Java Reference
In-Depth Information
Notice that its parameter,
o
, is of type
T
. This means that the actual type of
o
is determined
by the type passed to
T
when a
Gen
object is created. Also, because both the parameter
o
and the member variable
ob
are of type
T
, they will both be of the same actual type when
a
Gen
object is created.
The type parameter
T
can also be used to specify the return type of method, as is the case
with the
getob( )
method, shown here:
Because
ob
is also of type
T
, its type is compatible with the return type specified by
getob(
)
.
The
showType( )
method displays the type of
T
. It does this by calling
getName( )
on
the
Class
object returned by the call to
getClass( )
on
ob
. We haven't used this feature
defines the method
getClass( )
. Thus,
getClass( )
is a member of all class types. It returns
a
Class
object that corresponds to the class type of the object on which it is called.
Class
is
a class defined within
java.lang
that encapsulates information about a class.
Class
defines
several methods that can be used to obtain information about a class at run time. Among
these is the
getName( )
method, which returns a string representation of the class name.
The
GenDemo
class demonstrates the generic
Gen
class. It first creates a version of
Gen
for integers, as shown here:
Look carefully at this declaration. First, notice that the type
Integer
is specified within the
angle brackets after
Gen
. In this case,
Integer
is a
type argument
that is passed to
Gen
's
type parameter,
T
. This effectively creates a version of
Gen
in which all references to
T
are translated into references to
Integer
. Thus, for this declaration,
ob
is of type
Integer
,
and the return type of
getob( )
is of type
Integer
.
Before moving on, it's necessary to state that the Java compiler does not actually create
different versions of
Gen
, or of any other generic class. Although it's helpful to think in
these terms, it is not what actually happens. Instead, the compiler removes all generic type
information, substituting the necessary casts, to make your code
behave as if
a specific ver-
