Interface || abstract || both?

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Java

A lot of discussion has been made over their use but I just want to know the generally accepted practice.

I have written a dictionary class, it takes commands their methods as strings and a class, then maps the strings to the methods of the class.

I anticipate that in the future, either myself or others may wish to use this to create other dictionaries. Therefore I wish to make it as versatile as possible.

Usage:
Should I use abstraction and provide a blank interface for others to abstract?
Should I use an interface with a class, leaving abstraction to others?

Naming:
Should I prefix interfaces with I and abstract classes with Abstract or A?

IDictionary
AbstractCommandDictionary
CommandDictionary

What I have tried:

Currently have the interface/class design