Introduction - Java Software Solutions: Foundations of Program Design - page 4

popular, especially in larger computer systems. A version of Unix called Linux
was developed as an open source project, which means that many people contrib-
uted to its development and its code is freely available. Because of that, Linux has
become a particular favorite among some users. Mac OS X is an operating system
used for computing systems developed by Apple Computers.
An application is a generic term for just about any software other than the
operating system. Word processors, missile control systems, database managers,
Web browsers, and games all can be considered application programs. Each appli-
cation program has its own user interface that allows the user to interact with that
particular program.
The user interface for most modern operating systems and applications is a
graphical user interface (GUI, pronounced “gooey”), which, as the name implies,
make use of graphical screen elements. Among many others, these elements
include

windows, which are used to separate the screen into distinct work areas

■

icons, which are small images that represent computer resources, such as a file ■

menus, checkboxes, and radio buttons, which provide the user with select-
able options

■

sliders, which allow the user to select from a range of values

■

The mouse is the primary input device used with GUIs; thus, GUIs are some-
times called point-and-click interfaces. The screen shot in Figure 1.2 shows an
example of a GUI.
The interface to an application or operating system is an impor-
tant part of the software because it is the only part of the program
with which the user interacts directly. To the user, the interface is
the program. Throughout this topic we discuss the design and imple-
mentation of graphical user interfaces.
The focus of this topic is the development of high-quality application pro-
grams. We explore how to design and write software that will perform calcula-
tions, make decisions, and present results textually or graphically. We use the
Java programming language throughout the text to demonstrate various comput-
ing concepts.

buttons, which can be “pushed” with a mouse click to indicate a user selection

■

KEY CONCEPT
As far as the user is concerned, the
interface is the program.

Digital Computers
Two fundamental techniques are used to store and manage information: analog
and digital. Analog information is continuous, in direct proportion to the source
of the information. For example, an alcohol thermometer is an analog device