Java语言规范第二版

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"The Java Language Specification, 2nd Ed" 《Java语言规范》第二版是Java开发领域的权威指南，由James Gosling、Bill Joy、Guy Steele和Gilad Bracha等人撰写，是Java系列书籍的重要组成部分。这本书详细阐述了Java编程语言的各个方面，包括语法、语义、类型系统、内存管理、异常处理、多线程、输入/输出以及编译器和虚拟机的行为。 1. **Java语法与语义**：书中深入探讨了Java的语法结构，如声明、表达式、控制流结构和方法定义。同时，它也解释了语义，即程序的行为方式，包括变量的作用域、初始化规则和类型转换。 2. **类型系统**：Java是一种强类型语言，本书详细介绍了它的类型系统，包括基本类型（如int、char）和引用类型（类、接口、数组）。此外，还涵盖了类型检查、继承和多态性。 3. **内存管理**：Java中的内存管理主要通过垃圾收集机制实现，书中对此进行了详述，包括对象的生命周期、引用类型以及内存泄漏的预防。 4. **异常处理**：Java的异常处理机制是其特性之一，书中有详细的章节讲解如何使用try-catch-finally块来处理运行时错误，并介绍了受检异常和非受检异常的区别。 5. **多线程**：Java提供了内置的多线程支持，书里详细阐述了如何创建和管理线程，以及线程同步和互斥的概念，如synchronized关键字和wait/notify机制。 6. **输入/输出**：书中涵盖了I/O流的层次结构，包括字节流、字符流、对象流以及文件操作，同时还讨论了NIO（非阻塞I/O）和套接字通信。 7. **编译器和虚拟机**：对于Java虚拟机（JVM），书中解释了其工作原理，包括类加载、字节码执行以及JVM的内存模型。 8. **标准库API**：虽然不直接包含在本册中，但作为Java系列的一部分，读者可以了解到Java标准库API，如集合框架、I/O包、网络编程以及反射等。《Java语言规范》第二版是Java程序员必备的参考书，无论你是初学者还是经验丰富的开发者，都能从中获取深入理解Java语言精髓的知识。通过阅读这本书，开发者能够更准确地理解Java代码的运行方式，从而编写出更加高效、可靠的程序。

TABLE OF CONTENTS

xvi

15.12.4.8 Example: Overriding . . . . . . . . . . . . . . . . . . . . . . . . .361

15.12.4.9 Example: Method Invocation using super . . . . . . . . . 363

15.13 Array Access Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 364

15.13.1 Runtime Evaluation of Array Access . . . . . . . . . . . . . . . . . . . . . 364

15.13.2 Examples: Array Access Evaluation Order. . . . . . . . . . . . . . . . . 365

15.14 Postﬁx Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .367

15.14.1 Postﬁx Increment Operator ++ . . . . . . . . . . . . . . . . . . . . . . . . . .367

15.14.2 Postﬁx Decrement Operator --. . . . . . . . . . . . . . . . . . . . . . . . . .368

15.15 Unary Operators. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .368

15.15.1 Preﬁx Increment Operator ++ . . . . . . . . . . . . . . . . . . . . . . . . . . .369

15.15.2 Preﬁx Decrement Operator -- . . . . . . . . . . . . . . . . . . . . . . . . . .369

15.15.3 Unary Plus Operator +. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .370

15.15.4 Unary Minus Operator - . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 370

15.15.5 Bitwise Complement Operator ~. . . . . . . . . . . . . . . . . . . . . . . . .371

15.15.6 Logical Complement Operator !. . . . . . . . . . . . . . . . . . . . . . . . .371

15.16 Cast Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .372

15.17 Multiplicative Operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .373

15.17.1 Multiplication Operator * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .373

15.17.2 Division Operator /. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .374

15.17.3 Remainder Operator % . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .376

15.18 Additive Operators. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .377

15.18.1 String Concatenation Operator +. . . . . . . . . . . . . . . . . . . . . . . . .378

15.18.1.1 String Conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . 378

15.18.1.2 Optimization of String Concatenation. . . . . . . . . . . .379

15.18.1.3 Examples of String Concatenation . . . . . . . . . . . . . . 379

15.18.2 Additive Operators (+ and -) for Numeric Types . . . . . . . . . . . .381

15.19 Shift Operators. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .383

15.20 Relational Operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .384

15.20.1 Numerical Comparison Operators <, <=, >, and >=. . . . . . . . . . .384

15.20.2 Type Comparison Operator instanceof . . . . . . . . . . . . . . . . . . 385

15.21 Equality Operators. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .386

15.21.1 Numerical Equality Operators == and != . . . . . . . . . . . . . . . . . . 387

15.21.2 Boolean Equality Operators == and !=. . . . . . . . . . . . . . . . . . . . 388

15.21.3 Reference Equality Operators == and != . . . . . . . . . . . . . . . . . . 388

15.22 Bitwise and Logical Operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 388

15.22.1 Integer Bitwise Operators &, ^, and | . . . . . . . . . . . . . . . . . . . . . 389

15.22.2 Boolean Logical Operators &, ^, and | . . . . . . . . . . . . . . . . . . . . 389

15.23 Conditional-And Operator && . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .390

15.24 Conditional-Or Operator ||. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 390

15.25 Conditional Operator ?: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .391

15.26 Assignment Operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .392

15.26.1 Simple Assignment Operator = . . . . . . . . . . . . . . . . . . . . . . . . . .393

15.26.2 Compound Assignment Operators . . . . . . . . . . . . . . . . . . . . . . .398

15.27 Expression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .405

15.28 Constant Expression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .405

16 Deﬁnite Assignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 407

16.1 Deﬁnite Assignment and Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 412

TABLE OF CONTENTS

xvii

16.1.1 Boolean Constant Expressions. . . . . . . . . . . . . . . . . . . . . . . . . . 412

16.1.2 The Boolean Operator &&. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 413

16.1.3 The Boolean Operator ||. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 413

16.1.4 The Boolean Operator !. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 414

16.1.5 The Boolean Operator ?:. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 414

16.1.6 The Conditional Operator ?: . . . . . . . . . . . . . . . . . . . . . . . . . . 414

16.1.7 Assignment Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415

16.1.8 Operators ++ and --. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 416

16.1.9 Other Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 416

16.2 Deﬁnite Assignment and Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . 417

16.2.1 Empty Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 418

16.2.2 Blocks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 418

16.2.3 Local Class Declaration Statements. . . . . . . . . . . . . . . . . . . . . . 418

16.2.4 Local Variable Declaration Statements . . . . . . . . . . . . . . . . . . . 419

16.2.5 Labeled Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 419

16.2.6 Expression Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 419

16.2.7 if Statements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 420

16.2.8 switch Statements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 420

16.2.9 while Statements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 421

16.2.10 do Statements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 421

16.2.11 for Statements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 422

16.2.11.1 Initialization Part . . . . . . . . . . . . . . . . . . . . . . . . . . . 423

16.2.11.2 Incrementation Part. . . . . . . . . . . . . . . . . . . . . . . . . . 423

16.2.12 break, continue, return, and throw Statements. . . . . . . . . . 423

16.2.13 synchronized Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424

16.2.14 try Statements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424

16.3 Deﬁnite Assignment and Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425

16.4 Deﬁnite Assignment and Array Initializers . . . . . . . . . . . . . . . . . . . . . . . 425

16.5 Deﬁnite Assignment and Anonymous Classes. . . . . . . . . . . . . . . . . . . . . 426

16.6 Deﬁnite Assignment and Member Types . . . . . . . . . . . . . . . . . . . . . . . . . 426

16.7 Deﬁnite Assignment and Static Initializers . . . . . . . . . . . . . . . . . . . . . . . 426

16.8 Deﬁnite Assignment, Constructors, and Instance Initializers . . . . . . . . . 427

17 Threads and Locks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 429

17.1 Terminology and Framework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 431

17.2 Execution Order . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 433

17.3 Rules about Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 434

17.4 Nonatomic Treatment of double and long . . . . . . . . . . . . . . . . . . . . . . . 435

17.5 Rules about Locks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 436

17.6 Rules about the Interaction of Locks and Variables . . . . . . . . . . . . . . . . . 436

17.7 Rules for Volatile Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 437

17.8 Prescient Store Actions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 438

17.9 Discussion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 438

17.10 Example: Possible Swap. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 439

17.11 Example: Out-of-Order Writes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 443

17.12 Threads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 445

17.13 Locks and Synchronization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 445

17.14 Wait Sets and Notiﬁcation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 446

xix

Preface

THE Java

™

programming language was originally called Oak, and was designed

for use in embedded consumer-electronic applications by James Gosling. After

several years of experience with the language, and signiﬁcant contributions by Ed

Frank, Patrick Naughton, Jonathan Payne, and Chris Warth it was retargeted to the

Internet, renamed, and substantially revised to be the language speciﬁed here. The

ﬁnal form of the language was deﬁned by James Gosling, Bill Joy, Guy Steele,

Richard Tuck, Frank Yellin, and Arthur van Hoff, with help from Graham Hamil-

ton, Tim Lindholm, and many other friends and colleagues.

The Java programming language is a general-purpose concurrent class-based

object-oriented programming language, speciﬁcally designed to have as few

implementation dependencies as possible. It allows application developers to

write a program once and then be able to run it everywhere on the Internet.

This book attempts a complete speciﬁcation of the syntax and semantics of

the language. We intend that the behavior of every language construct is speciﬁed

here, so that all implementations will accept the same programs. Except for timing

dependencies or other non-determinisms and given sufﬁcient time and sufﬁcient

memory space, a program written in the Java programming language should com-

pute the same result on all machines and in all implementations.

We believe that the Java programming language is a mature language, ready

for widespread use. Nevertheless, we expect some evolution of the language in the

years to come. We intend to manage this evolution in a way that is completely

compatible with existing applications. To do this, we intend to make relatively few

new versions of the language, and to distinguish each new version with a different

ﬁlename extension. Compilers and systems will be able to support the several ver-

sions simultannously, with complete compatibility.

Much research and experimentation with the Java platform is already under-

way. We encourage this work, and will continue to cooperate with external groups

to explore improvements to the language and platform. For example, we have

already received several interesting proposals for parameterized types. In techni-

cally difﬁcult areas, near the state of the art, this kind of research collaboration is

essential.

PREFACE

We acknowledge and thank the many people who have contributed to this

book through their excellent feedback, assistance and encouragement:

Particularly thorough, careful, and thoughtful reviews of drafts were provided

by Tom Cargill, Peter Deutsch, Paul Hilﬁnger, Masayuki Ida, David Moon, Steven

Muchnick, Charles L. Perkins, Chris Van Wyk, Steve Vinoski, Philip Wadler,

Daniel Weinreb, and Kenneth Zadeck. We are very grateful for their extraordinary

volunteer efforts.

We are also grateful for reviews, questions, comments, and suggestions from

Stephen Adams, Bowen Alpern, Glenn Ammons, Leonid Arbuzov, Kim Bruce,

Edwin Chan, David Chase, Pavel Curtis, Drew Dean, William Dietz, David Dill,

Patrick Dussud, Ed Felten, John Giannandrea, John Gilmore, Charles Gust,

Warren Harris, Lee Hasiuk, Mike Hendrickson, Mark Hill, Urs Hoelzle, Roger

Hoover, Susan Flynn Hummel, Christopher Jang, Mick Jordan, Mukesh Kacker,

Peter Kessler, James Larus, Derek Lieber, Bill McKeeman, Steve Naroff,

Evi Nemeth, Robert O’Callahan, Dave Papay, Craig Partridge, Scott Pfeffer,

Eric Raymond, Jim Roskind, Jim Russell, William Scherlis, Edith Schonberg,

Anthony Scian, Matthew Self, Janice Shepherd, Kathy Stark, Barbara Steele, Rob

Strom, William Waite, Greg Weeks, and Bob Wilson. (This list was generated

semi-automatically from our E-mail records. We apologize if we have omitted

anyone.)

The feedback from all these reviewers was invaluable to us in improving the

deﬁnition of the language as well as the form of the presentation in this book. We

thank them for their diligence. Any remaining errors in this book—we hope they

are few—are our responsibility and not theirs.

We thank Francesca Freedman and Doug Kramer for assistance with matters

of typography and layout. We thank Dan Mills of Adobe Systems Incorporated for

assistance in exploring possible choices of typefaces.

Many of our colleagues at Sun Microsystems have helped us in one way or

another. Lisa Friendly, our series editor, managed our relationship with Addison-

Wesley. Susan Stambaugh managed the distribution of many hundreds of copies

of drafts to reviewers. We received valuable assistance and technical advice from

Ben Adida, Ole Agesen, Ken Arnold, Rick Cattell, Asmus Freytag, Norm Hardy,

Steve Heller, David Hough, Doug Kramer, Nancy Lee, Marianne Mueller, Akira

Tanaka, Greg Tarsy, David Ungar, Jim Waldo, Ann Wollrath, Geoff Wyant, and

Derek White. We thank Alan Baratz, David Bowen, Mike Clary, John Doerr, Jon

Kannegaard, Eric Schmidt, Bob Sproull, Bert Sutherland, and Scott McNealy for

leadership and encouragement.

The on-line Bartleby Library of Columbia University, at URL:

http://www.cc.columbia.edu/acis/bartleby/

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