Re: Class Literal ???
Roedy Green wrote:
This is so Alice in Wonderland. The whole reason you have a class
variable is because the precise class is variable and unknown at
compile time. With that generic form, you need to know the precise
class type at compile time. If you knew that, you would not need a
class variable.
....
My comment applies to Class<MyClass> only.
In that respect,
Class <MyClass> x = MyClass.class;
is similar to
List <MyClass> x = new ArrayList <MyClass> ();
When you have a generic type, you have to specify the generic type
parameter.
There are those who think that the compiler should infer the type
parameter in more cases, and IIRC that is making into Java 7. But
that's just notational sugar to spare programmers the incredibly,
overwhelmingly, exhaustingly strenuous effort of typing an extra dozen
or so characters per declaration. Don't sprain a finger, folks!
Once again, where you would use something like "Class <MyClass> x =
MyClass.class;" is to prepare a class variable for generic methods
that do *not* know ahead of time what the type parameter will be
("Class<T>" stuff). If you didn't need to do that, you wouldn't be
using the "Class <MyClass>" idiom, but more likely "Class <?>".
One of the most common uses of "Class<T>" is as a run-time type token
for generic classes/methods that need run-time type information, as in
the 'EntityManager#find( Class<T> clazz, Object key )' example I cited
upthread. While often the class literal is provided directly to the
call:
em.find( Foo.class, key );
it is also sometimes useful to declare a variable to hold the 'Class'
argument:
Class <Foo> claz = Foo.class;
...
em.find( claz, key );
Sure, it's all just a pack of cards, but you play the ones you're
dealt.
--
Lew