Re: Reflection, how to understand

John_Woo wrote:
Hi,

I'm trying understand jdk 5 reflection.

I know it's for loading/invoking method on the fly. I'm wondering, any
simple core-java example (not sort of EJB, rmi) illuestrated how an app
re-compile then invoke the newly classes/methods, and why need to do
that (recompile)?

AFAIK, it doesn't have to do with recompiling - it has to do with, as
you said, dynamically accessing to classes.

For example:

String classname = "org.some.class.TestClass";
Object[] parameters;
Object obj =
Class.forName(classname).getConstructor(Object[].class).newInstance(new
Object[] { parameters });

What this code snippet does is:

Get the class named "org.some.class.TestClass".
(Class.forName(classname)).
Then it proceeds to get a constructor for said class, one that requires
an object array as parameter ( getConstructor(Object[].class)).
Then it proceeds to instantiate the object using said constructor,
passing the Object array "parameters" as the parameters.

There you have it - I have loaded an instance of the class
org.some.class.TestClass - without having to know that name in the code
- the String classname could have been loaded from any source (in
particular, I use that code snippet for persistence of simple objects
from a database - load the className and the constructor parameters
from the database, execute the reflection voodoo to instantiate)

.

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