Preface X X I I I
Preface to the Second Edition X X V I I
Preface to the Third Edition X X X I
1 Introduction 1
1.1 Example Programs 5
1.2 Notation 6
1.3 Relationship to Predefined Classes and Interfaces 6
1.4 References 6
2 Grammars 9
2.1 Context-Free Grammars 9
2.2 The Lexical Grammar 9
2.3 The Syntactic Grammar 10
2.4 Grammar Notation 10
3 Lexical Structure 13
3.1 Unicode 13
3.2 Lexical Translations 14
3.3 Unicode Escapes 15
3.4 Line Terminators 16
3.5 Input Elements and Tokens 17
3.6 White Space 18
3.7 Comments 18
3.8 Identifiers 19
3.9 Keywords 21
3.10 Literals 21
3.10.1 Integer Literals 22
3.10.2 Floating-Point Literals 24
3.10.3 Boolean Literals 26
3.10.4 Character Literals 26
3.10.5 String Literals 28
3.10.6 Escape Sequences for Character and String Literals 30
3.10.7 The Null Literal 30
3.11 Separators 31
3.12 Operators 31
4 Types, Values, and Variables 33
4.1 The Kinds of Types and Values 34
4.2 Primitive Types and Values 34
4.2.1 Integral Types and Values 35
4.2.2 Integer Operations 36
4.2.3 Floating-Point Types, Formats, and Values 37
4.2.4 Floating-Point Operations 40
4.2.5 The boolean Type and boolean Values 43
4.3 Reference Types and Values 44
4.3.1 Objects 45
4.3.2 The Class Object 47
4.3.3 The Class String 48
4.3.4 When Reference Types Are the Same 49
4.4 Type Variables 49
4.5 Parameterized Types 51
4.5.1 Type Arguments and Wildcards 52
4.5.1.1 Type Argument Containment and Equivalence 55
4.5.2 Members and Constructors of Parameterized Types 55
4.6 Type Erasure 56
4.7 Reifiable Types 56
4.8 Raw Types 57
4.9 Intersection Types 62
4.10 Subtyping 63
4.10.1 Subtyping among Primitive Types 63
4.10.2 Subtyping among Class and Interface Types 63
4.10.3 Subtyping among Array Types 64
4.11 Where Types Are Used 65
4.12 Variables 67
4.12.1 Variables of Primitive Type 67
4.12.2 Variables of Reference Type 67
4.12.2.1 Heap Pollution 68
4.12.3 Kinds of Variables 69
4.12.4 final Variables 71
4.12.5 Initial Values of Variables 71
4.12.6 Types, Classes, and Interfaces 73
5 Conversions and Promotions 77
5.1 Kinds of Conversion 80
5.1.1 Identity Conversions 80
5.1.2 Widening Primitive Conversion 80
5.1.3 Narrowing Primitive Conversions 82
5.1.4 Widening and Narrowing Primitive Conversions 84
5.1.5 Widening Reference Conversions 85
5.1.6 Narrowing Reference Conversions 85
5.1.7 Boxing Conversion 86
5.1.8 Unboxing Conversion 88
5.1.9 Unchecked Conversion 89
5.1.10 Capture Conversion 89
5.1.11 String Conversions 92
5.1.12 Forbidden Conversions 92
5.1.13 Value Set Conversion 92
5.2 Assignment Conversion 93
5.3 Method Invocation Conversion 99
5.4 String Conversion 101
5.5 Casting Conversion 101
5.6 Numeric Promotions 108
5.6.1 Unary Numeric Promotion 108
5.6.2 Binary Numeric Promotion 110
6 Names 113
6.1 Declarations 114
6.2 Names and Identifiers 115
6.3 Scope of a Declaration 117
6.3.1 Shadowing Declarations 119
6.3.2 Obscured Declarations 122
6.4 Members and Inheritance 122
6.4.1 The Members of Type Variables, Parameterized Types, Raw Types and
Intersection Types 122
6.4.2 The Members of a Package 122
6.4.3 The Members of a Class Type 123
6.4.4 The Members of an Interface Type 124
6.4.5 The Members of an Array Type 125
6.5 Determining the Meaning of a Name 126
6.5.1 Syntactic Classification of a Name According to Context 127
6.5.2 Reclassification of Contextually Ambiguous Names 129
6.5.3 Meaning of Package Names 131
6.5.3.1 Simple Package Names 131
6.5.3.2 Qualified Package Names 132
6.5.4 Meaning of PackageOrTypeNames 132
6.5.4.1 Simple PackageOrTypeNames 132
6.5.4.2 Qualified PackageOrTypeNames 132
6.5.5 Meaning of Type Names 132
6.5.5.1 Simple Type Names 132
6.5.5.2 Qualified Type Names 132
6.5.6 Meaning of Expression Names 134
6.5.6.1 Simple Expression Names 134
6.5.6.2 Qualified Expression Names 135
6.5.7 Meaning of Method Names 137
6.5.7.1 Simple Method Names 137
6.5.7.2 Qualified Method Names 137
6.6 Access Control 138
6.6.1 Determining Accessibility 138
6.6.2 Details on protected Access 139
6.6.2.1 Access to a protected Member 139
6.6.2.2 Qualified Access to a protected Constructor 140
6.6.3 An Example of Access Control 140
6.6.4 Example: Access to public and Non-public Classes 141
6.6.5 Example: Default-Access Fields, Methods, and Constructors 142
6.6.6 Example: public Fields, Methods, and Constructors 143
6.6.7 Example: protected Fields, Methods, and Constructors 143
6.6.8 Example: private Fields, Methods, and Constructors 144
6.7 Fully Qualified Names and Canonical Names 145
6.8 Naming Conventions 146
6.8.1 Package Names 147
6.8.2 Class and Interface Type Names 147
6.8.3 Type Variable Names 148
6.8.4 Method Names 149
6.8.5 Field Names 150
6.8.6 Constant Names 150
6.8.7 Local Variable and Parameter Names 151
7 Packages 153
7.1 Package Members 154
7.2 Host Support for Packages 155
7.2.1 Storing Packages in a File System 155
7.2.2 Storing Packages in a Database 157
7.3 Compilation Units 157
7.4 Package Declarations 158
7.4.1 Named Packages 158
7.4.1.1 Package Annotations 158
7.4.2 Unnamed Packages 159
7.4.3 Observability of a Package 160
7.4.4 Scope of a Package Declaration 160
7.5 Import Declarations 160
7.5.1 Single-Type-Import Declaration 161
7.5.2 Type-Import-on-Demand Declaration 163
7.5.3 Single Static Import Declaration 164
7.5.4 Static-Import-on-Demand Declaration 165
7.5.5 Automatic Imports 165
7.5.6 A Strange Example 165
7.6 Top Level Type Declarations 166
7.7 Unique Package Names 169
8 Classes 173
8.1 Class Declaration 175
8.1.1 Class Modifiers 175
8.1.1.1 abstract Classes 176
8.1.1.2 final Classes 178
8.1.1.3 strictfp Classes 178
8.1.2 Generic Classes and Type Parameters 178
8.1.3 Inner Classes and Enclosing Instances 181
8.1.4 Superclasses and Subclasses 184
8.1.5 Superinterfaces 186
8.1.6 Class Body and Member Declarations 189
8.2 Class Members 190
8.2.1 Examples of Inheritance 192
8.2.1.1 Example: Inheritance with Default Access 192
8.2.1.2 Inheritance with public and protected 193
8.2.1.3 Inheritance with private 193
8.2.1.4 Accessing Members of Inaccessible Classes 194
8.3 Field Declarations 196
8.3.1 Field Modifiers 197
8.3.1.1 static Fields 198
8.3.1.2 final Fields 199
8.3.1.3 transient Fields 199
8.3.1.4 volatile Fields 199
8.3.2 Initialization of Fields 201
8.3.2.1 Initializers for Class Variables 202
8.3.2.2 Initializers for Instance Variables 202
8.3.2.3 Restrictions on the use of Fields during Initialization 203
8.3.3 Examples of Field Declarations 205
8.3.3.1 Example: Hiding of Class Variables 205
8.3.3.2 Example: Hiding of Instance Variables 206
8.3.3.3 Example: Multiply Inherited Fields 207
8.3.3.4 Example: Re-inheritance of Fields 209
8.4 Method Declarations 209
8.4.1 Formal Parameters 210
8.4.2 Method Signature 212
8.4.3 Method Modifiers 214
8.4.3.1 abstract Methods 214
8.4.3.2 static Methods 216
8.4.3.3 final Methods 217
8.4.3.4 native Methods 218
8.4.3.5 strictfp Methods 218
8.4.3.6 synchronized Methods 218
8.4.4 Generic Methods 220
8.4.5 Method Return Type 220
8.4.6 Method Throws 221
8.4.7 Method Body 223
8.4.8 Inheritance, Overriding, and Hiding 224
8.4.8.1 Overriding (by Instance Methods) 224
8.4.8.2 Hiding (by Class Methods) 225
8.4.8.3 Requirements in Overriding and Hiding 225
8.4.8.4 Inheriting Methods with Override-Equivalent Signatures 228
8.4.9 Overloading 229
8.4.10 Examples of Method Declarations 230
8.4.10.1 Example: Overriding 230
8.4.10.2 Example: Overloading, Overriding, and Hiding 231
8.4.10.3 Example: Incorrect Overriding 231
8.4.10.4 Example: Overriding versus Hiding 232
8.4.10.5 Example: Invocation of Hidden Class Methods 234
8.4.10.6 Large Example of Overriding 234
8.4.10.7 Example: Incorrect Overriding because of Throws 236
8.5 Member Type Declarations 237
8.5.1 Modifiers 238
8.5.2 Static Member Type Declarations 238
8.6 Instance Initializers 238
8.7 Static Initializers 239
8.8 Constructor Declarations 240
8.8.1 Formal Parameters and Formal Type Parameter 240
8.8.2 Constructor Signature 241
8.8.3 Constructor Modifiers 241
8.8.4 Generic Constructors 242
8.8.5 Constructor Throws 242
8.8.6 The Type of a Constructor 242
8.8.7 Constructor Body 242
8.8.7.1 Explicit Constructor Invocations 243
8.8.8 Constructor Overloading 246
8.8.9 Default Constructor 247
8.8.10 Preventing Instantiation of a Class 248
8.9 Enums 249
9 Interfaces 259
9.1 Interface Declarations 260
9.1.1 Interface Modifiers 260
9.1.1.1 abstract Interfaces 261
9.1.1.2 strictfp Interfaces 261
9.1.2 Generic Interfaces and Type Parameters 261
9.1.3 Superinterfaces and Subinterfaces 261
9.1.4 Interface Body and Member Declarations 263
9.1.5 Access to Interface Member Names 263
9.2 Interface Members 263
9.3 Field (Constant) Declarations 264
9.3.1 Initialization of Fields in Interfaces 265
9.3.2 Examples of Field Declarations 265
9.3.2.1 Ambiguous Inherited Fields 265
9.3.2.2 Multiply Inherited Fields 266
9.4 Abstract Method Declarations 266
9.4.1 Inheritance and Overriding 267
9.4.2 Overloading 268
9.4.3 Examples of Abstract Method Declarations 269
9.4.3.1 Example: Overriding 269
9.4.3.2 Example: Overloading 269
9.5 Member Type Declarations 270
9.6 Annotation Types 270
9.6.1 Predefined Annotation Types 277
9.6.1.1 Target 278
9.6.1.2 Retention 278
9.6.1.3 Inherited 279
9.6.1.4 Override 279
9.6.1.5 SuppressWarnings 280
9.6.1.6 Deprecated 280
9.7 Annotations 281
10 Arrays 287
10.1 Array Types 288
10.2 Array Variables 288
10.3 Array Creation 289
10.4 Array Access 289
10.5 Arrays: A Simple Example 290
10.6 Array Initializers 290
10.7 Array Members 292
10.8 Class Objects for Arrays 293
10.9 An Array of Characters is Not a String 294
10.10 Array Store Exception 294
11 Exceptions 297
11.1 The Causes of Exceptions 298
11.2 Compile-Time Checking of Exceptions 299
11.2.1 Exception Analysis of Expressions 299
11.2.2 Exception Analysis of Statements 300
11.2.3 Exception Checking 301
11.2.4 Why Errors are Not Checked 301
11.2.5 Why Runtime Exceptions are Not Checked 301
11.3 Handling of an Exception 302
11.3.1 Exceptions are Precise 303
11.3.2 Handling Asynchronous Exceptions 303
11.4 An Example of Exceptions 304
11.5 The Exception Hierarchy 306
11.5.1 Loading and Linkage Errors 307
11.5.2 Virtual Machine Errors 307
12 Execution 309
12.1 Virtual Machine Start-Up 309
12.1.1 Load the Class Test 310
12.1.2 Link Test: Verify, Prepare, (Optionally) Resolve 310
12.1.3 Initialize Test: Execute Initializers 311
12.1.4 Invoke Test.main 312
12.2 Loading of Classes and Interfaces 312
12.2.1 The Loading Process 313
12.3 Linking of Classes and Interfaces 314
12.3.1 Verification of the Binary Representation 314
12.3.2 Preparation of a Class or Interface Type 315
12.3.3 Resolution of Symbolic References 315
12.4 Initialization of Classes and Interfaces 316
12.4.1 When Initialization Occurs 316
12.4.2 Detailed Initialization Procedure 319
12.4.3 Initialization: Implications for Code Generation 321
12.5 Creation of New Class Instances 322
12.6 Finalization of Class Instances 325
12.6.1 Implementing Finalization 326
12.6.1.1 Interaction with the Memory Model 328
12.6.2 Finalizer Invocations are Not Ordered 329
12.7 Unloading of Classes and Interfaces 330
12.8 Program Exit 331
13 Binary Compatibility 333
13.1 The Form of a Binary 334
13.2 What Binary Compatibility Is and Is Not 339
13.3 Evolution of Packages 340
13.4 Evolution of Classes 340
13.4.1 abstract Classes 340
13.4.2 final Classes 341
13.4.3 public Classes 341
13.4.4 Superclasses and Superinterfaces 341
13.4.5 Class Formal Type Parameters 342
13.4.6 Class Body and Member Declarations 343
13.4.7 Access to Members and Constructors 344
13.4.8 Field Declarations 345
13.4.9 final Fields and Constants 347
13.4.10 static Fields 349
13.4.11 transient Fields 350
13.4.12 Method and Constructor Declarations 350
13.4.13 Method and Constructor Formal Type Parameters 351
13.4.14 Method and Constructor Parameters 352
13.4.15 Method Result Type 352
13.4.16 abstract Methods 352
13.4.17 final Methods 353
13.4.18 native Methods 354
13.4.19 static Methods 354
13.4.20 synchronized Methods 354
13.4.21 Method and Constructor Throws 354
13.4.22 Method and Constructor Body 354
13.4.23 Method and Constructor Overloading 355
13.4.24 Method Overriding 356
13.4.25 Static Initializers 356
13.4.26 Evolution of Enums 356
13.5 Evolution of Interfaces 356
13.5.1 public Interfaces 356
13.5.2 Superinterfaces 357
13.5.3 The Interface Members 357
13.5.4 Interface Formal Type Parameters 357
13.5.5 Field Declarations 358
13.5.6 Abstract Method Declarations 358
13.5.7 Evolution of Annotation Types 358
14 Blocks and Statements 359
14.1 Normal and Abrupt Completion of Statements 360
14.2 Blocks 361
14.3 Local Class Declarations 361
14.4 Local Variable Declaration Statements 363
14.4.1 Local Variable Declarators and Types 364
14.4.2 Scope of Local Variable Declarations 364
14.4.3 Shadowing of Names by Local Variables 367
14.4.4 Execution of Local Variable Declarations 367
14.5 Statements 368
14.6 The Empty Statement 370
14.7 Labeled Statements 370
14.8 Expression Statements 371
14.9 The if Statement 372
14.9.1 The if–then Statement 372
14.9.2 The if–then–else Statement 372
14.10 The assert Statement 373
14.11 The switch Statement 377
14.12 The while Statement 380
14.12.1 Abrupt Completion 381
14.13 The do Statement 382
14.13.1 Abrupt Completion 383
14.13.2 Example of do statement 383
14.14 The for Statement 384
14.14.1 The basic for Statement 384
14.14.1.1 Initialization of for statement 385
14.14.1.2 Iteration of for statement 385
14.14.1.3 Abrupt Completion of for statement 386
14.14.2 The enhanced for statement 387
14.15 The break Statement 388
14.16 The continue Statement 390
14.17 The return Statement 392
14.18 The throw Statement 393
14.19 The synchronized Statement 395
14.20 The try statement 396
14.20.1 Execution of try–catch 398
14.20.2 Execution of try–catch–finally 399
14.21 Unreachable Statements 402
15 Expressions 409
15.1 Evaluation, Denotation, and Result 409
15.2 Variables as Values 410
15.3 Type of an Expression 410
15.4 FP-strict Expressions 411
15.5 Expressions and Run-Time Checks 411
15.6 Normal and Abrupt Completion of Evaluation 413
15.7 Evaluation Order 414
15.7.1 Evaluate Left-Hand Operand First 415
15.7.2 Evaluate Operands before Operation 416
15.7.3 Evaluation Respects Parentheses and Precedence 417
15.7.4 Argument Lists are Evaluated Left-to-Right 418
15.7.5 Evaluation Order for Other Expressions 419
15.8 Primary Expressions 420
15.8.1 Lexical Literals 420
15.8.2 Class Literals 421
15.8.3 this 421
15.8.4 Qualified this 422
15.8.5 Parenthesized Expressions 422
15.9 Class Instance Creation Expressions 423
15.9.1 Determining the Class being Instantiated 424
15.9.2 Determining Enclosing Instances 425
15.9.3 Choosing the Constructor and its Arguments 427
15.9.4 Run-time Evaluation of Class Instance Creation Expressions 428
15.9.5 Anonymous Class Declarations 429
15.9.5.1 Anonymous Constructors 429
15.9.6 Example: Evaluation Order and Out-of-Memory Detection 430
15.10 Array Creation Expressions 431
15.10.1 Run-time Evaluation of Array Creation Expressions 432
15.10.2 Example: Array Creation Evaluation Order 433
15.10.3 Example: Array Creation and Out-of-Memory Detection 434
15.11 Field Access Expressions 435
15.11.1 Field Access Using a Primary 435
15.11.2 Accessing Superclass Members using super 438
15.12 Method Invocation Expressions 440
15.12.1 Compile-Time Step 1: Determine Class or Interface to Search 440
15.12.2 Compile-Time Step 2: Determine Method Signature 442
15.12.2.1 Identify Potentially Applicable Methods 443
15.12.2.2 Phase 1: Identify Matching Arity Methods Applicable by Subtyping
445
15.12.2.3 Phase 2: Identify Matching Arity Methods Applicable by
Method Invocation Conversion 446
15.12.2.4 Phase 3: Identify Applicable Variable Arity Methods 446
15.12.2.5 Choosing the Most Specific Method 447
15.12.2.6 Method Result and Throws Types 450
15.12.2.7 Inferring Type Arguments Based on Actual Arguments 451
15.12.2.8 Inferring Unresolved Type Arguments 466
15.12.2.9 Examples 466
15.12.2.10 Example: Overloading Ambiguity 468
15.12.2.11 Example: Return Type Not Considered 468
15.12.2.12 Example: Compile-Time Resolution 469
15.12.3 Compile-Time Step 3: Is the Chosen Method Appropriate? 471
15.12.4 Runtime Evaluation of Method Invocation 473
15.12.4.1 Compute Target Reference (If Necessary) 473
15.12.4.2 Evaluate Arguments 474
15.12.4.3 Check Accessibility of Type and Method 475
15.12.4.4 Locate Method to Invoke 476
15.12.4.5 Create Frame, Synchronize, Transfer Control 477
15.12.4.6 Example: Target Reference and Static Methods 479
15.12.4.7 Example: Evaluation Order 479
15.12.4.8 Example: Overriding 480
15.12.4.9 Example: Method Invocation using super 481
15.13 Array Access Expressions 482
15.13.1 Runtime Evaluation of Array Access 483
15.13.2 Examples: Array Access Evaluation Order 483
15.14 Postfix Expressions 485
15.14.1 Expression Names 485
15.14.2 Postfix Increment Operator ++ 485
15.14.3 Postfix Decrement Operator -- 486
15.15 Unary Operators 487
15.15.1 Prefix Increment Operator ++ 487
15.15.2 Prefix Decrement Operator -- 488
15.15.3 Unary Plus Operator + 489
15.15.4 Unary Minus Operator - 489
15.15.5 Bitwise Complement Operator ~ 490
15.15.6 Logical Complement Operator ! 490
15.16 Cast Expressions 490
15.17 Multiplicative Operators 491
15.17.1 Multiplication Operator * 492
15.17.2 Division Operator / 493
15.17.3 Remainder Operator % 495
15.18 Additive Operators 496
15.18.1 String Concatenation Operator + 497
15.18.1.1 String Conversion 497
15.18.1.2 Optimization of String Concatenation 498
15.18.1.3 Examples of String Concatenation 498
15.18.2 Additive Operators (+ and -) for Numeric Types 500
15.19 Shift Operators 502
15.20 Relational Operators 503
15.20.1 Numerical Comparison Operators <, <=, >, and >= 503
15.20.2 Type Comparison Operator instanceof 504
15.21 Equality Operators 505
15.21.1 Numerical Equality Operators == and != 506
15.21.2 Boolean Equality Operators == and != 507
15.21.3 Reference Equality Operators == and != 507
15.22 Bitwise and Logical Operators 508
15.22.1 Integer Bitwise Operators &, ^, and | 508
15.22.2 Boolean Logical Operators &, ^, and | 508
15.23 Conditional-And Operator && 509
15.24 Conditional-Or Operator || 509
15.25 Conditional Operator ? : 510
15.26 Assignment Operators 512
15.26.1 Simple Assignment Operator = 513
15.26.2 Compound Assignment Operators 518
15.27 Expression 525
15.28 Constant Expression 525
16 Definite Assignment 527
16.1 Definite Assignment and Expressions 533
16.1.1 Boolean Constant Expressions 533
16.1.2 The Boolean Operator && 533
16.1.3 The Boolean Operator || 534
16.1.4 The Boolean Operator ! 534
16.1.5 The Boolean Operator ? : 534
16.1.6 The Conditional Operator ? : 535
16.1.7 Other Expressions of Type boolean 535
16.1.8 Assignment Expressions 535
16.1.9 Operators ++ and -- 536
16.1.10 Other Expressions 536
16.2 Definite Assignment and Statements 538
16.2.1 Empty Statements 538
16.2.2 Blocks 538
16.2.3 Local Class Declaration Statements 539
16.2.4 Local Variable Declaration Statements 539
16.2.5 Labeled Statements 540
16.2.6 Expression Statements 540
16.2.7 if Statements 541
16.2.8 assert Statements 541
16.2.9 switch Statements 541
16.2.10 while Statements 542
16.2.11 do Statements 543
16.2.12 for Statements 543
16.2.12.1 Initialization Part 544
16.2.12.2 Incrementation Part 544
16.2.13 break, continue, return, and throw Statements 545
16.2.14 synchronized Statements 545
16.2.15 try Statements 545
16.3 Definite Assignment and Parameters 547
16.4 Definite Assignment and Array Initializers 547
16.5 Definite Assignment and Enum Constants 548
16.6 Definite Assignment and Anonymous Classes 548
16.7 Definite Assignment and Member Types 549
16.8 Definite Assignment and Static Initializers 549
16.9 Definite Assignment, Constructors, and Instance Initializers 550
17 Threads and Locks 553
17.1 Locks 554
17.2 Notation in Examples 554
17.3 Incorrectly Synchronized Programs Exhibit Surprising Behaviors 555
17.4 Memory Model 557
17.4.1 Shared Variables 558
17.4.2 Actions 558
17.4.3 Programs and Program Order 560
17.4.4 Synchronization Order 561
17.4.5 Happens-before Order 561
17.4.6 Executions 567
17.4.7 Well-Formed Executions 568
17.4.8 Executions and Causality Requirements 568
17.4.9 Observable Behavior and Nonterminating Executions 571
17.5 Final Field Semantics 573
17.5.1 Semantics of Final Fields 575
17.5.2 Reading Final Fields During Construction 576
17.5.3 Subsequent Modification of Final Fields 576
17.5.4 Write Protected Fields 578
17.6 Word Tearing 578
17.7 Non-atomic Treatment of double and long 579
17.8 Wait Sets and Notification 580
17.8.1 Wait 580
17.8.2 Notification 581
17.8.3 Interruptions 582
17.8.4 Interactions of Waits, Notification and Interruption 582
17.9 Sleep and Yield 583
18 Syntax 585
18.1 The Grammar of the Java Programming Language 585
Index 597
Credits 649
Colophon 651
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