I tried using both the model–view–controller (MVC) and model–view–presenter architectural patterns for doing android development. My findings are model–view–controller works fine, but there are a couple of “issues”. It all comes down to how you perceive the Android Activity class. Is it a controller, or is it a view? The actual Activity class doesn’t extend … Read more
As a summary, I would describe the wider impact of the repository pattern. It allows all of your code to use objects without having to know how the objects are persisted. All of the knowledge of persistence, including mapping from tables to objects, is safely contained in the repository. Very often, you will find SQL … Read more
There’s a book in Martin Fowler’s Signature Series called Refactoring Databases. That provides a list of techniques for refactoring databases. I can’t say I’ve heard a list of database patterns so much. I would also highly recommend David C. Hay’s Data Model Patterns and the follow up A Metadata Map which builds on the first … Read more
The static factory method pattern is a way to encapsulate object creation. Without a factory method, you would simply call the class’s constructor directly: Foo x = new Foo(). With this pattern, you would instead call the factory method: Foo x = Foo.create(). The constructors are marked private, so they cannot be called except from … Read more
Answer: Use a Singleton if: You need to have one and only one object of a type in system Do not use a Singleton if: You want to save memory You want to try something new You want to show off how much you know Because everyone else is doing it (See cargo cult programmer … Read more
I like thinking about design pattens in terms of my classes being ‘people,’ and the patterns are the ways that the people talk to each other. So, to me the factory pattern is like a hiring agency. You’ve got someone that will need a variable number of workers. This person may know some info they … Read more
Another option is to use the +(void)initialize method. From the documentation: The runtime sends initialize to each class in a program exactly one time just before the class, or any class that inherits from it, is sent its first message from within the program. (Thus the method may never be invoked if the class is … Read more
I’m not very familiar with the Visitor pattern. Let’s see if I got it right. Suppose you have a hierarchy of animals class Animal { }; class Dog: public Animal { }; class Cat: public Animal { }; (Suppose it is a complex hierarchy with a well-established interface.) Now we want to add a new … Read more
A couple of points: DI increases complexity, usually by increasing the number of classes since responsibilities are separated more, which is not always beneficial Your code will be (somewhat) coupled to the dependency injection framework you use (or more generally how you decide to implement the DI pattern) DI containers or approaches that perform type … Read more
The difference may seem slight, but even with the ServiceLocator, the class is still responsible for creating its dependencies. It just uses the service locator to do it. With DI, the class is given its dependencies. It neither knows, nor cares where they come from. One important result of this is that the DI example … Read more