InetAddress: getCanonicalHostName()

import java.net.InetAddress;

public class Main {
  public static void main(String[] argv) throws Exception {
    InetAddress addr = InetAddress.getByName("127.0.0.1");
    byte[] ipAddr = new byte[] { 127, 0, 0, 1 };
    addr = InetAddress.getByAddress(ipAddr);
    // Get the host name
    String hostname = addr.getHostName();
    // Get canonical host name
    String canonicalhostname = addr.getCanonicalHostName();

  }
}