Abstract Classes versus Interface

Abstract Classes versus Interfaces
Unlike interfaces, abstract classes can contain fields that are not static and final, and they can contain implemented methods. Such abstract classes are similar to interfaces, except that they provide a partial implementation, leaving it to subclasses to complete the implementation. If an abstract class contains only abstract method declarations, it should be declared as an interface instead.
Multiple interfaces can be implemented by classes anywhere in the class hierarchy, whether or not they are related to one another in any way. Think of Comparable or Clonable, for example.
By comparison, abstract classes are most commonly sub classed to share pieces of implementation. A single abstract class is sub classed by similar classes that have a lot in common (the implemented parts of the abstract class), but also have some differences (the abstract methods).

Advantages of UseCase Diagrams

Use case diagram presents the static view of the system that we are going to develop.

Normally use case diagrams are facilitated by the different entities involving in the software development. Those entities are client, development team , QA staff, Project Manager (PM) and System architect.

You are encouraged to elaborate this statement and further it will help your presentation preparation.

Interfaces Vs. Abstract Classes

Compare and Contrast Java Interfaces and Abstract Classes