String host = InetAddress.getByName( "192 . 168 . 82 . 249 ").getHostName();

create or replace and compile java source named Inet as

import java.net.*;
import java.io.*;

public class Inet {
  public static String getHostName (String ip) {
    String name = null;
    try {
      name = InetAddress.getByName(ip).getHostName();
    } catch (UnknownHostException e) {
      System.out.println(e.toString());
    }
    return name;
  }
}
/

create or replace function get_host_name(ip varchar2) return varchar2 is
  language java name
    'Inet.getHostName(java.lang.String) return java.lang.String';
/

select get_host_name('148.87.9.44') from dual;