Inheritence

Inheritence

1. Extending a class

   • Add "extends" after the class name and before the parent class

2. The is-a Relationship

   • The special relationship between a sub class and the super class
   • i.e. Animal & Bird, Fish, Dog
   • A subclass inherits all public methods & fields of its superclass (not private ones)

3. Accessibility

   • From within a subclass, you can access the superclass's public & protected methods/fields (but not private ones)
   • You can only reduce (not increase) visibility in the superclass from the subclass

4. Method Overriding

   • You can change the behavior of a method in the superclass within the subclass
   • Override a (non-final) method to change its behavior
   • No need to change anything in the Parent class
   • Simply write the new method in the subclass

5. Calling the Superclass's Constructors

   • Just like an ordinary class, use the "new" keyword to create an instance of it
   • Use "super" keyword to represent an instance of the direct superclass of the current object
     • Can be used to explicitly call the parent's constructor from a subclass's constructor
       • super must be the first statement in the constructor

6. Calling the Superclass's Hidden Members

   • The "super" keyword can be used to call a hidden member or an overridden method in a superclass

7. Type Casting

   • You can only cast an instance of a subclass to its parent class
   • Upcasting - casting an object to a parent class

8. The instanceof Keyword

   • Used to test if an object is of a specified type
   • normally used in an if statement