Java Reference
In-Depth Information
Introduction
Terms such as ''the Internet,'' which was unfamiliar just a few years ago, are now
common. Elementary school students regularly ''surf'' the Internet and use computers
to design their classroom projects. Many people use the Internet to look up information
and to communicate with others. These Internet activities are all made possible by the
availability of different software, also known as computer programs. Software is devel-
oped by using programming languages. The Java programming language is especially well
suited for developing software to accomplish specific tasks. Our main objective is to teach
you how to write programs in the Java programming language. Before you begin
programming, it is useful if you understand some of the basic terminology and different
components of a computer. We begin with an overview of the history of computers.
The first device known to carry out calculations was the abacus. The abacus was invented
in Asia but was used in ancient Babylon, China, and throughout Europe until the late
middle ages. The abacus uses a system of sliding beads on a rack for addition and
subtraction. In 1642, the French philosopher and mathematician Blaise Pascal invented
the calculating device called the Pascaline. It had eight movable dials on wheels that could
calculate sums up to eight figures long. Both the abacus and Pascaline could perform only
addition and subtraction operations. Later in the seventeenth century, Gottfried von
Leibniz invented a device that was able to add, subtract, multiply, and divide. In 1819,
Joseph Jacquard, a French weaver, discovered that the weaving instructions for his looms
could be stored on cards with holes punched in them. While the cards moved throughout the
loom in sequence, needles passed through the holes and picked up threads of the correct color
and texture. A weaver could rearrange the cards and change the pattern being woven. In
essence, the cards programmed a loom to produce patterns in cloth. The weaving industry
seemstohavelittleincommonwiththecomputer industry. However, the idea of storing
information by punching holes on a card turned out to be of great importance in the later
development of computers.
In the early and mid-1800s, Charles Babbage, an English mathematician and physical
scientist, designed two calculating machines—the difference engine and the analytical
engine. The difference engine could automatically perform complex operations, such as
squaring numbers. Babbage built a prototype of the difference engine, but did not build
the actual device. The first complete difference engine was completed in London in
2002, 153 years after it was designed. It consists of 8,000 parts, weighs five tons, and
measures 11 feet long. A replica of the difference engine was completed in 2008 and is on
display at the Computer History Museum in Mountain View, California (http://
www.computerhistory.org/babbage/). Most of Babbage's work is known through the writings
of his colleague Ada Augusta, Countess of Lovelace. Augusta is considered to be the first
computer programmer.
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