDY     
static final  int LAZY     
static final  int POSSESSIVE     
static final  int INDEPENDENT     
static  Node lookbehindEnd    For use with lookbehinds; matches the position where the lookbehind was encountered. 
static  Node accept    This must be the very first initializer. 
static  Node lastAccept     
Method from java.util.regex.Pattern Summary:
compile,   compile,   flags,   matcher,   matches,   namedGroups,   pattern,   quote,   split,   split,   toString
Methods from java.lang.Object:
clone,   equals,   finalize,   getClass,   hashCode,   notify,   notifyAll,   toString,   wait,   wait,   wait
Method from java.util.regex.Pattern Detail:
 public static Pattern compile(String regex) 
    Compiles the given regular expression into a pattern.

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

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

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

 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.

 Map<String, Integer> namedGroups() 
 public String pattern() 
    Returns the regular expression from which this pattern was compiled.

 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.
 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" }
 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" }
 public String toString() 

    Returns the string representation of this pattern. This is the regular expression from which this pattern was compiled.