Inheritance, extending a class

Inheritance, extending a class

1. Parent Class/ base class/superclass/orginal class

   • The object is the ultimate superclass
   • "Is-a" relationship with subclass
     • Consequence of this relationship is that it is legal to assign an instance of subclass to reference variable of parent type
       • Example: Animal animal = new Bird();
   • If constructor is not explicitly written in subclass, the compiler will implicitly add a no argument constructor

2. Child class/subclass/ derived of parent class

   • Add new method/fields, and override existing methods to change behaviors
   • Can be extended unless made inextensible by declaring it final
   • Special type of the superclass
   • inherits all public methods and fields of superclass.
   • Not able to access the private methods of superclass
   • Able to access default methods and fields, if superclass and subclass are in the same model
   • use new to create an instance of class
   • Type Casting: ability to cast an object to another type; rule is you can only cast an instance of a subclass to its parent class

3. Inheritance allows one to add some funcationality that does not exist in orginal class

   • To extend a class use the keyword "extend" keyword in class declaration; only one class can be extended in Java.

4. Method Overriding: changing the behavior of a method in parent class through extending a class

   • Happens when method in subclass has the same signature as method in parent class