Furthering the Object-Oriented Mindset
Identifying the Implementation
After the public interfaces are chosen, you need to identify the implementation. After the class is designed and all the methods required to operate the class properly are in place, the issue tends to be an either/or proposition.
What is Implementation?
Technically, anything that is not a public interface can be considered the implementation. This means that the user will never see any of the methods that are considered part of the implementation, including the method's signature (which includes the name of the method and the parameter list), as well as the actual code inside the method. The implementation is totally hidden from the user. In fact, the code within public methods is actually a part of the implementation because the user cannot see it. (The user should only see the calling structure of an interface—not the code inside it.)
The beauty of this approach is that, theoretically, anything that is considered the implementation can change without affecting how the user interfaces with the class. This assumes, of course, that the implementation is providing the answers the user expects.
Whereas the interface represents how the user sees the object, the implementation is really the nuts and bolts of the object. The implementation contains the code that represents that state of an object.
In the past two articles of this series, we have explored several areas that can get you started on the path to thinking in an OO way. Remember that there is no firm list of issues pertaining to the OO thought process. Doing things in an OO way is more of an art than a science. Try to think of your own ways to describe OO thinking.
Fowler, Martin. UML Distilled. Addison-Wesley Longman, 1997.
Gilbert, Stephen, and Bill McCarty. Object-Oriented Design in Java. The Waite Group, 1998.
Meyers, Scott. Effective C++. Addison-Wesley, 1992.
About the Author
Matt Weisfeld is a faculty member at Cuyahoga Community College (Tri-C) in Cleveland, Ohio. Matt is a part of the Information Technology department, teaching programming languages such as C++, Java, and C# .NET as well as various Web technologies. Prior to joining Tri-C, Matt spent 20 years in the information technology industry gaining experience in software development, project management, business development, corporate training, and part-time teaching. Matt holds an MS in computer science and an MBA in project management.
The articles in this series are adapted from The Object-Oriented Thought Process (published by Sams Publishing). Matt has published two other computer books, and more than a dozen articles in magazines and journals such as Dr. Dobb's Journal, The C/C++ Users Journal, Software Development Magazine, Java Report, and the international journal Project Management. Matt has presented at conferences throughout the United States and Canada.
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