Kevlin Henney

The question of what units you are working with is one that will at one time or other have plagued anyone who studied a science or a branch of physical engineering. Teachers go to great lengths to make sure students remember to specify their units. It is not enough to say that the answer is 42. Forty-two what? 42 metres? 42 …

ColumnPerhaps one of the most interesting things about TDD is not the specification-oriented and design-centred role in which testing is employed, but the amount of explanation it requires as a term. And I don't just mean expanding the abbreviation to Test-Driven Development or Test-Driven Design, as opposed to, say, …

ColumnIn the previous article, I made the following observation: A collection that holds its elements but doesn't allow you to traverse them is unlikely to prove popular. There are many ways to offer traversal, but if the caller needs to be able to know the position of elements in some way there are essentially only three general …

In the previous article, I made the following observation: A collection that holds its elements but doesn't allow you to traverse them is unlikely to prove popular. There are many ways to offer traversal, but if the caller needs to be able to know the position of elements in some way there are essentially only three general …

The standard advice on cohesion and coupling is that a design should strive to maximise cohesion and minimise coupling. This is a fine mantra, but, as is so often the case, without a good understanding of what is really intended, it becomes either misguidance or perceived as academic and irrelevant. A simple characterisation …

Long argument lists are a pain. Using them can be a test of memory or an exercise in guess work. In recent years, attention has increasingly been paid to the usability of user interfaces, exploring how users actually use — or work around — user interfaces in practice, tracking how long certain tasks take or how many errors are …

There are many reasons for getting cohesive. The principle of locality, which is normally considered with respect to locality of reference when using resources such as memory, can also apply to the organisation of APIs and classes and the partitioning of packages, components and header files. This criterion for cohesion is …

CommentTest-Driven Development (TDD) has increased in popularity both as a practice and as a term. Although there is a strong association with Extreme Programming, more generally there is a certain set of practices that can be honed in on and applied across various development models. Decoupling TDD from XP, which specifically …

ColumnA bug is no more and no less than a software defect. However, the less harsh and less direct name "bug" masks the nature of the beast and helps to ease the conscience of programmers and the organisations around them. The term also helps play down the frustrations of software users, to the point that defects have become accepted …

Column In my previous column I put the contract for object equality under the microscope in most detail for Object.equals in Java but also with a brief look at Object.Equals in C#. The idea that equality can also be assessed by relational comparison between two objects was also examined, looking again in most detail at the contract …

ColumnWhether formal or informal, a contract defines an (in principle) enforceable agreement between two or more parties with respect to a specific undertaking. The same is also true in code. The contract metaphor is an effective way of approaching API design and use [1]: "A contract is effectively an agreement on the requirements …

CommentIt is entirely possible to write applications as a monolithic slab of undifferentiated code. Indeed, for some this appears to approach an art form, with a stream-of-consciousness code style not dissimilar to Jack Kerouac's spontaneous, amphetamine-fuelled writing style. Caffeine is the more likely the drug of choice in …