Adding wildcards to the Java programming language

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 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 JavaTM 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” construc...

• Type: Conference
• Year: 2004
• Where: SAC
• Authors: Mads Torgersen, Christian Plesner Hansen, Erik Ernst, Peter von der Ahé, Gilad Bracha, Neal M. Gafter
• Keywords: Applied Computing, Paper Describes Wildcards, Parameterized Classes, SAC 2004, Wildcards