Java编程基础：精简版第七版概览

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"Java Software Solutions Foundations of Program Design (7th Edition)是一本专注于Java程序设计基础的教科书，旨在帮助初学者理解编程的核心概念。本书涵盖了计算机处理、软件类别、硬件组件、网络、Java编程语言、程序开发以及数据和表达式等主题。" 在本书中，作者首先介绍了计算机的基本概念，包括计算机处理、软件的不同类型，如系统软件和应用软件，以及数字计算机的工作原理。接着，深入探讨了二进制数字系统，这是理解计算机内部运作的关键。硬件组件部分讲解了计算机架构、输入/输出设备（如键盘和显示器）、主内存与辅助存储器以及中央处理器（CPU）的作用。网络章节则涉及了网络连接的重要性，区分了局域网（LAN）和广域网（WAN），特别是互联网及其组成部分，如万维网（WWW）和统一资源定位符（URL）。这些基础知识对于任何现代程序员来说都是不可或缺的。进入编程语言的主题，本书详细阐述了Java编程语言的特点。通过一个简单的Java程序示例，读者可以了解到程序的基本结构，以及注释、标识符、保留字和空白字符的使用规则。此外，还讨论了程序开发的过程，包括编程语言的层次、编辑器、编译器、解释器、开发环境，以及语法和语义的重要性。错误处理是编程中不可避免的部分，书中也有所提及。第2章则转向数据和表达式，讲解了字符字符串的使用，如`print`和`println`方法、字符串连接以及转义序列。变量和赋值的概念是编程的基础，书中详细介绍了变量的声明、赋值语句以及常量的运用。此外，还探讨了各种基本数据类型，包括整型、浮点型、字符型等，这些都是编写有效Java程序的基石。这本Java Software Solutions Foundations of Program Design (7th Edition)提供了全面的入门指导，适合对编程感兴趣的学生或自学者，帮助他们建立起扎实的Java编程基础，并理解计算机科学的基本原理。通过学习本书，读者能够逐步掌握解决问题的技巧，以及如何运用面向对象编程原则来设计和实现复杂的软件系统。

6 CHAPTER 1 Introduction

can be used to generate a continuous analog signal that is “close enough” to the

original. In most cases, the goal is to create a reproduction of the original signal

that is good enough to satisfy the human senses.

Figure 1.4 shows the sampling of an analog signal. When analog information

is converted to a digital format by breaking it into pieces, we say it has been

digitized. Because the changes that occur in a signal between samples are lost, the

sampling rate must be sufficiently fast.

Sound wave Analog signal of the sound wave

FIGURE 1.3 A sound wave and an electronic analog signal

that represents the wave

Information can be lost

between samples

Analog signal

Sampling process

Sam

led values

12 11 39 40 7 14 47

FIGURE 1.4 Digitizing an analog signal by sampling

1.1 Computer Processing 7

Sampling is only one way to digitize information. For example, a sentence of

text is stored on a computer as a series of numbers, where each number represents

a single character in the sentence. Every letter, digit, and punctuation symbol has

been assigned a number. Even the space character is assigned a number. Consider

the following sentence:

Hi, Heather.

The characters of the sentence are represented as a series of 12 numbers, as

shown in Figure 1.5 . When a character is repeated, such as the uppercase

'H' , the

same representation number is used. Note that the uppercase version of a letter is

stored as a different number from the lowercase version, such as the

'H' and 'h'

in the word Heather. They are considered separate and distinct characters.

Modern electronic computers are digital. Every kind of information, including

text, images, numbers, audio, video, and even program instructions is broken into

pieces. Each piece is represented as a number. The information is stored by storing

those numbers.

Binary Numbers

A digital computer stores information as numbers, but those numbers are not stored

as decimal values. All information in a computer is stored and managed as binary

values. Unlike the decimal system, which has 10 digits (0 through 9), the binary

number system has only two digits (0 and 1). A single b inary dig it is called a bit .

All number systems work according to the same rules. The base value of a

number system dictates how many digits we have to work with and indicates the

place value of each digit in a number. The decimal number system

is base 10, whereas the binary number system is base 2. Appendix B

contains a detailed discussion of number systems.

Modern computers use binary numbers because the devices that

store and move information are less expensive and more reliable if

they have to represent only one of two possible values. Other than

this characteristic, there is nothing special about the binary number

72 105 44 32 72 101 97 104 114116 101 46

Hi, He athe r.

FIGURE 1.5 Text is stored by mapping each character to a number

KEY CONCEPT

Binary is used to store and move

information in a computer because

the devices that store and manipu-

late binary data are inexpensive and

reliable.

8 CHAPTER 1 Introduction

system. Computers have been created that use other number systems to store and

move information, but they aren’t as convenient.

Some computer memory devices, such as hard drives, are magnetic in nature.

Magnetic material can be polarized easily to one extreme or the other, but intermedi-

ate levels are difficult to distinguish. Therefore, magnetic devices can be used to rep-

resent binary values quite effectively—a magnetized area represents a binary 1 and a

demagnetized area represents a binary 0. Other computer memory devices are made

up of tiny electrical circuits. These devices are easier to create and are less likely to fail

if they have to switch between only two states. We’re better off reproducing millions

of these simple devices than creating fewer, more complicated ones.

Binary values and digital electronic signals go hand in hand. They improve our

ability to transmit information reliably along a wire. As we’ve seen, an analog signal

has continuously varying voltage with infinitely many states, but a digital signal is

discrete, which means the voltage changes dramatically between one extreme (such

as +5 volts) and the other (such as –5 volts). At any point, the voltage of a digital

signal is considered to be either “high,” which represents a binary 1, or “low,”

which represents a binary 0. Figure 1.6 compares these two types of signals.

As a signal moves down a wire, it gets weaker and degrades due to environ-

mental conditions. That is, the voltage levels of the original signal change slightly.

The trouble with an analog signal is that as it fluctuates, it loses its original infor-

mation. Since the information is directly analogous to the signal, any change in

the signal changes the information. The changes in an analog signal cannot be

recovered because the degraded signal is just as valid as the original. A digital

signal degrades just as an analog signal does, but because the digital signal is

originally at one of two extremes, it can be reinforced before any information is

lost. The voltage may change slightly from its original value, but it still can be

interpreted correctly as either high or low.

The number of bits we use in any given situation determines the number of

unique items we can represent. A single bit has two possible values, 0 and 1, and

Analog signal Digital signal

FIGURE 1.6 An analog signal vs. a digital signal

10 CHAPTER 1 Introduction

We’ve seen how a sentence of text is stored on a computer by mapping char-

acters to numeric values. Those numeric values are stored as binary numbers.

Suppose we want to represent character strings in a language that contains 256

characters and symbols. We would need to use eight bits to store each character

because there are 256 unique permutations of eight bits (2

equals 256). Each bit

permutation, or binary value, is mapped to a specific character.

How many bits would be needed to represent 195 countries of the world?

Seven wouldn’t be enough, because 2

equals 128. Eight bits would be enough,

but some of the 256 permutations would not be mapped to a country.

Ultimately, representing information on a computer boils down to the number

of items there are to represent and determining the way those items are mapped

to binary values.

SELF-REVIEW QUESTIONS (see answers in Appendix N)

SR 1.1 What is hardware? What is software?

SR 1.2 What are the two primary functions of an operating system?

SR 1.3 The music on a CD is created using a sampling rate of 44,000 mea-

surements per second. Each measurement is stored as a number that

represents a specific voltage level. How many such numbers are used

to store a three-minute long song? How many such numbers does it

take to represent one hour of music?

SR 1.4 What happens to information when it is stored digitally?

SR 1.5 How many unique items can be represented with the following?

a. 2 bits

b. 4 bits

c. 5 bits

d. 7 bits

SR 1.6 Suppose you want to represent each of the 50 states of the United

States using a unique permutation of bits. How many bits would be

needed to store each state representation? Why?

1.2 Hardware Components

Let’s examine the hardware components of a computer system in more detail.

Consider the computer described in Figure 1.8. What does it all mean? Is the sys-

tem capable of running the software you want it to? How does it compare with

other systems? These terms are explained throughout this section.

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