精通Java：Android应用开发指南

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"这是一本关于学习Android应用开发的教程，特别强调了Java语言的重要性。由Jeff“JavaJeff”Friesen编著，书中详细介绍了使用Java开发Android应用所需的技能和知识。" 在Android开发中，Java是核心编程语言，尽管现在Kotlin已经成为了官方推荐的首选语言，但Java仍然是许多开发者熟悉并广泛使用的工具。本教程《Learn Java for Android Development》旨在帮助读者掌握Java语言，从而能够编写成功的Android应用程序。首先，理解Android平台的基础架构至关重要。Android是一个开放源代码的移动操作系统，包括操作系统、中间件和关键应用。开发者通过Android SDK（软件开发工具包）来构建应用，SDK提供了Java开发所需的工具和API接口。这些API允许开发者访问设备的各种功能，如相机、GPS、网络等。在Java编程方面，你需要了解基础语法、类与对象、封装、继承、多态等面向对象编程概念。此外，理解异常处理、集合框架、线程并发以及I/O流也是Android开发中的重要部分。Java的泛型和Lambda表达式能提高代码的可读性和效率，而注解在Android编程中也有着广泛应用，比如用于声明生命周期方法或元数据。 Android应用的基本结构通常包含多个组件，如活动（Activity）、服务（Service）、广播接收器（Broadcast Receiver）和内容提供者（Content Provider）。每个组件都有其特定的生命周期方法，理解和熟练掌握这些方法对于优化应用性能和避免内存泄漏至关重要。在Android开发中，布局设计也是重要一环。XML被用来定义用户界面，通过它可以创建复杂且响应式的布局。同时，Android Studio提供的布局编辑器和预览功能有助于提升开发效率。除此之外，理解Android的事件处理机制、资源管理和国际化、权限管理、数据库操作（SQLite）以及网络通信（例如使用HTTP/HTTPS和Retrofit库）都是开发者必备的技能。随着版本更新，Android引入了新的特性和最佳实践，如Jetpack库、Room数据库、LiveData和ViewModel，这些都是现代Android开发中的重要组成部分。最后，进行测试和调试是确保应用质量的关键。Android提供了多种测试框架，如JUnit和Espresso，用于单元测试和UI测试。理解如何使用Android Profiler进行性能分析和内存检测也对优化应用性能至关重要。《Learn Java for Android Development》这本书会引导读者从Java基础知识到Android特定概念，一步步深入Android应用开发的世界。通过学习，读者将具备编写高质量、健壮的Android应用所需的知识和技巧。

■ INTRODUCTION

xiv

Note: You can download this book’s source code by pointing your web browser to

www.apress.com/book/view/1430231564 and clicking the Source Code link under Book Resources.

Although most of this code is compilable with Java version 6, you will need Java version 7 to compile one

of the applications.

Chapter 1 introduces you to Java by first focusing on Java’s dual nature (language and

platform). It then briefly introduces you to Sun’s/Oracle’s Java SE, Java EE, and Java ME editions

of the Java development software, as well as Google’s Android edition. You next learn how to

download and install the Java SE Development Kit (JDK), and learn some Java basics by

developing and playing with a pair of simple Java applications. After receiving a brief

introduction to the NetBeans and Eclipse IDEs, you learn about application development in the

context of Four of a Kind, a console-based card game.

Chapter 2 starts you on an in-depth journey of the Java language by focusing on language

fundamentals (such as types, expressions, variables, and statements) in the contexts of classes

and objects. Because applications are largely based on classes, it is important to learn how to

architect classes correctly, and this chapter shows you how to do so.

Chapter 3 adds to Chapter 2’s pool of object-based knowledge by introducing you to those

language features that take you from object-based applications to object-oriented applications.

Specifically, you learn about features related to inheritance, polymorphism, and interfaces. While

exploring inheritance, you learn about Java’s ultimate superclass. Also, while exploring interfaces,

you discover the real reason for their inclusion in the Java language; interfaces are not merely a

workaround for Java’s lack of support for multiple implementation inheritance, but serve a

higher purpose.

Chapter 4 introduces you to four categories of advanced language features: nested types,

packages, static imports, and exceptions. While discussing nested types, I briefly introduce the

concept of a closure and state that closures will appear in Java version 7 (which many expect to

arrive later this year).

Note: I wrote this book several months before Java version 7’s expected arrival in the fall of 2010.

Although I have tried to present an accurate portrayal of version 7–specific language features, it is possible

that feature syntax may differ somewhat from what is presented in this book. Also, I only discuss closures

briefly because this feature was still in a state of flux while writing this book. For more information about

closures and other functional programming concepts (such as lambdas) being considered for Java version 7, I

recommend that you check out articles such as “Functional Programming Concepts in JDK 7” by Alex Collins

(

http://java.dzone.com/articles/lambdas-closures-jdk-7).

Chapter 5 continues to explore advanced language features by focusing on assertions,

annotations, generics, and enums. Although the topic of generics has brought confusion to many

developers, I believe that my discussion of this topic will clear up much of the murkiness. Among

other items, you learn how to interpret type declarations such as Enum<E extends Enum<E>>.

Chapter 6 begins a trend that focuses more on APIs than language features. This chapter first

introduces you to many of Java’s math-oriented types (such as Math, StrictMath, BigDecimal, and

BigInteger), and also introduces you to Java’s strictfp reserved word. It then looks at the

Package class, primitive wrapper classes, and the References API.

■ INTRODUCTION

Chapter 7 continues to explore Java’s basic APIs by focusing on reflection, string

management, the System class, and threading.

Chapter 8 focuses exclusively on Java’s collections framework, which provides you with a

solution for organizing objects in lists, sets, queues, and maps.

Chapter 9 continues to explore Java’s utility APIs by introducing you to the concurrency

utilities, internationalization, preferences, random number generation, and regular expressions.

Chapter 10 is all about input/output (I/O). In this chapter, you explore Java’s classic I/O

support in terms of its File class, RandomAccessFile class, various stream classes, and various

writer/reader classes. My discussion of stream I/O includes coverage of Java’s object serialization

and deserialization mechanisms.

Note: This book largely discusses APIs that are common to Java SE and Android. However, it diverges from

this practice in Chapter 9, where I use the Swing toolkit to provide a graphical user interface for one of this

chapter’s internationalization examples. (Android does not support Swing.)

After you complete this book, I recommend that you obtain a copy of Beginning Android 2 by

Mark L Murphy (Apress, 2010; ISBN: 1430226293) and start learning how to develop Android

apps. In that book, “you’ll learn how to develop applications for Android 2.x mobile devices,

using simple examples that are ready to run with your copy of the JDK.”

Note: Over the next few months, I will make available at my javajeff.mb.ca website six additional PDF-

based chapters. These chapters will introduce you to more Java APIs (such as networking and database

APIs) that I could not discuss in this book because the book has greatly exceeded its initial 400-page

estimate (and the good folks at Apress have been gracious enough to let me do so, but there are limits). I

present more information about these PDF files at the end of Chapter 10’s “Summary” section.

Thanks for purchasing my book. I hope you find it a helpful preparation for, and I wish you

lots of success in achieving, a satisfying and lucrative career as an Android app developer.

Jeff “JavaJeff” Friesen, August 2010

CHAPTER 1: Getting Started with Java

NOTE: Java has an interesting history that dates back to December 1990. At that time, James

Gosling, Patrick Naughton, and Mike Sheridan (all employees of Sun Microsystems) were given

the task of figuring out the next major trend in computing. They concluded that one trend would

involve the convergence of computing devices and intelligent consumer appliances. Thus was

born the Green project.

The fruits of Green were Star7, a handheld wireless device featuring a five-inch color LCD

screen, a SPARC processor, a sophisticated graphics capability, and a version of Unix; and Oak, a

language developed by James Gosling for writing applications to run on Star7, and which he

named after an oak tree growing outside of his office window at Sun. To avoid a conflict with

another language of the same name, Dr. Gosling changed this language’s name to Java.

Sun Microsystems subsequently evolved the Java language and platform until Oracle acquired

Sun in early 2010. Check out http://java.sun.com/ for the latest Java news from Oracle.

Java Is a Language

Java is a language in which developers express source code (program text). Java’s

syntax (rules for combining symbols into language features) is partly patterned after the

C and C++ languages to shorten the learning curve for C/C++ developers.

The following list identifies a few similarities between Java and C/C++:

 Java and C/C++ share the same single-line and multiline comment

styles. Comments let you document source code.

 Many of Java’s reserved words are identical to their C/C++

counterparts (for, if, switch, and while are examples) and C++

counterparts (catch, class, public, and try are examples).

 Java also supports character, double precision floating-point, floating-

point, integer, long integer, and short integer primitive types, and via

the same char, double, float, int, long, and short reserved words.

 Java also supports many of the same operators, including arithmetic

(+, -, *, /, and %) and conditional (?:) operators.

 Java also uses brace characters ({ and }) to delimit blocks of

statements.

The following list identifies a few differences between Java and C/C++:

 Java supports an additional comment style known as Javadoc. (I will

briefly introduce Javadoc later in this chapter.)

 Java provides reserved words not found in C/C++ (extends, strictfp,

synchronized, and transient are examples).

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精通Java：Android应用开发指南

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