Re: newbie java design question

"Oliver Wong" <>
Wed, 30 Aug 2006 16:22:59 GMT
"bob_roberts" <> wrote in message

- new to java (from C++ world)
1. Abstract class A
2. Child C inherits from A.
3. Child D inherits from A.

In a client, I want to determine which child implementation to use
(via a config file, for instance). The main catch is that I do not
want any dependencies on either C or D for the client. That is, if
C is an implementation that invokes third-party code, the client which
decided (via config) to invoke C should make no reference to jar files
for child D (or any of its third-party jar files).

I've been looking into the URLClassLoader option for this, since I could
dynamically determine which implementation class to load and have at it.

In C++, I could just use dlopen() on a shared object, and load a
which included references to third-party libraries. Then I would
reference the loaded child class through a base class pointer and I don't
have any dependencies on shared objects which may not exist
on the system in which I'm currently running the client. I'm kind of
looking for something along those lines.

Is there an accepted "pattern" or general rule of thumb that I should look

Or have I completely missed some key point in Java which would
allow me to do this more easily?

    For a "pattern", look at Factory or Abstract Factory.

    For Java support, look at

So your client code would see A and the factory. The factory would use the
ServiceRegistry to see what classes are available that implements A, and
return an appropriate instance of that class to the client.

    - Oliver

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