Lecture 20/21 - Programming with Objects/Inhertiance and the Implementation of Polymorphism

Classes in Java

• every class is a subclass of some other class (except for one)

• the “Object” class defines several instance method that are inherited by every other class

• toString() method, when you create a class u can write a new toString() method, when using the toString() if you concatat the object to a string it will automatically call the toString method

Designing a class to play the Card higher lower game

• objects candidates

  • game, player, hand, card, deck, value, suit

    • card and deck are most obviously reusable

• verbs that involed are the mthode

  • shuffle, deal, add remove card

BlackJackHand Class

• extend the original hand class but include extra functionality

• getBlackJackValue()

Inheritance

• refers to the fact that one class can inherit part of or all of its structure and behavior from another class

• Class A is the superclass, Class B is the subclass

• Class B inherits from class A

• Multiple Classes can be declared as subclasses of the super class

• subclasses can be referred to as sibling class

Protected Acess

• when you declare a method or member variable to be protected, you are saying that is part of the implementation of the class instead of the public interface

• allows subclasses to reuse and modify that part of the implementation

Overriding an Inherited Method

• the toString() method is designed to be overridden

• provides customizable string representation of the objects in that subclass

Polymorphism

• a method is polymorphic is the action performed by the method depends on the actual type of the object

Overriding

• run time polymorphism

• occurs between two classes using inheritance

• array elements are stored in contiguous locations, making it easy to determine relative location of elements

• methods involved must have the same name and same signature

• at runtime java determines the actual object type and invokes the most specific overridden method

Overloading

• compile time polymorphism

• occurs within the class

• insertion and deletion operations are slow as elements are supposed to be stored sequentially index wise

• methods involved must have the same name but different signatures

Dynamic Dispatch

• allows the selection of methods at runtime based on the actual object type rather than the reference type