Inheritance

Inheritance

1. It is what makes code extensible in any OOP language.

   • You extend a class by making a new class
     • Using the "extends" keyword
       • Ex. Parent and Child Class
     • All Java classes automatically extend the java.lang.Object class

2. Also called subclassing

   • You can use the "final" keyword" to prevent inheritance
   • Forms an is- a relationship between the subclass and the superclass

3. Allows you to add functionality that didn't exist in the original class

4. Accessibility

   • A subclass can access a superclass's public, protected and default methods
     • Cannot access private methods
     • Can also override only these types of methods
       • You override by simply writing a new method in the subclass
         • Don't need to change anything in parent class
   • Call a subclass just like any class with a constructor
     • "super" keyword represents an instance of the direct superclass of the current object
       • Can also be used to call hidden members

5. Casting

   • Cast an object to another type
     • Can only cast an instance of a subclass to its parent class (called upcasting)
       • Can downcast only if the object had been upcasted previously from that class

6. "Instanceof" Keyword

   • Used in an if statement to return a boolean
     • True, if the object is an instance of that class
     • False, if object is null or isn't of that class