The Java Language Specification, Third Edition

4.4 Type Variables TYPES, VALUES, AND VARIABLES
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Type variables have an optional bound, T & I 1 ... I n. The bound consists of
either a type variable, or a class or interface type T possibly followed by further
interface types I 1 , ..., I n. If no bound is given for a type variable, Object is
assumed. It is a compile-time error if any of the types I 1 ... I n is a class type or
type variable. The erasures (§4.6) of all constituent types of a bound must be pairwise
different, or a compile-time error occurs. The order of types in a bound is
only significant in that the erasure of a type variable is determined by the first type
in its bound, and that a class type or type variable may only appear in the first
position.
A type variable may not at the same time be a subtype of two interface types
which are different parameterizations of the same generic interface.
See section §6.3 for the rules defining the scope of type variables.
The members of a type variable X with bound T & I 1 ... I n are the members
of the intersection type (§4.9) T & I 1 ... I n appearing at the point where the type
variable is declared.
DISCUSSION
The following example illustrates what members a type variable has.
package TypeVarMembers;
class C {
void mCDefault() {}
public void mCPublic() {}
private void mCPrivate() {}
protected void mCProtected() {}
}
class CT extends C implements I {}
interface I {
void mI(); }
void test(T t) {
t.mI(); // OK
t.mCDefault(); // OK
t.mCPublic(); // OK
t.mCPrivate(); // compile-time error
t.mCProtected(); // OK
}
}
The type variable T has the same members as the intersection type C & I, which in
turn has the same members as the empty class CT, defined in the same scope with equivalent
supertypes. The members of an interface are always public, and therefore always
inherited (unless overridden). Hence mI is a member of CT and of T. Among the members
of C, all but mCPrivate are inherited by CT, and are therefore members of both CT and T.
DRAFT