Java编程实例精要

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"Java Examples In A Nutshell" 是一本由David Flanagan编写的教程伴侣书籍，旨在帮助读者深入理解并实践Java编程语言。这本书涵盖了广泛的Java主题，包括基础类库、网络编程、线程、虚拟机、AWT、语言参考、Swing、JDBC、分布式计算、Bean开发、安全性、加密、2D图形、性能调优和XML集成等多个方面。它为读者提供了丰富的示例代码，以便于学习和掌握Java技术。详细说明： 1. **Java基础**：书中的“Java Language Reference”部分会讲解Java语言的核心概念，如变量、数据类型、控制结构、函数、类和对象等，这对于初学者来说是至关重要的。 2. **Java虚拟机（JVM）**：了解Java虚拟机的工作原理是理解Java运行机制的关键，书中可能涵盖了类加载、内存管理和垃圾回收等内容。 3. **网络编程**：“Java Network Programming”章节可能包含套接字编程、HTTP协议、网络服务的实现等，使读者能够创建网络应用。 4. **多线程**：Java支持并发编程，"Java Threads"部分将讲解如何在Java程序中有效地使用线程，以及同步和通信机制。 5. **图形用户界面（GUI）**：“Java AWT Reference”和“Java Swing”章节将介绍如何使用Java构建桌面应用的用户界面，包括组件、布局管理器、事件处理等。 6. **数据库编程**：“JDBC and Java”部分将涵盖如何使用Java Database Connectivity（JDBC）与数据库进行交互，执行SQL查询和事务管理。 7. **分布式计算**：“Java Distributed Computing”可能讲解RMI（远程方法调用）、EJB（企业级JavaBean）等分布式系统开发技术。 8. **Java安全**：“Java Security”章节将涉及Java的安全模型，包括权限、证书、加密和安全策略。 9. **Java性能优化**：“Java Performance Tuning”可能包含分析和改进Java程序性能的技巧和工具。 10. **XML集成**：“Java and XML”部分将讨论如何在Java应用程序中处理XML文档，包括解析、生成和验证XML数据。 11. **企业级Java**：“Enterprise JavaBeans”章节将涵盖服务器端组件开发，如EJB的生命周期、容器服务和事务管理。 12. **帮助系统开发**：“Creating Effective Java Help”可能会介绍如何为Java应用创建和集成帮助系统。这本书是Java程序员的实用参考资料，无论是初学者还是有经验的开发者，都能从中找到有价值的信息和示例。通过这些实例，读者可以更直观地理解各种Java技术，并将其应用于实际项目中。

For more infor mation about this book and others, see the O’Reilly web site:

http://www.or eilly.com

Acknowledgments

My thanks, as always, to my editor Paula Ferguson for pulling everything together

into one coherent book and for putting up with my repeated schedule slippages.

Thanks also to Frank Willison and Tim O’Reilly for being willing and enthusiastic

to try this all-example book format.

I’ve had the help of a number of O’Reilly’s other Java authors with this book.

Jonathan Knudsen, author of several Java books from O’Reilly, reviewed the

graphics and the printing chapters. Bob Eckstein, coauthor of Java Swing,

reviewed the Swing chapter. Jason Hunter, author of Java Servlet Programming,

reviewed the servlets chapter. Hans Bergsten, author of a forthcoming book on

JavaServer Pages™’, also reviewed the servlets chapter but focused his review on

the JSP examples in particular. Brett McLaughlin, author of Java and XML,

reviewed the XML chapter. George Reese, author of Database Programming with

JDBC and Java, was kind enough to look over the database chapter. Jim Farley,

author of Java Distributed Computing and coauthor of Java Enterprise in a Nut-

shell, reviewed the RMI examples. The expertise contributed by these reviewers

has dramatically improved the quality of my examples. I am indebted to them all

and recommend their books highly!

The production team at O’Reilly & Associates has again done a great job of turning

the manuscript I submitted into a honest-to-goodness book. As usual, I am grateful

to and awestruck by them.

Finally, I want to thank Christie, for reasons too numerous to list here.

David Flanagan

http://www.davidﬂanagan.com

July 2000

xvi Preface

Example 1−1: Hello.java (continued)

System.out.println("Hello World!"); // Say hello!

} // This marks the end of main()

} // Marks the end of the class

The ﬁrst line of this program is the package declaration. It speciﬁes the name of

the package of which this program is part. The program’s name (as we’ll see in the

second line) is

Hello. The package name is com.davidflanagan.examples.basics.

We can combine these two names to produce a fully qualiﬁed name,

com.david-

flanagan.examples.basics.Hello. Using packages provides a unique namespace

for every Java program. By placing this

Hello pr ogram in a package, I’ve ensured

that no naming conﬂict will arise if someone else deﬁnes a program that is also

named

Hello. To ensur e that the package name I’ve chosen is unique, I’ve fol-

lowed the convention of reversing the components of my Internet domain name

to produce a package name preﬁx.

Each chapter of this book has its own pack-

age that begins with the preﬁx

com.davidflanagan.examples. In this case, since

this is the basics chapter, the package name is

com.davidflanagan.exam-

ples.basics.

The value of “Hello World” is that it is a template that you can expand on in your

later experiments with Java. The second and third lines lines of Example 1-1 are a

requir ed part of the template. Every program — every piece of Java code, really —

you write is a class. The second line of the example says that we’re writing a class

named

Hello. It also says the class is public, which means it can be used by any-

one.

Every standalone Java program requir es a

main() method. This is where the Java

interpr eter begins running a Java program. The third line of the example declares

this

main() method. It says that the method is public, that it has no retur n value

(i.e., its retur n value is

void), and that it is passed an array of strings as its argu-

ment. The name of the array is

args. The line also says that main() is a static

method. (In this chapter, we work exclusively with static methods. In Chapter 2,

when we start working with objects, you’ll learn what a

static method is, and

you’ll see that non-

static methods are actually the norm.)

In any case, you might as well go ahead and memorize this line:

public static void main(String[] args)

Every standalone Java program you ever write contains a line that looks exactly

like this one. (Actually, you can name the array of strings anything you want, but

it is usually called

args.)

The ﬁfth and sixth lines of Example 1-1 simply mark the end of the

main()

method and of the Hello class. Like most modern programming languages, Java is

a block-structur ed language. This means that such things as classes and methods

have bodies that comprise a “block” of code. In Java, the beginning of a block is

marked by a

{, and the end is marked by a matching }. Method blocks are always

deﬁned within class blocks, and as we’ll see in later examples, methods blocks can

contain such things as

if statements and for loops that form subblocks within the

* My web site is http://www.davidﬂanagan.com, so my package name begins com.davidflanagan.

4 Chapter 1 – Java Basics

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