regex second example

main.java

package com.alex.regex;

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class YourClassName {

    public static void main(String[] args) {

        // IP адрес
        String regexp = "(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)";
        // для сравнения работы find() и matches()
        String goodIp = "192.168.0.3";
        String badIp = "192.168.0.3g";

        Pattern pattern = Pattern.compile(regexp);

        Matcher matcher = pattern.matcher(goodIp);
        // matches() - true, find() - true
        matcher = pattern.matcher(badIp);
        // matches() - false, find() - true

        // а теперь получим дополнительную информацию
        System.out.println(matcher.find()
                ? "I found '" + matcher.group() + "' starting at index " + matcher.start() + " and ending at index " + matcher.end() + "."
                : "I found nothing!");
        // I found the text '192.168.0.3' starting at index 0 and ending at index 11.
    }
}