Inheritance, - PowerPoint Presentation

Slide1

Inheritance, Superclasses, SubclassesSlide2

Inheritance

Allows for more usability of code

Page 168 of Heads First book

Class –

SuperHero

(Classes) Suits; tights;

specialPower

(Methods)

useSpecialPower

;

putOnSuit

Think of Parent/Child Relationship

The sub-class Inherits from the

SuperClass

In Java, we say the

subclass

extends the

SuperClass

.Slide3

Overriding Methods

You have the ability to override the method that are received from the parent.

What you override is then specific to that subclass.

SuperClass

– class that is inherited from – more abstract

Subclass – the specific “children” of the

superclass

.Slide4

Page 169 Example -

Doctor –

superclass

Subclasses – Family Doctor, Surgeon

Any subclass of Doctor will have a

WorksAtHospital

& a

treatPatient

property

Extends – means “inherits from”

CODE

Public class

FamilyDoctor

extends Doctor

{

Can then put items specific to that class Slide5

Surgeon – page 169

Look at surgeon class

TreatPatient

method overrides the

TreatPatient

method in doctor class.

A surgeon treats a patient by performing surgery, so that method overrides the method in Doctor class.

Surgeon also has a

MakeIncision

methodSlide6

Page 170 – Inheritance Tree Design

Look for objects that have common attributes and behaviors

Use inheritance to avoid duplicating code in subclasses.

Design a class that represents the common state and behavior

All Animals – have a picture; eat food, have hunger, etc.Slide7

Inheritance Tree, cont’d

Decide if a subclass needs behaviors (method implementations) that are specific to that particular subclass type.

MakeNoise

and Eat are specific to each type of animal.

Look for more opportunities to use abstraction, by finding two or more

subclasses

that might need common behavior

.Slide8

Page 174

Finish the class Hierarchy

Since animals already have an organizational hierarchy, that makes the most sense for class design.

Felines – lion, tiger, cat (can use a common roam method)

Canine – wolf, dog (can use a common roam method)Slide9