Building Worlds on Abstract Class Pillars Abstract classes  represent abstract concepts. In our previous article, we created various classes that inherited properties and methods from its parent. Looking at the Animal class hierarchy, the Animal class itself is an abstract concept. We can vaguely say Animal, but what type of animal? A Dog may be a narrow enough concept, but a GermanShepherd is definitely a concrete class, not abstract. Abstract classes are classes that start with the word abstract. If a class contains at least one abstract method, it must be declared as abstract. If a method inside of an