tagged by: object collaboration design
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.
23 January 2004
Aggregate is a pattern in Domain-Driven Design. A DDD aggregate is a cluster of domain objects that can be treated as a single unit. An example may be an order and its line-items, these will be separate objects, but it's useful to treat the order (together with its line items) as a single aggregate.
In my view the Gang of Four is the best book ever written on object-oriented design - possibly of any style of design. This book has been enormously influential on the software industry - just look at the Java and .NET libraries which are crawling with GOF patterns.
A synonym for InversionOfControl.
Inversion of Control is a common phenomenon that you come across when extending frameworks. Indeed it's often seen as a defining characteristic of a framework.
26 June 2005
Tell-Don't-Ask is a principle that helps people remember that object-orientation is about bundling data with the functions that operate on that data. It reminds us that rather than asking an object for data and acting on that data, we should instead tell an object what to do. This encourages to move behavior into an object to go with the data.
5 September 2013
Brett L. Schuchert
The Dependency Inversion Principle (DIP) has been around since the early '90s, even so it seems easy to forget in the middle of solving a problem. After a few definitions, I'll present a number of applications of the DIP I've personally used on real projects so you'll have some examples from which to form your own conclusions.
21 May 2013
Flowing JSON data structures through a server is something I'm seeing more these days. JSON documents can be persisted directly, either by using an AggregateOrientedDatabase or a serialized LOB in a relational database. JSON documents can also be served directly to web browsers or used to transfer data to server-side page renderers. When JSON is being used in this way, I hear people saying that using an object-oriented language gets in the way because the JSON needs to be translated into objects only to be rendered out again - a waste of programming effort . I agree with the point about waste, but I argue that it's not a problem with objects but a failure to understand encapsulation.
4 June 2013
You can tell them by the twitch in the left hand side of the mouth when they see a getter method, there's swift pull on their battleaxe and a satisfied cry as another getter is hewn unmercifully from a class which immediately swoons in an ecstasy of gratefulness at the manly Getter Eradicator's feet.
22 February 2006
The practice of taking every class and pairing it with an interface. So as a result you see pairs of things - maybe ICustomer and Customer or Customer and CustomerImpl. In many ways it echoes the C/C++ habit of header files for each class, although in this case the interfaces and implementations are actually separate types.
Lazy Initialization is a technique that initializes a variable (in OO contexts usually a field of a class) on it's first access. It canonical form is something like this:
All services offered by a module should be available through a uniform notation, which does not betray whether they are implemented through storage or through computation.
-- Bertrand Meyer
Bertrand Meyer coined this principle in his highly-influential book Object-Oriented Software Construction.
The essential point of the principle is that if you have a person object and you ask it for its age, you should use the same notation whether the age is a stored field of the object or a computed value. It effectively means that a client of the person should neither know nor care whether the age is stored or computed.
20 April 2011