encapsulation and information hiding

8/7/2019 encapsulation and information hiding

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Class and objects



Topics for CAT II

Encapsulation and information hiding

Classes and subclasses

Separation of behavior and implementation

Modules in programming language

Inheritance

QUIZ II

Polymorphism

Collection class and protocol

Garbage collection Activation records

Object oriented design



Encapsulation and Information hiding

Encapsulation include behavior in the same container as data

encapsulation is the inclusion of one thing within anotherthing

the methods and the data

In Object Oriented Programming, encapsulation is anattribute of object design. It means that all of the object'sdata is contained and hidden in the object and access to itrestricted to members of that class.

± Public : All Objects can access it.

± Protected : Access is limited to members of the same class or descendants.

± Private : Access is limited to members of the same class.

± Internal : Access is limited to the current class

± Protected Internal : Access is limited to the current class or types derived from the containingclass.



Encapsulation refers to the binding of data

with the methods that operate on that data.

you can have encapsulated data that is not

hidden at all.

Hiding information in that manner isolates

uses from requiring knowledge of the design

to use a module and changing those decisions.



INFORMATION HIDING

Inf ormation hiding is the principle of

segregation of design decisions in a computer

program that are most likely to change, thus

protecting other parts of the program from

modifications.



Example of inf ormation hiding

Information hiding serves as an effective criterion fordividing any piece of equipment, software or hardware,into modules of functionality.

For instance a car is a complex piece of equipment. In order to make the design, manufacturing, and

maintenance of a car reasonable, the complex piece of equipment is divided into modules with particularinterfaces hiding design decisions.

By designing a car in this fashion, a car manufacturercan also offer various options while still having avehicle which is economical to manufacture.



Encapsulation

object contain both data structure and set of operation used to manipulate it

Information hidingseparate external aspect of an object from its

internal details which are hidden from outside

allows internal detail of an object to be

changed without affecting application that used itprovide external detail remain same

provides data independence



Methods and messages

METHOD

Define behavior of object as a set of

encapsulated function MESSAGE

Request from one object to another asking

second object to execute one of the method



Data Abstraction

Abstract

We can't access the private data of a class directly

class A

{int x;

};

main()

{A a1;

a1.x = 100; Error

}



Data Encapsulation

private datas and public functions binded together like a capsule

class A

{

int x;

public:

int y;

void getA()

{

x = 199;

cout << "X = " << x << endl;

}

};

main()

{

A a1;

a1.y = 200;

a1.getA();

}



Structure Oriented Programs

We write the programs for aimed Results

eg: C, Fortran, Cobol etc

Object Oriented Program

We write the programs for the DeclaredData



Types of Programming in Java

1. OOPS

Client/Server Applications

Using GUI Tools

2. NetworkProtocals (set of Rules and Regulations)

FTP

HTTP

3. InternetServer Side Programs

(servlet,jsp,ejb etc)



OOPS concepts not in Java

Operator Overloading

Multiple Inheritance(upto Interface)Hierarhical Inheritance

Hybrid Inheritance

TemplatesPointers



OOPS in Java

1. Class

2. Object3. Data Abstraction & Encapsulation

4. Polymorphism

5. Inheritance6. Exception



Class

Collection of private data/variables and public functions/methods

Variable

To store a value

Array

To store more than one value into a variable //int month[]; month = new int[12] ;Structure

To store more than one data type into a variable

struct Stud

{

int no;

char na;

};

Object

Allocates Memory

Its a variable

Used to access the class data and functions



Java

Collection of Packages(Directories)

Package

Collection of Classes and Interfaces

ClassCollection of private data and public functions

Interface

Collection of public final variables and public abstract methods

JVM

Java Virtual Machine

Used to convert the sourcecode to Machinecode



Structure of java Prg:

[package <Pname>;]

[import <Pname>.*;]

class <Cname>

{

}

class <Cname>

{

}

.

.

.

class <Cname>

{

public static void main(String args[])

{

}



The keyword public denotes that a method can becalled from code in other classes, or that a classmay be used by classes outside the class hierarchy.

The keyword static in front of a method indicates astatic method, which is associated only with theclass and not with any specific instance of thatclass. Only static methods can be invoked without a

reference to an object. Static methods cannotaccess any method variables that are not static.

The keyword void indicates that the main methoddoes not return any value to the caller.

T

he method name "main" is not a keyword in theJava language. It is simply the name of the methodthe Java launcher calls to pass control to theprogram.

String arg[]- command line arguments



Printing statement

print

Used to print the content and place the cursor insame line

syn:System.out.print([String]);

println

Used to print the content and place the cursor in

next linesyn:

System.out.println([String]);



class sample

{

public static void main(String args[]){

System.out.println(hello);

}

}



To Compile

javac clsname.java

(if there is no compile time errors in our prg then)clsname.class

T

o Run java clsname

We get the output



Class in javaclass box{

double width;

double height;

double depth;

}

class demo

{


{

box mybox =new box();

double vol;

mybox. Width=10;

mybox height=20;

mybox height=30;

Vol =mybox. Width*mybox height*mybox height

}



Class variable = new class()

Box mybox; ---------------->Mybox = new box()----

null

mybox

Width

Height

Depth



class box{

double width;

double height;

double depth;

}class demo

{


{

box mybox1 =new box();

box mybox 2=new box();

double vol;

mybox1. Width=10;

mybox1height=20;

mybox1 height=30;

mybox2. Width=10;

mybox2 height=20;mybox2 height=30;

Vol =mybox1. Width*mybox1 height*mybox1 height;

Vol =mybox2 Width*mybox2 height*mybox2 height;

}

}



class box{

double width;

double height;

double depth;

void volume(){

System.out.println(width*height*depth);

}

}

class demo

{


{


box mybox2=new box();

double vol;

mybox1 Width=10;

mybox1height=20;

mybox1 height=30;

mybox2 Width=10;mybox2 height=20;

mybox2 height=30;

mybox1.volume();

mybox2.volume();

}

}



class box{

double width;

double height;

double depth;

double volume(){

return (width*height*depth);}

}

class demo

{


{



double vol;

mybox1 Width=10;

mybox1height=20;

mybox1 height=30;

mybox2 Width=10;

mybox2 height=20;

mybox2 height=30;

vol = mybox1.volume();

system.out.println(volume is+vol);


system.out.println(volume is+vol);



METHODS THAT TAKES PARAMETER

class box{

double width;

double height;

double depth;

double volume(){

return (width*height*depth);

}

void setdimention( double w, double h,double d){

width =w;

height =h;

depth =d;

}

}



class demo

{




double vol;

mybox1.setdimention(10,20,15);

mybox2.setdimention(10,20,15);

mybox1 Width=10;

mybox1height=20;

mybox1 height=30;

mybox2 Width=10;mybox2 height=20;

mybox2 height=30;


system.out.println(³volume is´+vol);


system.out.println(³volume is´+vol);

}



Superclass and subclass

Superclass or parent class is the one from which

another class inherits attributes and behavior

Sub class or child class is the class that inherits

attribute and behavior from Superclass

Example air ticket can be of two types

confirmed and requested it has various attribute

such as flight number, date, time, destination both

types of air ticket inherits these common attributes

the conformed ticket will have seat number while

requested ticket will have a status attribute



Class: AIRTECKET

Attributes:FLIGHT NAME

DATE

TIME

DESTINATION

Class:

REQUESTEDTICKET

Attributes:

FLIGHT NAME

DATE

TIME

DESTINATION

Class:

CONFIRMTICKET

Attributes:

FLIGHT NAME

DATE

TIME

DESTINATION

Own Attribute:

SEATNUMBER

Own Attribute:

STATUS



Relation ship between class

Class and object are related to and interact

with each other

In oop object performs action in response tomessage from other object defining the

receiving object behaviour

Kind of

Is a

Part of

Has a



Kind of Relationship

Sub class is a type of superclass

Confirmed ticket Ticket



Is a Relationship

Sub class is a type of superclass

Ticket class is superclass confirm class is subclass conform ticket to newyork is an object of

confirm ticket class

Confirmed ticket

TicketTicket for

NEWYORK



Part of Relationship

When class is element of another class it is part

of class

address student



Has a Relationship

Reverse of part of relation ship

Student details address



Access specifiers

Public

Private

Protected Friendly or package



modifiers

Static

Final

Abstract Native

Modifiers determine how the data members andmethods are used in other class and objects



Diff between access specifier and

modifier

Access specifier defines the accessibility of

data member in the class

Modifier determines how these methods areused and modified by other class

Static variable, methods, innerclass

Final variable, methods, class

Abstract methods, class

Native methods



Passing arguments

Passing arguments by value

Passing arguments by reference



Formal parameter

Actual parameter

Value 1

Value 2

0X123456

0X123777

New

memory

PASSING ARGUMENTS AS VALUE



When arguments of primitive data type such

as int float are passed to method they arepassed as value

When arguments are passed by value a copy

of value of actual arguments is passed to

formal arguments of called method which is

maintained in different memory

When called method changes the value of the

arguments the changes is not reflected in theactual arguments



Class passbyvalue

{

void calling()

{

int value =5;S.o.pln(The value of variable is:+value);

called(value);//actual parameter

S.o.pln(The value of variable af ter change in called method is:+value);

}

void called( int passedvalue ) //f ormal parameter

{

passedvalue = 10;

}

}

Class passbyvaluetest

{


passbyvalue pbv = new passbyvalue();

pbv.calling();

}

}



Formal parameter

Actual parameter

Value 1

Value 2

0X123456

0X123456

Same

memory

PASSING ARGUMENTS AS REFERENCE

Cl f bj t



Class ref object

{

int val;

}

Class passbyref erence

{void calling()

{

rerobject ro new f erobject();

ro.val = 5;

S.o.pln(The value of variable is:+ ro.val);

called(ro);//actual parameter

S.o.pln(The value of variable af ter change in called method is:+ro.val);

}

void called( ref object ro ) //f ormal parameter

{

ro.val = 10;

}

}

Class passbyvalueref erence

{


{

passbyref erence pbr = new passbyref erence();

pbr.calling();

}



Creating Your Own Packages

Each package class must be stored in a file in an

appropriately named directory

The source code file for each package class must contain a

package statement as its first non-commented statement

package pack age_name;

Several packages can be stored in the same directory

Classes in different directories cannot be part of the same

package



class student{

int regno;

string name;

public string (int reg, string na)

{

regno = reg;name = na;

}

public void print()

{

S.o.pln(³\n register number:´+regno);

S.o.pln(³\n name:´ +name);}

}

class diploma



class diploma

{

int regno;

String disipline;

String year;

public diploma(int reg, String dis, String ye){

regno = reg;

disipline= dis;

year = ye;

}

public void print()

{ S.o.pln(³\n course:´+disipline);

S.o.pln(³\n year:´ +year);

}

}

class demo

{


student s1 =new student(1,´kumar´);

Diploma d1 = new diploma(1,´computer´,´I year´);

s1.print();

d1.print();

}

}

P k ll



Package college;

public class student

{

int regno;

string name;public string (int reg, string na)

{

regno = reg;

name = na;

}public void print()

{

S.o.pln(\n register number:+regno);

S.o.pln(\n name: +name);

}}

Package course;



Package course;

public class diploma

{

int regno;

String disipline;String year;

public diploma(int reg, String dis, String ye)

{

regno = reg;

disipline= dis;year = ye;

}

public void print()

{

S.o.pln(\n register number:+disipline);

S.o.pln(\n name: +year);

}

}



import college.*;

import course.*;class demo

{


{

student s1 =new student(1,kumar);Diploma d1 = new diploma(1,computer,I year);

s1.print();

d1.print();

}

}



Inheritance

Allows programmers to customize a class for a

specific purpose, without actually modifying the

original class (the superclass) The derived class (subclass) is allowed to add

methods or redefine them

The subclass can add variables, but cannot

redefine them





Inheritance Example

Class C is a subclass of class B (its superclass) if itsdeclaration has the form

class C extends B {«

}

The subclass is a s peci al izat ion of the superclass

The superclass is a gener al izat ion of the subclass



Types of inheritance

Single inheritance

Multilevel inheritance

Interface (multiple inheritance in c++)



Single inheritance

Sub class is derived from single superclass

AIRTICKET

CONFIRMED REQUEST

SUPERCLASS

SUBCLASS SUBCLASS



EXAMPLE

Class A

{

}Class B extends A

{

}Class C extends A

{

}



Inheritance in C++

Single inheritance

Multiple inheritance

Hierarchical inheritance Multilevel inheritance

Hybrid inheritance

Multipath inheritance



A

B C

B A

B

A

D

A

B

A

B

A

C D

C

B C C

D

Single inheritance Multiple inheritance Hierarchical inheritance

Multilevel inheritanceHybrid inheritance Multipath inheritance



Single Inheritance

Here we have only two classes. One is

called as parent class (Base) and other iscalled as child class (Derived).

Class B

Child or Derived Class

Class A

Parent or Base Class



syntax

class derivedclassname : visibilitymobe baseclassname

{

};

Visibility mode can be

private

public

protected



Visibility of inherited members

Base class visibility derived class visibility

Public derived

DCVPrivate derived

Private Not Not

Protected Protected Private

Public Public private

//single inheritance PUBLIC



g

class B

{

int a;

public:

int b;void getab();

void showa();

int geta();

};

Class D : public B

{int c;

Public:

Void mul();

Void display();

};

Main(){

D d;

d.getab();

d.mul();

d.display();

d.b=20;d.mul d.dis la

void B::getab()

{

a =5,b=10;

}

int B::geta()

{

return a;

}

void::showa()

{

cout<< a;}

void D::mul()

{

c =b *geta();

} void D::display()

{

cout<<b<<c;

}

Output

B=10C=50

A=5

B=20

C=100

//single inheritance private



g p

class B

{

int a;

public:

int b;void getab();

void showa();

int geta();

};

Class D : private B

{int c;

Public:

Void mul();

Void display();

};

int main(){

D d;

//d.getab();

d.mul();

d.display();

//d.b=20;

//not possible b is privated.mul d.dis la

void B::getab()

{

a =5,b=10;

}

int B::geta()

{

return a;

}

void::showa()

{

cout<< a;}

void D::mul()

{

getab();

c =b *geta();

}void D::display()

{

showa();

cout<<b<<c;

}

Output

510

50

5

10

50



PRIVATE

PROTECTED

PUBLIC

PRIVATE

PROTECTED

PUBLIC

PRIVATE

PROTECTED

PUBLIC

PRIVATE

PROTECTED

PUBLIC

CLASS D1:PUBLIC BCLASS D2:PRIVATE B

CLASS X:PUBLIC D1:PUBLIC D2



Multilevel Inheritance

Class A

Parent class for B & C

Class B

Child class for A

Parent class for C

Class C

Child class for A & B



Example for Multilevel

Inheritance

Student Class

Roll No

GetNum ( )

PutNum ( )

Test Class

Sub1, Sub2

GetMarks ( )

PutMarks ( )

Result Class

total

Display ( )

class studentvo s u en ::ge num er n a

{



class student

{

protected:

int rollnumber;

public:

void getnumber(int a);

void displaynumber();

};

class test:public student

{

protected:float sub1,sub2;

public:

void getmarks(float x,float y);

void displaymarks();

};

class result:public test

{

float total;

public:

void display();

};

{

rollnumber =a;

}

int main(){

result student1;

student1.getnumber(100);

student1.getmarks(50,50);

student1.display();

getch();

void result::display(){

total =sub1+sub2;

displaynumber();

displaymarks();

cout<<total;

}

void student::displaynumber()

{

cout<<rollnumber;

}

void test::getmarks(float x,float y)

{

sub1=x;

sub2=y;

}void test::displaymarks()

{

cout<<sub1<<sub2;

}



Multiple inheritance

Class N

Parent class2

Base Class2

Class M

Parent class1

Base class1

Class P

Child class

Derived Class

class Avoid A::geta(int x)



{

protected:

int a;

public:

void geta(int);

};

class B

{

protected:

int b;

public:

void getb(int);};

class C:public A,public B

{

int c;

public:

void add();

void display();

};

int main(){

C c;

c.geta(10);

c.getb(5);

c.add();

c.display();

getch();

}

void A::geta(int x)

{

a=x;

}

void B::getb(int y)

{

b=y;

}void C::add()

{

c=a+b;

}

void C:: display(){

cout<<a<<"\n";

cout<<b<<"\n";

cout<<c;}

C

Add()

Display()

a

Geta()

b

Getb()



Hybrid Inheritance

Class A

Parent class for B & C

Class B

Child class for A

Parent class for C

Class C

Child class for A & B

Class D

Parent class for C



Example for Hybrid Inheritance

Student Class

Roll No

GetNum ( )

PutNum ( )

Test Class

Sub1, Sub2

GetMarks ( )

PutMarks ( )

Result Class

Total=sub1+sub2+

score

Display ( )

Sports Class

Score

GetScore ( )

PutScore ( )

class student

{

void student::getnumber(int a)

{



{

protected:

int rollnumber;

public:

void getnumber(int a);

void displaynumber();

};

class test:public student

{

protected:

float sub1,sub2;

public:

void getmarks(float x,float y);

void displaymarks();

};

class result:public test

{

float total;

public:

void display();

};

{

rollnumber =a;

}

int main()

{

result student1;

student1.getnumber(100);

student1.getmarks(50,50);

student1.display();

getch();

}

void result::display(){

total =sub1+sub2;

displaynumber();

displaymarks();

cout<<total;

}

void student::displaynumber()

{

cout<<rollnumber;

}

void test::getmarks(float x,float y)

{

sub1=x;

sub2=y;

}

void test::displaymarks()

{

cout<<sub1<<sub2;

}

class sports

{

protected:

float score;

public:

void getscore(float s);

void displayscore();

};

void sports :: getscore(float s){

score =s;

}

void sports::displayscore()

{

cout<<score;

}

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