In the forthcoming release of the Java(TM) Platform (JDK1.5), the Java Programming Language will be extended with generics to allow for type parameterization of classes and methods. Generics greatly improve the type safety and clarity of both application code and libraries, such as the Java Platform Collection Framework. Traditionally, however, generic programming introduces a strong separation between similar classes with different type parameters, a situation which in many cases runs contrary to the aims of object-oriented programming.

Wildcards are a novel, type safe language mechanism included in the generic framework of JDK1.5 to enable a full and seamless integration of generic and object-oriented programming. Using '?' as type argument wildcards, List expresses a type that ranges over all different kinds of lists.

In the talk I will describe and motivate the wildcard mechanism, which was designed and implemented at DAIMI in close collaboration with Sun Microsystems