InetAddress: getByName(String host)

import java.net.InetAddress;

public class MainClass {

  public static void main(String[] args) {

    try {
      InetAddress ia = InetAddress.getByName("64.21.29.37");
      System.out.println(ia.getHostName());
    } catch (Exception ex) {
      System.err.println(ex);
    }

  }

}