2.1 Introduction

2 This chapter begins the examination of what programming is and how a programming language like Java works. In particular, it introduces the basic ideas and concepts of imperative programming, which is about writing programs using instruction sequences and updatable state. While Java is known as an object-oriented programming language it is also an imperative language and relies on the key principles introduced in this chapter. The following chapters will expand on these principles and show how they lead to the idea of object-oriented programming. To construct any computer-based system, we must use some process to translate the idea for the use of the computer into lines of source code which can be compiled and executed. This process typically includes the tasks of: requirements gathering, what we would like the system to do; analysis, finding out how the system should behave; design, deciding the structure of the system to be constructed; implementation, writing the source code; and testing, verification and validation, making sure the system does what we claim! The tasks of implementation and testing also include the task of debugging, which is the finding and removing of errors (usually called bugs, hence the term debugging) in our program. Measured in terms of the quantity of source code required for the implementation of the system, computer-based systems come in varying sizes from the very small to the very large. The term programming is usually applied to the task of constructing small-to medium-sized systems. The term information systems engineering (sometimes called software engineering) is usually applied to the activity of constructing medium-to large-sized systems. The basic process of development is essentially the same in all cases but because of the scale of the problem being addressed, information systems engineering not only subsumes programming but requires tools and techniques over and above those required for programming. It is not the purpose of this book to introduce information