- 浏览: 48056 次
- 性别:
- 来自: 北京
最新评论
JAVA Regex Expression
贪婪,勉强,侵占: greedy, reluctant, possesive
在贪婪、勉强和侵占三个量词间有着细微的不同。
贪婪(*, ?, +):读入整个串,从后往前匹配
勉强(*?, ??, +?):从前往后匹配
侵占(*+, ?+, ++):读入整个串,从前往后匹配,匹配的是整个串
贪婪量词之所以称之为“贪婪的”,这是由于它们强迫匹配器读入(或者称之为吃掉)整个输入的字符串,来优先尝试第一次匹配,如果第一次尝试匹配(对于整个输入的字符串)失败,匹配器会通过回退整个字符串的一个字符再一次进行尝试,不断地进行处理直到找到一个匹配,或者左边没有更多的字符来用于回退了。赖于在表达式中使用的量词,最终它将尝试地靠着 1 或 0 个字符的匹配。
但是,勉强量词采用相反的途径:从输入字符串的开始处开始,因此每次勉强地吞噬一个字符来寻找匹配,最终它们会尝试整个输入的字符串。
最后,侵占量词始终是吞掉整个输入的字符串,尝试着一次(仅有一次)匹配。不像贪婪量词那样,侵占量词绝不会回退,即使这样做是允许全部的匹配成功。
link: http://download.oracle.com/javase/tutorial/essential/regex/matcher.html
============================================================
JAVA中也有个类java.util.regex.Pattern实现正则表达式, 下面是引用jdk5的api说明:
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 on - off
(?idmsux-idmsux:X) X, as a non-capturing group with the given flags 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]]
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)
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 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.
相关推荐
import java.util.regex.Matcher; import java.util.regex.Pattern; public class StringCounter { /** * 正则统计字符串出现次数 * * @param source * @param regexNew * @return int */ public ...
Regular Expressions and the new java.util.regex package Muliplexing with java.nio Because the NIO APIs supplement the I/O features of version 1.3, rather than replace them, you'll also learn when ...
this edition has been updated throughout to reflect advances in other languages, including expanded in-depth coverage of Sun's java.util.regex package, which has emerged as the standard Java regex ...
(英语:Regular Expression,在代码中常简写为regex、regexp或RE),计算机科学的一个概念。正则表达式通常被用来检索、替换那些符合某个模式(规则)的文本。在众多语言中都可以支持正则表达式,如Perl、PHP、Java、...
一个非常完备,快速的Java正则表达式库,有详细的说明文档
this edition has been updated throughout to reflect advances in other languages, including expanded in-depth coverage of Sun's java.util.regex package, which has emerged as the standard Java regex ...
Java正则表达式生成器(reb4j)是一组简单的类,封装了java.util.regex.Pattern使用的正则表达式,并提供了从子表达式组成较大表达式的工具。
正则表达式到Java中的DFA 这是通过使用Java语言创建和使用语法树将regex(正则表达式)转换为DFA的方法。 该项目是我们在大学第五学期(@KNTU)的编译器课程中完成的一个较大项目的一部分,以创建一个简单的编译器。...
跟踪代理 TraceAgent是用于运行时跟踪的Java代理...REGEX (regular expression) :它与方法或字段的JNI(Java本机接口)签名匹配。 以“!”开头的正则REGEX 匹配后面的正则表达式的负数。 LOG_PATH :保存日志的路径
* Summary of regular-expression constructs 正则表达式结构简介: * Construct Matches * Characters 字符: * x The character x x 字符 x * \\ The ...
正则表达式,又称规则表达式,(Regular Expression,在代码中常简写为regex、regexp或RE),是一种文本模式,包括普通字符(例如,a 到 z 之间的字母)和特殊字符(称为"元字符"),是计算机科学的一个概念。...
使用VM方法进行正则表达式匹配正则表达式匹配模拟 java.util.regex 的 API 的迷你库。 该实现的灵感来自 Russ Cox 的文章“Regular Expression Matching: The Virtual Machine Approach”,并利用 Antlr4 来解析正则...
正则表达式,又称规则表达式,英文名为Regular Expression,在代码中常简写为regex、regexp或RE,是计算机科学的一个概念。正则表通常被用来检索、替换那些符合某个模式(规则)的文本。 正则表达式是对字符串(包括...
正则表达式,又称正规表示法、常规表示法(英语:Regular Expression,在代码中常简写为regex、regexp或RE),它是计算机科学的一个概念。正则表达式使用单个字符串来描述、匹配一系列符合某个句法规则的字符串。...
正则表达式,又称正规表示法、常规表示法(英语:Regular Expression,在代码中常简写为regex、regexp或RE),计算机科学的一个概念
java笔试题重复字符串 内容 一、简介 REGEX 表示 REGular EXpression,它只是字符序列。 例如,这些表达式表示 [0–9] 表示该表达式应包含数字。 正则表达式在计算机编程中的许多情况下使用。 主要在搜索、模式匹配...
(英语:Regular Expression,在代码中常简写为regex、regexp或RE),计算机科学的一个概念。正则表通常被用来检索、替换那些符合某个模式(规则)的文本。 许多程序设计语言都支持利用正则表达式进行字符串操作。...
java snmp源码DevOps-面试 去做 IO性能调优 Linux 命令 1. sed - Replace the first occurrence of a regular expression in each line of a file, and print the result: sed ' s/{{regex}}/{{replace}}/ ' {{...
DBGrep Java实用程序,用于在数据库中搜索值。
RegexToolbox.JS 适用于JavaScript开发人员的正则表达式工具。 正则表达式生成器 ... 出该库的Java版本 。 Kotlin开发人员? 出该库的Kotlin版本 。 RegexToolbox:现在,您可以成为而无需知道正则表达式。