We wrap up the season with the observer pattern and a review of what we have learned.  This pattern is one that you probably have already encountered.  Instead of an observer, you probably have heard it called a listener. The Observer Pattern Defined As always, we will start with the “Gang of Four” intent to set the stage for our discussion. “Define a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically.” Thus, the observer pattern is precisely what the name implies.  You assign an object to an observer, and when something changes in the observed object, the observer is notified.  The key to this is that it is a one-to-many... Read more

The visitor pattern is the last of the behavioral ones for us to review.  This is going to feel similar to some others that allow us to abstract functionality such as a command.  This one provides us with a way to group functionality and avoids duplication or even sprawl of our code. The Visitor Pattern Defined As always, we will start with the “Gang of Four” intent to set the stage for our discussion. “Represent an operation to be perfomed on the elements of an object structure. Visitor lets you define a new operation without changing the classes of the elements on which it operates.” Simply put, this pattern allows us to abstract and group functions that we will be performed on... Read more

In the last episode, we looked at abstracting algorithms.  Now we examine the template method pattern and how it allows us to abstract steps of an algorithm.  Thus, providing a template for implementation while leaving the freedom for subclasses to handle the details. The Template Method Pattern Defined As always, we will start with the “Gang of Four” intent to set the stage for our discussion. “Define the skeleton of an algorithm in an operation, deferring some steps to subclasses. Template Method lets subclasses redefine certain steps of an algorithm without changing the algorithm’s structure.” This is a rather simple pattern to understand.  We build a root or base class that lays out the steps of an algorithm.  Then we leave some... Read more

Our review of the behavioral design patterns moves on to look at the Strategy pattern.  This is one that you might not recognize from the name.  However, it is relatively common in use (or at least it should be). The Strategy Pattern Defined As always, we will start with the “Gang of Four” intent to set the stage for our discussion. “Define a family of algorithms, encapsulate each one, and make them interchangeable. Strategy lets the algorithm vary independently from clients that use it” Some people start to hear static when the word algorithm is used.  It seems too theoretical and does not apply to a practical approach.  Unfortunately, that is the core aspect of a strategy.  There is a process... Read more