OO (Object Oriented) Programming

Chapter 21

A method of Design, (make the major decisions first when designing programs)

OO object oriented programs“Balloon” as an example, a simulation of a balloonPrincipals of OOP1. Encapsulation (Chapter 9)2. Inheritance (Chapter 11)3. Polymorphism

Encapsulation

…group related information together and protected from the outside (world)Private = protected orOpen = open to the world

Inheritance

Use classes repeatedlyReuse parts of existing classes when possible

Polymorphism

Same methods used with others, multiple implementations

Design problems

Need to identify objects. An approach to problem solvingSimulation and Modeling Build a software model of something in the

real world Identify the object(s) in the problem Model them as objects Ignore irrelevant detail

Specification = what is requiredDesign = how it will be accomplished

Model – view - controller

An example:A cars engine (model) the observer = you gas pedal (controller) speedometer (some dial or gage) i.e. GUI

What user adjusts with (a scrollbar (controller) as an example)

A Balloon example

Model - car engine vs. BalloonView – speedometer vs. CircleController – steering wheel vs. change position of Balloon (left/right, up/down)

Hierarchy

An old example “Sphere” class as the parent and Orb, or Circle, or marble or whatever as child.Many other sub classes possibleAnalyze the specifications of what you are to model (design)Write in pseudocode before using Java

Case study in design

“One Armed Bandit” example “Slotmachine”: “Actions”DisplayGoQueryStop Reuse the components that your program can inherit

Relationships

“is a” vs. “has a”Is a = inheritance (java “extends”) from parent classHas a = (java “new”) an objectNeeds a = utility (java various methods) need of another object, may pass in a parameter)

Reuse components that your program can inherit