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Towards a Theory of Test-Driven Development

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This post examines how well we really understand the practice of Test-Driven Development (TDD).                   Red, Green, Refactor By now we all know that Test-Driven Development (TDD) follows a simple cycle consisting of these steps: Start by writing a test. Since there is no code, it will fail (Red) Write just enough ...

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Processing huge files with Java

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I recently had to process a set of files containg historical tick-by-tick fx market data and quickly realized that none of them could be read into memory using a traditional InputStream because every file was over 4 gigabytes in size. Emacs couldn’t even open them. In this particular case I could write a simple bash script that divide files into ...

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Clojure: Reading and writing a reasonably sized file

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In a post a couple of days ago I described some code I’d written in R to find out all the features with zero variance in the Kaggle Digit Recognizer data set and yesterday I started working on some code to remove those features. Jen and I had previously written some code to parse the training data in Clojure so ...

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MapReduce Algorithms – Secondary Sorting

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We continue with our series on implementing MapReduce algorithms found in Data-Intensive Text Processing with MapReduce book. Other posts in this series: Working Through Data-Intensive Text Processing with MapReduce Working Through Data-Intensive Text Processing with MapReduce – Local Aggregation Part II Calculating A Co-Occurrence Matrix with Hadoop MapReduce Algorithms – Order Inversion       This post covers the pattern ...

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Hibernate Search 4.2 final released: spatial query supported

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JBoss has announced the release of Hibernate Search 4.2 final. You may download it from Sourceforge or use the Maven artifacts. In the new release, some interesting features are included: Hibernate Search now supports spatial queries. With the Spatial extensions you can combine fulltext queries with restrictions based on distance from a point in space, filter results based on distances ...

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Garbage Collection Analysis of PCGen

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Introduction I decided to combine two software loves of mine and perform some analysis on PCGen, a popular Java based open source character generator for role-playing games. I used Censum, our ( jClarity‘s) new Garbage Collection log analysis tool to perform the analysis. This write-up assumes you have a passing familiarity with Garbage Collection (GC) on the JVM. If you’re ...

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How many threads do I need?

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It depends on your application. But for those who wish to have some insight about how to squeeze out most from all those expensive cores you have purchased for your production site – bear with me and I will shed some light on the mysteries surrounding multi-threaded Java applications.                 The content is ...

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Dev vs QA, should there really be a distinction?

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We had our scrum of scrum meetings last Wednesday where all scrum masters meet up with our line manager to discuss issues, bottlenecks and success stories of our previous sprint. One issue highlighted was the fact that sometimes the QA(Quality assurance) personnel are clogged up with testing issues that are in the ‘Ready for test’ stage. So one idea that ...

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QOTD: Java Thread vs. Java Heap Space

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The following question is quite common and is related to OutOfMemoryError: unable to create new native thread problems during the JVM thread creation process and the JVM thread capacity. This is also a typical interview question I ask to new technical candidates (senior role). I recommend that you attempt to provide your own response before looking at the answer.   ...

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@Cacheable overhead in Spring

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Spring 3.1 introduced great caching abstraction layer. Finally we can abandon all home-grown aspects, decorators and code polluting our business logic related to caching.                   Since then we can simply annotate heavyweight methods and let Spring and AOP machinery do the work: @Cacheable("books") public Book findBook(ISBN isbn) {...} "books" is a cache ...

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