Re: hierarchy of interface/implementations.

From:

Eric Sosman <Eric.Sosman@sun.com>

Newsgroups:

comp.lang.java.programmer

Date:

Tue, 24 Mar 2009 18:10:29 -0400

Message-ID:

<1237932577.482618@news1nwk>

horos11@gmail.com wrote:

I had a quick question about implementing interfaces and storing those
implementations..

suppose I have a implementation that I defined:

package mycom;

public interface MyInterface
{
public void mymethod();
}

     Let's get picky about terminology for a moment, because I
think it's at the root of your confusion. In Java, an "interface"
(which is what you've shown above) is something like a "contract."
It doesn't implement anything: Look at the code, and there's no
executable body to mymethod(), you have no idea what a mymethod()
call will actually do.

     An implementation of an interface is an ordinary class that
does two things: It declares `implements MyInterface' to advertise
its intent, and it provides actual runnable code for each method
the interface specifies. So in your case an implementation of
MyInterface would be something like

    class MyImplementation implements MyInterface {
        public void mymethod() {
            System.out.println("Wowza!");
        }
        // other fields and methods as desired
    }

and I put it in file:

mycom/MyInterface.java

and I want to have several different implementations defined for it,
that I want to stick under:

mycom/MyInterface/Implentation1.java
mycom/MyInterface/Implentation2.java
mycom/MyInterface/Implentation3.java

Can you do this? when I go to make my Implementation1, I say:

package mycom.MyInterface;

I get a conflict, apparently with the interface. But this seems the
logical way to structure things.

It would have been helpful if you'd showed us the code for
at least one of these implementations, and showed us the actual
error message(s) you got ...

There's nothing fundamentally wrong with what you *have*
shown. The naming for your mycom.MyInterface package is a bit
strange (Java has naming conventions and the name you've chosen
violates them, but they're only conventional), but I see no reason
for outright errors. (Of course, I may have overlooked something.)

My workaround is to make a directory:

mycom/MyInterfaceImpl

and stuff all implementations there, but this IMO is a hack and I'm
hoping that there are other ways around this (that make sense, camel
case promotes spelling errors, isn't compiler checkable, etc.)

I don't see any difference other than the spelling between this
"hack" and what you've been trying to do.

Actual code, please, and actual error messages. Sometimes I can
debug what I can't see, but my accuracy suffers.

--
Eric.Sosman@sun.com