The purpose of this chapter is to familiarize you with the concept of programming. It reviews the
architecture of a computer and discusses the difference between machine code and high-level
programming languages. Finally, you will see how to compile and run your first Java program, and how to
diagnose errors that may occur when a program is compiled or executed.
Copyright © 2008 John Wiley & Sons, Inc. All rights reserved.
1.1 What is Programming?
You have probably used a computer for work or fun. Many people use computers for everyday tasks such as balancing
a checkbook or writing a term paper. Computers are good for such tasks. They can handle repetitive chores, such as
totaling up numbers or placing words on a page, without getting bored or exhausted. Computers also make good
game machines because they can play sequences of sounds and pictures, involving the human user in the process.
The flexibility of a computer is quite an amazing phenomenon. The same machine can balance your checkbook, print
your term paper, and play a game. In contrast, other machines carry out a much narrower range of tasks—a car
drives and a toaster toasts.
A computer must be programmed to perform tasks. Different tasks require different programs.
To achieve this flexibility, the computer must be programmed to perform each task. A computer itself is a machine
that stores data (numbers, words, pictures), interacts with devices (the monitor screen, the sound system, the
printer), and executes programs. Programs are sequences of instructions and decisions that the computer carries out
to achieve a task. One program balances checkbooks; a different program, perhaps designed and constructed by a
different company, processes words; and a third program, probably from yet another company, plays a game.
A computer program executes a sequence of very basic operations in rapid succession.
Today's computer programs are so sophisticated that it is hard to believe that they are all composed of extremely
primitive operations.
A typical operation may be one of the following:
· Put a red dot onto this screen position.
·
Send the letter A to the printer.
· Get a number from this location in memory.
· Add up two numbers.
· If this value is negative, continue the program at that instruction.
A computer program tells a computer, in minute detail, the sequence of steps that are needed to complete a task. A
program contains a huge number of simple operations, and the computer executes them at great speed. The
computer has no intelligence—it simply executes instruction sequences that have been prepared in advance.
