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