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Bad Smells in Code-COMPUTING 0016 CS002-BadSmells-2019/2021

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Bad Smells in Code Dr. Kevan Buckley6CS002, Dr K Buckley 2 Lecture Outcomes • To be familiar with Bad Smells – Indicators that your code is structured poorly • By the end of this session yo ... u should be able to start evaluating code with respect to bad smells.6CS002, Dr K Buckley 3 References • The material presented here is covered in: – Refactoring: Improving the Design of Existing Code by Martin Fowler. • Available from Safari and in the Harrison Library • Concentrate on pages 75 to 88 (http://www.laputan.org/pub/patterns/fowler/smells.pdf) • See http://sourcemaking.com/refactoring/bad-smells-in-code • An alternative perspective is presented in: – Clean Code: A Handbook for Agile Software Craftsmanship by Robert C. Martin • Some useful additions, but a lot that is out of the scope of our work • Try to use Fowler as the primary reference, but if there are things that you do not understand try reading the alternative book.6CS002, Dr K Buckley Bad Smells in Code • Smells are the symptoms of bad code • Fowler (1999) provides a catalogue of smells and refactorings – When you identify a smell, you select one of the suggested refactorings then carefully follow a step by step process to safely refactor the code. • Code should be self-documenting – There should be no need for comments – If you can't understand it there are probably bad smells • See the following for a summary – http://wiki.java.net/bin/view/People/SmellsToRefactorings • See the following for Fowler's catalogue – http://www.refactoring.com/catalog/index.html6CS002, Dr K Buckley Bad Smells in Code • Duplicate code – Results from "cut and paste" coding or poor design – Common code can be put into methods that can be called from many places. – Breaks the DRY principle • Long method – The longer a method is, the more difficult it is to understand. – Short methods with good names improve readability. – Methods may be reusable elsewhere in the program – Poor cohesion breaks SRP • (you can apply these principals to structured programming) • Large class – When a class is trying to do too much it can have too many instance variables and is susceptible to duplication and confusion. • e.g. a complex GUI application could be split into separate classes for the data and behaviour (see http://java.sun.com/blueprints/patterns/MVC.html) – Poor cohesion breaks SRP6CS002, Dr K Buckley Bad Smells in Code • Long parameter list – Hard to understand (and remember) lots of parameters – Often better to pass a small number of objects – Indication that a metho [Show More]

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