COMPUTER APPLICATION
Chapter 1
Concept of Objects
1) Concept of Objects.
Ans. An Object is an identifiable entity with certain characteristics and behaviour.
You yourself are an example of an object. Your:
Characteristics – Eyes, Ears, Nose, Hands, Legs.
Behaviour – Walk, Talk, Eat ,Sleep, Dance.
DOG. Its:
Characteristics – Name, Colour, Breed.
Behaviour – Barking, Wagging tail.
BIKE. Its:
Characteristics – No of gears, No of brakes, Wheels.
Behaviour – Braking, Accelerating, Change gear.
An object has a state. It has certain characteristics and attributes like size, shape and colour. A change in these attributes are called as the objects behaviour. Each object has a unique identity just as we all have our names to identify ourselves.
Take for example TV:
The screen size(17”), buttons for switching it on and off and channel change are its state. The motion picture of a TV is its behaviour. The serial number(TI974) which distinguishes it from other TVs is its identity.

2) Concept of converting real world objects into software objects.
Ans. Our aim is to implement a real world object into a software object.
Real world objects have physical characteristics(state) and behaviour.
EXAMPLE – Motor Bike
Characteristics - Two wheels, No of gears, Current gear.
Behaviour – Braking, Accelerating, Changing gears.
Software objects also have state and behaviour .
• State is maintained through variables and data items.
• Behaviour is implemented through functions called methods.
Object - Calculator
Characteristics is implemented through variables and attributes – 0 to 9.
Behaviour is implemented by functions/methods +,-,*,/.
Object – Person
Attributes – First name, Last name, Age, Weight.
Methods – getFirstname(), getLastname(), getAge(), setAge().
Class Object
• Abstract.
• A class is a set of objects.

• A class is an object maker. • Real.
• An object is an identifiable entity. Building is an object.
• Two objects cannot be same in the real world. Different in name and location.

3) Concept of Data Abstraction.
Ans. Data Abstraction refers to the act of representing essential features without including the background details or explanations.
Example: You are driving a car. You only know the essential features to drive a car. Example: gear handling, steering handling, use of clutch, accelerator, brakes, etc. But while driving do get into internal details of car like wiring, motor working, etc? You can change the gears or apply brakes. What is happening inside is hidden from you. This is abstraction where you only know the essential things to drive a car without including background details or explanations. Example: Computer – We are using the computer but what is happening inside is hidden from you.
Example: Map of Bombay – HVB Academy will not be shown.

4) Concept of Encapsulation.
Ans. Every real world object has :
• Characteristics – variables – num1, num2.
• Behaviour – functions - add(), sub().
The wrapping up of data and functions into a single unit called a class is called Encapsulation.
Example: ATM
• Variables/Characteristics – balance, withdraw, deposit.
• Behaviour/Methods – getBalance(), setDeposit(), setWithdraw().
To access variables we have to use methods. Variables depend on methods.
Data Abstraction – User does not know from where balance is going to come.

5) Message passing among objects.
Ans. When objects need to interact with one another, they pass/request information to one another. This interaction is known as message passing. That is objects interact with each other through messages.
Example: One department object sends message to another department object to retrieve some information. This is known as message passing.
Sometimes the object receiving the message needs more information so it knows what exactly to do. For example to send a message to change gears, you have to indicate which gear you want. This information passed along with messages are known as parameters.
Example: To change the gear of a bike to the 2nd gear, you need to send a message to the method changeGear of object bike. Also, a parameter needs to be sent that you want to change to 2nd gear. Software objects interact and communicate with each other using messages. 6) How do objects encapsulate state and behaviour?
Ans. An Object is an identifiable entity with certain characteristics, attributes and behaviour. The state of an object depends upon the values of its attributes at any given point of time.
Since state and behaviour are interwoven, they are said to be encapsulate state and behaviour. For instance, a car object has characteristics like number of wheels, seats, etc. Its state is represented as halted, moving or stationary. And its behaviour is: it can move, stop, blow horn, etc. Now all these are wrapped up in the form of a car. We cannot segregate them. Thus, we can say that objects encapsulate their ‘state’ and ‘behaviour’ and as both of these are interlinked, they cannot exist separately.

7) How is abstraction relative to the user or perspective?
Ans. An abstraction is a named collection of attributes and behaviour relevant to modelling a given entity for some particular purpose. Abstraction is always relative to the purpose of the user. For instance, if we talk of a student, we can talk of anything that belongs to her in the real world like her name, brothers, sisters, parents, profession, locality she lives in, marks obtained by her, her roll-number in the class, her medical history, her talents, her awards, etc. But when we talk of student result tracking system, the abstraction for it would be- her roll number, name, marks obtained. For extra-curricular activities, the abstraction would be- her roll number, talents, awards, etc.

8) What are methods?
Ans. Methods are member functions representing some behaviour of an object.

9) What is information hiding?
Ans. It is the process of hiding all the secrets of an object that do not contribute to its essential characteristics ; the structure of an object is hidden, as well as the implementation of its methods. Only the essential characteristics of object are visible.

10) How is Data Abstraction associated with Encapsulation?
Ans. Both are complementary: abstraction focuses upon the observable behaviour of an object, whereas encapsulation focuses upon the implementation that gives rise to this behaviour.

Chapter 2
Introducing Classes

1)Concept of classes.
Ans. In object oriented programming objects are defined by defining a suitable class for them. A class is a set of objects which share certain common characteristics and behaviour.
A manufacturer of TV company first makes a blueprint of a TV according to some specifications that are common to all TV’s. Once the blueprint is approved TV’s are made as specified in the blueprint. There is no need for a blueprint for every TV manufactured. A single blueprint is enough to make a number of TV’s. In OOP terminology this blueprint that defines the common characteristics of objects is termed as class.

2)Concept of Polymorphism.
Ans. Many forms. One object acting different in different situations.
EXAMPLE:
Student in a class – is a student.
In family – brother or sister.
At playground – player or goalkeeper.
In computer terms it can be implemented through method overloading. Same function name acting different in different situations.
EXAMPLE:
Area(int s);
Area(int l,int b);
Area(double r);

3) Creating classes with attributes and methods’
Ans. The below tables show some of the classes with their attributes and methods.
• Class – Employee.
ATTRIBUTES METHODS empno addEmp() empname deleteEmp() desig editEmp() dept searchEmp() basic calcSalary() dob calcDA() address • Class – Student.
ATTRIBUTES METHODS rollno getData() name showData() grno computeData() engMarks computePercent() mathsMarks dob address evsMarks

• Class – Teacher
ATTRIBUTES METHODS teachersname getData() subjectTaught showData() classesTaught computeExp() noOfYearsExp computeSalary() dob address
• Class – Building.
ATTRIBUTES METHODS buildingName getData() noOfStoreys showData() noOfFlats CalcData() noOfWatertanks maintainance color 4)What do you understand by Object Factory?
Ans. An object factory is a producer of objects. It accepts some information about how to create an object such as, values depicting it’s state, and then returns an instance of that object. Valid representation and the nature of the information that are determined by the object factory and are closely tied to an abstraction represented by a class as an object factory.

5)How can you say that class is an object factory?
Ans. Basically the class is an object maker or object factory. It contains all the statements needed to create an object, it’s attributes, as well as the statements to describe operations that an object will perform. Therefore, for a student class, there can be many classes represents various abstractions, eg. a separate class for result tracking system, a separate class for extra-curricular activities, and so on.