The Java Language Specification, Third Edition

TYPES, VALUES, AND VARIABLES Subtyping among Class and Interface Types 4.10.2
4.10 Subtyping
The subtype and supertype relations are binary relations on types. The supertypes
of a type are obtained by reflexive and transitive closure over the direct supertype
relation, written S > 1 T, which is defined by rules given later in this section. We
write S :> Tto indicate that the supertype relation holds between S and T. S is a
proper supertype of T, written S > T,
if S :> T and S ≠ T.
The subtypes of a type T are all types U such that T is a supertype of U, and the
null type. We write T 1 int
int > 1 char
int > 1 short
short > 1 byte
4.10.2 Subtyping among Class and Interface Types
DRAFT
Let C be a type declaration (§4.12.6, §8.1, §9.1) with zero or more type parameters
(§4.4) F1, ..., Fn which have corresponding bounds B1, ..., Bn. That type declaration
defines a set of parameterized types (§4.5) Cı, where each argument
type Ti ranges over all types that are subtypes of all types listed in the
corresponding bound. That is, for each bound type Si in Bi, Ti is a subtype of Si[
F1 := T1, ..., Fn := Tn].
Given a type declaration for C, the direct supertypes of the parameterized
type (§4.5) C are all of the following:
• the direct superclasses of C.
• the direct superinterfaces of C.
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