Java Reference
In-Depth Information
sion of
Gen
was created. Thus, there is really only one version of
Gen
that actually ex-
ists in your program. The process of removing generic type information is called
erasure
,
which is discussed later in this chapter.
The next line assigns to
iOb
a reference to an instance of an
Integer
version of the
Gen
class.
Notice that when the
Gen
constructor is called, the type argument
Integer
is also specified.
This is because the type of the object (in this case
iOb
) to which the reference is being as-
signed is of type
Gen<Integer>
. Thus, the reference returned by
new
must also be of type
Gen<Integer>
. If it isn't, a compile-time error will result. For example, the following as-
signment will cause a compile-time error:
Because
iOb
is of type
Gen<Integer>
, it can't be used to refer to an object of
Gen<Double>
. This type of checking is one of the main benefits of generics because it en-
sures type safety.
As the comments in the program state, the assignment
makes use of autoboxing to encapsulate the value 88, which is an
int
, into an
Integer
. This
works because
Gen<Integer>
creates a constructor that takes an
Integer
argument. Be-
cause an
Integer
is expected, Java will automatically box 88 inside one. Of course, the as-
signment could also have been written explicitly, like this:
However, there would be no benefit to using this version.
The program then displays the type of
ob
within
iOb
, which is
Integer
. Next, the pro-
gram obtains the value of
ob
by use of the following line:
Because the return type of
getob( )
is
T
, which was replaced by
Integer
when
iOb
was
declared, the return type of
getob( )
is also
Integer
, which auto-unboxes into
int
when as-
