Software Engineering for Students A Programming Approach

CHAPTER
15 Object-oriented
programming
This chapter:
■ explains how encapsulation, inheritance and polymorphism are provided in a
programming language
■ explains the role of libraries in object-oriented programming
■ explains the idea of generics or templates
■ explains provision for dynamic data structures and garbage collection.
15.1 ● Introduction
Most current mainstream languages embody OOP. The three pillars of OOP are encapsulation,
inheritance and polymorphism. This chapter explains how the programming
language can support these concepts. The language used for illustration is Java, and the
case study is the cyberspace invaders game (Appendix A).
We go on to explain how classes can be made more general using the concept of
generics, sometimes termed templates.
Next we discuss approaches to creating dynamic data structure – structures that
expand and contract as necessary. In particular, we look at using pointers.
Finally we explore the challenge of garbage collection – what happens to computer
memory after it has been used as part of a dynamic data structure.
15.2 ● Encapsulation
Encapsulation means bringing together data and actions that are related. In OOP such
a collection is called a class. It consists of some related variable declarations and some
methods. A class is a template or blueprint for any number of objects that can be created
from it. In many programming languages, including Java, this is accomplished
using the key word new. Creating an object is also known as instantiating an object.
We will use the example of the cyberspace invaders game, Figure 15.1, to illustrate
encapsulation. The program displays a number of graphical objects at various times on