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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.
The character with hexadecimalvalue0xh...h
(Character.MIN_CODE_POINT
=0xh...h =
Character.MAX_CODE_POINT)
The tab character ( u0009)
The newline (line feed) character ( u000A)
The carriage-return character ( u000D)
The form-feed character ( u000C)
The alert (bell) character ( u0007)
The escape character ( u001B)
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)
A digit: [0-9]
A non-digit: [^0-9]
A horizontal whitespace character:
[ \t\xA0 u1680 u180e u2000- u200a u202f u205f u3000]
A non-horizontal whitespace character: [^\h]
A whitespace character: [ \t\n\x0B\f\r]
A non-whitespace character: [^\s]
A vertical whitespace character: [\n\x0B\f\r\x85 u2028 u2029]
A non-vertical whitespace character: [^\v]
A word character: [a-zA-Z_0-9]
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 Latinscript character (script)
\p{InGreek}
A character in the Greekblock (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
A word boundary
A non-word boundary
The beginning of the input
The end of the previous match
The end of the input but for the final
terminator, ifany
The end of the input
Linebreak matcher
Any Unicode linebreak sequence, is equivalent to
u000D u000A[ u000A u000B u000C u000D u0085 u2028 u2029]
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:
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 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:
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.
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
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.
\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}
A digit: \p{IsDigit}
A non-digit: [^\d]
A whitespace character: \p{IsWhite_Space}
A non-whitespace character: [^\s]
A word character: [\p{Alpha}\p{gc=Mn}\p{gc=Me}\p{gc=Mc}\p{Digit}\p{gc=Pc}\p{IsJoin_Control}]
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:
\XMatch 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)XY),
The embedded code constructs (?{code})
and (??{code}),
The embedded comment syntax (?#comment), and
The preprocessing operations \l u,
\L, and \U.
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.
static int
CASE_INSENSITIVE
Enables case-insensitive matching.
static int
UNICODE_CASE
Enables Unicode-aware case folding.
static int
UNICODE_CHARACTER_CLASS
Enables the Unicode version of Predefined character classes and
POSIX character classes.
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
public static finalint 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
public static finalint 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
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
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:
See Also:
Constant Field Values
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
public static finalint 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
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
public static finalint 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:
See Also:
Constant Field Values
compile
public staticPatterncompile(Stringregex)
Compiles the given regular expression into a pattern.
Parameters:
regex - The expression to be compiled
Returns:
the given regular expression compiled into a pattern
Throws:
PatternSyntaxException - If the expressions syntax is invalid
pattern
publicStringpattern()
Returns the regular expression from which this pattern was compiled.
Returns:
The source of this pattern
toString
publicStringtoString()
Returns the string representation of this pattern. This
is the regular expression from which this pattern was
compiled.
Overrides:
toStringin classObject
Returns:
The string representation of this pattern
Since:
matcher
publicMatchermatcher(CharSequenceinput)
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
matches
public staticbooleanmatches(Stringregex,
CharSequenceinput)
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
Returns:
whether or not the regular expression matches on the input
Throws:
PatternSyntaxException - If the expressions syntax is invalid
split
publicString[]split(CharSequenceinput,
intlimit)
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.
When there is a positive-width match at the beginning of the input
sequence then an empty leading substring is included at the beginning
of the resulting array. A zero-width match at the beginning however
never produces such empty leading substring.
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 arrays
length will be no greater than n, and the arrays 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:
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
publicString[]split(CharSequenceinput)
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:
quote
public staticStringquote(Strings)
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:
asPredicate
publicPredicate String asPredicate()
Creates a predicate which can be used to match a string.
Returns:
The predicate which can be used for matching on a string
Since:
splitAsStream
publicStream String splitAsStream(CharSequenceinput)
Creates a stream from the given input sequence around matches of this
pattern.
The stream 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 stream are in the order in which they occur in the
input. Trailing empty strings will be discarded and not encountered in
the stream.
If this pattern does not match any subsequence of the input then
the resulting stream has just one element, namely the input sequence in
string form.
When there is a positive-width match at the beginning of the input
sequence then an empty leading substring is included at the beginning
of the stream. A zero-width match at the beginning however never produces
such empty leading substring.
If the input sequence is mutable, it must remain constant during the
execution of the terminal stream operation. Otherwise, the result of the
terminal stream operation is undefined.
Parameters:
input - The character sequence to be split
Returns:
The stream of strings computed by splitting the input
around matches of this pattern
Since:
See Also:
split(CharSequence)
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