Java Reference
In-Depth Information
main()
next creates a one-element
Class
array that describes the types of
ob-
jectMethod()
'sparameterlist.Thisarrayisusedinthesubsequentcallto
Class
's
Method getMethod(String name, Class<?>... parameterTypes)
method to return a
Method
object for invoking a
public
method named
ob-
jectMethod
with this parameter list. This method throws
java.lang.NoSuchMethodException
when the named method doesn't exist.
Continuing,
main()
createsan
Object
arraythatspecifiesthedatatobepassedto
themethod'sparameters;inthiscase,thearrayconsistsofasingle
String
argument.It
thenreflectivelyinvokes
objectMethod()
bypassingthisarrayalongwiththeob-
ject reference stored in
x
to the
invoke()
method.
At this point,
main()
shows you how to reflectively invoke a class method. The
(Class<?>[])
and
(Object[])
castsareusedtosuppresswarningmessagesthat
havetodowithvariablenumbersofargumentsandnullreferences.Noticethatthefirst
argument passed to
invoke()
is
null
when invoking a class method.
The
java.lang.reflect.AccessibleObject
class is the superclass of
Constructor
,
Field
,and
Method
.Thissuperclassprovidesmethodsforreporting
aconstructor's,field's,ormethod'saccessibility(isitprivate?)andmakinganinaccess-
ibleconstructor,field,ormethodaccessible.
AccessibleObject
'smethodsinclude
the following:
•
T getAnnotation(Class<T> annotationType)
returns the con-
structor's,field's,ormethod'sannotationofthespecifiedtypewhensuchanan-
notation is present; otherwise, null returns.
•
boolean isAccessible()
returns true when the constructor, field, or
method is accessible.
•
boolean isAnnotationPresent(Class<? extends Annota-
tion> annotationType)
returnstruewhenanannotationofthetypespe-
cified by
annotationType
has been declared on the constructor, field, or
method. This method takes inherited annotations into account.
•
void setAccessible(boolean flag)
attemptstomakeaninaccess-
ible constructor, field, or method accessible when
flag
is
true
.
Note
The
java.lang.reflect
package also includes an
Array
class whose
class methods make it possible to reflectively create and access Java arrays.
I previously showed you how to obtain a
Class
object via
Class
's
forName()
method. Another way to obtain a
Class
object is to call
Object
's
getClass()
