J2ME入门到精通：详述Game API、Form与Network等核心技术

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《 BeginningJ2ME：从新手到专业者，第三版》是一本深入讲解Java ME（Java 2 Micro Edition）的教程，由SingLi和Jonathan Knudsen编写，版权属于2005年。该书旨在为初学者提供一个全面的学习路径，从零开始，逐步引导读者掌握J2ME平台的各种关键知识点。 J2ME，也称为Java ME，是Java语言的一个轻量级版本，特别设计用于嵌入式设备和移动电话，如游戏机、手机和平板电脑。这本书涵盖了以下几个核心主题： 1. Game API：J2ME提供了游戏开发的基础，包括图形用户界面（GUI）、音频处理、动画和游戏逻辑，让读者能够创建适用于移动设备的交互式游戏。 2. Forms：J2ME支持用户界面设计，通过Forms API，开发者可以构建可定制的界面元素，实现数据输入、显示和交互功能，这对于移动应用开发至关重要。 3. Networking：书中会讲解如何利用J2ME的网络支持进行数据传输，包括HTTP、SMTP、Socket编程等，帮助开发者实现跨设备的数据通信和互联网连接。 4. Storage：针对移动设备有限的存储空间，书中会介绍如何有效管理应用程序的数据存储，如文件I/O操作、序列化和文件系统管理。 5. 其他技术：此外，本书还会涉及内存管理、线程处理、异常处理、安全性和性能优化等实用技巧，帮助读者成为具备专业技能的J2ME开发者。《 BeginningJ2ME》第三版的特点是详尽且实用，适合那些希望进入移动开发领域，特别是对游戏和应用开发感兴趣的读者。它不仅提供理论知识，还包含了大量的代码示例和实战项目，有助于读者通过实践加深理解。书中还强调了版权和商标使用规范，确保在合法范围内进行学习和分享。阅读这本书，读者将获得完整的J2ME开发旅程，从入门到精通，无论是为了构建简单的移动应用还是准备进军游戏开发领域，都将受益匪浅。

xix

About the Technical Reviewer

■CHRIS HARRIS is from Dublin, Ireland, and received his BS in mathematics and computer

science from the Dublin Institute of Technology. He has worked in the wireless software industry

for over five years, and has been involved in the Java Community Process as both Specification

Lead and Expert Group member. He currently works in Bordeaux, France, for a mobile games

company called IN-FUSIO.

xxiii

Preface

This book describes how to program mobile telephones, pagers, PDAs, and other small devices

using Java technology. It is about the Mobile Information Device Profile (MIDP), which is part

of the Java 2 Platform, Micro Edition (J2ME). It is concise and complete, describing all of MIDP

as well as moving into several exciting advanced concepts such as 3D graphics and cryptography.

This third edition covers MIDP 2.0, and has been updated to track the Java Technology for

the Wireless Industry (JTWI 1.0) de facto standard. Every chapter has been revised and meticu-

lously updated, and four completely new chapters have been added.

Who Are You?

You’re probably reading this book because you’re excited about building wireless applications

with Java. This book is aimed at people who already have experience programming in Java. At a

minimum, you should understand the Java programming language and the fundamentals of

object-oriented programming. Some chapters delve into subjects that in themselves could

occupy entire books. These chapters include suggested reading if you want to get up to speed

on a particular subject.

If you are unfamiliar with Java, we suggest you read an introductory book or take a course.

Learning Java, Second Edition (O’Reilly 2002) is a good introduction to Java for programmers

who are already experienced in another language such as C or C++.

The Structure of This Book

This book is organized into 18 chapters and one appendix. There are basically three sections. The

first two chapters are introductory material. Chapters 3 through 16 provide complete coverage of

the MIDP 2.0 and JTWI 1.0 APIs, together with some of the most frequently used optional APIs

available. Chapters 17 and 18 cover advanced topics. The complete breakdown of chapters is

listed here:

• Chapter 1, “Introduction,” provides context and motivation for the rest of the book.

J2ME is explained in detail, gradually zooming in to MIDP and JTWI.

• Chapter 2, “Building MIDlets,” is intended to be a teaser. It includes an example applica-

tion that allows you to look up the definitions of words over the Internet using any MIDP

device. Along the way you’ll learn a lot about developing applications for the MIDP platform.

• Chapter 3, “All About MIDlets,” goes into detail about the life cycle and packaging of

MIDP applications. It includes coverage of the MIDP 2.0 security architecture.

• Chapter 4, “Almost the Same Old Stuff,” describes the pieces of the MIDP API that will be

familiar to Java programmers.

xxiv

■PREFACE

• Chapter 5, “Creating a User Interface,” is the first of a handful of chapters devoted to

MIDP’s user interface packages. It provides an overview of MIDP’s user interface package

and goes into detail about the simple visual components.

• Chapter 6, “Lists and Forms,” picks up where Chapter 5 left off, describing MIDP’s

advanced user interface components.

• Chapter 7, “Custom Items,” shows how to create your own form items in MIDP.

• Chapter 8, “Persistent Storage I: MIDP Record Store,” describes MIDP’s mechanism for

storing data.

• Chapter 9, “Persistent Storage II: File Connection and PIM API,” covers popular optional

APIs for accessing a device’s file system, memory cards, and PIM features.

• Chapter 10, “Connecting to the World,” contains all the juicy details about how MIDP

applications can send and receive data over the Internet.

• Chapter 11, “Wireless Messaging API,” describes WMA, a standard component of JTWI 1.0

that can be used to access the rich Short Message Service (SMS) and Cell Broadcast Service

(CBS) available on modern wireless networks. This chapter also covers the new WMA 2.0

for working with audio and video messages via Multimedia Messaging Service (MMS).

• Chapter 12, “Bluetooth and OBEX,” provides coverage of the optional API that enables

communications of devices through Bluetooth radio Personal Area Networks (PANs)

and infrared links.

• Chapter 13, “Programming a Custom User Interface,” describes the low-level API that

can be used for specialized application user interfaces.

• Chapter 14, “The Game API,” describes MIDP 2.0 features for creating games, including

sprites and tiled layers.

• Chapter 15, “3D Graphics,” includes a hands-on, easy-to-understand introduction to the

Mobile 3D Graphics optional API (M3G), providing you with a springboard into the

fascinating world of 3D graphics programming on mobile devices.

• Chapter 16, “Sound, Music, and Video: MMAPI,” is about MIDP 2.0 new multimedia

capabilities and the Mobile Media API (MMAPI). You’ll learn how to produce simple

tones, play sampled audio data, play MP3 music, play video clips, and even take snap-

shots with your camera-phone.

• Chapter 17, “Performance Tuning,” describes techniques for coping with the limited

resources that are available on small devices.

• Chapter 18, “Protecting Network Data,” discusses how to protect valuable data on the

insecure Internet. It includes two sample applications that demonstrate cryptographic

techniques for protecting data.

• Finally, the appendix, “MIDP API Reference,” contains an API reference for the classes

and interfaces that make up MIDP. The method signatures for the public API of each

class and interface are listed for handy quick reference.

■ ■ ■

CHAPTER 1

Introduction

Java 2 Platform, Micro Edition (J2ME) is the second revolution in Java’s short history. When

Java was introduced in 1995, it looked like the future of computing was in applets, small programs

that could be downloaded and run on demand. A slow Internet and a restrictive all-or-nothing

sandbox security model accounted for the initially slow adoption of applets. Java, as a platform,

really took off with the advent of servlets, Java programs that run on a server (offering a modular

and efficient replacement for the vulnerable CGI). Java further expanded into the server side of

things, eventually picking up the moniker of Java 2 Platform, Enterprise Edition (J2EE). This

was the first revolution, the blitz of server-side Java.

The second revolution is the explosion of small-device Java, and it’s happening now. The

market for small devices is expanding rapidly, and Java is important for two reasons. First,

developers can write code and have it run on dozens of small devices, without change. Second,

Java has important safety features for downloadable code.

Understanding J2ME

J2ME isn’t a specific piece of software or specification. All it means is Java for small devices.

Small devices range in size from pagers, mobile phones, and personal digital assistants (PDAs)

all the way up to things like set-top boxes that are just shy of being desktop PCs.

J2ME is divided into configurations, profiles, and optional APIs, which provide specific

information about APIs and different families of devices. A configuration is designed for a

specific kind of device based on memory constraints and processor power. It specifies a Java

Virtual Machine (JVM) that can be easily ported to devices supporting the configuration. It also

specifies a strict subset of the Java 2 Platform, Standard Edition (J2SE) APIs that will be used

on the platform, as well as additional APIs that may be necessary. Device manufacturers are

responsible for porting a specific configuration to their devices.

Profiles are more specific than configurations. A profile is based on a configuration and

provides additional APIs, such as user interface, persistent storage, and whatever else is necessary

to develop running applications for the device.

Optional APIs define specific additional functionality that may be included in a particular

configuration (or profile). The whole caboodle—configuration, profile, and optional APIs—

that is implemented on a device is called a stack. For example, a possible future device stack

might be CLDC/MIDP + Mobile Media API. See the section “Platform Standardization” later in

this chapter for information on JSR 185, which defines a standard J2ME stack.

Currently, there are a handful of configurations and profiles; the most relevant ones for

J2ME developers are illustrated in Figure 1-1.

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