An abstract class, although well defined, is one that is never instantiated. For example, a pet would never be instantiated as such, but could exist in the form of a dog or a cat. The pet class would be at the top of an inheritance hierarchy where derived classes like the dog or cat class inherit their attributes and behavior from the pet class. Can you give other examples of inheritance hierarchies where the top level is an abstract class, and furthermore, what are the advantages of using such hierarchies? Select one Swing component and describe its functionality. Provide example on how would you use it. How would you implement a menu in Java? The Container class is a subclass of the Component class. A container is a component that can hold other components. What are common containers? What is a top level container? What is an abstract class and how we should use it? Please provide examples of hierarchies where the top level is an abstract class.