Lesson 19 - Abstract class, comparing and anonymous classes in Java

In the previous lesson, Type casting and object hierarchy in Java, we learned about type casting and created an object hierarchy with a common ancestor in Java. In today's tutorial, we're going to continue with that project.

Abstract class

An abstract class is a class whose instance does not make sense. Mainly because it is too vague, e.g. our Animal class. The point is to call on specific Animal descendants, e.g. a dog, so we won't actually instantiate the Animal class directly ever. In other words, it's better to prevent any instantiation of the class overall. To do that, we simply add the "abstract" modifier before the Animal class:

public abstract class Animal {
    . . .

The program works the same as before, but if we try to create an instance of the Animal class, we'll get an error:

// this code won't work
animals.add(new Animal());

Other than preventing instantiation, abstract classes can do several other things

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