The Java Language Specification, Third Edition

CONVERSIONS AND PROMOTIONS Casting Conversion 5.5
❖ If S is a final class (§8.1.1), then S must implement T, or a compiletime
error occurs.
◆ If T is a type variable, then this algorithm is applied recursively, using the
upper bound of T in place of T.
◆ If T is an array type, then S must be the class Object, or a compile-time
error occurs.
• If S is an interface type:
◆ If T is an array type, then T must implement S, or a compile-time error
occurs.
◆ If T is a type that is not final (§8.1.1), then if there exists a supertype X of
T, and a supertype Y of S, such that both X and Y are provably distinct parameterized
types, and that the erasures of X and Y are the same, a compile-time
error occurs. Otherwise, the cast is always legal at compile time (because
even if T does not implement S, a subclass of T might).
◆ If T is a type that is final, then:
❖ If S is not a parameterized type or a raw type, then T must implement S,
and the cast is statically known to be correct, or a compile-time error
occurs.
❖ Otherwise, S is either a parameterized type that is an invocation of some
generic type declaration G, or a raw type corresponding to a generic type
declaration G. Then there must exist a supertype X of T, such that X is an
invocation of G, or a compile-time error occurs. Furthermore, if S and X
are provably distinct parameterized types then a compile-time error
occurs.
DRAFT
• If S is a type variable, then this algorithm is applied recursively, using the
upper bound of S in place of S.
• If S is an array type SC[], that is, an array of components of type SC :
◆ If T is a class type, then if T is not Object, then a compile-time error occurs
(because Object is the only class type to which arrays can be assigned).
◆ If T is an interface type, then a compile-time error occurs unless T is the
type java.io.Serializable or the type Cloneable, the only interfaces
implemented by arrays.
◆ If T is a type variable, then:
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