Article

Adding wildcards to the Java programming language

Authors:

Mads Torgersen,

Christian Plesner Hansen,

Peter von der Ahé,

Neal GafterAuthors Info & Claims

SAC '04: Proceedings of the 2004 ACM symposium on Applied computing

Pages 1289 - 1296

https://doi.org/10.1145/967900.968162

Published: 14 March 2004 Publication History

Abstract

This paper describes wildcards, a new language construct designed to increase the flexibility of object-oriented type systems with parameterized classes. Based on the notion of use-site variance, wildcards provide a type safe abstraction over different instantiations of parameterized classes, by using '?' to denote unspecified type arguments. Thus they essentially unify the distinct families of classes often introduced by parametric polymorphism. Wildcards are implemented as part of the upcoming addition of generics to the Java™ programming language, and will thus be deployed world-wide as part of the reference implementation of the Java 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 capture, polymorphic methods can be used to give symbolic names to unspecified types, in a manner similar to the "open" construct known from existential types. Wildcards show up in numerous places in the Java Platform APIs of the upcoming release, and some of the examples in this paper are taken from these APIs.

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Cited By

Belyakova JChung BTate RVitek J(2024)Decidable Subtyping of Existential Types for JuliaProceedings of the ACM on Programming Languages10.1145/36564218:PLDI(1091-1114)Online publication date: 20-Jun-2024
https://dl.acm.org/doi/10.1145/3656421
Soha PPataki N(2022)Instantiation of Java GenericsActa Cybernetica10.14232/actacyb.28407325:4(897-908)Online publication date: 21-Jan-2022
https://doi.org/10.14232/actacyb.284073
Kumari NKumar R(2021)Type Inference in Java: Characteristics and LimitationsCybernetics, Cognition and Machine Learning Applications10.1007/978-981-33-6691-6_15(131-137)Online publication date: 31-Mar-2021
https://doi.org/10.1007/978-981-33-6691-6_15
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Index Terms

Adding wildcards to the Java programming language
1. Software and its engineering
  1. Software notations and tools
    1. General programming languages
      1. Language features

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cover image ACM Conferences

SAC '04: Proceedings of the 2004 ACM symposium on Applied computing

March 2004

1733 pages

ISBN:1581138121

DOI:10.1145/967900

Conference Chair:
Hisham M. Haddad
Kennesaw State University
,
Program Chairs:
Andrea Omicini
Università degli Studi di Bologna a Cesena
,
Roger L. Wainwright
University of Tulsa
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Lorie M. Liebrock
New Mexico Institute of Mining and Technology

Copyright © 2004 ACM.

Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. Copyrights for components of this work owned by others than ACM must be honored. Abstracting with credit is permitted. To copy otherwise, or republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. Request permissions from [email protected]

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Published: 14 March 2004

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Cited By

Belyakova JChung BTate RVitek J(2024)Decidable Subtyping of Existential Types for JuliaProceedings of the ACM on Programming Languages10.1145/36564218:PLDI(1091-1114)Online publication date: 20-Jun-2024
https://dl.acm.org/doi/10.1145/3656421
Soha PPataki N(2022)Instantiation of Java GenericsActa Cybernetica10.14232/actacyb.28407325:4(897-908)Online publication date: 21-Jan-2022
https://doi.org/10.14232/actacyb.284073
Kumari NKumar R(2021)Type Inference in Java: Characteristics and LimitationsCybernetics, Cognition and Machine Learning Applications10.1007/978-981-33-6691-6_15(131-137)Online publication date: 31-Mar-2021
https://doi.org/10.1007/978-981-33-6691-6_15
Zhang YMyers A(2017)Familia: unifying interfaces, type classes, and family polymorphismProceedings of the ACM on Programming Languages10.1145/31338941:OOPSLA(1-31)Online publication date: 12-Oct-2017
https://dl.acm.org/doi/10.1145/3133894
AbdelGawad M(2017)Towards a Java Subtyping OperadProceedings of the 19th Workshop on Formal Techniques for Java-like Programs10.1145/3103111.3104043(1-6)Online publication date: 18-Jun-2017
https://dl.acm.org/doi/10.1145/3103111.3104043
Amin NTate R(2016)Java and scala's type systems are unsound: the existential crisis of null pointersACM SIGPLAN Notices10.1145/3022671.298400451:10(838-848)Online publication date: 19-Oct-2016
https://dl.acm.org/doi/10.1145/3022671.2984004
Amin NTate RVisser ESmaragdakis Y(2016)Java and scala's type systems are unsound: the existential crisis of null pointersProceedings of the 2016 ACM SIGPLAN International Conference on Object-Oriented Programming, Systems, Languages, and Applications10.1145/2983990.2984004(838-848)Online publication date: 19-Oct-2016
https://dl.acm.org/doi/10.1145/2983990.2984004
Ryu S(2016)ThisType for Object-Oriented LanguagesACM Transactions on Programming Languages and Systems10.1145/288839238:3(1-66)Online publication date: 8-Apr-2016
https://dl.acm.org/doi/10.1145/2888392
Zhang YLoring MSalvaneschi GLiskov BMyers A(2015)Lightweight, flexible object-oriented genericsACM SIGPLAN Notices10.1145/2813885.273800850:6(436-445)Online publication date: 3-Jun-2015
https://dl.acm.org/doi/10.1145/2813885.2738008
Zhang YLoring MSalvaneschi GLiskov BMyers AGrove DBlackburn S(2015)Lightweight, flexible object-oriented genericsProceedings of the 36th ACM SIGPLAN Conference on Programming Language Design and Implementation10.1145/2737924.2738008(436-445)Online publication date: 3-Jun-2015
https://dl.acm.org/doi/10.1145/2737924.2738008
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