Adding Wildcards to the Java Programming Language

Source: bracha.org
Topic: Java Programming

Short Desciption:
For some time it has been clear that the Java programming. language was going to be extended ... known as genericity or generics in the Java programming ...

 

Content Inside:
Adding Wildcards to the Java Programming LanguagePage 1Adding Wildcards to the Java Programming LanguageMads TorgersenChristian Plesner HansenErik Ernst andPeter von der AheUniversity of Aarhusbogade 34DK8200 rhus N Denmark{madstplesnereernstpahe}@daimi.au.d kGilad Bracha andNeal GafterSun Microsystems Inc.4150 Network CycleSanta Clara CA 95054 USA{Gilad.BrachaNeal.Gafter}@sun.comABSTRA CTThis paper describes wildcards a new language constructdesigned to increase the flexibility of objectoriented typesystems with parameterized classes. Based on the notion ofusesite variance wildcards provide a type safe abstractionover different instantiations of parameterized classes by using ? to denote unspecified type arguments. Thus theyessentially unify the distinct families of classes often introduced by parametric polymorphism. Wildcards are implemented as part of the upcoming addition of generics to theJavaTMprogramming language and will thus be deployedworldwide as part of the reference implementation of theJava compiler javac available from Sun Microsystems Inc.By providing a richer type system wildcards allow for an improved type inference scheme for polymorphic method calls.Moreover by means of a novel notion of wildcard capturepolymorphic methods can be used to give symbolic namesto unspecified types in a manner similar to the open construct known from existential types. Wildcards show up innumerous places in the Java Platform APIs of the upcomingrelease and some of the examples in this paper are takenfrom these APIs.Categories and Subject DescriptorsD.3.3 Language Constructs and Features]: Classes andobjects Data types and structures PolymorphismKeywordsWildcards genericity parameterized types1. INTRODUCTIONParametric polymorphism is wellknown from functional languages such as Standard ML 22] and over the past twoPermission to make digital or hard copies of all or part of this work forpersonal or classroom use is granted without fee provided that copies arenot made or d ...

 

 

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