In this HackerRank Java Regex problem in the java programming language, you need to write a class called MyRegex which will contain a string pattern. You need to write a regular expression and assign it to the pattern such that it can be used to validate an IP address. 

HackerRank Java Regex problem solution.

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

class Solution{

    public static void main(String[] args){
        Scanner in = new Scanner(System.in);
        while(in.hasNext()){
            String IP = in.next();
            System.out.println(IP.matches(new MyRegex().pattern));
        }

    }
}

//Write your code here
class MyRegex {

String ip0to255 = "(\\d{1,2}||(0|1)\\d{2}||2[0-4]\\d||25[0-5])";

public String pattern = ip0to255 + "\\." + ip0to255 + "\\." + ip0to255 + "\\." + ip0to255; 
}

Second solution

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

class Solution{

    public static void main(String[] args){
        Scanner in = new Scanner(System.in);
        while(in.hasNext()){
            String IP = in.next();
            System.out.println(IP.matches(new MyRegex().pattern));
        }

    }
}

//Write your code here
class MyRegex {
    public String pattern = "((\\d|\\d\\d|[0-1]\\d\\d|2[0-4][0-9]|25[0-5])\\.){3}(\\d|\\d\\d|[0-1]\\d\\d|2[0-4][0-9]|25[0-5])";
}

A solution in java8 programming.

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

class Solution{

    public static void main(String[] args){
        Scanner in = new Scanner(System.in);
        while(in.hasNext()){
            String IP = in.next();
            System.out.println(IP.matches(new MyRegex().pattern));
        }

    }
}

//Write your code here
class MyRegex {
    public String pattern = "((\\d|\\d\\d|[0-1]\\d\\d|2[0-4][0-9]|25[0-5])\\.){3}(\\d|\\d\\d|[0-1]\\d\\d|2[0-4][0-9]|25[0-5])";
}