Most language environments now have frameworks that make it easy to create mock objects. What's often not realized, however, is that mock objects are but one form of special case test object, one that enables a different style of testing. In this article I'll explain how mock objects work, how they encourage testing based on behavior verification, and how the community around them uses them to develop a different style of testing. Inversion of Control Containers and the Dependency Injection pattern.
In the Java community there's been a rush of lightweight containers that help to assemble components from different projects into a cohesive application.
Underlying these containers is a common pattern to how they perform the wiring, a concept they refer under the very generic name of "Inversion of Control". In this article I dig into how this pattern works, under the more specific name of "Dependency Injection", and contrast it with the Service Locator alternative. The choice between them is less important than the principle of separating configuration from use.
One of the entertaining things about the enterprise Java world is the huge amount of activity in building alternatives to the mainstream J2EE technologies, much of it happening in open source. Master-Slave Pattern. The Master-Slave pattern is often used for multi-threaded applications in which many instances of the same problem must be solved.
(Travelling Salesman Problem, for example.) The master creates and launches slaves to solve these instances in "parallel". When all of the slaves have finished, the master harvests the results. Master-Slave pattern is also used for user interfaces and servers. In both cases the master listens for commands coming either from the user or from clients.