You extend a class by creating a new class.
The former and the latter will then have a parent-child relationship.
The original class is the parent class or the base class or the superclass.
The new class is called a child class or a subclass or a derived class of the parent.
The process of extending a class in object-oriented programming is called inheritance.
In a subclass you can add new methods and new fields as well as override existing methods in the parent class to change their behaviors.
Inheritance gives you the opportunity to add some functionality that does not exist in the original class.
Inheritance can also change the behaviors of the existing class to better suit your needs.
The subclass and the superclass has an “is-a” relationship.