A Comparison

Firstly, I’ll show a short comparison between some Java code and some code from a language that doesn’t have NullPointerExceptions, but does have something that allows you to accomplish anything you might want to do with null pointers.

This Java code:

AnObject thing = someMethod();

is equivalent to the following Haskell:

let thing = Maybe AnObject

That is, every Java object reference is possibly null. What this means is that (using the type notation mentioned in earlier posts) every Java reference has the type:

(Every object reference for an object is either to ‘null’ (AKA ‘unit’ or ‘singleton’, or the object itself.)

… and when you’re dealing with so many objects—Java is, after all, an object-oriented language, so (almost) everything is an object—this simple little “+1″ gets lost easily.

Why so bad?

This wouldn’t seem to be such a big deal, but when contrasted against Java’s penchant for making things (sometimes painfully) explicit—think public static void main (string argh!)—a small, implicit item like this is easily overlooked. Conversely, one might say that the verbosity of Java increases the cognitive load of understanding its code; thus helping the chances of a small mistake like this sneaking through.

Either way, I think I can say that this is objectively A Bad Thing. C# has gone some of the way to a ‘correct’ solution in its introduction of possibly-null primitives, which are explicitly marked with a ? (such as int?), but unfortunately this hasn’t been ‘back-ported’ to the rest of the language. If one were able to force between possibly-null and definitely-not-null references in C#—perhaps by the analogous object? vs. object, this would help to reduce the number of errors ‘hidden’ by the syntax.

Intrigued at what I first thought was a joke, I downloaded one of the proudly-presented documents on the front page: Understanding the BPMN-XPDL-BPEL value chain. I chose it because of the three as-yet-unknown acronyms in the title… and I wasn’t disappointed.

I present you with the following gem, lifted from one paragraph of the article:

Several BPM engines are able to run XPDL natively, which allows run-time modification and process migration to be readily supported. Where these processes focus on broader-scope collaboration among people, they can remain within XPDL/BPMN. Where pieces are decomposed into system-to-system interactions, these can be translated to BPEL for transmission to an EAI-oriented BPM engine. These are three very different and very compatible roles. But that’s the nature of the value chain—BPEL and XPDL are entirely different things for entirely different purposes.

I suppose the warning sign should have been their slogan:

Process Thought Leadership™

Don’t use this method any more! I have a much easier way to do it in a more recent post.

But for posterity…

First install resolvconf and pdnsd: sudo apt-get install pdnsd resolvconf. Resolvconf handles the messy interaction between different programs fighting over the /etc/resolv.conf file, and pdnsd provides a persistent DNS daemon, which will cache the DNS lookups on your machine in order to make browsing faster.

Next, you just need to edit pdnsd’s configuration file, /etc/pdnsd.conf as root. Edit it to look like this:

global {
        perm_cache=512;
        cache_dir="/var/cache/pdnsd";
        max_ttl=604800;
        run_as="pdnsd";
        paranoid=on;
#       next setting allows ppp/ip-up update the name servers -- ABa / 20040213
        status_ctl=on;
        server_port=53;
        server_ip="127.0.0.1";
}

#Edit these to be your own servers if wished:
server {
        label = "OpenDNS";
        ip=208.67.222.222,208.67.220.220;
        proxy_only=on;
        timeout=10;
}

# if you installed resolvconf, and status_ctl=on
server {
    label="resolvconf";
}

source {
        ttl=86400;
        owner="localhost.";
#       serve_aliases=on;
        file="/etc/hosts";
}

And finally, restart pdnsd with sudo /etc/init.d/pdnsd restart to use the new settings. In the example above, I've used OpenDNS's servers, but you can change these to whatever you want. As far as actual results go:

~$ dig example.com

; <<>> DiG 9.3.2 <<>> example.com
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 17447
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;example.com. IN A

;; ANSWER SECTION:
example.com. 172800 IN A 192.0.34.166

;; Query time: 513 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Thu Oct 5 15:24:19 2006
;; MSG SIZE rcvd: 45

$ dig example.com

; <<>> DiG 9.3.2 <<>> example.com
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 19338
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;example.com. IN A

;; ANSWER SECTION:
example.com. 172799 IN A 192.0.34.166

;; Query time: 0 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Thu Oct 5 15:24:20 2006
;; MSG SIZE rcvd: 45


Not only does Google search fail to recognize that “it’s” is a word, it also ignores the quote marks, searching for the phrase as individual words.