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

We tackle the memento pattern in this episode.  If you ever wanted to store the state of an object, then this is the one for you.  You can think of this pattern as a way to take note of your instance and store it for later. The Memento Pattern Defined As always, we will start with the “Gang of Four” intent to set the stage for our discussion. “Without violating encapsulating, capture and externalize an object’s internal state so that the object can be restored to this state later.” The trick to this intent is to avoid violating encapsulation.  The whole point of this pattern is to allow us to store and pass around the memento without having to keep track... Read more

In this episode, we look at the state pattern.  It is a design that uses object-oriented tactics to provide a class with very different functionality based on its current state.  I think you will find this to be one that is not often going to be evident in your first pass of a design. The State Pattern Defined As always, we will start with the “Gang of Four” intent to set the stage for our discussion. “Allow an object to alter its behavior when its internal state changes. The object will appear to change its class.” We have not had many cases of helpers or partner classes in the patterns we have explored so far.  This pattern uses a primary (context)... Read more