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The Java Language Specification13.5.513.5.613.5.713.5.8Interface Type Parameters 480Field Declarations 480Interface Method Declarations 480Annotation Interfaces 48114 Blocks, Statements, and Patterns 4.22Normal and Abrupt Completion of Statements 484Blocks 485Local Class and Interface Declarations 486Local Variable Declarations 48814.4.1 Local Variable Declarators and Types 48914.4.2 Local Variable Declaration Statements 491Statements 491The Empty Statement 493Labeled Statements 493Expression Statements 495The if Statement 49614.9.1 The if-then Statement 49614.9.2 The if-then-else Statement 497The assert Statement 497The switch Statement 50014.11.1 Switch Blocks 50014.11.2 The Switch Block of a switch Statement 50314.11.3 Execution of a switch Statement 503The while Statement 50614.12.1 Abrupt Completion of while Statement 507The do Statement 50714.13.1 Abrupt Completion of do Statement 508The for Statement 50914.14.1 The basic for Statement 51014.14.1.1 Initialization of for Statement 51014.14.1.2 Iteration of for Statement 51114.14.1.3 Abrupt Completion of for Statement 51214.14.2 The enhanced for statement 513The break Statement 516The continue Statement 518The return Statement 521The throw Statement 522The synchronized Statement 524The try statement 52514.20.1 Execution of try-catch 52914.20.2 Execution of try-finally and try-catch-finally 53014.20.3 try-with-resources 53214.20.3.1 Basic try-with-resources 53514.20.3.2 Extended try-with-resources 538The yield Statement 538Unreachable Statements 540xi

The Java Language Specification14.30 Patterns 54614.30.1 Kinds of Patterns 54714.30.2 Pattern Matching 54815 Expressions 54915.115.215.315.415.515.615.7Evaluation, Denotation, and Result 549Forms of Expressions 550Type of an Expression 551Floating-point Expressions 552Expressions and Run-Time Checks 556Normal and Abrupt Completion of Evaluation 558Evaluation Order 56015.7.1 Evaluate Left-Hand Operand First 56015.7.2 Evaluate Operands before Operation 56215.7.3 Evaluation Respects Parentheses and Precedence 56215.7.4 Argument Lists are Evaluated Left-to-Right 56315.7.5 Evaluation Order for Other Expressions 56515.8 Primary Expressions 56515.8.1 Lexical Literals 56615.8.2 Class Literals 56715.8.3 this 56815.8.4 Qualified this 56915.8.5 Parenthesized Expressions 56915.9 Class Instance Creation Expressions 57015.9.1 Determining the Class being Instantiated 57215.9.2 Determining Enclosing Instances 57315.9.3 Choosing the Constructor and its Arguments 57615.9.4 Run-Time Evaluation of Class Instance CreationExpressions 58115.9.5 Anonymous Class Declarations 58215.9.5.1 Anonymous Constructors 58315.10 Array Creation and Access Expressions 58415.10.1 Array Creation Expressions 58415.10.2 Run-Time Evaluation of Array Creation Expressions 58615.10.3 Array Access Expressions 58915.10.4 Run-Time Evaluation of Array Access Expressions 58915.11 Field Access Expressions 59215.11.1 Field Access Using a Primary 59215.11.2 Accessing Superclass Members using super 59515.12 Method Invocation Expressions 59715.12.1 Compile-Time Step 1: Determine Type to Search 59815.12.2 Compile-Time Step 2: Determine Method Signature 60115.12.2.1 Identify Potentially Applicable Methods 60715.12.2.2 Phase 1: Identify Matching Arity Methods Applicableby Strict Invocation 60915.12.2.3 Phase 2: Identify Matching Arity Methods Applicableby Loose Invocation 611xii

The Java Language .2015.2115.2215.2315.2415.2515.12.2.4 Phase 3: Identify Methods Applicable by Variable ArityInvocation 61115.12.2.5 Choosing the Most Specific Method 61215.12.2.6 Method Invocation Type 61615.12.3 Compile-Time Step 3: Is the Chosen Method Appropriate? 61715.12.4 Run-Time Evaluation of Method Invocation 62015.12.4.1 Compute Target Reference (If Necessary) 62015.12.4.2 Evaluate Arguments 62215.12.4.3 Check Accessibility of Type and Method 62315.12.4.4 Locate Method to Invoke 62415.12.4.5 Create Frame, Synchronize, Transfer Control 629Method Reference Expressions 63115.13.1 Compile-Time Declaration of a Method Reference 63415.13.2 Type of a Method Reference 64015.13.3 Run-Time Evaluation of Method References 641Postfix Expressions 64415.14.1 Expression Names 64515.14.2 Postfix Increment Operator 64515.14.3 Postfix Decrement Operator -- 646Unary Operators 64615.15.1 Prefix Increment Operator 64815.15.2 Prefix Decrement Operator -- 64815.15.3 Unary Plus Operator 64915.15.4 Unary Minus Operator - 64915.15.5 Bitwise Complement Operator 65015.15.6 Logical Complement Operator ! 650Cast Expressions 651Multiplicative Operators 65215.17.1 Multiplication Operator * 65315.17.2 Division Operator / 65415.17.3 Remainder Operator % 655Additive Operators 65715.18.1 String Concatenation Operator 65815.18.2 Additive Operators ( and -) for Numeric Types 660Shift Operators 662Relational Operators 66315.20.1 Numerical Comparison Operators , , , and 66315.20.2 The instanceof Operator 665Equality Operators 66715.21.1 Numerical Equality Operators and ! 66815.21.2 Boolean Equality Operators and ! 66915.21.3 Reference Equality Operators and ! 669Bitwise and Logical Operators 67015.22.1 Integer Bitwise Operators &, , and 67015.22.2 Boolean Logical Operators &, , and 671Conditional-And Operator && 672Conditional-Or Operator 672Conditional Operator ? : 673xiii

The Java Language Specification15.2615.2715.2815.2915.25.1 Boolean Conditional Expressions 68115.25.2 Numeric Conditional Expressions 68115.25.3 Reference Conditional Expressions 682Assignment Operators 68315.26.1 Simple Assignment Operator 68415.26.2 Compound Assignment Operators 690Lambda Expressions 69615.27.1 Lambda Parameters 69815.27.2 Lambda Body 70215.27.3 Type of a Lambda Expression 70515.27.4 Run-Time Evaluation of Lambda Expressions 707switch Expressions 70815.28.1 The Switch Block of a switch Expression 70915.28.2 Run-Time Evaluation of switch Expressions 710Constant Expressions 71216 Definite Assignment 71516.116.216.3xivDefinite Assignment and Expressions 72116.1.1 Boolean Constant Expressions 72116.1.2 Conditional-And Operator && 72116.1.3 Conditional-Or Operator 72216.1.4 Logical Complement Operator ! 72216.1.5 Conditional Operator ? : 72216.1.6 switch Expressions 72316.1.7 Other Expressions of Type boolean 72616.1.8 Assignment Expressions 72616.1.9 Operators and -- 72616.1.10 Other Expressions 727Definite Assignment and Statements 72816.2.1 Empty Statements 72816.2.2 Blocks 72816.2.3 Local Class and Interface Declarations 73016.2.4 Local Variable Declaration Statements 73016.2.5 Labeled Statements 73016.2.6 Expression Statements 73116.2.7 if Statements 73116.2.8 assert Statements 73116.2.9 switch Statements 73216.2.10 while Statements 73216.2.11 do Statements 73316.2.12 for Statements 73316.2.12.1 Initialization Part of for Statement 73416.2.12.2 Incrementation Part of for Statement 73516.2.13 break, yield, continue, return, and throw Statements 73516.2.14 synchronized Statements 73516.2.15 try Statements 735Definite Assignment and Parameters 737

The Java Language Specification16.416.516.616.716.816.9Definite Assignment and Array Initializers 737Definite Assignment and Enum Constants 738Definite Assignment and Anonymous Classes 738Definite Assignment and Member Classes and Interfaces 739Definite Assignment and Static Initializers 739Definite Assignment, Constructors, and Instance Initializers 74017 Threads and Locks 74317.117.217.317.417.517.617.7Synchronization 744Wait Sets and Notification 74417.2.1 Wait 74517.2.2 Notification 74717.2.3 Interruptions 74717.2.4 Interactions of Waits, Notification, and Interruption 748Sleep and Yield 748Memory Model 74917.4.1 Shared Variables 75217.4.2 Actions 75217.4.3 Programs and Program Order 75317.4.4 Synchronization Order 75417.4.5 Happens-before Order 75517.4.6 Executions 75817.4.7 Well-Formed Executions 75917.4.8 Executions and Causality Requirements 75917.4.9 Observable Behavior and Nonterminating Executions 762final Field Semantics 76417.5.1 Semantics of final Fields 76617.5.2 Reading final Fields During Construction 76717.5.3 Subsequent Modification of final Fields 76717.5.4 Write-Protected Fields 768Word Tearing 769Non-Atomic Treatment of double and long 77018 Type Inference 77118.118.218.3Concepts and Notation 77218.1.1 Inference Variables 77218.1.2 Constraint Formulas 77318.1.3 Bounds 773Reduction 77518.2.1 Expression Compatibility Constraints 77518.2.2 Type Compatibility Constraints 78018.2.3 Subtyping Constraints 78118.2.4 Type Equality Constraints 78318.2.5 Checked Exception Constraints 784Incorporation 78618.3.1 Complementary Pairs of Bounds 78718.3.2 Bounds Involving Capture Conversion 788xv

The Java Language Specification18.418.5Resolution 788Uses of Inference 79118.5.1 Invocation Applicability Inference 79118.5.2 Invocation Type Inference 79318.5.2.1 Poly Method Invocation Compatibility 79318.5.2.2 Additional Argument Constraints 79518.5.3 Functional Interface Parameterization Inference 80018.5.4 More Specific Method Inference 80119 Syntax 805A Limited License Grant 833xvi

C H A P T E R1IntroductionTHE Javaprogramming language is a general-purpose, concurrent, classbased, object-oriented language. It is designed to be simple enough that manyprogrammers can achieve fluency in the language. The Java programming languageis related to C and C but is organized rather differently, with a number of aspectsof C and C omitted and a few ideas from other languages included. It is intendedto be a production language, not a research language, and so, as C. A. R. Hoaresuggested in his classic paper on language design, the design has avoided includingnew and untested features. The Java programming language is strongly and statically typed. This specificationclearly distinguishes between the compile-time errors that can and must be detectedat compile time, and those that occur at run time. Compile time normally consistsof translating programs into a machine-independent byte code representation.Run-time activities include loading and linking of the classes needed to executea program, optional machine code generation and dynamic optimization of theprogram, and actual program execution.The Java programming language is a relatively high-level language, in that detailsof the machine representation are not available through the language. It includesautomatic storage management, typically using a garbage collector, to avoidthe safety problems of explicit deallocation (as in C's free or C 's delete).High-performance garbage-collected implementations can have bounded pauses tosupport systems programming and real-time applications. The language does notinclude any unsafe constructs, such as array accesses without index checking, sincesuch unsafe constructs would cause a program to behave in an unspecified way.The Java programming language is normally compiled to the bytecode instructionset and binary format defined in The Java Virtual Machine Specification, Java SE17 Edition.1

1.1Organization of the SpecificationINTRODUCTION1.1 Organization of the SpecificationChapter 2 describes grammars and the notation used to present the lexical andsyntactic grammars for the language.Chapter 3 describes the lexical structure of the Java programming language, whichis based on C and C . The language is written in the Unicode character set. Itsupports the writing of Unicode characters on systems that support only ASCII.Chapter 4 describes types, values, and variables. Types are subdivided intoprimitive types and reference types.The primitive types are defined to be the same on all machines and in allimplementations, and are various sizes of two's-complement integers, IEEE 754floating-point numbers, a boolean type, and a Unicode character char type. Valuesof the primitive types do not share state.Reference types are the class types, the interface types, and the array types. Thereference types are implemented by dynamically created objects that are eitherinstances of classes or arrays. Many references to each object can exist. All objects(including arrays) support the methods of the class Object, which is the (single)root of the class hierarchy. A predefined String class supports Unicode characterstrings. Classes exist for wrapping primitive values inside of objects. In many cases,wrapping and unwrapping is performed automatically by the compiler (in whichcase, wrapping is called boxing, and unwrapping is called unboxing). Classesand interfaces may be generic, that is, they may be parameterized by referencetypes. Parameterized types of such classes and interfaces may then be invoked withspecific type arguments.Variables are typed storage locations. A variable of a primitive type holds a valueof that exact primitive type. A variable of a class type can hold a null reference ora reference to an object that is an instance of the named class or any subclass ofthat class. A variable of an interface type can hold a null reference or a referenceto an instance of any class that implements the named interface. A variable of anarray type can hold a null reference or a reference to an array. A variable of classtype Object can hold a null reference or a reference to any object, whether classinstance or array.Chapter 5 describes conversions and numeric promotions. Conversions change thecompile-time type and, sometimes, the value of an expression. These conversionsinclude the boxing and unboxing conversions between primitive types andreference types. Numeric promotions are used to convert the operands of a numericoperator to a common type where an operation can be performed. There are no2

INTRODUCTIONOrganization of the Specification1.1loopholes in the language; casts on reference types are checked at run time to ensuretype safety.Chapter 6 describes declarations and names, and how to determine what namesmean (that is, which declaration a name denotes). The Java programming languagedoes not require classes and interfaces, or their members, to be declared before theyare used. Declaration order is significant only for local variables, local classes, localinterfaces, and the order of field initializers in a class or interface. Recommendednaming conventions that make for more readable programs are described here.Chapter 7 describes the structure of a program, which is organized into packages.The members of a package are classes, interfaces, and subpackages. Packages,and consequently their members, have names in a hierarchical name space; theInternet domain name system can usually be used to form unique package names.Compilation units contain declarations of the classes and interfaces that aremembers of a given package, and may import classes and interfaces from otherpackages to give them short names.Packages may be grouped into modules that serve as building blocks in theconstruction of very large programs. The declaration of a module specifies whichother modules (and thus packages, and thus classes and interfaces) are required inorder to compile and run code in its own packages.The Java programming language supports limitations on external access to themembers of packages, classes, and interfaces. The members of a package may beaccessible solely by other members in the same package, or by members in otherpackages of the same module, or by members of packages in different modules.Similar constraints apply to the members of classes and interfaces.Chapter 8 describes classes. The members of classes are classes, interfaces, fields(variables) and methods. Class variables exist once per class. Class methods operatewithout reference to a specific object. Instance variables are dynamically createdin objects that are instances of classes. Instance methods are invoked on instancesof classes; such instances become the current object this during their execution,supporting the object-oriented programming style.Classes support single inheritance, in which each class has a single superclass.Each class inherits members from its superclass, and ultimately from the classObject. Variables of a class type can reference an instance of the named class orany subclass of that class, allowing new classes to be used with existing methods,polymorphically.Classes support concurrent programming with synchronized methods. Methodsdeclare the checked exceptions that can arise from their execution, which allows3

1.1Organization of the SpecificationINTRODUCTIONcompile-time checking to ensure that exceptional conditions are handled. Objectscan declare a finalize method that will be invoked before the objects are discardedby the garbage collector, allowing the objects to clean up their state.For simplicity, the language has neither declaration "headers" separate from theimplementation of a class nor separate type and class hierarchies.A restricted kind of class, enum classes, supports the definition of small sets ofvalues and their manipulation in a type safe manner. Unlike enumerations in otherlanguages, enum constants are objects and may have their own methods.Another restricted kind of class, record classes, supports the compact expressionof simple objects that serve as aggregates of values.Chapter 9 describes interfaces. The members of interfaces are classes, interfaces,constant fields, and methods. Classes that are otherwise unrelated can implementthe same interface. A variable of an interface type can contain a reference to anyobject that implements the interface.Classes and interfaces support multiple inheritance from interfaces. A class thatimplements one or more interfaces may inherit instance methods from both itssuperclass and its superinterfaces.Annotations are metadata that may be applied to declarations in a program, as wellas to the uses of types in declarations and expressions. The form of an annotationis defined by an annota

Aug 09, 2021 · The Java Language Specification 8.2 Class Members 259 8.3 Field Declarations 263 8.3.1 Field Modifiers 268 8.3.1.1 static Fields 268 8.3.1.2 final Fields 272 8.3.1.3 transient Fields 272 8.3.1.4 volatile Fields 272 8.3.2 Field Initialization 274 8