Think Java：循序渐进的计算机科学与编程入门指南

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"《Think Java》是由Allen B. Downey和Chris Mayfield合著的一本计算机科学和编程入门教材，专为那些对计算机科学一无所知或只有少量经验的读者设计。这本书从最基本的概念出发，注重术语的清晰定义，确保初学者能够逐步理解。作者采用逻辑连贯的方式介绍新概念，如递归和面向对象编程这样的较大主题，会通过多个章节分解成小例子逐步引入，让读者在学习过程中逐步掌握。《Think Java》遵循了《如何像计算机科学家一样思考》（HOWTOTHINKLIKEACOMPUTERSCIENTIST）的理念，强调实践和理论相结合的教学方法。本书不仅适合个人自学，也适用于教育机构或企业的培训，提供纸质版和在线版本供选择。第一版于2016年5月出版，由O'Reilly Media公司发行，版权归属于Allen B. Downey和Chris Mayfield，所有权利受到保护。编辑方面，该书由Brian Foster担任，生产编辑为Kristen Brown，而Copyeditor Charles Roumeliotis负责校对，Christina Edwards担任校对员。此外，目录由两位作者亲自编撰，内部设计由David Futato负责，封面设计由Karen Montgomery操刀，插图则由Rebecca Demarest绘制。书中每个细节都经过精心策划，旨在为读者提供一个循序渐进、易于理解的学习环境。《Think Java》的修订历史记录在书的末尾，显示出作者对于持续更新和优化教材的承诺，确保内容始终紧跟技术发展和教学需求。作为一本经典的Java编程入门书籍，它不仅教授语言基础知识，还引导读者培养批判性思维和问题解决能力，是学习编程的理想起点。"

• Marius Margowski found an inconsistency in a code example.

• Leslie Klein discovered another error in the series expansion of exp − x

, iden‐

tified typos in the card array figures, and gave helpful suggestions to clarify sev‐

eral exercises.

• Micah Lindstrom reported half a dozen typos and sent corrections.

• James Riely ported the textbook source from LaTeX to Sphinx: http://

fpl.cs.depaul.edu/jriely/thinkapjava/.

•

Peter Knaggs ported the book to C#: http://www.rigwit.co.uk/think/sharp/.

•

Heidi Gentry-Kolen recorded several video lectures that follow the book: https://

www.youtube.com/user/digipipeline.

We are especially grateful to our technical reviewers: Blythe Samuels, David Wisneski,

and Stephen Rose. They found errors, made many great suggestions, and helped

make the book much better.

Additional contributors who found one or more typos: Stijn Debrouwere, Guy Drie‐

sen, Andai Velican, Chris Kuszmaul, Daniel Kurikesu, Josh Donath, Rens Findham‐

mer, Elisa Abedrapo, Yousef BaAfif, Bruce Hill, Matt Underwood, Isaac Sultan, Dan

Rice, Robert Beard, Daniel Pierce, Michael Giftthaler, and Min Zeng.

If you have additional comments or ideas about the text, please send them to:

feedback@greenteapress.com.

xiv | Preface

input:

Get data from the keyboard, a file, a sensor, or some other device.

output:

Display data on the screen, or send data to a file or other device.

math:

Perform basic mathematical operations like addition and division.

decisions:

Check for certain conditions and execute the appropriate code.

repetition:

Perform some action repeatedly, usually with some variation.

Believe it or not, that’s pretty much all there is to it. Every program you’ve ever used,

no matter how complicated, is made up of small instructions that look much like

these. So you can think of programming as the process of breaking down a large,

complex task into smaller and smaller subtasks. The process continues until the sub‐

tasks are simple enough to be performed with the basic instructions provided by the

computer.

What Is Computer Science?

One of the most interesting aspects of writing programs is deciding how to solve a

particular problem, especially when there are multiple solutions. For example, there

are numerous ways to sort a list of numbers, and each way has its advantages. In

order to determine which way is best for a given situation, we need techniques for

describing and analyzing solutions formally.

Computer science is the science of algorithms, including their discovery and analy‐

sis. An algorithm is a sequence of steps that specifies how to solve a problem. Some

algorithms are faster than others, and some use less space in computer memory. As

you learn to develop algorithms for problems you haven’t solved before, you also

learn to think like a computer scientist.

Designing algorithms and writing code is difficult and error-prone. For historical rea‐

sons, programming errors are called bugs, and the process of tracking them down

and correcting them is called debugging. As you learn to debug your programs, you

will develop new problem solving skills. You will need to think creatively when unex‐

pected errors happen.

Although it can be frustrating, debugging is an intellectually rich, challenging, and

interesting part of computer programming. In some ways, debugging is like detective

work. You are confronted with clues, and you have to infer the processes and events

2 | Chapter 1: The Way of the Program

that led to the results you see. Thinking about how to correct programs and improve

their performance sometimes even leads to the discovery of new algorithms.

Programming Languages

The programming language you will learn is Java, which is a high-level language.

Other high-level languages you may have heard of include Python, C and C++, Ruby,

and JavaScript.

Before they can run, programs in high-level languages have to be translated into a

low-level language, also called “machine language”. This translation takes some time,

which is a small disadvantage of high-level languages. But high-level languages have

two advantages:

• It is much easier to program in a high-level language. Programs take less time to

write, they are shorter and easier to read, and they are more likely to be correct.

• High-level languages are portable, meaning they can run on different kinds of

computers with few or no modifications. Low-level programs can only run on

one kind of computer, and have to be rewritten to run on another.

Two kinds of programs translate high-level languages into low-level languages: inter‐

preters and compilers. An interpreter reads a high-level program and executes it,

meaning that it does what the program says. It processes the program a little at a time,

alternately reading lines and performing computations. Figure 1-1 shows the struc‐

ture of an interpreter.

Figure 1-1. How interpreted languages are executed.

In contrast, a compiler reads the entire program and translates it completely before

the program starts running. In this context, the high-level program is called the

source code, and the translated program is called the object code or the executable.

Once a program is compiled, you can execute it repeatedly without further transla‐

tion. As a result, compiled programs often run faster than interpreted programs.

Java is both compiled and interpreted. Instead of translating programs directly into

machine language, the Java compiler generates byte code. Similar to machine lan‐

guage, byte code is easy and fast to interpret. But it is also portable, so it is possible to

compile a Java program on one machine, transfer the byte code to another machine,

Programming Languages | 3

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