Java tutorial
//package com.java2s; import java.util.regex.Matcher; import java.util.regex.Pattern; public class Main { private static final String IPADDRESS_PATTERN = "^([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\." + "([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\." + "([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\." + "([01]?\\d\\d?|2[0-4]\\d|25[0-5])$"; private static boolean validateIP(final String ip) { Pattern pattern = Pattern.compile(IPADDRESS_PATTERN); Matcher matcher = pattern.matcher(ip); return matcher.matches(); } }