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This article will explain in detail how to use regular expressions in Java. The editor thinks it is very practical, so I share it for you as a reference. I hope you can get something after reading this article.

Learn regular expressions and use java.util.regex after Jdk1.4

Mode:

Let's take a look at some of the more commonly used types of expressions

Literal: any character within an expression that does not have a special meaning is treated as a text and matches itself.

Quantifier (Quantifier): characters or expressions used to calculate the number of times a word or group can appear in a character sequence

Number so that the sequence matches the expression. Grouping is specified by a set of characters in parentheses.

? It means to appear once or not at all.

* indicates zero or more occurrences (including one)

+ indicates one or more occurrences

Character class (Character class): a character class is a character set in square brackets, where the match can be any of the characters in brackets

One character. You can combine character classes with quantifiers, for example, [acegikmoqsuwy] * will contain only odd numbers in the alphabet

Any sequence of characters of the parent. Some character classes are predefined:

D-number (0 to 9)

D-non-numeric

S-white space characters, such as tabs or newline characters

S-non-white space character

W-word characters (a to z, A to Z, 0 to 9, and underscore)

W-non-word character (any other character)

Posix character classes (Posix character class): some character classes are valid only for US-ASCII comparisons. For example:

P {Lower}-lowercase character

P {Upper}-uppercase character

P {ASCII}-all ASCII characters

P {Alpha}-alphabetic character (p {Lower} combined with p {Upper})

P {Digit}-A number from 0 to 9

P {Alnum}-alphanumeric character

Range: use short lines (dash) to specify character classes that include a range of characters. For example, [AmurJ] means from A to J

Capital letters of

Negative (Negation): delimited (^) negates the content of a character class. For example, [^ AmurJ] represents any character except A to J.

The backslash character () needs to be escaped in the String constant.

W + is similar to p {Alnum} +, but with an underscore (_).

The backslash (.) represents a period. If there is no backslash in front, a single period represents any character.

P {Alpha} {2,3} indicates two or three alphabetic characters

Java.util.regex is a class library package that matches strings using patterns customized by regular expressions (other:

Jakarta-ORO)

It includes two classes: Pattern and Matcher

Pattern A Pattern is a compiled representation of a regular expression.

Matcher A Matcher object is a state machine that performs a match check on a string according to the Pattern object as a matching pattern.

A regular expression, that is, a string of characters with a specific meaning, must first be compiled into an instance of the Pattern class, which

The Pattern object will use the matcher () method to generate an instance of Matcher, which can then be used to compile

Matches the target string based on the regular expression of, and multiple Matcher can share a Pattern object.

In the java.util.regex package, we just need to generate a Pattern class and directly use its compile ()

A Matcher instance is used to base the target string on an existing schema (that is, a regular table compiled by a given Pattern

All inputs to Matcher are provided through the CharSequence interface in order to make sure that

To support matching of data provided from multiple data sources.

★ matches () / lookingAt () / find ():

A Matcher object is generated by a Pattern object calling its matcher () method. Once the Matcher object is generated, it can

To perform three different matching lookup operations:

The matches () method attempts to match the entire target character, that is, it returns the true value only if the entire target string matches exactly.

The lookingAt () method detects whether the target string starts with a matching substring.

The find () method attempts to find the next matching substring in the target string.

All three methods will return a Boolean value to indicate success.

★ replaceAll () / appendReplacement () / appendTail ():

The Matcher class also provides four methods to replace a matching substring with a specified string:

ReplaceAll ()

ReplaceFirst ()

AppendReplacement ()

AppendTail ()

Mode of use

one. Pattern wordBreakPattern = Pattern.compile ("mode")

two. Matcher lineMatcher = linePattern.matcher (string that needs to match)

three. Match functions such as find/lookat, check the results

This is the end of this article on "how to use regular expressions in Java". I hope the above content can be of some help to you, so that you can learn more knowledge. if you think the article is good, please share it for more people to see.

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