java.util.regex.Pattern
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Java™ Platform Standard Ed. 6 |
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java.lang.Object
public final class Pattern
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"); 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 nth 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 |
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 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:
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.
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:
If The regular expression . matches any character except a line
terminator unless the 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 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: 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.
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
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.
The 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 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
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.
Character Classes
1
Literal escape
\x 2
Grouping
[...] 3
Range
a-z 4
Union
[a-e][i-u] 5
Intersection
[a-z&&[aeiou]] Line terminators
UNIX_LINES mode is activated, then the only line terminators
recognized are newline characters.
DOTALL flag is specified.
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
1
((A)(B(C))) 2
(A) 3
(B(C)) 4
(C) Unicode support
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.
Comparison to Perl 5
Pattern engine performs traditional NFA-based matching
with ordered alternation as occurs in Perl 5.
Matcher class: Repeated invocations of the find method will resume where the last match left off,
unless the matcher is reset. PatternSyntaxException if it encounters them.
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 |
|---|
public static final int UNIX_LINES
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
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
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
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
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.
public static final int DOTALL
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
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
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.
| Method Detail |
|---|
public static Pattern compile(String regex)
regex - The expression to be compiled
PatternSyntaxException - If the expression's syntax is invalid
public static Pattern compile(String regex,
int flags)
regex - The expression to be compiledflags - Match flags, a bit mask that may include
CASE_INSENSITIVE, MULTILINE, DOTALL,
UNICODE_CASE, CANON_EQ, UNIX_LINES,
LITERAL and COMMENTS
IllegalArgumentException - If bit values other than those corresponding to the defined
match flags are set in flags
PatternSyntaxException - If the expression's syntax is invalidpublic String pattern()
public String toString()
Returns the string representation of this pattern. This is the regular expression from which this pattern was compiled.
toString in class Objectpublic Matcher matcher(CharSequence input)
input - The character sequence to be matched
public int flags()
public static boolean matches(String regex,
CharSequence input)
An invocation of this convenience method of the form
behaves in exactly the same way as the expressionPattern.matches(regex, input);
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.
regex - The expression to be compiledinput - The character sequence to be matched
PatternSyntaxException - If the expression's syntax is invalid
public String[] split(CharSequence input,
int limit)
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" }
input - The character sequence to be splitlimit - The result threshold, as described above
public String[] split(CharSequence input)
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" }
input - The character sequence to be split
public static String quote(String s)
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.
s - The string to be literalized
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Java™ Platform Standard Ed. 6 |
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