Java Regular Expression Tutorial - Java Regex Matcher

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Matcher class performs a match on a sequence of characters by interpreting the compiled pattern defined in a Pattern object.

The matcher() method of the Pattern class creates an instance of the Matcher class.

import java.util.regex.Matcher;
import java.util.regex.Pattern;
/*from  ww  w .  ja  v  a2s.co m*/
public class Main {
  public static void main(String[] args) {
    String regex   = "[a-z]@.";
    Pattern p  = Pattern.compile(regex);
    String str = "abc@yahoo.com,123@cnn.com,abc@google.com";
    Matcher  m   = p.matcher(str);
  }
}

The following methods of the Matcher performs the match.

• find() method
• start() method
• end() method
• group() method

find method

The find() method finds a match for the pattern in the input.

If the find succeeds, it returns true. Otherwise, it returns false.

The first call to find() starts the search at the beginning of the input. The next call would start the search after the previous match.

We can use while loop with find() method to find all the matches.

find() method is an overloaded method. Another version of the find() method takes an integer argument, which is the offset to start the find for a match.

start() method

The start() method returns the start index of the previous match. It is used after a successful find() method call.

end() method

The end() method returns the index of the last character in the matched string plus one.

After a match, str.substring(m.start(), m.end()) gives you the matched string.

import java.util.regex.Matcher;
import java.util.regex.Pattern;
//w ww.ja  v  a 2 s. co  m
public class Main {
  public static void main(String[] args) {
    String regex   = "[a-z]@.";
    Pattern p  = Pattern.compile(regex);
    String str = "abc@yahoo.com,123@cnn.com,abc@google.com";
    Matcher  m   = p.matcher(str);
    
    if (m.find())  {
      String  foundStr = str.substring(m.start(),  m.end());
      System.out.println("Found string  is:" + foundStr);
    }
  }
}

The code above generates the following result.

group() method

The group() method returns the found string by the previous successful find() method call.

import java.util.regex.Matcher;
import java.util.regex.Pattern;
//from w  w  w  . j av a 2 s .co  m
public class Main {
  public static void main(String[] args) {
    String regex = "[a-z]@.";
    Pattern p = Pattern.compile(regex);
    String str = "abc@yahoo.com,123@cnn.com,abc@google.com";
    Matcher m = p.matcher(str);

    if (m.find()) {
      String foundStr = m.group();
      System.out.println("Found text is:" + foundStr);
    }
  }
}

The code above generates the following result.

Example

import java.util.regex.Pattern;
import java.util.regex.Matcher;
/*from   w w  w .j  a  v a 2s. c o  m*/
public class Main {
  public static void main(String[] args) {
    String regex = "[abc]@.";
    String source = "abc@example.com";
    findPattern(regex, source);
  }
  public static void findPattern(String regex, String source) {
    Pattern p = Pattern.compile(regex);
    Matcher m = p.matcher(source);

    System.out.println("Regex:" + regex);
    System.out.println("Text:" + source);
    while (m.find()) {
      System.out.println("Matched  Text:" + m.group() + ", Start:" + m.start()
          + ", " + "End:" + m.end());
    }
  }
}

The code above generates the following result.

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