ACO 101 – Intro to Computer Science. 28object-oriented_programming%29

ACO 101 – Intro to Computer Science

http://en.wikipedia.org/wiki/Encapsulation_%28object-oriented_programming%29

Encapsulate complexity

divide program into classes

each class has its own responsibilities and data

class has only one purpose

class has simple interface

hide implementation details

Encapsulate change

each class presents only a simple public interface

class hides implementation details

as a result...

we can localize the effect of change

Reuse code

classes are reusable

polymorphism lets us interchange parts

inheritance lets us build new classes that reuse code from old classes.

Better abstraction

objects make good models for things in the real world (problem domain)

let us think about the problem instead of the code

simplify the problem so we can think about problem without too many details

An OO program consists of objects that interact with each other. (this picture is a UML Sequence Diagram)

The tenets of:

InheritanceEncapsulationPolymorphism

The child gets it all. If an object inherits from another

object – it can do EVERYTHING that object can do in addition to doing all the stuff it can do.

The word Polymorphism is derived from two Greek words, namely Poly and Morphos.  Poly indicates many and Morphos indicates forms.  

Therefore, it is the existence of the same thing in different forms.

Polymorphism is behavior that varies depending on the class in which the behavior is invoked. 

In other words, two or more classes can react differently to the same message.

This is a duck object This is a common

example in learning OOP so I am using it here.

What are its attributes? Color Eyes Bill Appendages Surface Size

What are its behaviors? Sound Movement

One quacks, one talks and one squeaks – their sound behavior will all be different

One has feathers, one has clothes and one is rubber – their surface attribute will all be different

They will all inherit from the duck object and polymorphism allows them to be different from each other and still share attributes and behaviors of the base duck object.

Another name for this is: information hiding Hides the way something works away from the

user who can do all its operations without seeing how it does it.

A way to understand this is to think of a car, we now how to get from destination A to B without knowing how the engine works under the hood or seeing it work.

Class Libraries You can buy some

▪ http://www.qoppa.com/

With Java and C# there is a library that ships with them▪ C# Framework location = C:\Windows\Microsoft.NET\Framework\

v2.0.50727▪ Java API location = The Java SE Runtime Environment

▪ contains the Java virtual machine, runtime class libraries, and Java application launcher

▪ For more info read this: C:\Program Files\Java\jdk1.6.0_21\jre\README.txt▪ http://en.wikipedia.org/wiki/List_of_Java_APIs

Game Engines They slap a GUI on the front end of it so that game designers can build

games without having to code all the physics, animation and complicated math etc.

A class is a recipe for an objectAnd just like any recipe you can

make as many of the object as you want to… [Pass out recipe here]

But I wouldn’t want to eat a recipe – would you ?

During design, you need to identify the classes. Classes are used to model things:

Tangible things in the design: nouns, such as purse, mailbox, bank account, keypad, email message

Users Student, Administrator, Bank Manager

Agents ("-er" or "-or" words) Scanner, file reader, sentence reader, CSVreader agents perform some operation (sentence reader)

Events and Transactions Button click, ATM Withdrawal, Register for Course are all events transactions are uses for interactions between classes, usually

contain info that doesn't "belong" in a thing class

Verbs in specification often are responsibilities

depositwithdrawconfirm

Best Design:A class should have only one purpose

(but may have several related behaviors)

Purse: responsible for managing coins in a purse

More than one CLOSELY related responsibilities OK

Bank: purpose is to manage bank accounts and assets

A class should have well defined responsibilities

ATM: communicate with the client and execute transactions (but not verify them... that's the Bank's job)

What behavior (methods) must a class provide to perform its responsibilities?

A Purse is responsible for managing coins in a purse.

Behavior a purse should have:

1. insert coins

2. withdraw coins

3. get balance

4. is it full? purse has a limited capacity

Behavior should be related (coherent) don't put unrelated responsibilities into the

same class

avoid assigning too many behaviors to a classA Purse is not responsible for:

printing the balance

asking the user what he wants

computing the price of stuff

Customer

getAccounts()

Account

getBalance()

getOwner()

deposit( )

withdraw()

doInteterest()handle responsibilities directly related to customer. handle responsibilities

directly related to bank accounts.

Good Design

Customer

countAccounts( )

getBalance( k )

deposit( k, amt )

withdraw( k, amt )

doInteterest( k )

handle responsibilities directly related to bank accounts.

Bad Design

A class is a blueprint or definition for a kind of object.

A class defines the attributes and behavior of objects.

Cat

birthday

color

sex

sleep( )

eat( Food )

play( )

chase( Object )

attributes are characteristics of objects. In Java: attributes, "fields"

behavior is what the object can do. In Java: methods

Objects are instances of a class. [Pass out baked goods here ]

In Java, to create a new object use "new", e.g.

Cat somecat = new Cat( ); create the object in memory invoke the constructor of Cat class to initialize

values.

Object creation can use values, too:

Cat kitten = new Cat( Color.BLACK, "male", ... );

Objects have: state - the current condition of an

object behavior - the actions or messages

an object can accept identity - every object is

distinguishable, even if two objects have the same state

The definition of a HondaCivic consists of:

specifications design documents blue prints list of parts list of qualified suppliers instructions for assembly inspection procedure and check lists operating instructions maintenance manual and procedures

But, the Honda Civic owner doesn't need to know all these details. He needs to know about a Honda Civic's properties (public attributes) and behavior.

For example (simplified):HondaCivic

bodyStylebodyColortrimColorengineSizedoorstransmissionType

turnLeft( )turnRight( )brake( )accelerate( )isEngineOn( )fuelAmount( )

properties(attributes)

behavior

You go to the Honda dealer and say...

I want aHonda Civic Yes, sir. This

way, please...

the dealer offers you the class for a HondaCivic...

Here you are! All the documents and blue prints for a Honda Civic.

... that will be 1,000,000,000 Baht, please.

Construction and operation of a Honda Civic: complete documents.

but you can't drive blue prints and documents That's not exactly what I

had in mind. I want a car I can drive...

I see... you want an instance of Honda Civic -- a Honda Civic object.

Silver, 4 door, automatic transmission, tinted windows, ...

yourcar : HondaCivic

bodyStyle = sedanbodyColor = silvertrimColor = silverengineSize = 1600ccdoors = 4transmissionType = auto

turnLeft( )turnRight( )brake( )accelerate( )isEngineOn( )fuelAmount( )

yourcar = new HondaCivic("silver", 4door, automatic,... );

attributes

behavior

HondaCivic

Class = Defines the properties and behavior for all instances (objects) of this class.

Object = Specific realization of the class

Two Honda Civic cars can be distinguished even if they exactly the same features and same state (brand new)

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Reading HomeWorkReading03-TheDifference.pdf HomeWorkReading04-ClassStructure.pdf OnComplexity.pdf OnAbstraction.pdf