Java Regular Expression Learning record

Java Regular Expression Learning record

　A regular expression (regular expressions) is a method that describes a set of strings, based on the common characteristics of each string in a string set. Regular expressions can be used to search, edit, or manipulate text and data. It goes beyond the standard syntax of the Java programming language, so it is necessary to learn specific syntax to build regular expressions. The changes in regular expressions are complex, and once you understand how they are structured, you can parse or construct arbitrary regular expressions.

Character class

Character class
[ABC]	A, B or C (simple Class)
[^ABC]	Any character except A, B, or C (inverse)
[A-za-z]	A to Z, or A to Z, including (range)
[A-d[m-p]]	A to D, or M to P:[a-dm-p] (set)
[A-z&&[def]]	D,e or F (intersection)
[A-Z&&[^BC]]	A to Z characters other than B and C: [Ad-z] (difference set)
[A-z&&[^m-p]]	A to Z, and does not include M to P:[a-lq-z] (difference set)

Predefined character classes

Predefined character classes
.	Any character (matches or does not match the line terminator)
\d	numeric characters: [0-9]
\d	Non-numeric characters: [^0-9]
\s	whitespace characters: [\t\n\x0b\f\r]
\s	Non-whitespace characters: [^\s]
\w	Word character: [a-za-z_0-9]
\w	Non-word characters: [^\w]

Word Quantity

Type of quantifier			Significance
Greed	Barely	Occupation
X?	X??	x?+	Match X 0 or one time
x*	X*?	x*+	Match X 0 or more times
x+	X+?	X + +	Match X one or more times
X{n}	X{n}?	x{n}+	Match X N Times
X{n,}	X{n,}?	x{n,}+	Match X at least n times
X{N,M}	X{n,m}?	x{n,m}+	Match X at least n times, but not more than m times

Boundary Matching Device
^	Header
$	End of Line
\b	Word boundaries
\b	Non-word boundary
\a	Start of input
\g	End of last match
\z	The end of the input, only for the last terminator (if any)
\z	End of input

Example: Using grouping to go to file extensions

Import Java.util.regex.Matcher;

Import Java.util.regex.Pattern;

Public class Foo {

public static string Testfoo (stringsource) {

// two groups

pattern p = pattern. Compile("(\\w+)." (. +)");

Matcher mat = p. Matcher (source);

Mat. Find ();

// print number of groups

System. out . println (Mat. GroupCount ());

// Returns the second grouped content

returnMatGroup (2);

   }

public staticvoid main (string[]args) {

System. out. println (testfoo("User3.java"));

   }

}

Printing results:

2

Java

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Java Regular Expression Learning record