05-CCFP4.0_OOP Using Java

OO Programming using Java

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Copyright 2013-2014, Infosys Limited ConfidentialConfidential

Copyright Guideline 2013 Infosys Limited, Bangalore, India. All Rights Reserved.

Infosys believes the information in this document is accurate as of its publication date; suchinformation is subject to change without notice. Infosys acknowledges the proprietary rights ofother companies to the trademarks, product names and such other intellectual property rightsmentioned in this document. Except as expressly permitted, neither this documentation norany part of it may be reproduced, stored in a retrieval system, or transmitted in any form or byany means, electronic, mechanical, printing, photocopying, recording or otherwise, without theprior permission of Infosys Limited and/ or any named intellectual property rights holdersunder this document.

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Course Information

Course Code: CCFP4.0-OOP

Course Name: OO Programming using Java

Document Number: OOP-05

Version Number: V4.0

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OO Concepts - II



OO Constructs - II Static Polymorphism

Method and Constructor Overloading

Relationships

Inheritance

Aggregation

Association

Interfaces

Packages

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Static Polymorphism



Method Overloading

Two or more methods in a class can have the same name, if their argument listsare different

Argument list could differ in

Number of parameters

Data type of parameters

Sequence of data type of parameters

Binding of method call to its definition happens at compile time

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Guided Activity: Advanced OO Concepts - Assignment 61

Demo: Advanced OO Concepts - Assignment 62

Quiz: OO Concepts - Part I - Assignment 63


Constructor Overloading

Just like other methods, constructors also can be overloaded

Based on constructor invoked during object creation, either the parameterized or default constructor will be invoked

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Demo: Advanced OO Concepts Assignment - 64

Guided Activity: Advanced OO Concepts- Assignment - 65

Introduction to Relationships

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Relationships

Few kinds of relationships between classes :

Generalization and specialization (is-a relationship)

Aggregation (has-a relationship)

Association (uses-a relationship)

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Inheritance

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Inheritance (1 of 2)

Concept wherein a class shares some common structure or behavior with one or more classes

Generalized class also known as parent class or base class or super class

Specialized class also known as child class or derived class or sub class

Types of inheritance

Single level inheritance

Multilevel inheritance

Hierarchical inheritance

Base class constructors are not inherited in the derived class

Base class constructors may need to be invoked to initialize the inherited datamembers in the derived class during the creation of derived class object

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Inheritance (2 of 2) Base class constructors may be default or parameterized constructors

If the base class constructor is a default one, it is automatically invoked when the objectof the base/derived class is created

If the base class constructor is a parameterized one, it has to be explicitly invoked by thederived class during the object creation

Base class constructors can be invoked using super keyword

The super keyword can be used to refer members and constructors of a base class from a derived class

super keyword can also be used to prevent instance variable hiding

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Quiz: Advanced OO Concepts Assignment 68


Inheritance protected access specifier If an instance variable in the base class has the protected access specifier

It can be directly accessed inside the subclasses

This is useful as methods of the child class can access the parent class variables directly

In UML notation # is used to represent the protected access specifier

Note: More on protected access specifier would be dealt along with packages topic

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Aggregation

A simplified version of the demo is provided here to summarize aggregation

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Demo: Advanced OO Concepts - Assignment - 69

classAddress{privateStringaddressLine;publicAddress(StringaddressLine){

this.addressLine=addressLine;}publicStringgetAddressLine(){

returnaddressLine;}

}classCustomer{privateAddressaddress;publicCustomer(Addressaddress){

this.address=address;}publicAddressgetAddress(){

returnaddress;}

}

classRetail{publicstaticvoidmain(Stringargs[]){

Addressadd=newAddress(No.333);CustomercustObj=newCustomer(add);//CheckifaddressiscorrectlysavedAddresstemp=custObj.getAddress();System.out.println("Address:");System.out.println(temp.getAddressLine());

}}

Stack Heap

add addressLine No.333

custObj

addresstemp


Quiz

A. Consider a scenario of an employee management system. The employee details stored are empID, empName and dateOfJoining. The developer creates two classes called Employee and Date to store the employee details and the date respectively. What is the relationship between the classes?

B. Write a Java code to implement the above scenario.

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Association Loosely coupled relationship

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Method Overriding



Method Overriding

A child class can modify methods inherited from a parent class

The child class can create a method with different functionality than the parents method but with the same:

Name

Return type

Argument list and order

This feature is known as Method Overriding

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Dynamic Polymorphism (1 of 2)

A child class(ex. Derived) object can be assigned to a parent class reference(ex.Base)

The parent class reference can be used to access the child class methods

Only those methods that were originally present in the parent class and later overriddenby the child class can be called in this way

A new method defined in the child class cannot be called using the base class reference

JVM calls a method based on the data type of the object referred by it and NOTbased on the data type of the reference

This decision is taken at runtime and hence this is known as dynamic binding-linking between the method call and the method definition happens at runtime

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BasebObj=newDerived();


Dynamic Polymorphism (2 of 2)22

Demo: Advanced OO Concepts - Assignment 74, 75


Method overloading vs. method overriding23

Method Overloading Method Overriding

More than one method having same namebut different argument list and with differentimplementation

More than one method having the samename and same argument list and withdifferent implementation

Return type may or may not be different Return type should be the same in theoverridden method and correspondingmethod in the base class

Overloaded methods can be in the sameclass

Overriding happens between base andderived class

Invoking is done based on signature of themethod

Invoking is done based on the data type ofthe object referred by the reference

Binding happens at compile time Binding happens at Runtime

abstract keyword



abstract keyword (1 of 2)

The abstract keyword can be used with method to make it abstract

An abstract method signifies that its functionality is not defined, but the prototypeis known

Abstract methods

Only the signature of the method is specified, no implementation for the method

Used to put some kind of compulsion on the class which inherits from this class. i.e., theclass which inherits MUST provide the implementation of the method else it should bedeclared abstract

There is only the declaration of the method followed by a semicolon

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abstractpublicvoiddisplayCustomerInformation();

Guided Activity : Advanced OO Concepts - Assignment 76


abstract keyword (2 of 2)

Abstract Class -

If a class has one or more abstract methods declared inside it, then the class must bedeclared abstract

An abstract class cannot be instantiated ie. objects cannot be created for an abstractclass but a reference variable of abstract class can be created

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abstractclassCustomer{abstractpublicvoiddisplayCustomerInformation();

}

Guided Activity : OO Concepts - Part II Assignment 78



Quizabstract class Example{public void disp(){System.out.println("disp in Example");}public abstract void display();}abstract class Example1 extends Example{public void display1(){System.out.println("display in Example1");}}

class Example2 extends Example1{public void display(){System.out.println("display in Example2");}}class Demo{public static void main(String args[]){Example1 obj=new Example1();obj.display();}}

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Food for thought Consider the modified Purchase class diagram

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PurchaseBillbillId:intcustomer:CustomerbillAmount:floattypeOfCustomer:String+Purchase(Customer,float,String)+getBillId():int+getCustomer():Customer+calculateBillAmount(String,float):void+displayBill():void

The customer reference is placed as an instance variable inside the Purchase class. Depending upon thetype of customer decided during billing time , this customer reference can be made to point to an objectof Regular customer or Privileged Customer. In addition, a variable typeOfCustomer is kept to keep trackof the kind of customer

This is possible because a base class reference can point to an object of derived type.

Identifytherelationshipbetween

CustomerandPurchaseclass?

Interfaces



Interfaces

Interfaces are useful when an unrelated set of classes have a common set of method(s)

Interface can be defined as follows:

All the variables are public static final variables by default

All the methods are public and abstract by default

It is represented by the UML symbol

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Guided Activity: Interfaces - Assignment 79

{//methods}

Demo: Interfaces - Assignment 80


Abstract Classes vs. Interfaces31

Abstract Classes Interfaces

Can have concrete methods Can have only abstract methods

Can have variables of any access specifier

Can have only public static final (constant) data members

Concrete methods can have any access specifier

All member methods are public and abstract by default

A class can extend only one abstract class

A class can implement any number of interfaces


Quiz Say true or false

An abstract class may have a non abstract method

If the class has one abstract method then that class should be declared abstract

All the methods of an interface are abstract by default

All the methods of an abstract class are abstract by default

A class can implement any number of interfaces

An object of an interface can be instantiated

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Quiz What is the output of the following code snippet?

interface Example{int num=90;public abstract void disp();public abstract void display();}class Example1 implements Example{public void display(){System.out.println("display in Example1");}}class Demo{public static void main(String args[]){Example1 obj=new Example1();obj.display();}}

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Quiz What is the output of the following code snippet?

interface Example{int num=90;public abstract void disp();public abstract void display();}class Example1 implements Example{public void display(){System.out.println("display in Example1");}public void disp(){int num=900;System.out.println(num);}}class Demo{public static void main(String args[]){Example1 obj=new Example1();obj.display();obj.disp();}

}

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Packages



Method1Using the fully qualified class name

Eg: java.lang.Math.sqrt(varOne);

Method2Import the package and use the class name

Eg: import java.lang.Math;Math.sqrt(varOne);

Packages (1 of 4)

In Java, Packages are used for grouping a number of related classes and interfaces together into a single unit

In other object oriented languages like C++ a similar concept of namespaces exist

Package types Built in and user defined

Accessing Classes from the Packages

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Guided Activity: Packages - Assignment 81

Demo: Packages - Assignment 82

Copyright 2013-2014, Infosys Limited ConfidentialConfidential37

Built-in-Packages (2 of 4)

These packages provide the set of classes, interfaces andmethods for the programmer to develop an application in an easierway

Programmer can reuse everything from the package and saveeffort

Few examples of built in packages java.lang

java.io

java.sql java.awt java.net Java.util


Packages (3 of 4)38

Accessibleonlywithintheclassprivate Nokeyword,Accessibleonlywithinthepackagedefault Similartodefaultwiththeadditionthatitisavailabletoallchildclasses;thatis,evenifchildclassisinadifferentpackageprotected

Accessibletoallpublic

Accessibleto public protected default privateSame class Yes Yes Yes Yes

All classesinthesamepackage Yes Yes Yes No

All subclassesinthedifferentpackage Yes Yes No No

All classesinthedifferentpackage Yes No No No


Packages (4 of 4)

Benefits

Logical grouping of classes and interfaces

Avoids name clashes

Provides four level of access specification to the members of a class in a package

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overriddenmethodinchildclass

Methodinparentclass

public protected default private

public Yes No No No

protected Yes Yes No No

default Yes Yes Yes No

private Privatemethodscannot beoverridden


Scanner class The java.util.Scanner class is a simple text scanner which can parse primitive

types and strings using regular expressions. To read a string or integer,

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import java.util.Scanner;public class ScannerDemo {

public static void main(String[] args) {// TODO Auto-generated method stubScanner ob=new Scanner(System.in);System.out.println("Enter your username: ");String name=ob.nextLine();System.out.println("Enter a Number");int number=ob.nextInt();System.out.println(name); System.out.println(number);

}

}


Quiz Consider the following scenario:

Let us consider a Package1 has a public class called class A. class A has the following member variables:

private int num1

protected int num2

int num3

Let us consider another package Package2 which has a class called class B which is extended from class A of Package1.

Which of the data members of class A can be accessed in class B?

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Quizclass Base{int basevar;public void commonMethod(){System.out.println("Common method of base");}}class Der extends Base{private void commonMethod(){System.out.println("Common method of derived");}}class Demo{public static void main(String args[]){Der obj=new Der();obj.commonMethod();}}

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Quizabstract class Example{public void disp(){System.out.println("disp in Example");}public abstract void display();}class Example1 extends Example{private void display(){System.out.println("display in Example1");}}class Demo{public static void main(String args[]){Example obj=new Example1();obj.display();}}

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Roy and the Retail Application Roy and team was successful in coming up with the first version of the retail

application

Roy wants you to have a look at the application

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Demo : Packages - Assignment 83


Retail Application we have learnt45

1. Static Polymorphism2. Introduction to Relationships3. Dynamic Polymorphism4. Abstract5. Interface


Self-Study46

1. Refer to udacity course: https://www.udacity.com/courses

Course name: Introduction to Programming in Java

Lessons: Interfaces and Inheritance

Links: http://sourcemaking.com/refactoring/replace-conditional-with-polymorphism

2013 Infosys Limited, Bangalore, India. All Rights Reserved. Infosys believes the information in this document is accurate as of its publication date; such information is subject to changewithout notice. Infosys acknowledges the proprietary rights of other companies to the trademarks, product names and such other intellectual property rights mentioned in this document. Exceptas expressly permitted, neither this documentation nor any part of it may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, printing,photocopying, recording or otherwise, without the prior permission of Infosys Limited and/ or any named intellectual property rights holders under this document.

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05-CCFP4.0_OOP Using Java