Andrew Pollack's Blog

Technology, Family, Entertainment, Politics, and Random Noise

So, why re-invent the wheel?

By Andrew Pollack on 03/28/2005 at 01:17 PM EDT

One of you sent me an email asking how the code I wrote was different from simply using:

InetAddress addr = InetAddress.getByName("");
System.out.println("IP Address = " + addr.getHostAddress());

I have to admit, its not all that different. The truth is, I didn't even know it could be done so simply. Aside from that, there are a few advantages from having written my own code. The two biggest are that I learned a great deal doing it about writing for tcp sockets and UDP packets in Java -- something which is surprisingly easy. I also got a deeper understanding of how the conversion from data type to data type happens in the JVM. For example, a byte converts to an integer of course, by assigning the 8 bits of the byte to the lower 8 bits of the integer -- but I didn't realize that when it do so it would treat the high order bit of the byte as the sign - meaning you get a value between -127 and +127 rather than between 0 and 255. There's probably a way around that, which I'll run into accidentally no doubt -- but for my purposes it was enough to know it, and simply test the result for being negative, and if so, add 256 to the result.

It makes sense to do it this way I suppose. You can't really go the other way. If what you're expecting isn't always positive, but is mixed, you'd never be able to figure out which was which. At least this way, if negatives don't make sense you know what to do. Its unusual to need a numeric value, but not ever need one larger than 255, but one such case is in IP addresses. The DNS protocol was written in the days when people still cared about specific bits to save space and transfer time. If it was re-implemented today, no doubt it would be DNS:XML and it couldn't be UDP because the packet would be too big. It would happen on Port 80 over a web service, require an application server to handle, and perform about a thousand time slower.

Of course, the other cool thing is that rather than relying on the operating system to resolve the value, I'm able to specify the dns server to use. That makes the code useful for blackhole lists and other such things. Its also a proven protocol so I can use this code for lots of other kind of lookups that are similar. That may help me in some of the anti-spam work I'm doing.

Knowing that the built in method exists, it would probably make more sense to try to extending the class and adding the ability to specify a name server rather than starting from scratch with my own class. Still, I'm glad I did this. It was a day's work not at all wasted.

If you're interested in the code, let me know. Obviously its not going to something I can or should sell.

There are  - loading -  comments....

My own thoughts on this are...By Alan Bell on 03/29/2005 at 07:00 AM EDT
adding 256 to negatives is quite right, but this is why . . . It uses 2's
complement to represent negative numbers, basically this means a negative
number and it's positive equivalent sum to 256 which overflows the 8 bits and
leaves zero. A 2's complement number is formed by inverting all the bits and
adding 1, so for example 42 in 8 bit binary is 00101010 so -42 is 11010101 +1
which is 11010110. So if treated as a 2's complement signed short int 11010110
is -42, you would then add 256 to this which gives 214, and 214 in binary is
11010110. If you add 11010110 and 00101010 you get 100000000 (9 bits - it
overflows and leaves a byte of zero)

There are 10 types of people in the world, those who understand binary and
those who don't :-)

Other Recent Stories...

  1. 01/26/2023Better Running VirtualBox or VMWARE Virtual Machines on Windows 10+ Forgive me, Reader, for I have sinned. I has been nearly 3 years since my last blog entry. The truth is, I haven't had much to say that was worthy of more than a basic social media post -- until today. For my current work, I was assigned a new laptop. It's a real powerhouse machine with 14 processor cores and 64 gigs of ram. It should be perfect for running my development environment in a virtual machine, but it wasn't. VirtualBox was barely starting, and no matter how many features I turned off, it could ...... 
  2. 04/04/2020How many Ventilators for the price of those tanks the Pentagon didn't even want?This goes WAY beyond Trump or Obama. This is decades of poor planning and poor use of funds. Certainly it should have been addressed in the Trump, Obama, Bush, Clinton, Bush, and Reagan administrations -- all of which were well aware of the implications of a pandemic. I want a military prepared to help us, not just hurt other people. As an American I expect that with the ridiculous funding of our military might, we are prepared for damn near everything. Not just killing people and breaking things, but ...... 
  3. 01/28/2020Copyright Troll WarningThere's a copyright troll firm that has automated reverse-image searches and goes around looking for any posted images that they can make a quick copyright claim on. This is not quite a scam because it's technically legal, but it's run very much like a scam. This company works with a few "clients" that have vast repositories of copyrighted images. The trolls do a reverse web search on those images looking for hits. When they find one on a site that looks like someone they can scare, they work it like ...... 
  4. 03/26/2019Undestanding how OAUTH scopes will bring the concept of APPS to your Domino server 
  5. 02/05/2019Toro Yard Equipment - Not really a premium brand as far as I am concerned 
  6. 10/08/2018Will you be at the NYC Launch Event for HCL Domino v10 -- Find me! 
  7. 09/04/2018With two big projects on hold, I suddenly find myself very available for new short and long term projects.  
  8. 07/13/2018Who is HCL and why is it a good thing that they are now the ones behind Notes and Domino? 
  9. 03/21/2018Domino Apps on IOS is a Game Changer. Quit holding back. 
  10. 02/15/2018Andrew’s Proposed Gun Laws 
Click here for more articles.....

pen icon Comment Entry
Your Name
*Your Email
* Your email address is required, but not displayed.
Your thoughts....
Remember Me  

Please wait while your document is saved.