Inheritance

Inheritance

1. We can create a new class by extending an existing one

   • Orginial = parent class or superclass
   • New = child class or subclass
   • Any class can be extended unless declared as "Final"
   • With "extends" keyword
   • A class can only extend one class

2. A subclass inherits all public fields and methods of the superclass

   • A subclass can also access all the superclass' protected methods/fields
     • A protected method is not accessible outside of the class except by a subclass
     • Another class cannot access the protected through a subclass

3. It is legal to assign an instance of a subclass to a reference variable of the parent type.

   • Every object of subclass type is guaranteed to also be of superclass type. Though this does not work the other way around

4. Method overriding: a subclass can change the behavior of a parent class method

   • A method in the subclass with the same signature is overriding
   • You cannot override a final method or a method that is private in the parent class

5. When you create a child object, all its parent classes are instantiated

   • You can explicitly call a superclass' constructor from first line of the subclass constructer with the "super" keyword
     • Elsewhere, the super keyword can call overriden methods or hidden members from a superclass
   • You can cast an instance of a subclass to a parent class