Creating Abstract Classes

Let's say you want to define a parent class that other developers are going to subclass. Your goal is to provide some reusable variables and methods to developers in the parent class, whereas the developers provide specific implementations or overrides of other methods in the child classes. Furthermore, let's say you also don't want an instance of the parent class to be instantiated unless it is an instance of the child class.

For example, you might define an Animal parent class that a number of classes extend from and use but for which an instance of Animal itself cannot be instantiated. All subclasses of the Animal class, such as Swan, are required to implement a getName() method, but there is no implementation for the method in the parent Animal class. How do you ensure all classes that extend Animal provide an implementation for this method?

In Java, you can accomplish this task by using an abstract class and abstract method. An abstract class...