anatomy of an object every object has 2 parts: data function data (fields) can be...

Anatomy of an object• Every object has 2 parts:

• Data• Function

• Data (Fields)• Can be "primitive" data types:

• int, long, double, byte• Or other objects:

• String, Date, Name, Person, etc…• Function (Methods)

• A method is a discreet piece of functionality that an object can perform

• Like functions/procedures in other languages it can take parameters and return a value/object.

Anatomy of an object (continued)

Person

String firstName

String lastName

Date dateOfBirth

String getInitials()

int getAge( Date )

The class named Personhas 3 fields:firstName (type = String)lastName (type = String)dateOfBirth (type = Date)

and 2 methods:getInitials (no parmaters, returns a StringgetAge (1 parameter, returns an int)

A Class

Classes vs Instances• Class - an object that defines all data and

behavior for a particular type of object. Classes can be thought of as templates or factories for objects.

• Instance - an object that represents a “for real” manifestation of a class. While a class defines the data items and functions, an instance actually holds the values and “runs” the functions. There is also an allocation of memory for each instance.

Classes vs Instances (continued)

Person

String firstName

String lastName

Date dateOfBirth


int getAge( Date )

Person Class Person InstancesfirstName = "Joseph"

lastName = "Smith"

dateOfBirth = 1/1/1960

firstName = "Betty"

lastName = "Boop"


getInitials() -> "JS"getAge(12/7/2003) -> 43

getInitials() -> "BB"getAge(12/7/2003) -> 71

Think of a class as a “vending machine”. Each time you “pull the lever”, an instance comes

out.

Classes vs Instances (continued)• An Instance is created from a Class

… new Person()… or, better yet

… new Person( "Joseph", "Smith", 1/1/1960 )

• The new keyword invokes a special method called a constructor method which creates an instance from a class.

Classes vs Instances (continued)Person p1, p2;

p1 = new Person("Sammy", "Sosa", 4/13/1972 );

p2 = new Person("Mickey", "Mouse", 11/2/1928);

p1.getInitials(); /* returns "SS" */

p1.getAge( 12/7/2003 ); /* returns 31 */

p2.getInitials(); /* returns "MM" */

p2.getAge( 12/7/2003 ); /* returns 75 */

3 Principles of Object Orientation (OO)

• Encapsulation• Information hiding

• Inheritance• Polymorphism

Encapsulation• The bundling of data and function together into 1

logical unit• Data and the functions that are associated with it

are closely bound together• No more "global data"

• Allows for modularity• Promotes reuse when done properly

Encapsulation (continued)

Person

String firstName

String lastName

Date dateOfBirth

String addressLine

String city

String state

String zipCode


int getAge( Date )

boolean isForeign()

double salesTax()

Person

String firstName

String lastName

Date dateOfBirth


int getAge( Date )

Address

String addressLine

String city

String state

String zipCode

boolean isForeign()

double salesTax()

Better…Good…

Encapsulation (continued)

Person

String firstName

String lastName

Date dateOfBirth

Address currentAddress

Address previousAddress


int getAge( Date )

Address

String addressLine

String city

String state

String zipCode

boolean isForeign()

double salesTax()

Reuse in action…

Organization

String orgName

Address currentAddress

Information Hiding• Goes hand-in-hand with encapsulation• The internal workings of an object are private to that object

• this includes all data that that object holds• the only way to access any object is through its public

interface• Public – anyone can see/use it• Private – no one (only the owning class itself) can see/use

it.

public interface - the public methods of a class

Why? If everyone knew about your internal workings, any change made would make everything else break!

Information hiding (continued)Salesman

String firstName

String lastName

int itemsSold


int getAge( Date )

For this Salesman class, the only thingsI can do are: getInitials() getAge()

What if I want to see the number ofItems sold?


String firstName

String lastName

int itemsSold


int getAge( Date )

I can make my field itemsSold public

Salesman

String firstName

String lastName

int itemsSold


int getAge( Date )

int getItemsSold()

I can add a new public method getItemsSold()

OR


String firstName

String lastName

int itemsSold


int getAge( Date )

This approach reveals the internal representation of my data.

Salesman

String firstName

String lastName

int itemsSold


int getAge( Date )

int getItemsSold()

This approach says that when you want itemsSold, you will get backan integer. You have no idea howit is stored or derived.

OR

Information hiding (continued)• Company policy changes and the “items sold” by

a salesperson is the average sales per-person of that salesperson group

• Everyone who directly accessed the itemsSold field will now be incorrect

• The getItemsSold() method should be updated to use this group average instead• Everyone who used the method will still be correct.

Inheritance• What is inheritance?

• The "passing on" of data and function from a parent class (superclass), to its children (subclasses)

• A child class automatically gets all of the data elements and functions from its parent

• Another form of reuse• Why inherit?

• You inherit from a superclass if you want to build a class that is very similar to the superclass but some differences are needed.

• Create a subclass if you want to extend existing functionality or add new functionality

Inheritance examplePerson

String firstName

String lastName

Date dateOfBirth


int getAge( Date )

Student

String classYear

String getClassLevel()

Professor

String department

String getDepartment()

Student and Professorboth inherit from Person.

Inheritance example

PersonString firstName

String lastName

Date dateOfBirth


int getAge( Date )

StudentString classYear


ProfessorString department

String getDeptName()

Student (instance)firstName = "Sam"

lastName = "Smith"


classYear = "2006"

getInitials() -> "SS"

getAge( today ) -> 17

getClassLevel() -> "Sophomore"

Professor (instance)firstName = "Talka"

lastName = "Lotta"


dept = "0078"

getInitials() -> "TL"


getDeptName() -> "Chemistry"

Both Student and Professor inherit all of thefields and methods from their superclassPerson.Both extend Student by adding more functionality.

Adding functionality…

Inheritance example

PersonString firstName

String lastName

Date dateOfBirth


int getAge( Date )

String printName()

StudentString classYear


ProfessorString department

String getDeptName()

String printName()

/* add Prof. in front… */

Student (instance)firstName = "Sam"

lastName = "Smith"


classYear = "2006"

getInitials() -> "SS"


getClassLevel() -> "Sophomore“

printName() “Sam Smith”

Professor (instance)firstName = "Talka"

lastName = "Lotta"


dept = "0078"

getInitials() -> "TL"


getDeptName() -> "Chemistry“

printName() “Prof. Talka Lotta”

aStudent.printName() -> "Sam Smith"

aProf.printName() -> "Prof. Talka Lotta"

Overriding functionality…

Polymorphism• What is Polymorphism?

• A number of classes may all have the same method name foo(); but that method does different things depending on the class on which it is called

• This allows us to treat a group of classes similarly yet each can express its own "individuality"

Polymorphism exampleAnimal

speak();

Dog

speak(); //bark

Duck

speak(); //quack

Cat

speak(); //meow

Polymorphism example 2Loan

applyPayment( amount )

calculatePaymentSchedule()

getPayoffAmount()

SimpleLoan



getPayoffAmount()

Mortgage



getPayoffAmount()

LoanManager

applyPayments()

printCoupons()

Polymorphism example 2• LoanManager code…/* get all payments that came in today and apply to the loans */

List allPayments = getAllPayments();

/* for each payment P, find the loan for it */

…for each payment…P

Loan aLoan = findLoanForPayment( P );

/* apply the $ to the loan */

aLoan.applyPayment( P ); /* what kind of loan is this? We don't know! */

/* print out coupon booklet */

PaymentSchedule paySchedule := aLoan.calculatePaymentSchedule();

paySchedule.print(); /* another polymorphic method… */

Polymorphism example 2Loan



getPayoffAmount()

SimpleLoan



getPayoffAmount()

Mortgage



getPayoffAmount()

MultiDisbursementLoan



getPayoffAmount()

LoanManager continues to work as is when a new loan type is added.

Design Patterns• What is a design pattern?

• a.k.a. – "design approach"• A specific design approach that solves a particular

problem. • It is used so frequently that is becomes

"standardized".• It has a name

• Why do we need them?• We don't "need" them, but they can make life

easier

Design Patterns• Why use design patterns?

• A design pattern is well-understood so there is a less likely chance of the design "failing"

• Patterns have been "tested" in the real world across various application types

• Simplifies maintenance because if all developers are familiar with patterns

• Shorter learning curve

Design Patterns (examples)Factory pattern:

A Factory is a class that allows us to create instances of other classes depending on the information it is given. The factory is smart enough to figure out what instance to create

Design Patterns (examples)

Loan

SimpleLoan Mortgage

LoanFactorycreateLoan( loan info )

LoanFactory

Loaninformation

createLoan()

LoanFactory

Loaninformation

createLoan()

SimpleLoan

Mortgage

Frameworks• What is a framework

• A set of reusable designs and objects used to build applications

• Defines how objects work together to get something done

• Defines the superclasses or public interface for the object that you develop

• Your objects work within the framework

• A framework is a "semi-complete" application

Frameworks• A framework usually supports a very specific

domain• GUI (large)• Collections (small)

• Usual characteristics of a good framework• Relatively easy to understand and use• Provides a solution to a common problem• Can be used over and over again

Frameworks• To use a framework, you work with the base

classes that come with the framework• Create subclasses from base classes• Your classes implement a public interface as

defined by the framework

FrameworksPros• A lot of work is done for you

already• Shorter development time• Developers can

concentrate on business, not technology

• Shielded from technology changes

• Framework will handle changes as the vendor upgrades it

• Greater consistency across applications if they all use the same framework(s)

Cons• Tight coupling between

application and framework• "vendor lock-in"

• Extra learning curve• Framework may not

provide everything you need• Extend the FW yourself

Frameworks• STRUTS

• http://jakarta.apache.org/struts/• Web Application framework

• Provides all the “techie” stuff needed for a web application• You configure it to work the way you want it to

• Navigation• Form validation

• Easily extensible• Add your own classes if Struts doesn’t have what you need

• Lots of contributors• Constant improvement

• Supported by major IDEs• UPortal is a framework AND application!

Components• What is a component?

• An object or group of objects with a well defined public interface that provides a discreet set of functionality

• Black box• Utility object

• Different from a framework• Your objects are not tightly coupled with a component

• Do not subclass from a component

• Components are interchangeable• New component must have same API as old component

Components

LDAPAuthenticationMgr

authenticate()

Some object Authenticate( id, password)

LDAPDB

DBAuthenticationMgrauthenticate()

Authenticate( id, password)

Components• A component may look like just one object, but

there may be a great many supporting objects unknown to you• A component makes it look like “one thing”

• Simple components• Authenticator (see example)

• Complex components• Interest calculator

anatomy of an object every object has 2 parts: data function data (fields) can be...

Documents

string getage

string dateofbirth type

string lastname type

class slide

class new person

person p1

firstname type

new person joseph