Tuesday, February 27, 2007

JRuby Setup

Recently got a JRuby/Rails system with Java integration up and running. Unfortunately, it took quite a few hours, as most of the docs and code you find through Google are out of date.

If you use JRuby 0.9.2 from Codehaus, you will get an error similar to this when you try to access a rails application:

[2007-02-26 17:54:59] INFO WEBrick::HTTPServer start: pid=22540508 port=3000
<ArgumentError: Anonymous modules have no name to be referenced by>
active_support/dependencies.rb:402:in `to_constant_name'...

If you're stuck in this rut, fear not! Nick Sieger has written very helpful instructions which outline how to get and set up the latest development snapshot. Please note that in addition to the instructions, you need to set your JRUBY_HOME environment variable. Under Windows, do something like this:

set JRUBY_HOME=c:\jruby

If you'd prefer not to use the snapshot, you can get the source code through subversion from:


but at the time of this post, you need to run svn checkout or update with "--ignore-externals" to avoid the following error:

Error: URL 'svn://rubyforge.org/var/svn/bfts/bfts/trunk' doesn't exist

Many thanks to Nick Sieger and the JRuby user mailing list for their help.

Monday, February 26, 2007

Holiday 2007 - Venice and Padua

It was a sudden decision to take a sleeper train to Venice. We didn't really know what to expect. By chance, we arrived at Carnivale (mask and costume festival), probably the busiest time of the year. Venice was filled to the rafters with tourists, prices were high and it was difficult to walk in many areas due to the number of people in the narrow streets! The solution was to take to the water - catching the ferry was fun and it got you out of the crowds.

Venice is really beautiful. The Doges (ruler's) palace and nearby Cathedral in St Marco square are amazing. The palace has huge painted ceiling murals by famous artists and enormous open halls. In the Cathedral, there are golden mosaics over the whole ceiling, and even the floor is an artwork in tiles. There's also some impressive golden relics from when the Venetians sacked Constantinople during the crusades.

In Venice, most streets lead to the water, and the best facades are turned towards the canals. It really is a city designed to be traversed on the water. The buildings are mainly standing on foundations made from hundreds of pine trees hammered into the silty mud under Venice. Historically, Venice's influence peaked in the 13th century or so, and from then on, it was a slow decline in power. But to make up for this, the wealthy families spent lavishly on buildings, clothes and decorations.

On our last day in Italy, we went to Padua to take a look at a more typical Italian city. It was a friendly and fun place with few tourists, but good food and a nice atmosphere. Last picture is of Padua, all the rest are from Venice!

Holiday 2007 - Monaco

Monaco is easily accessible from Nice - about 1/2h by train. We spent an enjoyable afternoon and evening there, visiting the cactus "exotic" garden, castle, casino and cave. The cave was particularly interesting - it was about 18degC inside (despite winter temperatures outside), and walkways for visitors had been made using explosives and diamond drills! Despite the damage, it was still a lovely cave. Monaco was clean and tidy, and felt almost like a movie set.

Sunday, February 25, 2007

Using floating point variables to represent money => not a good idea!

I was reading through some code the other day and was surprised to find that it was using doubles to represent dollar amounts. Reason for the alarm bells is that doubles and floats cannot accurately represent many decimal fractions (eg, 0.1), since doubles and floats internally work with powers of 2 rather than powers of 10. These inaccuracies are likely to lead to significant errors, especially when performing arithmetic (eg, adding up a table of dollar amounts). See this IBM article for a more in depth explanation and examples. The solution is to use types that work with powers of ten internally. In C#, you can use 'decimal' and in Java or Ruby, 'BigDecimal', to avoid these problems.

Holiday 2007 - Provence & Cote D'Azure in the South of France

France supposedly is the number 1 tourist destination in the world, and certainly it is one of my personal favourites! Besides the pleasure of speaking French, we had the opportunity to eat a lot of good food, and visit really pretty coastal areas, medieval towns, castles and ancient Roman remains.

Our itinerary looked roughly like this:
Marseilles -> Aix En Provence -> Avignon -> Nimes -> Arles -> Tarascon -> (Italy) -> Nice -> Antibes -> (Monaco)

In terms of hotels, it was very much 'get what you pay for'. We tended to stay in two star places around 40-50 euros per night. Our first hotel in Marseilles was only 37E per night, and it convinced us that the extra 10E or so was really worth it! Hotels were fairly easy to find (well sign posted), though often not too close to transport.

We tried the random approach to finding good restaurants to start with, but this led to a number of disappointments. The solution was to ask our hoteliers for their favourite restaurants - this led to some really great meals :-)

We had planned to rent a car for some parts of the trip.. however, make sure you learn to drive a manual before attempting this! Autos in France are horribly expensive to rent, so we ended up doing everything by public transport - bit tricky in winter time especially, but we managed. Tourist offices were generally very helpful.