Adding Wildcards to the Java Programming Language

Source: www.bracha.org
Topic: Java Programming

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Adding Wildcards to the Java Programming Language Mads Torgersen Christian Plesner Hansen Erik Ernst, and Peter von der Ah´ e University of Aarhus Åbogade 34 DK-8200 ÅrhusN ...

 

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Adding Wildcards to the Java Programming Language Mads Torgersen Christian Plesner Hansen Erik Ernst, and Peter von der Ah´ e University of Aarhus Åbogade 34 DK-8200 ÅrhusN, Denmark { madst,plesner,eernst,pahe } @daimi.au.dk Gilad Brachaand Neal Gafter Sun Microsystems, Inc. 4150 NetworkCycle Santa Clara, CA 95054, USA { Gilad.Bracha,Neal.Gafter } @sun.com ABSTRACT This paper describeswildcards, anew language construct designed to increase the flexibility of object-oriented type systems with parameterized classes. Based on the notion of use-site variance, wildcardsprovidea type safe abstraction overdierent instantiations of parameterized classes, by using?      to denote unspecified type arguments. Thus they essentially unify the distinct families of classes often intro- ducedby parametric polymorphism. Wildcardsareimple- mentedaspartof the upcoming addition of generics to the JavaTM programming language, and will thus be deployed world-wide as part of the reference implementation of the Java compilerjavac available from Sun Microsystems, Inc. By providing a richer type system, wildcardsallow for an improved       type inference scheme for polymorphic method calls. Moreover, by means of a novel notion of wildcard capture, polymorphic methods can be used to give symbolic names to unspecified types, in a manner similar to the"open"con- structknownfrom existential types. Wildcardsshowup in numerous places in the Java Platform APIsofthe upcoming release, and some of the examples in this paper are taken from these APIs. Categories and Subject Descriptors D.3.3[Language Constructs and Features]: Classes and objects, Data types and structures, Polymorphism Keywords Wildcards, genericity, parameterized types 1. INTRODUCTION Parametric polymorphism is well-known from functional lan- guagessuchas Standard ML[22], and over the past two Permissi ...

 

 

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