Pattern (Java SE 6 Javadoc and Source)

java.lang.Object
- java.util.regex.Pattern

All Implemented Interfaces:: Serializable

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
`\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

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]]

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)

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

Nested Class Summary

Nested Classes
Modifier and Type	Class and Description
`(package private) static class`	`Pattern.All` Implements the Unicode category ALL and the dot metacharacter when in dotall mode.
`(package private) static class`	`Pattern.BackRef` Refers to a group in the regular expression.
`(package private) static class`	`Pattern.Begin` Node to anchor at the beginning of input.
`(package private) static class`	`Pattern.Behind` Zero width positive lookbehind.
`(package private) static class`	`Pattern.BehindS` Zero width positive lookbehind, including supplementary characters or unpaired surrogates.
`(package private) static class`	`Pattern.BnM` Attempts to match a slice in the input using the Boyer-Moore string matching algorithm.
`(package private) static class`	`Pattern.BnMS` Supplementary support version of BnM().
`(package private) static class`	`Pattern.Bound` Handles word boundaries.
`(package private) static class`	`Pattern.Branch` Handles the branching of alternations.
`(package private) static class`	`Pattern.BranchConn` A Guard node at the end of each atom node in a Branch.
`(package private) static class`	`Pattern.Caret` Node to anchor at the beginning of a line.
`(package private) static class`	`Pattern.Category` Node class that matches a Unicode category.
`(package private) static class`	`Pattern.CIBackRef`
`(package private) static class`	`Pattern.Conditional`
`(package private) static class`	`Pattern.Ctype` Node class that matches a POSIX type.
`(package private) static class`	`Pattern.Curly` Handles the curly-brace style repetition with a specified minimum and maximum occurrences.
`(package private) static class`	`Pattern.Dollar` Node to anchor at the end of a line or the end of input based on the multiline mode.
`(package private) static class`	`Pattern.Dot` Node class for the dot metacharacter when dotall is not enabled.
`(package private) static class`	`Pattern.End` Node to anchor at the end of input.
`(package private) static class`	`Pattern.First` Searches until the next instance of its atom.
`(package private) static class`	`Pattern.GroupCurly` Handles the curly-brace style repetition with a specified minimum and maximum occurrences in deterministic cases.
`(package private) static class`	`Pattern.GroupHead` The GroupHead saves the location where the group begins in the locals and restores them when the match is done.
`(package private) static class`	`Pattern.GroupRef` Recursive reference to a group in the regular expression.
`(package private) static class`	`Pattern.GroupTail` The GroupTail handles the setting of group beginning and ending locations when groups are successfully matched.
`(package private) static class`	`Pattern.LastMatch` Node to match the location where the last match ended.
`(package private) static class`	`Pattern.LastNode`
`(package private) static class`	`Pattern.LazyLoop` Handles the repetition count for a reluctant Curly.
`(package private) static class`	`Pattern.Loop` Handles the repetition count for a greedy Curly.
`(package private) static class`	`Pattern.Neg` Zero width negative lookahead.
`(package private) static class`	`Pattern.Node` Base class for all node classes.
`(package private) static class`	`Pattern.NotBehind` Zero width negative lookbehind.
`(package private) static class`	`Pattern.NotBehindS` Zero width negative lookbehind, including supplementary characters or unpaired surrogates.
`(package private) static class`	`Pattern.Pos` Zero width positive lookahead.
`(package private) static class`	`Pattern.Prolog` This sets up a loop to handle a recursive quantifier structure.
`(package private) static class`	`Pattern.Ques` The 0 or 1 quantifier.
`(package private) static class`	`Pattern.Single` Optimization -- matches a given BMP character
`(package private) static class`	`Pattern.SingleI` Case insensitive matches a given BMP character
`(package private) static class`	`Pattern.SingleS` Node class that matches a Supplementary Unicode character
`(package private) static class`	`Pattern.SingleU` Unicode case insensitive matches a given Unicode character
`(package private) static class`	`Pattern.Slice` Node class for a case sensitive/BMP-only sequence of literal characters.
`(package private) static class`	`Pattern.SliceI` Node class for a case_insensitive/BMP-only sequence of literal characters.
`(package private) static class`	`Pattern.SliceIS` Node class for a case insensitive sequence of literal characters including supplementary characters.
`(package private) static class`	`Pattern.SliceNode` Base class for all Slice nodes
`(package private) static class`	`Pattern.SliceS` Node class for a case sensitive sequence of literal characters including supplementary characters.
`(package private) static class`	`Pattern.SliceU` Node class for a unicode_case_insensitive/BMP-only sequence of literal characters.
`(package private) static class`	`Pattern.SliceUS` Node class for a case insensitive sequence of literal characters.
`(package private) static class`	`Pattern.Start` Used for REs that can start anywhere within the input string.
`(package private) static class`	`Pattern.StartS`
`(package private) static class`	`Pattern.TreeInfo` Used to accumulate information about a subtree of the object graph so that optimizations can be applied to the subtree.
`(package private) static class`	`Pattern.UnixCaret` Node to anchor at the beginning of a line when in unixdot mode.
`(package private) static 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.
`(package private) static class`	`Pattern.UnixDot` Node class for the dot metacharacter when dotall is not enabled but UNIX_LINES is enabled.

Field Summary

Fields
Modifier and Type	Field and Description
`(package private) static Pattern.Node`	`accept` This must be the very first initializer.
`(package private) int[]`	`buffer` Temporary storage used by parsing pattern slice.
`static int`	`CANON_EQ` Enables canonical equivalence.
`(package private) int`	`capturingGroupCount` The number of capturing groups in this Pattern.
`static int`	`CASE_INSENSITIVE` Enables case-insensitive matching.
`static int`	`COMMENTS` Permits whitespace and comments in pattern.
`static int`	`DOTALL` Enables dotall mode.
`(package private) static int`	`GREEDY`
`(package private) Pattern.GroupHead[]`	`groupNodes` Temporary storage used while parsing group references.
`(package private) static int`	`INDEPENDENT`
`(package private) static Pattern.Node`	`lastAccept`
`(package private) static int`	`LAZY`
`static int`	`LITERAL` Enables literal parsing of the pattern.
`(package private) int`	`localCount` The local variable count used by parsing tree.
`(package private) static Pattern.Node`	`lookbehindEnd` For use with lookbehinds; matches the position where the lookbehind was encountered.
`(package private) Pattern.Node`	`matchRoot` The root of object tree for a match operation.
`(package private) static int`	`MAX_REPS`
`static int`	`MULTILINE` Enables multiline mode.
`(package private) static int`	`POSSESSIVE`
`(package private) Pattern.Node`	`root` The starting point of state machine for the find operation.
`static int`	`UNICODE_CASE` Enables Unicode-aware case folding.
`static int`	`UNIX_LINES` Enables Unix lines mode.

Method Summary

Methods
Modifier and Type	Method and Description
`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
- root
```
transient Pattern.Node root
```
  The starting point of state machine for the find operation. This allows a match to start anywhere in the input.
- matchRoot
```
transient Pattern.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.
- buffer
```
transient int[] buffer
```
  Temporary storage used by parsing pattern slice.
- groupNodes
```
transient Pattern.GroupHead[] groupNodes
```
  Temporary storage used while parsing group references.
- capturingGroupCount
```
transient int capturingGroupCount
```
  The number of capturing groups in this Pattern. Used by matchers to allocate storage needed to perform a match.
- localCount
```
transient int localCount
```
  The local variable count used by parsing tree. Used by matchers to allocate storage needed to perform a match.
- MAX_REPS
```
static final int MAX_REPS
```
  See Also:
  Constant Field Values
- GREEDY
```
static final int GREEDY
```
  See Also:
  Constant Field Values
- LAZY
```
static final int LAZY
```
  See Also:
  Constant Field Values
- POSSESSIVE
```
static final int POSSESSIVE
```
  See Also:
  Constant Field Values
- INDEPENDENT
```
static final int INDEPENDENT
```
  See Also:
  Constant Field Values
- lookbehindEnd
```
static Pattern.Node lookbehindEnd
```
  For use with lookbehinds; matches the position where the lookbehind was encountered.
- accept
```
static Pattern.Node accept
```
  This must be the very first initializer.
- lastAccept
```
static Pattern.Node lastAccept
```

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" }

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

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

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

Class Pattern [ source ]

Summary of regular-expression constructs

Backslashes, escapes, and quoting

Character Classes

Line terminators

Groups and capturing

Unicode support

Comparison to Perl 5

Nested Class Summary

Field Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

UNIX_LINES

CASE_INSENSITIVE

COMMENTS

MULTILINE

LITERAL

DOTALL

UNICODE_CASE

CANON_EQ

root

matchRoot

buffer

groupNodes

capturingGroupCount

localCount

MAX_REPS

GREEDY

LAZY

POSSESSIVE

INDEPENDENT

lookbehindEnd

accept

lastAccept

Method Detail

compile

compile

pattern

toString

matcher

flags

matches

split

split

quote