Java Regular Expressions

I. Some features of regular expressions in Java

1.java \ \ Represents a regular expression, so ^\d+ (\.\d+), can match the instance: "5", "1.5" and "2.21". But in the program to write ^\\d+ (\\.\\d+)?

2. The normal backslash is expressed as: \\\\

　　

Two. String built-in regular expression function

1.boolean matches (string regex) verifies that the string matches the given regex (regular expression)

Cases:

System.out.println ("+911". Matches ("-|\\+)" \\d+))//true

2. string[] Split (string regex) string split

String[] Split (String regex, int limit)

3. Replace

　　String Replacefirst (string regex,string replacement)

String ReplaceAll (string regex,string replacement)

Three. Pattern and Matcher

Pattern: Mode Matcher: Match (Engine)

Customary usage:

Pattern pattern == pattern.matcher (text);

After getting the Matcher object, using the method on Matcher, we can determine whether the different types of matches are successful

Boolean matches () Boolean Lookingat () Boolean Find () boolean find (int  start)int  start ()int End ()

Four. Regular expression syntax

Character

B	Specify character B
\xhh	Characters with a hexadecimal value of oxhh
\uhhhh	Hexadecimal representation of Unicode characters as Oxhhhh
\ t	TAB tab
\ n	Line break
\ r	Enter
\f	Page change
\e	Escaping (Escape)

Character class

.	Any character
[ABC]	Any character that contains a, B, and C (same as A|b|c action)
[^ABC]	Any character except A, B, and C (negation)
[A-za-z]	Any character (range) from A to Z or from A to Z
[Abc[hij]]	Arbitrary a,b,c,h,i and J characters (same as A|B|C|H|I|J) (consolidated)
[A-z&&[hij]]	Any h,i or J (cross)
\s	whitespace characters (spaces, tab, wrap, page feed, and carriage return)
\s	Non-whitespace character ([^\s])
\d	Number [0-9]
\d	Non-digital [^0-9]
\w	Word character [a-za-z0-9_]
\w	Non-word character [a-za-z0-9_]

logical operators

Xy	Y followed by X.
X| Y	X or Y
X	Capturing group (capturing group) can refer to the I-capturing group in an expression using \i

Boundary Match character

^	Start of a row
$	End of Line
\b	The boundary of the word
\b	The boundaries of non-words
\g	The end of the previous match

Quantifiers

Greedy mode	Hunger mode	Exclusive mode
X?	X??	x?+	Match 0 or 1 times
x*	X*?	x*+	Match 0 or more times
x+	X+?	X + +	Match 1 or more times
X{n}	X{n}?	x{n}+	Match n Times
X{n,}	X{n,}?	x{n,}+	Match at least N times
X{n, M}	X{n, M}?	X{n, m}+	Matches at least n times, up to M times

Java Regular Expressions