BBIT 212/ CISY 111 Object Oriented Programming (OOP)

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BBIT 212/ CISY 111

Object Oriented Programming (OOP)

OOP Concepts and getting started

with Java

08.02.2011

• Today

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• Recap

– Course objective: introduce Object Oriented Programming (using Java) and prepare us for advanced programming courses

– Your programming ideas :: will be reviewed after we have a start on java

– OOP paradigm (and in context)

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• Programming Paradigm

– programming “technique” (?) – way of thinking about programming – view of a program

• Programming Language

– consists of words, symbols, and rules for writing a program

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• Imperative Programming

– program as a collection of statements and procedures affecting data (variables)

• Object-Oriented Programming

– program as a collection of classes for interacting objects

• Functional Programming

– program as a collection of (math) functions

What is Object Oriented

Programming?

• About:

– objects and assigning responsibilities

– Objects communicate to other objects by sending messages

– Messages are received by the methods of an object

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• What are objects?

– an object represents an individual, identifiable item, unit, or entity, either real or abstract, with a well-defined role in the problem domain.

– An "object" is anything to which a concept applies

• Objects

– An object is like a black box. The internal details are hidden.

– Tangible Things as a car, printer, ...

– Roles as employee, boss, ...

– Incidents as flight, overflow, ...

– Interactions as contract, sale, ...

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• Why do we care about objects?

– Modularity - large software projects can be split up in smaller pieces.

– Reuseability - Programs can be assembled from pre-written software components.

– Extensibility - New software components can be written or developed from existing ones.

Example

• The Person class

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public class Person {

//Data

String dateOfBirth; // e.g. "21/03/1985" String name = "Salesio";

double identification;

//Methods

String getPersonName(){ return name; }

void setDateOfBirth(String newDateOfBirth){ dateOfBirth = newDateOfBirth; }

//The main method

public static void main (String [] args){

System.out.println("A Person Says: 'Hello World!!'"); }

}

public class Person { //Data

String dateOfBirth; // e.g. "21/03/1985" String name = "Salesio";

double identification; //Methods

String getPersonName(){ return name; }

void setDateOfBirth(String newDateOfBirth){ dateOfBirth = newDateOfBirth; }

//the main method

public static void main (String [] args){

System.out.println("A Person Says: 'Hello World!!'"); Person kemuStudent = new Person();

System.out.println( kemuStudent.getPersonName() ) ;

kemuStudent.setDateOfBirth("21/03/1985"); System.out.println(kemuStudent.dateOfBirth); }

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• The two parts of an object

– Object = Data + Methods i.e. An object has the responsibility to know and the responsibility to do.

Exercise

• Objective:

– Identify objects and identify relevant data and methods (members of the class)

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• In the context of the ongoing police reforms in

Kenya, the Officer Commanding (a local police)

Station has approached you to design a simple

system for the station. The idea is to

automate/computerize the police occurrence book

(OB). The OB is used to record complaints from the

wananchi at the police station. A record of a

complaint shows, among other things the following:

– The police officer who attended to the mwananchi, the date of incidence, details of the person reporting, the report from the mwananchi, etc

• After listening to the mwananchi, the police officer

must indicate on the form whether the reported

incident is a theft, murder, disagreement, accident

or any other

Exercise

• In two classes have been indentified:

– PoliceOfficer – OccurrenceBook

• Required:

– Identify associated data and methods (please work with a colleague next to you)

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• 10 Minutes

• Consolidation of results

Please note down the results!

• Basic terminologies/concepts of OOP

– Abstraction – Encapsulation – Inheritance – Polymorphism – Aggregation

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Basic terminologies/concepts of OOP

• Abstraction is the representation of the

essential features of an object. These are

‘encapsulated’ into an abstract data type.

Create a model from a problem with abstraction.

Represents (relevant) features of the problem domain (from your perspective).

• Encapsulation is the practice of including in an

object everything it needs hidden from other

objects. The internal state is usually not

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• Inheritance means that one class inherits the

characteristics of another class.

– This is also called a “is a” relationship:

• A car is a vehicle • A dog is an animal • Etc

• Polymorphism means “having many forms”. It

allows different objects to respond to the

same message in different ways, the response

specific to the type of the object.

• E.g.

– the message displayDetails() of the Person class should give different results when send to a PoliceOfficer object (e.g. the rank number).

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• Aggregation describes a “has a” relationship.

One object is a part of another object.

• E.g.

– A Bus/car has wheels

– A company has departments

• In an aggregation relationship, the child class instance can outlive its parent class (Basic aggregation)

• There are cases that a child class's instance lifecycle is dependent on the parent class's instance lifecycle (composition aggregation)

– a parent class instance will always have at least one child class instance. when the parent instance is removed/destroyed, the child instance is

automatically removed/destroyed.

– A part (child) class can only be related to one instance of the parent class

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• Behaviour and Messages

– The most important aspect of an object is its

behaviour (the things it can do). A behaviour is

initiated by sending a message to the object (calling a method)

• Basic terminologies/concepts of OOP

– Abstraction – Encapsulation – Inheritance – Polymorphism – Aggregation

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• Questions?

JAVA

• Is used for creating:

– intelligent consumer-electronic devices (cell phones)

– Web pages with dynamic content – large-scale enterprise applications

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16 • Java programs normally undergo four phases:

• Edit (Source code (.java))

Programmer writes program (and stores program on disk) • Compile (Byte codes (.class) , as (.exe) in c++

Compiler creates bytecodes from program (.class as .exe in c++₎

• Load

Class loader stores bytecodes in memory • Execute

Interpreter: translates bytecodes into machine language

• Other concepts

– The Java Application Programming Interface (API)

• a large collection of ready-made software components. It is grouped into libraries of related classes and interfaces; these libraries are known as packages.

• E.g. System.out.*; java.util.* – Java Virtual Machine (JVM)

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Portability of Java

• Through the Java VM, the same application is

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Java technology series

• Java EE vs. Java SE

– EE: enterprise edition (web services, distribution, RMI, …) – SE: standard edition (stand alone applications)

• Development Tools

– The main tools you'll be using are the javac compiler, the java launcher (java), and the javadoc documentation tool.

• Application Programming Interface (API)

– Java SE Development Kit 6 (JDK 6)

– Offers a wide array of useful classes ready for use in your own applications.

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• User Interface Toolkits

– Swing and Java 2D toolkits to create Graphical User Interfaces (GUIs).

• Integration Libraries

– Application Programming Interface (API) – Java RMI (Remote Method Invocation) over

Internet and Inter-ORB (Object Request Broker) protocol technology enable database access

• Part 2: Getting started with Java (Using

Jcreator)

• Exercise objective:

– Get started with Java and understand foundations of a Java program

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• Required

– Using jCreator, edit (create), compile (build)and run a simple java application that displays “Hello World”

– 20 Mins (because of the typing involved) setting up JCreator?

public class HelloWorld

{

//main method

public static void main (String args [])

{

System.out.println("Hello World!");

}

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A closer look

• In the Java programming language, every

application must contain a main method whose

signature is:

• public static void main(String[] args)

– The modifiers public and static can be written in either order (public static or static public).

– You can name the argument anything you want, but most programmers choose "args" or "argv.“

– This is the string array that will contains the command line arguments.

• The main method is the entry point for your application and will subsequently invoke all the other methods required by your program.

• System.out.println("Hello World!");

– uses the System class from the API to print the "Hello World!" message to standard output.

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• Extended Assignment

– 1. include simple arithmetic in the “HelloWorld” – 2. Create sample classes (with relevant methods)

from the “police reforms” example

Testing a better way of communication

• Visit the address:

http://oop2011jan.wordpress.com/

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• Thanks

• The two steps of Object Oriented

Programming

– Making Classes: Creating, extending or reusing abstract data types.

– Making Objects interact: Creating objects from abstract data types and defining their