Java Reference
In-Depth Information
removed all type names. This
main
method can be used to test any sub-
class of
SortDouble
that provides a no-arg constructor. You don't have to
write a
main
for each type of sorting algorithmthis generic
main
works for
them all. All you need to do is execute
java TestSort
TestClass
...
for any sorting class (such as
SimpleSortDouble
) and it will be loaded and
run.
Note that whereas
newInstance
returns a
T
,
Class.forName
returns a
Class<?>
. This means that the actual kind of object returned by
newIn-
stance
is unknown, so the cast is needed. You could instead get a class
object of the exact type needed using
asSubclass
, and invoke
newInstance
without needing a cast:
Class<? extends SortDouble> classFor =
Class.forName(name).asSubclass(SortDouble.class);
SortDouble sorter = classFor.newInstance();
In either case, if the named class is not a subtype of
SortDouble
, then a
ClassCastException
will be thrown.
The
newInstance
method can throw a number of different exceptions if
used inappropriately. If the class doesn't have a no-arg constructor, is
an abstract class, or interface, or if the creation fails for some other
reason, you will get an
InstantiationException
. If the class or the no-arg
constructor is not accessible an
IllegalAccessException
is thrown. If the
current security policy disallows the creation of a new object a
Secur-
ityException
is thrown. Finally, creating a new object may require the
class to be initialized so it is also possible for an
ExceptionInInitializer-
Error
to be thrown.
