regular expression for IPv4 validation (demo with Java code)

gistfile1.txt

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));
        }

    }
}

class MyRegex {
    public String pattern;
    public MyRegex(){
        String single_number = "([0]{0,2}[0-9]|[0]{0,1}[1-9][0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5])";
        this.pattern = "(" + single_number + "\\.){3}" + single_number;
    }
}