You need to understand object-oriented (OO) concepts before you can successfully apply them to systems development. Because OO techniques grew, in part, out of the disciplines of software engineering, artificial intelligence, and information modeling, many of them will seem familiar to you. Do not let this make you complacent—you also need to understand several new concepts.

This chapter explores the following:

• A brief overview of OO concepts;

• OO concepts from a structured point of view;

• The diagrams of the unified modeling language (UML 2);

• Objects and classes;

• Attributes and operations;

• Abstraction, encapsulation, and information hiding;

• Inheritance;

• Persistence;

• Relationships;

• Collaboration;

• Polymorphism;

• Interfaces;

• Components; and

• Patterns.

A BRIEF OVERVIEW OF OO CONCEPTS

This chapter discusses the concepts that make up the foundation of OO development techniques. People experienced with structured technologies such as COBOL and FORTRAN will have seen some of these concepts before, and some will be new to you. For example, many concepts that go to the heart of OO—encapsulation, coupling, and cohesion—come from software engineering. These concepts are important because they underpin good design regardless of the technology you are working with. The main point to be made here is you do not want to deceive yourself: just because you have seen some of these concepts before, it does not mean you were doing OO; it just means you were doing good design. While good design is a big part of object orientation, there is a lot more to it than that.

OO concepts appear deceptively simple. Do not be fooled.