The concept of abstraction is that we focus on essential qualities, rather than the specific characteristics of one particular example. In Java, abstraction is achieved using abstract classes and interfaces. An abstract class is defined using the abstract keyword. - If a class is declared abstract it cannot be instantiated (you cannot create objects of that type). - To use an abstract class, you have to inherit it from another class. - Any class that contains an abstract method should be defined as abstract.
An abstract method is a method that is declared without an implementation (without braces, and followed by a semicolon): abstract void walk();