public class StringTest { public static void main(String[] args) { String regex = "\A(25[0-5]|2[0-4]\d|[0-1]?\d?\d)(\.(25[0-5]|2[0-4]\d|[0-1]?\d?\d)){3}\z"; String str1 = "1.1.1.0"; boolean flag1 = str1.matches(regex); System.out.println(flag1); String str2 = "222"; boolean flag2 = str2.matches(regex); System.out.println(flag2); } }