Towards a Java Subtyping Operad
Moez A. AbdelGawad · 2017
The subtyping relation in Java exhibits self-similarity. The self-similarity in Java subtyping is interesting and intricate due to the existence of wildcard types and, accordingly, the existence of three subtyping rules for generic types: covariant subtyping, contravariant subtyping and invariant subtyping. Supporting bounded type variables adds to the complexity of the subtyping relation in Java and other similar generic nominally-typed OO languages such as C# and Scala.