Example1.java

package problem13;

import java.net.InetAddress;
import java.net.UnknownHostException;

public class Example1{
  public static void main(String[] args) throws UnknownHostException{
    long ip = ip_to_long(InetAddress.getByName("10.100.202.34")); // enter your ip
    long mask =ip_to_long(InetAddress.getByName("255.255.240.0")); // enter your mask
    ip = (ip & mask) + ((mask ^ 0xFFFFFFFFL) + 1) - 2; // result
    System.out.printf("%d.%d.%d.%d", (ip >> 24) & 0xFF,(ip >> 16) & 0xFF,(ip >> 8) & 0xFF,ip & 0xFF); // output with dots, answer without it.
  }

  private static long ip_to_long(InetAddress ip){
    byte[] octets = ip.getAddress();
    long result = 0;
    for(byte octet: octets){
      result <<= 8;
      result |= (octet & 0xFF);
    }
    return result;
  }

}