Goal Give an overview of generics for the Java programming language - - PDF document

1 2005 JavaOneSM Conference | Session TS-5627

Generics Written in the Java™ Programming Language with Parameterized Types in Java Platform 5.0

Angelika Langer Trainer/Consultant www.AngelikaLanger.com

TS-5627

2005 JavaOneSM Conference | Session TS-5627 | 2

Give an overview of generics for the Java™ programming language What are generics?

Language features of generics

What are generics used for?

Idioms for use of generics

Goal

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Speaker’s Qualifications

• Author of Java Generics FAQ online
• www.AngelikaLanger.com/GenericsFAQ/

JavaGenericsFAQ.html

• Independent trainer/consultant/author
• Teaching C++ and Java for 10+ years

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Agenda

Language Features Usage

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Non-Generic Collections

• No homogeneous collections
• Lots of casts required
• No compile-time checks
• Late error detection at runtime

Li nkedLi st l i st = new Li nkedLi st ( ) ; l i st . add( new I nt eger ( 0) ) ; I nt eger i = ( I nt eger ) l i st . get ( 0) ; St r i ng s = ( St r i ng) l i st . get ( 0) ;

Casts Required Fine at Compile-time, but Fails at Runtime

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Generic Collections

• Collections are homogeneous
• No casts necessary
• Early compile-time checks
• Based on static type information

Li nkedLi st <I nt eger > l i st = new Li nkedLi st <I nt eger > ( ) ; l i st . add( new I nt eger ( 0) ) ; I nt eger i = l i st . get ( 0) ; St r i ng s = l i st . get ( 0) ;

Compile-time Error

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Benefits of Generic Types

• Increased expressive power
• Improved type safety
• Explicit type parameters and implicit type casts

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Definition of Generic Types

• Type variable = “placeholder” for an unknown type
• Similar to a type, but not really a type
• Several restrictions
• Not allowed in newexpressions, cannot be derived from,

no class literal

i nt er f ace Col l ect i on<A> { publ i c voi d add ( A x) ; publ i c I t er at or <A> i t er at or ( ) ; } cl ass Li nkedLi st <A> i m pl em ent s Col l ect i on<A> { pr ot ect ed cl ass Node { A el t ; Node next = nul l ; Node ( A el t ) { t hi s. el t = el t ; } } . . . }

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Type Parameter Bounds

publ i c cl ass Tr eeM ap<K ext ends Com par abl e <K>, V> { pr i vat e st at i c cl ass Ent r y<K, V> { . . . } … pr i vat e Ent r y<K, V> get Ent r y( K key) { … whi l e ( p ! = nul l ) { i nt cm p = k. com par eTo ( p. key) ; … } … } … } publ i c i nt er f ace Com par abl e<T> { publ i c i nt com par eTo( T ar g) ; }

• Bounds = supertype of a type variable
• Purpose: make available non-static methods of a type variable
• Limitations: gives no access to constructors or static methods

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Using Generic Types

• Can use generic types with or without

type argument specification

• With concrete type arguments
• Concrete instantiation
• Without type arguments
• Raw type
• With wildcard arguments
• Wildcard instantiation

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Concrete Instantiation

• Type argument is a concrete type
• More expressive type information
• Enables compile-time type checks

voi d pr i nt Di r ect or yNam es( Col l ect i on<Fi l e> f i l es) { f or ( Fi l e f : f i l es) i f ( f . i sDi r ect or y( ) ) Syst em . out . pr i nt l n( f ) ; } Li st <Fi l e> t ar get Di r = new Li nkedLi st <Fi l e>( ) ; ... fill list with Fi l e objects ... pr i nt Di r ect or yNam es( t ar get Di r ) ;

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Raw Type

• No type argument specified
• Permitted for compatibility reasons
• Permits mix of non-generic (legacy) code with generic code

voi d pr i nt Di r ect or yNam es( Col l ect i on f i l es) { f or ( I t er at or i t = f i l es. i t er at or ( ) ; i t . hasNext ( ) ; ) { Fi l e f = ( Fi l e) i t . next ( ) ; i f ( f . i sDi r ect or y( ) ) Syst em . out . pr i nt l n( f ) ; } } Li st <Fi l e> t ar get Di r = new Li nkedLi st <Fi l e>( ) ; ... fill list with Fi l e objects ... pr i nt Di r ect or yNam es( t ar get Di r ) ;

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Wildcard Instantiation

• Type argument is a wildcard
• A wildcard stands for a family of types
• Bounded and unbounded wildcards supported

voi d pr i nt El em ent s( Col l ect i on<?> c) { f or ( O bj ect e : c) Syst em . out . pr i nt l n( e) ; } Col l ect i on <Fi l e> t ar get Di r = new Li nkedLi st <Fi l e>( ) ; ... fill list with Fi l e objects ... pr i nt El em ent s( t ar get Di r ) ;

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Wildcards

• A wildcard denotes a representative

from a family of types

• Unbounded wildcard

?

• All types
• Lower-bound wildcard

? extends supertype

• All types that are subtypes of supertype
• Upper-bound wildcard

? super subtype

• All types that are supertypes of subtype

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Example of a Bounded Wildcard

• Consider a method
• That draws objects from a class hierarchy of shapes
• Method cannot draw a list of circles
• Because list<circle> is not a subtype of list<shape>

voi d dr awAl l ( Li st <Shape> shapes) { f or ( Shape s : shapes)

• s. dr aw

( ) ; }

Naïve approach

Li st <Ci r cl e> ci r cl es = . . . ; dr awAl l ( ci r cl es) ;

Incompatible Argument Type

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Trying to Fix It…

• Try a wildcard instantiation
• Compiler needs more information

about “unknown” type

voi d dr awAl l ( Li st <?> shapes) { f or ( Shape s : shapes)

• s. dr aw

( ) ; }

Wildcarded version

Error: ? Does Not Have a Draw Method

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Solution: Upper Bound Wildcard

• "? Ext ends shape" stands for “any subtype of shape”
• Shape is the upper bound of the bounded wildcard
• Col l ect i on<? Ext ends shape> stands for

“collection of any kind of shapes”

• Is the supertype of all collections that contain shapes

(or subtypes thereof)

Li st <Ci r cl e> ci r cl es = . . . ; dr awAl l ( ci r cl es) ;

fine

voi d dr awAl l ( Li st <? ext ends Shape > shapes) { f or ( Shape s : shapes)

• s. dr aw

( ) ; }

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Generic Methods

• Defining a generic method

cl ass Ut i l i t i es { publ i c st at i c <A ext ends Com par abl e <A>> A m ax( I t er abl e<A> c) { A r esul t = nul l ; f or ( A a : c) { i f ( r esul t == nul l | | r esul t . com par eTo( a) < 0) r esul t = a; } } }

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Type Inference

• Invoking a generic method
• No special invocation syntax
• Type arguments are inferred from actual arguments

(! type inference)

publ i c st at i c voi d m ai n ( St r i ng[ ] ar gs) { Li nkedLi st <Byt e> byt eLi st = new Li nkedLi st <Byt e>( ) ; . . . Byt e y = Ut i l i t i es. m ax ( byt eLi st ) ; }

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Compilation Model

• Code specialization
• New representation for every instantiation of a

generic type or method

• e.g., Different code for a list of strings and list of integers
• Downside: code bloat
• Code sharing
• Only one representation of a generic type or method
• All concrete instantiations are mapped to this representation
• Implicit type checks and type conversions where needed
• Downside: no primitive types

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Type Erasure—Class Definition

• Generic type

cl ass Li nkedLi st <A> i m pl em ent s Col l ect i on<A> { pr ot ect ed cl ass Node { A el t ; Node next = nul l ; Node ( A el t ) { t hi s. el t = el t ; } } publ i c voi d add ( A el t ) { . . . } . . . } cl ass Li nkedLi st i m pl em ent s Col l ect i on { pr ot ect ed cl ass Node { Obj ect el t ; Node next = nul l ; Node ( Obj ect el t ) { t hi s. el t = el t ; } } publ i c voi d add ( Obj ect el t ) { . . . } . . . }

• After type erasure

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Type Erasure—Usage Context

f i nal cl ass Test { publ i c st at i c voi d m ai n ( St r i ng[ ] ar gs) { Li nkedLi st <St r i ng> ys = new Li nkedLi st <St r i ng> ( ) ;

• ys. add( " zer o" ) ; ys. add( " one" ) ;

St r i ng y = ys. i t er at or ( ) . next ( ) ; } } f i nal cl ass Test { publ i c st at i c voi d m ai n ( St r i ng[ ] ar gs) { Li nkedLi st ys = new Li nkedLi st ( ) ;

• ys. add( " zer o" ) ; ys. add( " one" ) ;

St r i ng y = ( St r i ng)ys. i t er at or ( ) . next ( ) ; } }

Additional Cast

• Generic type
• After type erasure

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Agenda

Language Features Usage

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Categories of Usage

• Using predefined generic types/methods
• e.g., using collections such as Li st <Dat e>
• Requires relatively little learning effort
• Provide concrete type arguments to generic types
• Rely on type inference when calling generic methods
• Designing and defining generic types/methods
• e.g., implementing a generic Li nkedLi st <T> class
• Requires sound understanding of generics

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Using a Predefined Generic Type

• Demonstrates a key benefit of generics
• Source code is more readable and precise

than without generics

publ i c st at i c Col l ect i on<St r i ng> r em

• veDi r ect or y( Col l ect i on<Fi l e> absol ut eFi l es,

St r i ng di r ect or yToBeRem

• vedFr om

Pat h) { Col l ect i on<St r i ng> r el at i veFi l eNam es = new HashSet <St r i ng> ( ) ; I t er at or <Fi l e> i t er = absol ut eFi l es. i t er at or ( ) ; whi l e ( i t er . hasNext ( ) ) { r el at i veFi l eNam

• es. add(

Fi l eUt i l i t y. r el at i vePat h( i t er . next ( ) . get Pat h( ) , di r ect or yToBeRem

• vedFr om

Pat h) ) ; } r et ur n r el at i veFi l eNam es; }

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Same Code Without Generics

• It’s difficult to tell what the collections contain

publ i c st at i c Col l ect i on r em

• veDi r ect or y( Col l ect i on absol ut eFi l es,

St r i ng di r ect or yToBeRem

• vedFr om

Pat h) { Col l ect i on r el at i veFi l eNam es = new HashSet ( ) ; I t er at or i t er = absol ut eFi l es. i t er at or ( ) ; whi l e ( i t er . hasNext ( ) ) { r el at i veFi l eNam

• es. add(

Fi l eUt i l i t y. r el at i vePat h( ( ( Fi l e) i t er . next ( ) ) . get Pat h( ) , di r ect or yToBeRem

• vedFr om

Pat h) ) ; } r et ur n r el at i veFi l eNam es; }

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Designing and Defining a Generic Type

• Case study
• Implement a class that

holds two elements

• f different types
• Constructors
• Getters and setter
• Equality and hashing
• Comparability
• Cloning
• Value semantics

f i nal cl ass Pai r <X, Y> { pr i vat e X f i r st ; pr i vat e Y second; . . . }

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Getters and Setters

• Add setters that take the new value

from another pair

f i nal cl ass Pai r <X, Y> { . . . publ i c X get Fi r st ( ) { r et ur n f i r st ; } publ i c Y get Second( ) { r et ur n second; } publ i c voi d set Fi r st ( X x) { f i r st = x; } publ i c voi d set Second( Y y) { second = y; } }

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Constructors—First Naïve Approach

f i nal cl ass Pai r <X, Y> { . . . publ i c Pai r ( X x, Y y) { f i r st = x; second = y; } publ i c Pai r ( ) { f i r st = nul l ; second = nul l ; } publ i c Pai r ( Pai r ot her ) { i f ( ot her == nul l ) { f i r st = nul l ; second = nul l ; } el se { f i r st = ot her . f i r st ; second = ot her . second; } } }

er r or : i ncom pat i bl e t ypes

Obj ect Y

• Does not compile

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Constructors—Tentative Fix

f i nal cl ass Pai r <X, Y> { . . . publ i c Pai r ( X x, Y y) { f i r st = x; second = y; } publ i c Pai r ( ) { f i r st = nul l ; second = nul l ; } publ i c Pai r ( Pai r ot her ) { i f ( ot her == nul l ) { f i r st = nul l ; second = nul l ; } el se { f i r st = ( X) ot her . f i r st ; second = ( Y) ot her . second; } } }

war ni ng: unchecked cast

Y Y

• Insert cast

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Ignoring Unchecked Warnings

• What happens if we ignore the warnings?
• Error detection at runtime
• Long after debatable assigment in constructor

Pai r <St r i ng, I nt eger> p1 = new Pai r <St r i ng, I nt eger >( " Bobby" , 10) ; Pai r <St r i ng, Dat e > p2 = new Pai r <St r i ng, Dat e>( p1) ; . . . Dat e bobbysBi r t hday = p2. get Second( ) ; Cl assCast Except i on

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Constructors—What’s the Goal?

• A constructor that takes the same type of pair?
• Allow creation of one pair from another pair of

a different type, but with compatible members?

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Same Type Argument

f i nal cl ass Pai r <X, Y> { … publ i c Pai r ( Pai r <X, Y> ot her ) { i f ( ot her == nul l ) { f i r st = nul l ; second = nul l ; } el se { f i r st = ot her . f i r st ; second = ot her . second; } } } Pai r <St r i ng, I nt eger> p1 = new Pai r <St r i ng, I nt eger >( " Bobby" , 10) ; Pai r <St r i ng, Dat e > p2 = new Pai r <St r i ng, Dat e>( p1) ; . . . Dat e bobbysBi r t hday = p2. get Second( ) ;

er r or : no m at chi ng ct or

• Accepts same

type pair

• Rejects alien pair

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Downside

• Implementation also rejects useful cases

Pai r <St r i ng, I nt eger> p1 = new Pai r <St r i ng, I nt eger >( " pl anet ear t h" , 10000) ; Pai r <St r i ng, Num ber> p2 = new Pai r <St r i ng, Num ber >( p1) ; l ong t hePl anet sAge = p2. get Second( ) . l ongVal ue( ) ;

er r or : no m at chi ng ct or

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Compatible Type Argument

f i nal cl ass Pai r <X, Y> { … publ i c <A ext ends X, B ext ends Y > Pai r ( Pai r <A, B> ot her ) { i f ( ot her == nul l ) { f i r st = nul l ; second = nul l ; } el se { f i r st = ot her . f i r st ; second = ot her . second; } } } Pai r <St r i ng, I nt eger> p1 = new Pai r <St r i ng, I nt eger >( " pl anet ear t h" , 10000) ; Pai r <St r i ng, Num ber> p2 = new Pai r <St r i ng, Num ber >( p1) ; l ong t hePl anet sAge = p2. get Second( ) . l ongVal ue( ) ; now f i ne

• Accepts

compatible pair

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Equivalent Implementation

• Permits the same invocations

f i nal cl ass Pai r <X, Y> { … publ i c Pai r ( Pai r <? ext ends X, ? ext ends Y> ot her ) { i f ( ot her == nul l ) { f i r st = nul l ; second = nul l ; } el se { f i r st = ot her . f i r st ; second = ot her . second; } } } Pai r <St r i ng, I nt eger> p1 = new Pai r <St r i ng, I nt eger >( " pl anet ear t h" , 10000) ; Pai r <St r i ng, Num ber> p2 = new Pai r <St r i ng, Num ber >( p1) ; l ong t hePl anet sAge = p2. get Second( ) . l ongVal ue( ) ; f i ne

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Equivalent Implementation

• Permit same invocations
• Difference lies in access to wildcard argument
• Not all methods of wildcard pair can be called
• Doesn’t matter here, since we do not invoke any

methods

f i nal cl ass Pai r <X, Y> { … publ i c Pai r ( Pai r <? ext ends X, ? ext ends Y> ot her ) { … } } f i nal cl ass Pai r <X, Y> { … publ i c <A ext ends X, B ext ends Y > Pai r ( Pai r <A, B> ot her ) { … } }

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Wildcard Access Rules

• Disallowed
• Invoking methods that take arguments of

“unknown” type

• We do not know which type of elements a l i st <?> Contains
• Hence we cannot add anything, except the typeless null
• Allowed:
• Invoking methods that return objects of “unknown” type
• After all it’s an obj ect

Pai r <?, ?> p = new Pai r <Dat e, Dat e>( ) ;

• p. set Fi r st ( " xm

as" ) ;

• p. set Fi r st ( nul l ) ;

O bj ect

• = p. get Fi r st ( ) ;

Error

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Value Semantics

• Alternative semantics
• Hold copies of constructor arguments,

instead of just references

f i nal cl ass Val uePai r <X, Y> { publ i c Val uePai r ( X x, Y y) { f i r st = ( x==nul l ) ?nul l : cl oneObj ect( x) ; second = ( y==nul l ) ?nul l : cl oneObj ect( y) ) ; }

pr i vat e st at i c <T> T cl oneO bj ect ( T t ) { t r y { r et ur n ( T) t . get Cl ass( ) . get M et hod( " cl one" , nul l ) . i nvoke( t , nul l ) ; } cat ch ( Except i on e) { r et ur n nul l ; } }

}

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Cloning

• Unchecked cast cannot be avoided
• Use @

Suppr essW ar ni ngs annotation

f i nal cl ass Val uePai r <X, Y> { pr i vat e st at i c <T> T cl oneObj ect ( T t ) { … r et ur n ( T) t . get Cl ass( ) . get M et hod( " cl one" , nul l ) . i nvoke( t , nul l ) ; … } } war ni ng: unchecked cast f i nal cl ass Val uePai r <X, Y> { @ Suppr essW ar ni ngs( " unchecked" ) pr i vat e st at i c <T> T cl oneObj ect ( T t ) { … r et ur n ( T) t . get Cl ass( ) . get M et hod( " cl one" , nul l ) . i nvoke( t , nul l ) ; … } }

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Default Constructed Value Pair

• Default construction of a value pair is a problem
• Generic construction not permitted
• Generic construction only possible via reflection
• Typically by a factory method

f i nal cl ass Val uePai r <X , Y> { … publ i c Val uePai r ( ) { f i r st = new X( ); second = new Y( ); } … }

er r or : t ype var i abl e not per m i t t ed i n new expr essi on

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Generic Object Creation

• Static helper method that produces an object
• If information about requested type of object

is provided

f i nal cl ass Val uePai r <X, Y> { publ i c Val uePai r ( ) { f i r st = m akeObj ect( X. cl ass) ; second = m akeObj ect( Y. cl ass) ; } pr i vat e st at i c <T> T m akeObj ect ( Cl ass<T> cl azz){ t r y { r et ur n cl azz. get Const r uct or ( new Cl ass[ 0] ) . newI nst ance( new O bj ect [ 0] ) ; } cat ch ( Except i on e) { r et ur n nul l ; } } }

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Class Cl ass<T>

• Class Cl ass is generic
• Type parameter is the type that the Cl ass object represents
• e.g., St r i ng. cl ass is of type Cl ass<St r i ng>
• Used here to ensure consistency
• To create a T object a Cl ass<T> object must be provided
• Nonsense will not compile

pr i vat e st at i c <T> T m akeO bj ect ( Cl ass<T> cl azz) { … } Dat e dat e = m akeO bj ect ( St r i ng. cl ass ) ;

er r or

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No Class Literals for Type Variables

• Default construction is still a problem
• We cannot call the helper method
• Type variables have no class literal

f i nal cl ass Val uePai r <X, Y> { publ i c Val uePai r ( ) { f i r st = m akeObj ect( X. cl ass) ; second = m akeObj ect( Y. cl ass) ; }

pr i vat e st at i c <T> T m akeO bj ect ( Cl ass<T> cl azz) { … }

}

er r or : cl ass l i t er al does not exi st

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Provide Class Objects

• Special purpose constructor
• Takes the required class objects as arguments
• The constructor would be used like this
• Note the highly redundant repetition of type information

f i nal cl ass Val uePai r <X, Y> { publ i c Val uePai r ( Cl ass<X> xType, Cl ass<Y> yType) { f i r st = m akeO bj ect ( xType) ; second = m akeO bj ect ( yType) ; }

pr i vat e st at i c <T> T m akeO bj ect ( Cl ass<T> cl azz) { … }

} Val uePai r <St r i ng, Dat e> pai r = new Val uePai r <St r i ng, Dat e>( St r i ng. cl ass , Dat e. cl ass) ;

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Factory Method for Value Pair

• Factory method = static method that produces an object
• Use instead of a constructor
• Factory method is more convenient to use
• Type information is automatically inferred

f i nal cl ass Val uePai r <X, Y> { publ i c st at i c <U, V> Val uePai r <U, V> m akeDef aul t Pai r( Cl ass<U> uType, Cl ass<V> vType) { r et ur n new Val uePai r <U, V>( m akeO bj ect ( uType) , m akeO bj ect ( vType) ) ; } pr i vat e st at i c <T> T m akeO bj ect ( Cl ass<T> cl azz) { … } } Val uePai r <St r i ng, Dat e> pai r = Val uePai r . m akeDef aul t Pai r ( St r i ng. cl ass , Dat e. cl ass ) ;

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Comparison

• Use bounds to require that members be comparable

f i nal cl ass Pai r <X, Y> i m pl em ent s Com par abl e<Pai r <X, Y>> { … publ i c i nt com par eTo( Pai r <X, Y> ot her ) { . . . f i r st . com par eTo( ot her . f i r st ) . . . . . . second. com par eTo( ot her . second) . . . } } er r or : cannot f i nd com par eTo m et hod f i nal cl ass Pai r <X ext ends Com par abl e<X> , Y ext ends Com par abl e<Y> > i m pl em ent s Com par abl e<Pai r <X, Y>> { … publ i c i nt com par eTo( Pai r <X, Y> ot her ) { . . . f i r st . com par eTo( ot her . f i r st ) . . . . . . second. com par eTo( ot her . second) . . . } } now f i ne

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Comparison

• The proposed implementation does not

permit pairs of “incomparable” types

• Such as Pai r <Num

ber , Num ber >

• Two flavours of parameterized pair class

would be ideal

f i nal cl ass Pai r <X, Y> { . . . }

er r or : i dent i cal t ype er asur e

f i nal cl ass Pai r <X ext ends Com par abl e<X>, Y ext ends Com par abl e<Y> > i m pl em ent s Com par abl e<Pai r <X, Y>> { . . . }

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Multi-Class Solution

• Defining separate classes
• Leads to an inflation of classes

f i nal cl ass Com par abl ePai r<X ext ends Com par abl e<X>, Y ext ends Com par abl e<Y>> i m pl em ent s Com par abl e<Com par abl ePai r <X, Y>> { publ i c i nt com par eTo( Com par abl ePai r <X, Y> ot her ) { . . . f i r st . com par eTo( ot her . f i r st ) . . . . . . second. com par eTo( ot her . second) . . . } } f i nal cl ass Pai r <X, Y> { . . . }

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Single-Class Solution

• Requires cast
• Use @

Suppr essW ar ni ngs annotation

f i nal cl ass Pai r <X, Y> i m pl em ent s Com par abl e<Pai r <X, Y>> { publ i c i nt com par eTo( Pai r <X, Y> ot her ) { . . . ( ( Com par abl e<X>)f i r st ) . com par eTo( ot her . f i r st ) . . . . . . ( ( Com par abl e<Y>)second) . com par eTo( ot her . second) . . . } } war ni ng: unchecked cast f i nal cl ass Pai r <X, Y> i m pl em ent s Com par abl e<Pai r <X, Y>> { @ Suppr essW ar ni ngs( " unchecked" ) publ i c i nt com par eTo( Pai r <X, Y> ot her ) { . . . ( ( Com par abl e<X>) f i r st ) . com par eTo( ot her . f i r st ) . . . . . . ( ( Com par abl e<Y>) second) . com par eTo( ot her . second) . . . } }

2005 JavaOneSM Conference | Session TS-5627 | 51

Summary

• Java platform 5.0 has language features for

definition and use of generic types and methods

• Type parameters and arguments, wildcards, bounds…
• Using predefined generic types is easy
• Designing and implementing generic APIs

is challenging

• Requires understanding of compilation model,

various restrictions, and options…

2005 JavaOneSM Conference | Session TS-5627 | 52

For More Information

• Generics in the Java Programming Language
• A tutorial by Gilad Bracha, July 2004
• http://java.sun.com/j2se/1.5/pdf/generics-tutorial.pdf
• Java Language Specification, 3rd Edition
• By Gosling, Joy, Steele, Bracha, May 2005
• http://java.sun.com/docs/books/jls
• Java Generics FAQ
• A FAQ by Angelika Langer
• http://www.AngelikaLanger.com/GenericsFAQ/JavaGenericsFAQ.html
• More links...
• http://www.AngelikaLanger.com/Resources/Links/

JavaGenerics.htm

2005 JavaOneSM Conference | Session TS-5627 | 53

Q&A

Angelika Langer

2005 JavaOneSM Conference | Session TS-5627 | 54

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55 2005 JavaOneSM Conference | Session TS-5627

Generics Written in the Java™ Programming Language with Parameterized Types in Java Platform 5.0

Angelika Langer Trainer/Consultant www.AngelikaLanger.com

TS-5627