Java Matcher Class

In Java,Matcherthe class isjava.util.regexan important class in the package, used to perform various matching operations on strings.MatcherThe class itself cannot be directly instantiated; instead, it needs to be created throughPatternthe class'smatcher()method to create.

MatcherThe main functions of the class include:

  • Perform regular expression matching operations
  • Find subsequences in the string that match the pattern
  • Replace matched text

Creating a Matcher Object

To useMatcherclass, you first need to create aPatternobject, then use it to createMatcherobject:

Example

import java.util.regex.*;

// Create a Pattern object
Pattern pattern = Pattern.compile("a*b");

// Create a Matcher object
Matcher matcher = pattern.matcher("aaaaab");

Common Methods of the Matcher Class

Matching Operation Methods

matches() Method

matches()The method attempts to match the entire input sequence against the pattern:

Example

boolean result = matcher.matches(); // Returns true or false

lookingAt() Method

lookingAt()The method attempts to match the pattern starting from the beginning of the input sequence:

Example

boolean result = matcher.lookingAt(); // Does not need to match the entire string

find() Method

find()The method finds the next matching subsequence in the input sequence:

Example

while(matcher.find()) {
    System.out.println("Found match: " + matcher.group());
}

Methods for Getting Match Information

group() Method

group()The method returns the input subsequence matched by the previous match operation:

Example

String matchedText = matcher.group();

start() and end() Methods

start()andend()The methods return the start and end indices of the previous match:

Example

int start = matcher.start(); // Match start position
int end = matcher.end();     // Match end position

groupCount() Method

groupCount()Returns the number of capturing groups in this matcher's pattern:

Example

int count = matcher.groupCount();

Replacement Operation Methods

replaceAll() Method

replaceAll()The method replaces every subsequence in the input sequence that matches the pattern:

Example

String result = matcher.replaceAll("replacement");

replaceFirst() Method

replaceFirst()The method replaces the first subsequence in the input sequence that matches the pattern:

Example

String result = matcher.replaceFirst("replacement");

Example

Below is a complete example showing how to useMatcherclass:

Example

import java.util.regex.*;

public class MatcherExample {
    public static void main(String[] args) {
        String text = "The quick brown fox jumps over the lazy dog";
        Pattern pattern = Pattern.compile("\\b\\w{4}\\b"); // Match 4-letter words
        Matcher matcher = pattern.matcher(text);
       
        System.out.println("Original text: " + text);
        System.out.println("Matching 4-letter words:");
       
        while(matcher.find()) {
            System.out.println("Found '" + matcher.group() +
                              "' at position " + matcher.start() + "-" + (matcher.end()-1));
        }
       
        // Replace all 4-letter words with "****"
        String replaced = matcher.replaceAll("****");
        System.out.println("\n"Replaced text: " + replaced);
    }
}

Output Result

原始文本: The quick brown fox jumps over the lazy dog
匹配4字母单词:
找到 'quick' 在位置 4-8
找到 'brown' 在位置 10-14
找到 'jumps' 在位置 20-24
找到 'over' 在位置 26-29
找到 'lazy' 在位置 35-38

替换后的文本: The **** **** fox **** **** the **** dog

Summary

Java'sMatcherclass provides powerful regular expression matching functionality, through which you can:

  1. Check whether a string matches a specific pattern
  2. Find pattern matches in a string
  3. Extract matched substrings
  4. Replace matched text

MasteringMatcherthe class is very important for handling string and text pattern matching, and is a very practical tool in Java programming.

Matching Operation Methods

Method Description
boolean matches() Attempts to match the entire region against the pattern
boolean lookingAt() Attempts to match the pattern starting from the beginning of the region
boolean find() Attempts to find the next matching subsequence
boolean find(int start) Finds the next match starting from the specified position

Methods for Getting Match Results

Method Description
String group() Returns the subsequence of the previous match
String group(int group) Returns the matched content of the specified capturing group
String group(String name) Returns the matched content of the named capturing group (Java 7+)
int groupCount() Returns the number of capturing groups in the pattern
int start() Returns the start index of the previous match
int start(int group) Returns the start index of the match for the specified group
int end() Returns the end index of the previous match
int end(int group) Returns the end index of the match for the specified group

Replacement Operation Methods

Method Description
Matcher appendReplacement(StringBuffer sb, String replacement) Performs a non-terminal replacement operation
StringBuffer appendTail(StringBuffer sb) Performs a terminal replacement operation
String replaceAll(String replacement) Replaces all matching subsequences
String replaceFirst(String replacement) Replaces the first matching subsequence
static String quoteReplacement(String s) Returns the literal of the replacement string

Region Control Methods

Method Description
Matcher region(int start, int end) Sets the search region of the matcher
int regionStart() Returns the start index of the matcher's region
int regionEnd() Returns the end index of the matcher's region
boolean hasTransparentBounds() Checks whether transparent bounds are used
Matcher useTransparentBounds(boolean b) Sets whether transparent bounds are used
boolean hasAnchoringBounds() Checks whether anchoring bounds are used
Matcher useAnchoringBounds(boolean b) Sets whether anchoring bounds are used

Other Methods

Method Description
Pattern pattern() Returns the pattern of this matcher
Matcher reset() Resets the matcher
Matcher reset(CharSequence input) Resets the matcher with new input
boolean hitEnd() Indicates whether the matcher has reached the end of the input
boolean requireEnd() Indicates whether more input is needed for a match
Other Extensions