Introduction

---

Building complex, well-behaved, object-oriented software is a difficult task for several reasons. First, simply programming in C++ does not automatically make your application object-oriented. A legacy C application rewritten in C++ without a proper object-oriented architecture design is just Cplusplusified C code. This comes as a shock to those who embrace and adopt C++ in hopes of finding a panacea.

Second, the process by which you become proficient at object-oriented design is characterized by experience. It takes a lot of time and money to learn the lessons of bad architecture design and then apply those lessons-learned to create good object-oriented architectures.

This chapter will help you jump-start your object-oriented architecture design efforts. It begins with a discussion of the preferred characteristics of a well-designed object-oriented architecture. It then presents and discusses three important object-oriented design principles and guidelines you can immediately apply to your architecture designs to drastically improve performance, reliability, and maintainability.

The three design principles include the Liskov substitution principle, the open-closed principle, and the dependency inversion principle. Bertrand Meyer's design by contract programming is discussed in the context of its close relationship to, and extension of, the Liskov substitution principle.

An understanding of these three design principles, along with an understanding of how to apply them using the C++ language, will significantly improve your ability to design robust, object-oriented architectures.

---