Inheritence

Inheritence

1. Makes classes extensible in any OOP Language

2. The process of extending a class

   • You extend a class by making a new class
     • This new class creates a parent child relationship
       • In the new sub class you can create new methods and fields while having the ability to override existing methods and changing behavior
       • The child class can also be extended to create new parent-child relationship, unless you declare it final, therefore making it inextensible
   • Extend key words:
     • public parent class{ }
     • public Child class extends Parent {}

3. Creates a is-a relationship between parent and child classes

   • Example: The parent class being animal, with child classes that are bird, dog, and cat
     • Each sub class "is a" animal which is why it has a is a relationship, each class is related in a way to the parent class
       • The animal class is defined with a weight field and a eat method, each sub class also has these two characteristics but like class bird has a new field being numberOfWings which is not given from the parent
     • Legal = Animal animal = new Bird, illegal= Dog dog = new Animal
       • The parents class can create new sub classes but the sub classes cannot create new values in the parent class
         • This is because the bird class is always a animal but for the illegal ,the animal is not always a dog so it would not work to define it in that manor

4. Method Override

   • When extending a class, the sub class has the ability to change methods in the parent if it shares the same signature
   • You override a method to change its behavior
     • Can't override a final method
   • To override a method, you have to write the new method in the subclass, without having to change anything in the parent class.
     • It is legal to change the visibility of the method in the subclass, but you can only make it more visible, it is illegal to make something more private.