Interface and implementation erorr

Hi,
:confused:
I have a problem finishing my assignment which requires:Detail : Create the following:
1. Interface (clientInterface)
2. Implementation (clientImpl)
3. Excption class (clientException)
4. main test class

Interface should be named clientInterface
with at least 6 methods
Implementation should be named clientImpl and should implement the
clientInterface
Exception class should be named clientException and should be utilized by the
clientImpl class

Create a test application that instantiates a number of the clientImpl
objects, invoke a clientException.

I already created all class files, but my clientimpl and clientException class is not working!!!
Can anybody help. I have attached file.

Thanks a lot.