According to the java.net.InetAddress.getAllByName(String) API, the host name can either be a machine name or a textual representation of its IP address.

If you specify a textual representation of an IP address, the java.net.InetAddress.toString() method ignores the hostname since J2SE 1.4.2. The output produced by the following application will demonstrate this regression.

% cat Addr.java
import java.net.*;

public class Addr {
  public static void main(String args[]) {
      InetAddress addrs[] = null;
      try {
          addrs = InetAddress.getAllByName(args[0]);
      } catch (Exception e) {
          e.printStackTrace();
          return;
      }

      for (int i = 0; i < addrs.length; i++) {
          System.out.println(addrs[i]);
      }
  }
}

See the comments section for an output of the program.
With J2SE 1.2.2 and J2SE 1.3.1 the addrs[i].toString() returns both hostname and IP-address. Since J2SE 1.4.2 we only get the IP-address, the hostname is not present.

If you change

System.out.println(addrs[i]);

to

System.out.println(addrs[i].getHostName()+"/"+addrs[i].getHostAddress());

in the snippet above, it also works with 1.4.2_x and 1.5.0_y.

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