Getting Started regular Expressions (Java)-named captures

Getting Started regular Expressions (Java)-Introduction

Get started regular Expressions (Java)-1-Basics of Getting Started
Get started regular Expressions (Java)-2-Basic instances

Getting Started regular Expressions (Java)-3-Regular usage in Java

Getting Started regular Expressions (Java)-matching principle-1-engine classification and pervasive principles

Getting Started regular Expressions (Java)-matching principle-2-backtracking

Getting Started regular Expressions (Java)-named captures

Many regular engines support named groupings, in whichJava is introduced in Java7, with syntax and. Net-like (. NET allows the same expression to appear in the same name grouping, Java is not allowed).

A named grouping is a good idea, which is to name the group. Here's a quick walkthrough of how to use Java and what to consider.

1. Define a group named name in the regular

(? <name>x)

Here x is for us to match the content, Note that in this name can not be repeated, the name can not start with a number!

2. Reverse referencing what the name group matches to

\k<name>

Note that the reverse reference is for the content that the group matches to, not the group's expression.

3. Replace, the string that is captured in the reference group name

${name}

4. Get the string captured by the name group

Group (String NAME)

Note: You can also use the ordinal to reference a named capture, starting at 1, and 0 as the full matching result of the regular sequence.

The following is an example of using a simple regular to obtain the month and day respectively:

string s = "2015-10-26"; Pattern p = pattern.compile ("(? <year>\\d{4})-(? <month>\\d{2})-(? <day>\\d{2})"); Matcher m = P.matcher (s), if (M.find ()) {System.out.println ("year:" + M.group ("year")); Year System.out.println ("Month:" + m.group ("month")); Month System.out.println ("Day:" + m.group ("Day")); Day System.out.println ("year:" + m.group (1)); The first set of System.out.println ("month:" + m.group (2)); The second group of System.out.println ("Day:" + m.group (3)); The third group of}system.out.println (S.replaceall (? <year>\\d{4})-(? <month>\\d{2})-(? <day>\\d{2}), "${ Day}-${month}-${year} ")); Change the date of the year-month-day format to day-month-year form 

Output results

year:2015month:10day:26year:2015month:10day:2626-10-2015

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Getting Started regular Expressions (Java)-named captures