The Java Language Specification, Third Edition

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5.1.8 Unboxing Conversion CONVERSIONS AND PROMOTIONS 88 5.1.8 Unboxing Conversion Unboxing conversion converts values of reference type to corresponding values of primitive type. Specifically, the following 8 conversion are called the unboxing conversions: • From type Boolean to type boolean • From type Byte to type byte • From type Character to type char • From type Short to type short • From type Integer to type int • From type Long to type long • From type Float to type float • From type Double to type double At run time, unboxing conversion proceeds as follows: • If r is a reference of type Boolean, then unboxing conversion converts r into r.booleanValue() • If r is a reference of type Byte, then unboxing conversion converts r into r.byteValue() • If r is a reference of type Character, then unboxing conversion converts r into r.charValue() • If r is a reference of type Short, then unboxing conversion converts r into r.shortValue() DRAFT • If r is a reference of type Integer, then unboxing conversion converts r into r.intValue() • If r is a reference of type Long, then unboxing conversion converts r into r.longValue() • If r is a reference of type Float, unboxing conversion converts r into r.floatValue() • If r is a reference of type Double, then unboxing conversion converts r into r.doubleValue() • If r is null, unboxing conversion throws a NullPointerException
CONVERSIONS AND PROMOTIONS Capture Conversion 5.1.10 A type is said to be convertible to a numeric type if it is a numeric type, or it is a reference type that may be converted to a numeric type by unboxing conversion. A type is said to be convertible to an integral type if it is an integral type, or it is a reference type that may be converted to an integral type by unboxing conversion. 5.1.9 Unchecked Conversion Let G name a generic type declaration with n formal type parameters. <strong>The</strong>re is an unchecked conversion from the raw type (§4.8) G to any parameterized type of the form G. Use of an unchecked conversion generates a mandatory compile-time warning (which can only be suppressed using the SuppressWarnings annotation (§9.6.1.5)) unless the parameterized type G is a parameterized type in which all type arguments are unbounded wildcards (§4.5.1). DISCUSSION Unchecked conversion is used to enable a smooth interoperation of legacy code, written before the introduction of generic types, with libraries that have undergone a conversion to use genericity (a process we call generification). In such circumstances (most notably, clients of the collections framework in java.util), legacy code uses raw types (e.g., Collection instead of Collection). Expressions of raw types are passed as arguments to library methods that use parameterized versions of those same types as the types of their corresponding formal parameters. Such calls cannot be shown to be statically safe under the type system using generics. Rejecting such calls would invalidate large bodies of existing code, and prevent them from using newer versions of the libraries. This in turn, would discourage library vendors from taking advantage of genericity. To prevent such an unwelcome turn of events, a raw type may be converted to an arbitrary invocation of the generic type declaration the raw type refers to. While the conversion is unsound, it is tolerated as a concession to practicality. A warning (known as an unchecked warning) is issued in such cases. DRAFT 5.1.10 Capture Conversion Let G name a generic type declaration with n formal type parameters A1 ... An with corresponding bounds U1 ... Un. <strong>The</strong>re exists a capture conversion from G to G, where, for 1 ≤i≤n: 89
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The Java Language Specification Th
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The Java Language Specification Th
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Copyright © 1996-2005 Sun Microsys
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“When I use a word,” Humpty Dum
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Preface XXIII Preface to the Second
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5.4 String Conversion 101 5.5 Casti
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8.2.1.3 Inheritance with private 19
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10 Arrays 287 10.1 Array Types 288
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14 Blocks and Statements 359 14.1 N
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15.12.4.4 Locate Method to Invoke 4
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17.4.2 Actions 558 17.4.3 Programs
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Preface THE Java programming langua
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PREFACE was invaluable to us during
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Preface to the Second Edition ... t
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PREFACE TO THE SECOND EDITION Trici
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Preface to the Third Edition This e
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PREFACE TO THE THIRD EDITION Joe Da
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1.0 CHAPTER1 Introduction If I have
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INTRODUCTION Introduction 1 declare
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INTRODUCTION Example Programs 1.1 B
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INTRODUCTION References 1.4 Goldber
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CHAPTER2 Grammars Grammar, which kn
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GRAMMARS Grammar Notation 2.4 actua
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CHAPTER3 Lexical Structure Lexicogr
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LEXICAL STRUCTURE Unicode Escapes 3
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LEXICAL STRUCTURE Input Elements an
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LEXICAL STRUCTURE Identifiers 3.8 E
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LEXICAL STRUCTURE Literals 3.10 3.9
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LEXICAL STRUCTURE Integer Literals
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LEXICAL STRUCTURE Floating-Point Li
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LEXICAL STRUCTURE Character Literal
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LEXICAL STRUCTURE String Literals 3
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LEXICAL STRUCTURE Operators 3.12 3.
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CHAPTER4 Types, Values, and Variabl
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TYPES, VALUES, AND VARIABLES Integr
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Page 79 and 80: TYPES, VALUES, AND VARIABLES Object
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Page 83 and 84: TYPES, VALUES, AND VARIABLES Type V
Page 85 and 86: TYPES, VALUES, AND VARIABLES Parame
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Page 89 and 90: TYPES, VALUES, AND VARIABLES Member
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Page 103 and 104: TYPES, VALUES, AND VARIABLES Kinds
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Page 111 and 112: CHAPTER5 Conversions and Promotions
Page 113 and 114: CONVERSIONS AND PROMOTIONS Conversi
Page 115 and 116: CONVERSIONS AND PROMOTIONS Widening
Page 117 and 118: CONVERSIONS AND PROMOTIONS Narrowin
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Page 121: CONVERSIONS AND PROMOTIONS Boxing C
Page 125 and 126: CONVERSIONS AND PROMOTIONS Capture
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Page 135 and 136: CONVERSIONS AND PROMOTIONS Casting
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Page 147 and 148: CHAPTER6 Names The Tao that can be
Page 149 and 150: NAMES Names and Identifiers 6.2 ❖
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NAMES Details on protected Access 6
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NAMES Example: Access to public and
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NAMES Example: protected Fields, Me
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NAMES Fully Qualified Names and Can
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NAMES Class and Interface Type Name
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NAMES Method Names 6.8.4 DISCUSSION
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NAMES Local Variable and Parameter
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CHAPTER7 Packages Good things come
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PACKAGES Storing Packages in a File
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PACKAGES Compilation Units 7.3 7.2.
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PACKAGES Unnamed Packages 7.4.2 on
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PACKAGES Single-Type-Import Declara
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PACKAGES Type-Import-on-Demand Decl
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PACKAGES A Strange Example 7.5.6 7.
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PACKAGES Top Level Type Declaration
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PACKAGES Unique Package Names 7.7 t
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PACKAGES Unique Package Names 7.7 o
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CHAPTER8 Classes Origins: A Short E
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CLASSES Class Modifiers 8.1.1 8.1 C
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CLASSES Class Modifiers 8.1.1 class
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CLASSES Generic Classes and Type Pa
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CLASSES Inner Classes and Enclosing
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CLASSES Inner Classes and Enclosing
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CLASSES Superclasses and Subclasses
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CLASSES Superinterfaces 8.1.5 resul
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CLASSES Class Body and Member Decla
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CLASSES Class Members 8.2 Construct
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CLASSES Examples of Inheritance 8.2
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CLASSES Examples of Inheritance 8.2
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CLASSES Field Modifiers 8.3.1 If a
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CLASSES Field Modifiers 8.3.1 of ac
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CLASSES Initialization of Fields 8.
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CLASSES Initialization of Fields 8.
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CLASSES Examples of Field Declarati
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CLASSES Examples of Field Declarati
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CLASSES Method Declarations 8.4 fie
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CLASSES Formal Parameters 8.4.1 of
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CLASSES Method Signature 8.4.2 Two
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CLASSES Method Modifiers 8.4.3 an i
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CLASSES Method Modifiers 8.4.3 resp
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CLASSES Method Modifiers 8.4.3 Thes
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CLASSES Method Throws 8.4.6 • If
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CLASSES Method Body 8.4.7 Object do
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CLASSES Inheritance, Overriding, an
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CLASSES Inheritance, Overriding, an
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CLASSES Overloading 8.4.9 DISCUSSIO
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CLASSES Examples of Method Declarat
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CLASSES Member Type Declarations 8.
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CLASSES Static Initializers 8.7 aga
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CLASSES Constructor Modifiers 8.8.3
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CLASSES Constructor Body 8.8.7 clas
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CLASSES Constructor Body 8.8.7 •
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CLASSES Default Constructor 8.8.9 8
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CLASSES Enums 8.9 8.9 Enums An enum
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CLASSES Enums 8.9 DISCUSSION This i
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CLASSES Enums 8.9 Note that the exa
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CLASSES Enums 8.9 DIME: 10¢ SILVER
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CLASSES Enums 8.9 public static voi
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CHAPTER9 Interfaces My apple trees
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INTERFACES Superinterfaces and Subi
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INTERFACES Interface Members 9.2 9.
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INTERFACES Examples of Field Declar
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INTERFACES Inheritance and Overridi
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INTERFACES Examples of Abstract Met
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INTERFACES Annotation Types 9.6 DIS
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INTERFACES Predefined Annotation Ty
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INTERFACES Predefined Annotation Ty
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INTERFACES Annotations 9.7 • The
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INTERFACES Annotations 9.7 TypeName
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INTERFACES Annotations 9.7 The seco
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CHAPTER10 Arrays Even Solomon in al
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ARRAYS Array Access 10.4 Here are s
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ARRAYS Array Initializers 10.6 Arra
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ARRAYS Class Objects for Arrays 10.
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ARRAYS Array Store Exception 10.10
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CHAPTER11 Exceptions If anything ca
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EXCEPTIONS Exception Analysis of Ex
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EXCEPTIONS Why Runtime Exceptions a
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EXCEPTIONS Handling Asynchronous Ex
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EXCEPTIONS An Example of Exceptions
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EXCEPTIONS Virtual Machine Errors 1
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CHAPTER12 Execution We must all han
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EXECUTION Initialize Test: Execute
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EXECUTION The Loading Process 12.2.
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EXECUTION Resolution of Symbolic Re
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EXECUTION When Initialization Occur
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EXECUTION Detailed Initialization P
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EXECUTION Initialization: Implicati
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EXECUTION Creation of New Class Ins
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EXECUTION Finalization of Class Ins
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EXECUTION Implementing Finalization
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EXECUTION Finalizer Invocations are
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EXECUTION Program Exit 12.8 ers. A
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CHAPTER13 Binary Compatibility Desp
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BINARY COMPATIBILITY The Form of a
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BINARY COMPATIBILITY The Form of a
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BINARY COMPATIBILITY What Binary Co
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BINARY COMPATIBILITY Superclasses a
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BINARY COMPATIBILITY Class Body and
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BINARY COMPATIBILITY Field Declarat
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BINARY COMPATIBILITY final Fields a
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BINARY COMPATIBILITY static Fields
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BINARY COMPATIBILITY Method and Con
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BINARY COMPATIBILITY final Methods
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BINARY COMPATIBILITY Method and Con
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BINARY COMPATIBILITY Interface Form
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CHAPTER14 Blocks and Statements He
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BLOCKS AND STATEMENTS Local Class D
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BLOCKS AND STATEMENTS Local Variabl
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BLOCKS AND STATEMENTS Scope of Loca
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BLOCKS AND STATEMENTS Execution of
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BLOCKS AND STATEMENTS Statements 14
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BLOCKS AND STATEMENTS Expression St
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BLOCKS AND STATEMENTS The assert St
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BLOCKS AND STATEMENTS The assert St
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BLOCKS AND STATEMENTS The switch St
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BLOCKS AND STATEMENTS The switch St
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BLOCKS AND STATEMENTS Abrupt Comple
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BLOCKS AND STATEMENTS Example of do
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BLOCKS AND STATEMENTS The basic for
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BLOCKS AND STATEMENTS The enhanced
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BLOCKS AND STATEMENTS The break Sta
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BLOCKS AND STATEMENTS The continue
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BLOCKS AND STATEMENTS The throw Sta
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BLOCKS AND STATEMENTS The synchroni
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BLOCKS AND STATEMENTS The try state
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BLOCKS AND STATEMENTS Unreachable S
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CHAPTER15 Expressions When you can
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EXPRESSIONS Expressions and Run-Tim
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EXPRESSIONS Normal and Abrupt Compl
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EXPRESSIONS Evaluate Left-Hand Oper
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EXPRESSIONS Evaluation Respects Par
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EXPRESSIONS Evaluation Order for Ot
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EXPRESSIONS this 15.8.3 ing-point l
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EXPRESSIONS Class Instance Creation
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EXPRESSIONS Determining Enclosing I
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EXPRESSIONS Choosing the Constructo
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EXPRESSIONS Anonymous Class Declara
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EXPRESSIONS Array Creation Expressi
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EXPRESSIONS Example: Array Creation
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EXPRESSIONS Field Access Using a Pr
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EXPRESSIONS Field Access Using a Pr
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EXPRESSIONS Accessing Superclass Me
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EXPRESSIONS Compile-Time Step 1: De
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EXPRESSIONS Compile-Time Step 3: Is
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EXPRESSIONS Runtime Evaluation of M
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EXPRESSIONS Examples: Array Access
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EXPRESSIONS Postfix Increment Opera
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EXPRESSIONS Prefix Increment Operat
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EXPRESSIONS Unary Minus Operator -
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EXPRESSIONS Multiplicative Operator
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EXPRESSIONS Division Operator / 15.
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EXPRESSIONS Remainder Operator % 15
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EXPRESSIONS String Concatenation Op
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EXPRESSIONS String Concatenation Op
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EXPRESSIONS Additive Operators (+ a
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EXPRESSIONS Numerical Comparison Op
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EXPRESSIONS Equality Operators 15.2
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EXPRESSIONS Reference Equality Oper
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EXPRESSIONS Conditional-Or Operator
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EXPRESSIONS Conditional Operator ?
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EXPRESSIONS Simple Assignment Opera
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EXPRESSIONS Compound Assignment Ope
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EXPRESSIONS Constant Expression 15.
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CHAPTER16 Definite Assignment All t
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DEFINITE ASSIGNMENT Definite Assign
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DEFINITE ASSIGNMENT The Boolean Ope
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DEFINITE ASSIGNMENT Assignment Expr
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DEFINITE ASSIGNMENT Other Expressio
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DEFINITE ASSIGNMENT Local Variable
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DEFINITE ASSIGNMENT switch Statemen
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DEFINITE ASSIGNMENT for Statements
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DEFINITE ASSIGNMENT try Statements
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CHAPTER17 Threads and Locks And oft
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THREADS AND LOCKS Incorrectly Synch
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THREADS AND LOCKS Memory Model 17.4
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THREADS AND LOCKS Actions 17.4.2
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THREADS AND LOCKS Happens-before Or
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THREADS AND LOCKS Executions 17.4.6
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THREADS AND LOCKS Executions and Ca
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THREADS AND LOCKS Observable Behavi
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THREADS AND LOCKS Final Field Seman
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THREADS AND LOCKS Semantics of Fina
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THREADS AND LOCKS Subsequent Modifi
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THREADS AND LOCKS Non-atomic Treatm
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THREADS AND LOCKS Notification 17.8
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THREADS AND LOCKS Sleep and Yield 1
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CHAPTER18 Syntax Is there grammar i
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SYNTAX The Grammar of the Java Prog
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A abrupt completion See completion,
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definite assignment before, 548 det
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See also numbers literals, term def
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See local class member See member c
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See also hiding; obscuring; scope;
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in assignment conversion context, 9
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of blank final class variables, 199
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interface, multiply inherited, 266
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division, evaluation, 493 equality
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easons why constructors cannot be,
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identity conversion in assignment c
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order, 428 expressions as statement
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L labeled statements identifiers in
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term definition, 122 type, 44 memor
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class, 175 constructor, 241 declara
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conversions of and to See conversio
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importing all public types from a,
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Q superclasses, accessing instances
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internal symbolic reference table,
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declaring class methods with, 216 h
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applicable by subtyping, 445 applic
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unchecked, 301 executed, 409 exit o
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precision, loss of, 81 preparation,
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termination and virtual machine exi
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members and constructors, 55 reifia
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of binary representation, of classe
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Colophon CAMERA-READY electronic co
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