Static state: Evil as well

Static state: Evil as well

Today in our project we suddenly had 10 failing unit-tests on our integration server (Hudson). Opening Hudson and looking at the first failed build I was in for a surprise. The only code changed that commit was mine!

The scare

Quickly I looked around and went into overdrive mode:
I need to fix this bug before somebody sees it!
I’m always yelling at people who break the build, and now it has happend to me…!

Looking at the SVN comment it only said: “cleaned up some code” (or something)
That isn’t very helpfull of myself…

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Checked Exceptions: Evil

Checked Exceptions: Evil

Today somebody posted a comment:

‘Could you write a post giving more details on why you think
checked exceptions are “the embodiment of evil”?’

So here it is.

As you can see I haven’t written a post in a long time (sorry). This post is also not going to be very comprehensive. Of course I could explain everything, but I’d rather link to another site which sums it up very nicely:
http://c2.com/cgi/wiki?TheProblemWithCheckedExceptions

Basically, I don’t want to be forced to handle exceptions. Also, having to catch checked exceptions makes code unreadable, complex and harder to...

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De Bruijn sequence in constant amortized time

De Bruijn sequence in constant amortized time

Follow up on the previous blogpost.

Yesterday I wrote an algorithm in Java to generate de Bruijn sequences. But I had a breakthrough after reading:

K. Cattell, F. Ruskey, J. Sawada, M. Serra, C.R. Miers, Fast algorithms to generate necklaces, unlabeled necklaces, and irreducible polynomials over GF(2)

It has an algorithm which generates Lyndon words in CAT. CAT stands for Constant Amortized Time. This means that it isn’t really constant time, but approaches it very much. Calculating the worst-case scenario isn’t worth it. For example using an ArrayList in Java. The time to do insertions is said to be O(1),...

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Generating de Bruijn sequences and Lyndon words

Generating de Bruijn sequences and Lyndon words

Not so long ago I encountered something called the de Bruijn sequence. For now I’ll only use this for an alphabet of (0,1), binary. But everything said here could also be applied to other alphabets. In this post I’ll describe what this sequence is, and how you can generate them, using Lyndon words.

What is a de Bruijn sequence?

Well, it is a sequence (again, in this case binary) which contains all combinations/permutations of a specific length. And it does this only once.
For example: B(2,4)

  • 000100110101111 (000)

This sequence contains all possible permutations...

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Testing a chess engine

Testing a chess engine

About a week ago I decided to try and write a chess engine. I’ve encountered bitboards before, and I really liked working with them. Most references I found had to do with chess engines, so I decided to have a go.

The single most important and time consuming aspect of building a chess engine is legal move generation. In all situations, be able to generate all legal moves that can be made on the board. At first this seems pretty straight forward, all pieces can move and attack in certain ways. But when you get to specific rules...

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Exception mailing

Exception mailing

A couple of weeks ago our Scrum team was thinking about exception handling. We don’t use checked exceptions, since they are the embodiment of evil. So everything is translated into runtime exceptions whenever possible. But this is where the problems start: What do you do with the uncatched runtime exceptions?

Taking it one step further

Most projects will decide to just write the exceptions to the console, maybe to a log file. In some cases there is specialized software which will analyze log files, detect stacktraces and act on them. We decided to create a fast specialized solution. We...

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Rainbow tables, reverse hash lookup

Rainbow tables, reverse hash lookup

Today I’ve been looking into rainbow tables. These are tables used to do a reverse lookup for a hash function. For example MD5, or Windows LAN Manager. Usually these tables are used to find passwords if the hash is known. Now I’m not looking for a method to crack somebodies computer, but the technology and algorithms involved are very advanced and might be usefull in other fields as well!

Hashing

First off, lets talk about ‘hashing’, what is hashing? Well, a hash-function is a one-way function which turns some data (usually text) into a hashcode. For example… passwords:

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Finding performance problems

Finding performance problems

Many projects I’ve worked on, especially the projects using micro-optimization, had memory leaks and surprising performance hits. Most coders who work on for example Al Zimmermann’s programming contests use C/C++ and maybe even CUDA to get the most out of their system.

I’m usually using Java, just because I’m most at home in this language. It allows me to quickly get some working code and test some algorithms. But when I reach the final phase of the project it is time to micro-optimize everything.

The first tool I’ve tried it Java Visual VM. This tool is available in all...

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XOR doubly linked list

XOR doubly linked list

Since a couple of days I’ve been working hard on the new Al Zimmermann’s Programming Contest: Cards (also called Topswops).

The challenge

The idea is very easy, you take a series of numbers, from 1 to N. You shuffle the numbers around, for example:

  • 5,3,1,2,4

Now we reverse the amount of numbers as stated by the first entry in the list. So in this case we reverse 5, and we get:

  • 4,2,1,3,5

We keep doing this, now reversing 4:

  • 3,1,2,4,5
  • 2,1,3,4,5
  • 1,2,3,4,5

At this point, 1 is in front, we are done!...

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Patent infringement (part 2)

Patent infringement (part 2)

After a lot of comments on my blog asking about the code I decided to try getting it released one more time. Thus I mailed Digital Landmark Services again, telling them this is just a hobby project, and will (in its current form) never be a replacement for Shazam. Also, I explained a lot of people hated Shazam and deleted the application after reading this blog… the only thing they got out of it is bad marketing.

So I asked them for a peaceful solution, I’ll release the code, tell everybody Landmark Digital Services is a good company after all, and that’s it, both will benefit.

This is the reply I got:

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Handling 'Frame switching'

Handling 'Frame switching'

A couple of days ago I noticed this tweet:

berenguel: What is your view on ‘frame switching’?How do you manage (forced) interruptions of your workflow?How do you get the interruptor to give up?

This is something I’m currently not experiencing, but I have been fighting this in the past. And I’ve come up with a quite effective way to eliminate this.

Post-it

Priority todo-list

I’m just a regular guy, and just like all men I can only focus on a single thing. Context swithing/frame of reference switching is hard. If I’m working on a...

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Bug Fix Day!

Bug Fix Day!

After a couple of iterations our software started to show some wear and tear. With all fat-GUI clients you always have some behaviour that isn’t exacly what you want, there are always glitches. More and more (Scrum) iterations followed and more and more glitches started accumulating in the application. These glitches are sometimes hard to fix and/or hard to reproduce, and they never made their way to our backlog.
computer-bug

How do you solve this?

“Bug Fix Day” concept

To improve the quirkiness and general impression of our application, as well as the teamspirit,...

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(Annotated) Field injection vs Constructor injection

(Annotated) Field injection vs Constructor injection

A couple of people replied to my last article about constructor vs setter injection that they prefer a third option, field injection. This is a slight variant of setter injection in which we magically let the setter dissapear.

So, another blogpost here!

Let me first show what field injection looks like:

public class Apple { @Inject private Orange orange; }

This is an example from the PicoContainer website, but Spring and Google Guice can do this too. So, you ask, what is wrong with this?

Testability

...

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Setter vs Constructor injection

Setter vs Constructor injection

Recently I’ve had a discussion with a collegue about Setter vs Constructor injection. For those who don’t know what I’m talking about a quick example:

Setter injection:

public class SomeClass {
	
	private SomeDependency someDependency;
	
	public SomeClass() {
		//Empty constructor
	}

	public void setSomeDependency(SomeDependency someDependency) {
		this.someDependency = someDependency;
	}
}

Constructor injection:

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Dinosaurize your street

Dinosaurize your street

After looking at The Wilderness Downtown, a fantastic Chrome Experiment, I felt like I had to do something similair! Three hours later (first time experimenting with Google Maps and Street View) the result is below.

It is nothing like The Wilderness Downtown, but still I’d like to share it ;-)

Enter streetname, town and country:

Image 1
Image 1
Image 1

walking

Yes, there are a LOT of bugs… And no, I’m not going to fix them, so there is no need to notify me.

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