MELJUN CORTES JEDI Slides-2.1 Object-Oriented Concepts

7/29/2019 MELJUN CORTES JEDI Slides-2.1 Object-Oriented Concepts

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Software Engineering 1

Object-orientedConcepts

TOPIC ONE

Object-oriented Software

Engineering


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Object-oriented Software

Engineering Object-oriented Software Engineering is the use of object

technologies in building software.


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Pressman, 1997

Object technologies is often used to encompass all aspects of anobject-oriented view and includes analysis, design, and testingmethods; programming languages; tools; databases; and

applications that are created using object-oriented approach.

Taylor, 1997, Object Technology

Object technology is a set of principles guiding software constructiontogether with languages, databases, and other tools that supportthose principles.

Object Technology


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It leads to reuse, and reuse (of program components) leadsto faster software development and higher-quality programs.

It leads to higher maintainability of software modules

because its structure is inherently decoupled. It leads to object-oriented system that are easier to adapt

and easier to scale, ie, large systems are created byassembling reusable subsystems.

Benefits of Object

Technology


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It is a representation of anentity either physical,conceptual, or software.

It allows softwaredevelopers to representreal-world concepts in theirsoftware design.

Airplane

ChemicalProcess

Linked List

Object


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It is an entity with a well-defined boundary andidentity that encapsulatesstate and behavior.

Operations

Attributes

Object


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It is one of the possibleconditions that an objectmay exists in.

It is implemented by a setof properties calledattributes, along with itsvalues and the links it mayhave on other objects.

AthleteID: 3556

Name: Joel Santos

Status:NEW

Squad:None

Object's State


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It determines how an objectacts and reacts.

It is represented by theoperations that the objectcan perform.

Joel Santos

Enrolls()

updateSquad()

Object's Behavior


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Although two objects may share the same state (attributesand relationships), they are separate, independent objectswith their own unique identity.

AthleteID: 3556

Name Joel SantosStatus:NEW

Squad:None

AthleteID: 3557

Name: Arjay SolamoStatus:NEW

Squad:None

Object's Identity


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Abstraction

Encapsulation

Modularity

Hierarchy

Four Basic Principles of

Object-orientation


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Abstraction is a kind of representation that includes only thethings that are important or interesting from a particularpoint of view.

It is the process of emphasizing the commonalities whileremoving distinctions.

It allows us to manage complexity systems by concentratingon the essential characteristics that distinguish it from allother kinds of systems.

It is domain and perspective dependent.

Abstraction


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Sample Abstraction

An applicant submits a club membership application to theclub staff.

A club staff schedules an applicant for the mock try-outs.

A coach assigns an athlete to a squad. A squad can be a training or competing squad.

Teams are formed from a squad.


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Encapsulation localizes features of an entity into a singleblackbox abstraction, and hides the implementation of thesefeatures behind a single interface.

It is also known as information-hiding; it allows users touse the object without knowing how the implementationfulfils the interface.

It offers two kinds of protection: it protects the object's statefrom being corrupted and client code from changes in the

object's implementation.

Encapsulation


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Encapsulation Illustrated

Joel Santos is assigned tothe Training Squad.

The key is in the message

interface.

submitApplication()

UpdateSquad()

updateSquad(Training)


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Modularity is the physical and logical decomposition of largeand complex things into smaller and manageablecomponents that achieve the software engineering goals.

It is about breaking up a large chunk of a system into smalland manageable subsystems. The subsystems can beindependently developed as long as their interactions arewell understood.

Modularity


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Modularity Illustrated

Ang Bulilit LigaSquad and Team System

Club MembershipMaintenance

System

Coach InformationMaintenance

System

Squad and TeamMaintenanceSystem


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Any ranking or ordering of abstractions into a tree-likestructure.

Kinds of Hierarchy

Aggregation Class

Containment

Inheritance

Partition

Specialization

Type

Hierarchy


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Hierarchy Illustrated

Squad

TrainingSquad

CompetingSquad


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It is a form of association wherein one class shares thestructure and/or behavior of one or more classes.

It defines a hierarchy of abstractions in which a subclassinherits from one or more superclasses.

Single Inheritance

Multiple Inheritance

It is an is a kind ofrelationship.

Generalization


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It is a mechanism by whichmore-specific elementsincorporate the structureand behavior of more-

general elements. A class inherits attributes,

operations and relationship.

InheritanceSquad

NameCoachMemberList

listMembers()changeCoach()

Training Squad CompetingSquad


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Software Engineering 21The use of the slide has prior approval from the original author (Ms. Florence Balagtas) from the JEDI Introduction to Programming I Course Materials.

Inheritance In Java, all classes, including the classes that make up the

Java API, are subclassed from the Object superclass.

A sample class hierarchy is shown below.

Superclass Any class above a specific class in the class hierarchy.

Subclass

Any class below a specific class in the class hierarchy.


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Inheritance Superclass

Any class above a specific class in the class hierarchy.

Subclass

Any class below a specific class in the class hierarchy.


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Inheritance

Benefits of Inheritance in OOP : Reusability

Once a behavior (method) is defined in a superclass, that behavioris automatically inherited by all subclasses.

Thus, you can encode a method only once and they can be used by

all subclasses.

A subclass only needs to implement the differences between itselfand the parent.


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Inheritance

To derive a class, we use the extends keyword.

In order to illustrate this, let's create a sample parent class.

Suppose we have a parent class called Person./***D nstructor*/publi esn)Sys em. u.prin ln( Iside ers nConst uct r);nam"";adress="";}....}


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Inheritance

Now, we want to create another class named Student.

Since a student is also a person, we decide to just extendthe class Person, so that we can inherit all the propertiesand methods of the existing class Person.

To do this, we write,


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Inheritance

When a Student object is instantiated, the defaultconstructor of its superclass is invoked implicitly to do thenecessary initializations.

After that, the statements inside the subclass's constructor

are executed.


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Inheritance:

To illustrate this, consider the following code,

In the code, we create an object of class Student. Theoutput of the program is,


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Inheritance

The program flow is shown below.


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The super keyword

A subclass can also explicitly call a constructor of itsimmediate superclass.

This is done by using the superconstructor call.

A superconstructor call in the constructor of a subclass willresult in the execution of relevant constructor from thesuperclass, based on the arguments passed.


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The super keyword

For example, given our previous example classes Personand Student, we show an example of a super constructorcall.

Given the following code for Student,


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The super keyword

Few things to remember when using the super constructorcall:

The super() call MUST OCCUR AS THE FIRST STATEMENT IN ACONSTRUCTOR.

The super() call can only be used in a constructor definition.

This implies that the this() construct and the super() calls CANNOTBOTH OCCUR IN THE SAME CONSTRUCTOR.


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The super keyword

Another use of super is to refer to members of thesuperclass (just like the this reference ).

For example,


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Overriding methods

If for some reason a derived class needs to have a differentimplementation of a certain method from that of thesuperclass, overriding methods could prove to be veryuseful.

A subclass can override a method defined in its superclassby providing a new implementation for that method.


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Example

Suppose we have the following implementation for thegetName method in the Person superclass,


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Example

To override, the getName method of the superclass Person,we write in the subclass Student,

Now, when we invoke the getName method of an object ofthe subclass Student, the overridden getName methodwould be called, and the output would be,


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Final Classes Final Classes

Classes that cannot be extended

To declare final classes, we write,publicfinalClassName{. . .}

Example:

Other examples of final classes are your wrapper classes

and Strings.


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Final Methods and Classes

Final Methods

Methods that cannot be overridden

To declare final methods, we write,publicfinal[returnType] [met hodName]([parameter]{. . .}

Static methods are automatically final.


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Example


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Software Engineering39

It is the ability to hide manydifferent implementationbehind a single interface.

It allows the same

message to be handleddifferently by differentobjects.

Polymorphism

Asset

getValue();

Stock

getValue();

Bond

getValue();

Mutual Fund

getValue();


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Polymorphism

Polymorphism

The ability of a reference variable to change behavior according towhat object it is holding.

This allows multiple objects of different subclasses to be treated as

objects of a single superclass, while automatically selecting theproper methods to apply to a particular object based on the subclassit belongs to.

To illustrate polymorphism, let us discuss an example.


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Software Engineering41

The use of the slide has prior approval from the original author (Ms. Florence Balagtas) from the JEDI Introduction to Programming I Course Materials.

Polymorphism

Given the parent class Person and the subclass Student ofthe previous examples, we add another subclass of Personwhich is Employee.

Below is the class hierarchy for that,


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Polymorphism

In Java, we can create a reference that is of type superclassto an object of its subclass. For example,

ref=studentOb ect// erson referencepointstoa //Studentobje}


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Polymorphism

Now suppose we have a getName method in our superclassPerson, and we override this method in both the subclassesStudent and Employee.

publicclassEmployee{ publicStringgetName() Sys em. u.prin ln( EployeNa e+n me)retur ae}}


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Polymorphism

Going back to our main method, when we try to call thegetName method of the reference Person ref, the getNamemethod of the Student object will be called.

Now, if we assign ref to an Employee object, the getNamemethod of Employee will be called.


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Polymorphism


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Polymorphism

Another example that illustrates polymorphism is when wetry to pass references to methods.

Suppose we have a static method printInformation thattakes in a Person reference as parameter.


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Polymorphism

We can actually pass a reference of type Employee andtype Student to the printInformation method as long as it is asubclass of the class Person.

pri tnormatin(tdnO ect)pri tnormatin(mlye jec;}


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It formalizes polymorphism. It defines polymorphism in adeclarative way, unrelated to implementation.

It is the key to theplug-n-playability of an architecture.

Interface


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It is a special form of association that models a whole-partrelationship between an aggregate (whole) and its parts.

Aggregation

Team Athletes


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Summary

Object Technologies

Objects

Object's State

Object's Behavior

Object's Identity

Four Basic Principles of Object-orientation

Abstraction

Encapsulation

Modularity

Hierarchy

Documents

MELJUN CORTES JEDI Slides-2.1 Object-Oriented Concepts