Java Regular Expression Tutorial - Java Regex Quantifiers

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We can specify the number of times a character in a regular expression may match the sequence of characters.

To express a pattern "one digit or more" using a regular expression, we can use the quantifiers.

Quantifiers and their meanings are listed in the following Table.

The quantifiers must follow a character or character class.

Example

import java.util.regex.Matcher;
import java.util.regex.Pattern;
//from w  ww  . java 2s  .co m
public class Main {
  public static void main(String[] args) {
    // A group of 3 digits followed by 7 digits.
    String regex = "\\b(\\d{3})\\d{7}\\b";
    // Compile the regular expression
    Pattern p = Pattern.compile(regex);
    String source = "12345678, 12345, and 9876543210";
    // Get the Matcher object
    Matcher m = p.matcher(source);
    // Start matching and display the found area codes
    while (m.find()) {
      String phone = m.group();
      String areaCode = m.group(1);
      System.out.println("Phone: " + phone + ", Area  Code:  " + areaCode);
    }
  }
}

The code above generates the following result.

Example 2

* matches zero or more d.

import java.util.regex.Pattern;
//  w  ww .  j  a v a  2 s . c  om
public class Main {
  public static void main(String args[]) {
    String regex = "ad*";
    String input = "add";
    boolean isMatch = Pattern.matches(regex, input);
    System.out.println(isMatch);
  }
}

The code above generates the following result.

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