DevoxxUK Lambdas Lab (original) (raw)

Martijn Verburg martijnverburg at gmail.com
Wed Apr 3 07:25:41 PDT 2013

Hi all,

On 3 April 2013 15:08, Richard Warburton <richard.warburton at gmail.com>wrote:

> > If the problem was computing word frequency, the reason it is horrible > is not the API :) > > Map<String, Integer> m > = reader.lines() > .flatMap(s -> Arrays.stream(s.split(" "))) > .groupingBy(Functions.identity(), > reducing(s -> 1, Integer::sum))); >

This is pretty much Identical to the code that Stuart produced, and its perfectly fine as far as addressing the question "Can you write an elegant solution to the problem using the streams api?" Unfortunately the important question is "Will blue collar Java developers be able to write a usable solution to the problem using the streams api?" My conclusion from running this lab is no. None of the people who attended realised that the use of the downstream collector for the values of the group was important in writing the code. I think this issue could be solved with better documentation pointing them to look at that method. I tested the hypothetical that this documentation was in place by pointing two attendees of the lab, who had successfully solved the easier exercises, in its direction. They still didn't produce "reducing(s -> 1, Integer::sum)". I'm honestly quite sceptical that people would make that leap. I don't think many developers when asked "produce something that collects the count of a list" Will intuitively go in the direction of: [ "dad", "dad", "dad" ] -> [1, 1, 1] -> 3 Elsewhere in this thread there is a suggestion that a counting method should be provided. That's not only a good suggestion because counting things is a common method of collecting them, but its also a good suggestion to use this as an example, in the javadoc, in order to help developers build the intuition of this kind of Collector. I'm not quite as negative as Stephen on the issue, because when getting people to try out the streams API I think broadly people have picked things up easily and been able to comprehend the problems quickly. This is definitely one of the areas where they struggled a lot.

As one of the test subjects after the lab, I tend to agree, I certainly did not instinctively move to reducing(s -> 1, Integer::sum), I instead wanted a count method/function. That may say more about my lack of familiarity with Lambdas than anything, but hopefully it's another small data point.

Cheers, Martijn

More information about the lambda-dev mailing list