Java Reference
In-Depth Information
16.9. Generic Type Inspection
As you saw in
Figure 16-1
on page
400
, there are a number of interfaces
to represent the different kinds of types that can exist in your programs.
So far we have focussed on
Class
objects and
Member
objects since they
are the more commonly used reflection objects, and we have only men-
tioned the other kinds of
Type
objects in passing. This section looks at
those other
Type
interfaces in more detail.
16.9.1. Type Variables
The
GenericDeclaration
interface, which is implemented by
Class
,
Method
,
and
Constructor
, has the single method
getTypeParameters
, which returns
an array of
TypeVariable
objects. The
TypeVariable
interface is itself a gen-
eric interface, declared as
interface TypeVariable<D extends GenericDeclaration>
So, for example, the
TypeVariable
objects
Method.getTypeParameter
s returns
would be of type
TypeVariable<Method>
.
Each type variable has a name returned by
getName
. It also has one or
more upper bounds, obtained as a
Type[]
from
getBounds
. Recall that if
there is no explicit upper bound then the upper bound is
Object
.
The
getGenericDeclaration
method returns the
Type
object for the
Gen-
ericDeclaration
in which the
TypeVariable
was declared. For example,
the expression
TypeVariable.class.getTypeParameters()[0]
would yield a
TypeVariable
object that represents
D
in the declaration above. If you in-
voked
getGenericDeclaration
on this object, it would return the
Class
ob-
ject for the
TypeVariable
interface. More generally, for any
GenericDeclar-
ation
object
g
with at least one type parameter,
g.getTypeParameters()[i].getGenericDeclaration() == g
