Slide 13.1: Inheritance

Inheritance

Inheritance is a mechanism in which one object acquires all the properties and behaviors of a parent object. It facilitates:

Method overriding (so runtime polymorphism can be achieved), which allows us to perform a single action in different ways, and
Code reusability, which saves developers’ time and efforts.

The idea behind inheritance is that you can create new classes that are built upon existing classes. When you inherit from an existing class, you can reuse methods and fields of the parent class. Moreover, you can add new methods and fields in your current class also. Inheritance represents the IS-A relationship which is also known as a parent-child relationship.

Inheritance Terminology

Class: A class is a group of objects which have common properties. It is a template or blueprint from which objects are created.
Subclass/child class: A subclass (derived class, extended class, or child class) is a class which inherits the other class.
Superclass/parent class: A superclass (base class or parent class) is the class from where a subclass inherits the features.
Reusability: It is a mechanism which facilitates you to reuse the fields and methods of the existing class when you create a new class.

The extends Keyword
The extends keyword indicates that you are making a new class that derives from an existing class.

The meaning of “extends” is to increase the functionality. A class which is inherited is called a parent or superclass, and the new class is called child or subclass.

class Super {
   .....
}
class Sub extends Super {
   .....
}