Object-Oriented Programming (Cambridge (CIE) A Level Computer Science): Exam Questions

Objects and classes form the basic structure of Object‑Oriented Programming (OOP).

Outline the structure of a class.

Give three differences between an object and a class.

Define the term class in Object-Oriented Programming (OOP).

A library program is written using Object-Oriented Programming (OOP).

The program has one class, Book. When the program runs, it creates a separate Book object for each of the 3000 books in the library.

Explain the relationship between the class Book and the 3000 Book objects.

A cinema wants a program to manage ticket sales. Each film showing is called a screening. The program will use a class, Screening.

Draw a class diagram for Screening, to include:

• attributes and data types for the film title, the screen number, the date of the screening, the ticket price (for example 7.50) and the number of seats still available

• a method to create a Screening object and set its attributes

• a method to return the number of seats still available

• a method to change the ticket price

• a method to reduce the number of seats still available by the number of tickets sold.

A weather program uses a class, WeatherStation. The pseudocode for the class is shown. Four parts are missing and are labelled A, B, C and D.

CLASS ..........A..........

   PRIVATE StationName : STRING

   PRIVATE Temperature : REAL

   PUBLIC PROCEDURE ..........B..........(GivenName : STRING)

      StationName ← GivenName

      Temperature ← 0.0

   ..........C..........

..........D..........

Complete the pseudocode by writing the missing item for each label.

Encapsulation is one of the features of Object-Oriented Programming (OOP).

State what is meant by encapsulation, and identify the pseudocode keyword used in a class so that an attribute can only be accessed by the class's own methods.

A delivery company uses a class, Parcel. A programmer has written this pseudocode to declare the class and its constructor. The line numbers are for reference only.

01 CLASS Parcel

02    PRIVATE TrackingCode : STRING

03    PRIVATE Weight : REAL

04    PRIVATE Delivered : BOOLEAN

05    PUBLIC PROCEDURE Parcel(Code : STRING, ParcelWeight : REAL)

06       TrackingCode ← Code

07       ParcelMass ← ParcelWeight

08       Delivered ← "FALSE"

09    ENDFUNCTION

10 ENDCLASS

The pseudocode contains four errors.

Identify the line number of each error and write the corrected line.

A cinema uses an object-oriented program to sell tickets. Part of the class Ticket is shown.

CLASS Ticket

   PRIVATE TicketID : STRING

   PRIVATE Price : REAL

   PUBLIC PROCEDURE NEW(GivenID : STRING, GivenPrice : REAL)

      TicketID ← GivenID

      Price ← GivenPrice

   ENDPROCEDURE

   PUBLIC FUNCTION GetPrice() RETURNS REAL

      RETURN Price

   ENDFUNCTION

ENDCLASS

Explain how encapsulation is used in the class Ticket.

A hotel booking program uses a class, Room.

The class has these attributes:

• the room number, for example 214

• the room type, for example "Double"

• the nightly rate, for example 85.50

• whether the room is occupied

• the name of the guest in the room.

All attributes must be available only through the methods of the class.

When a Room object is created, the constructor is given the room number, the room type and the nightly rate. A new room is always unoccupied and has no guest, so the constructor sets the room to unoccupied and the guest name to an empty string.

Write pseudocode to declare the class Room, its attributes and its constructor. Do not write any other methods.

An airline uses a program written using Object-Oriented Programming (OOP). The class Flight stores the attributes FlightNumber, Destination and SeatsBooked. The class also contains several methods.

Describe what is meant by a method in a class.

A program uses the class Ticket. Part of the class is shown. The bodies of the two methods are not shown.

PRIVATE Price : REAL

PUBLIC FUNCTION GetPrice() RETURNS REAL

PUBLIC PROCEDURE SetPrice(NewPrice : REAL)

Identify which method is the getter and which method is the setter. Explain why one method is written as a function and the other as a procedure.

A weather station uses an object-oriented program. The class diagram for Sensor is shown. All the attributes are PRIVATE and all the methods are PUBLIC. The method TakeReading() reads the sensor and stores the result in LastReading.

Code outside the class now needs to output the value of LastReading. A programmer suggests changing the declaration of LastReading from PRIVATE to PUBLIC.

Explain why this change is not appropriate, and describe what the programmer should do instead.

A program for a football league is written using Object-Oriented Programming (OOP). The class Match has a constructor with two parameters.

This statement is executed:

Game12 ← NEW Match("Lions", "Eagles")

Complete the two sentences about this statement.

Game12 is an ............................................ of the class Match.

The process of creating Game12 from the class Match is called ............................................

A bank uses a program written using Object-Oriented Programming (OOP). Part of the class Account is shown.

CLASS Account

    PRIVATE AccountNumber : STRING

    PRIVATE OwnerName : STRING

    PRIVATE Balance : REAL

    PUBLIC PROCEDURE NEW(GivenNumber : STRING, GivenName : STRING)

        AccountNumber ← GivenNumber

        OwnerName ← GivenName

        Balance ← 0

    ENDPROCEDURE

    PUBLIC FUNCTION GetBalance() RETURNS REAL

        RETURN Balance

    ENDFUNCTION

    PUBLIC PROCEDURE SetOwnerName(NewName : STRING)

        OwnerName ← NewName

    ENDPROCEDURE

    PUBLIC FUNCTION Withdraw(Amount : REAL) RETURNS BOOLEAN

        IF Amount > Balance THEN

            RETURN FALSE

        ELSE

            Balance ← Balance - Amount

            RETURN TRUE

        ENDIF

    ENDFUNCTION

ENDCLASS

Complete the table. For each method, write constructor, getter or setter, or write none of these. Give a reason from the code for each answer.

A weather station program uses the class Sensor. The class contains this attribute declaration:

PRIVATE Reading : REAL

Code outside the class must be able to find the current value of Reading.

Write pseudocode for the public getter method GetReading().

A teacher uses an object-oriented program to store students' test marks. Part of the class Student is shown.

CLASS Student

   PRIVATE StudentName : STRING

   PRIVATE TestMark : INTEGER

   PUBLIC PROCEDURE NEW(GivenName : STRING)

      StudentName ← GivenName

      TestMark ← 0

   ENDPROCEDURE

   PUBLIC PROCEDURE SetTestMark(NewMark : INTEGER)

      TestMark ← NewMark

   ENDPROCEDURE

   PUBLIC FUNCTION GetTestMark() RETURNS INTEGER

      RETURN TestMark

   ENDFUNCTION

ENDCLASS

This code is written in the main program, outside the class. Line numbers are shown for reference.

01  Pupil ← NEW Student("Aisha")

02  Pupil.SetTestMark(65)

03  Pupil.TestMark ← Pupil.TestMark + 5

04  OUTPUT Pupil.GetTestMark()

Identify the line number that breaks encapsulation, and give the reason.

A hotel review program uses the class Review. The class contains this attribute declaration:

PRIVATE Rating : INTEGER

A valid rating is a whole number from 1 to 5 inclusive.

Write pseudocode for the public setter method SetRating(). The method:

• takes the new rating as a parameter

• updates Rating only if the new rating is valid

• leaves Rating unchanged if the new rating is not valid.

A program for a fuel station is written using Object-Oriented Programming (OOP). The class FuelPump has a constructor that takes a pump number and a fuel type.

The main program executes this statement:

Pump3 ← NEW FuelPump(3, "Diesel")

Describe what happens when this statement is executed.

A shop uses an object-oriented program to manage its stock. Part of the class Product is shown. The attributes must be available only through the methods of the class.

CLASS Product

   PRIVATE ProductID : STRING

   PRIVATE Price : REAL

   PRIVATE Stock : INTEGER

   PUBLIC PROCEDURE NEW(GivenID : STRING, GivenPrice : REAL, GivenStock : INTEGER)

      ProductID ← GivenID

      Price ← GivenPrice

      Stock ← GivenStock

   ENDPROCEDURE

   PUBLIC PROCEDURE SetStock(NewStock : INTEGER)

      Stock ← NewStock

   ENDPROCEDURE

   PUBLIC FUNCTION GetStock() RETURNS INTEGER

      RETURN Stock

   ENDFUNCTION

   PUBLIC FUNCTION GetPrice() RETURNS REAL

      RETURN Price

   ENDFUNCTION

ENDCLASS

This code is written in the main program, outside the class. It records the sale of 3 items and then outputs the total value of the remaining stock.

01  Item ← NEW Product("P101", 2.50, 40)

02  Item.Stock ← Item.Stock - 3

03  OUTPUT "Value of stock: ", Item.Stock * Item.Price

Lines 02 and 03 break encapsulation.

Write the pseudocode to replace lines 02 and 03 so that they perform the same task without breaking encapsulation.

A program to control the lights in an office is written using Object-Oriented Programming (OOP). The class Lamp is shown.

CLASS Lamp

   PRIVATE Room : STRING

   PRIVATE Watts : INTEGER

   PRIVATE IsOn : BOOLEAN

   PUBLIC PROCEDURE NEW(GivenRoom : STRING, GivenWatts : INTEGER)

      Room ← GivenRoom

      Watts ← GivenWatts

      IsOn ← FALSE

   ENDPROCEDURE

   PUBLIC PROCEDURE SwitchOn()

      IsOn ← TRUE

   ENDPROCEDURE

ENDCLASS

Write pseudocode statements in the main program to:

• create an object called DeskLamp with a power of 40 watts, for the room "Office"

• switch DeskLamp on.

A water supply company uses the class WaterTank. Part of the class is shown:

CLASS WaterTank

    PRIVATE Capacity : INTEGER

    PRIVATE Level : INTEGER

    PUBLIC PROCEDURE NEW(GivenCapacity : INTEGER)

        Capacity ← GivenCapacity

        Level ← 0

    ENDPROCEDURE

ENDCLASS

The attributes Capacity and Level are both measured in litres.

Two more public methods are needed. Each method takes one parameter, the number of litres. The parameter is always a positive integer.

• AddWater() adds water to the tank. If all the water fits, Level increases by the number of litres and the method returns 0. If it does not all fit, the tank is filled to Capacity and the method returns the number of litres that did not fit.

• Drain() removes water from the tank. Level must never fall below 0. This method does not return a value.

Write pseudocode for the methods AddWater() and Drain().

A program that monitors water tanks is written using Object-Oriented Programming (OOP). The class Tank is shown.

CLASS Tank

   PRIVATE Capacity : INTEGER

   PRIVATE Level : INTEGER

   PUBLIC PROCEDURE NEW(GivenCapacity : INTEGER)

      Capacity ← GivenCapacity

      Level ← 0

   ENDPROCEDURE

   PUBLIC PROCEDURE Fill(Amount : INTEGER)

      Level ← Level + Amount

      IF Level > Capacity THEN

         Level ← Capacity

      ENDIF

   ENDPROCEDURE

   PUBLIC FUNCTION GetLevel() RETURNS INTEGER

      RETURN Level

   ENDFUNCTION

ENDCLASS

The main program is:

TankA ← NEW Tank(600)

TankB ← NEW Tank(300)

TankA.Fill(250)

TankB.Fill(200)

OUTPUT TankA.GetLevel()

TankB.Fill(150)

OUTPUT TankB.GetLevel()

TankA.Fill(TankB.GetLevel())

OUTPUT TankA.GetLevel()

State the three values output by the main program, in order.

A game uses an object-oriented program. The class Character has these members:

• Health, an integer attribute that stores the character's health points

• TakeDamage(Amount : INTEGER), a procedure that the main program calls each time the character is hit. It subtracts Amount from Health and then calls CheckHealth()

• GetHealth(), a function that the main program calls to display the character's health points

• CheckHealth(), a procedure that sets another attribute, IsActive, to FALSE when Health is 0 or less. It is only called by TakeDamage()

The value of Health must only be changed by TakeDamage().

Complete the table. For each member, write the access level PUBLIC or PRIVATE and justify your choice.

In object-oriented programming (OOP), a class is made up of attributes and methods.

Describe what is meant by an attribute in OOP.

A school system is written using object-oriented programming. It has a class Person and a class Student.

The class Student inherits from the class Person.

Describe what is meant by inheritance, using these two classes in your answer.

A zoo uses an object-oriented program to keep records of its animals. The class inheritance diagram shows a parent class Animal and two derived classes, Bird and Fish.

In each class box the class name is at the top, then the attributes, then the methods.

An object Parrot is created from the class Bird.

Complete the table. Write Yes if Parrot has the attribute or method. Write No if it does not.

A sports club program uses object-oriented programming (OOP). The class Member stores the details of one club member.

The table shows some of the attributes of Member. One row has been completed for you.

Complete the table by writing the most appropriate data type for each attribute.

A sports centre is writing a program using object-oriented programming (OOP). The class CourtBooking stores the details of one booking of a tennis court.

The class has the attribute BookingRef, of data type STRING. It needs four more attributes, one for each item of data in the table. An example value is given for each item.

Complete the table. For each attribute, write a suitable identifier and the most appropriate data type.

A concert venue sells tickets using a program written with Object-Oriented Programming (OOP). The class Ticket is shown.

CLASS Ticket

   PRIVATE TicketID : STRING

   PRIVATE Price : REAL

   PRIVATE Sold : BOOLEAN

   PUBLIC PROCEDURE NEW(GivenID : STRING, GivenPrice : REAL)

      TicketID ← GivenID

      Price ← GivenPrice

      Sold ← FALSE

   ENDPROCEDURE

   PUBLIC FUNCTION GetTicketID() RETURNS STRING

      RETURN TicketID

   ENDFUNCTION

   PUBLIC FUNCTION GetPrice() RETURNS REAL

      RETURN Price

   ENDFUNCTION

   PUBLIC PROCEDURE SetPrice(NewPrice : REAL)

      Price ← NewPrice

   ENDPROCEDURE

   PUBLIC PROCEDURE SellTicket()

      Sold ← TRUE

   ENDPROCEDURE

ENDCLASS

Write pseudocode for the main program to:

• take as input a ticket ID and a price

• create a Ticket object called ThisTicket using the input values

• reduce the price of ThisTicket by 10% if its price is greater than 100.0

• sell ThisTicket

• output the ticket ID and the final price of ThisTicket.

The main program must use the methods of the class to access the attributes of ThisTicket.

An airline is writing a program to manage its staff using object-oriented programming.

The following data are stored for every member of staff:

• staff ID

• name

• date joined

• hourly rate of pay, in dollars and cents (can be edited).

There are two types of staff, and each type needs its own class.

• A pilot records the total number of whole hours they have flown.

• A cabin crew member records whether they hold a first-aid certificate or not. A cabin crew member also has a method to assign them to a section of the aircraft.

Complete the class inheritance diagram to show the attributes, methods and inheritance. In each class box the class name is at the top, then the attributes, then the methods. Use the middle row of the diagram to show the inheritance.

A library program uses object-oriented programming (OOP). The class Book has these two attributes:

• NumberOfPages stores the number of pages in the book

• OnLoan stores whether or not the book is currently borrowed.

Both attributes must be declared as PRIVATE.

Write the pseudocode declaration for each attribute.

A bank program uses object-oriented programming. The class Account is declared as follows.

CLASS Account

   PRIVATE AccountNumber : STRING

   PRIVATE Balance : REAL

   PUBLIC PROCEDURE NEW(GivenNumber : STRING)

      AccountNumber ← GivenNumber

      Balance ← 0

   ENDPROCEDURE

ENDCLASS

The class SavingsAccount inherits from Account. Its constructor must call the constructor of Account to set the account number.

Complete the pseudocode for the class SavingsAccount.

CLASS SavingsAccount .............................. Account

   PRIVATE InterestRate : REAL

   PUBLIC PROCEDURE NEW(GivenNumber : STRING, GivenRate : REAL)

      ..............................(GivenNumber)

      InterestRate ← GivenRate

   ENDPROCEDURE

ENDCLASS

A car park program uses object-oriented programming (OOP). The class ParkingTicket has three attributes. All three attributes are PRIVATE.

The constructor has already been written:

CLASS ParkingTicket

   ..............................................

   ..............................................

   ..............................................

   PUBLIC PROCEDURE NEW(GivenReg : STRING, GivenHours : REAL)

      Registration ← GivenReg

      HoursStayed ← GivenHours

      Paid ← FALSE

   ENDPROCEDURE

ENDCLASS

Complete the pseudocode by writing the three attribute declarations.

A shop program uses object-oriented programming. Three of its classes are shown.

The class Product:

CLASS Product

   PRIVATE Name : STRING

   PRIVATE Price : REAL

   PUBLIC PROCEDURE NEW(GivenName : STRING, GivenPrice : REAL)

      Name ← GivenName

      Price ← GivenPrice

   ENDPROCEDURE

ENDCLASS

The class Food:

CLASS Food INHERITS Product

   PRIVATE ShelfLife : INTEGER

   PUBLIC PROCEDURE NEW(GivenName : STRING, GivenPrice : REAL, GivenDays : INTEGER)

      SUPER.NEW(GivenName, GivenPrice)

      ShelfLife ← GivenDays

   ENDPROCEDURE

ENDCLASS

The class ChilledFood:

CLASS ChilledFood INHERITS Food

   PRIVATE Temperature : INTEGER

   PUBLIC PROCEDURE NEW(GivenName : STRING, GivenPrice : REAL)

      SUPER.NEW(GivenName, GivenPrice, 7)

      Temperature ← 4

   ENDPROCEDURE

ENDCLASS

This statement is executed:

Snack ← NEW ChilledFood("Yoghurt", 1.25)

The object Snack has four attributes.

Complete the table to show, for each attribute, the class in which it is declared and the value it holds after the statement has been executed.

A garage program uses object-oriented programming. The class Car is declared as follows. Its other methods are not shown.

CLASS Car

   PRIVATE Registration : STRING

   PRIVATE FuelType : STRING

   PRIVATE Mileage : INTEGER

   PUBLIC PROCEDURE NEW(GivenRegistration : STRING, GivenFuel : STRING)

      Registration ← GivenRegistration

      FuelType ← GivenFuel

      Mileage ← 0

   ENDPROCEDURE

ENDCLASS

A new class ElectricCar inherits from Car. It needs:

• a private attribute for the battery capacity, for example 57.5

• a private attribute for the charge level, stored as a whole-number percentage

• a constructor that takes the registration and the battery capacity as its only parameters.

When an ElectricCar object is created:

• the fuel type is always set to "Electric"

• the charge level is set to 100.

Write pseudocode for the class ElectricCar. You only need to write the attributes and the constructor.

In Object-Oriented Programming (OOP), a parent class can have one or more derived classes.

Define the term polymorphism.

A drawing program is written using Object-Oriented Programming (OOP). The class inheritance diagram shows a parent class Shape and two derived classes, Rectangle and Circle.

In each class box the class name is at the top, then the attributes, then the methods.

The method GetColour() is not listed in Rectangle or in Circle, but objects of both classes can still use it.

The method GetArea() is listed in all three class boxes.

Explain why GetArea() is listed again in Rectangle and in Circle.

A music teaching app is written using Object-Oriented Programming (OOP). The class inheritance diagram is shown.

In each class box the class name is at the top, then the attributes, then the methods. Every class has its own Constructor(). Any other method listed in a derived class box has been redefined in that class.

Three objects are created:

• MyDrum from the class Drum

• MyViolin from the class Violin

• MyGuitar from the class Guitar

Complete the table. For each method call, write the name of the class whose version of the method runs.

A messaging program is written using Object-Oriented Programming (OOP). The class Message is shown.

CLASS Message

   PRIVATE Text : STRING

   PUBLIC PROCEDURE NEW(GivenText : STRING)

      Text ← GivenText

   ENDPROCEDURE

   PUBLIC PROCEDURE Show()

      OUTPUT Text

   ENDPROCEDURE

ENDCLASS

The class UrgentMessage inherits from Message. It redefines the method Show().

CLASS UrgentMessage INHERITS Message

   PUBLIC PROCEDURE NEW(GivenText : STRING)

      SUPER.NEW(GivenText)

   ENDPROCEDURE

   PUBLIC PROCEDURE Show()

      OUTPUT "URGENT"

      SUPER.Show()

   ENDPROCEDURE

ENDCLASS

The main program runs these statements. Each OUTPUT statement displays its value on a new line.

M1 ← NEW Message("Meeting at 10")

M2 ← NEW UrgentMessage("Fire drill")

M2.Show()

M1.Show()

Write the output from the main program.

A mobile phone company uses a program written using Object-Oriented Programming (OOP). The class PhonePlan is shown.

CLASS PhonePlan

   PRIVATE PlanName : STRING

   PRIVATE BasePrice : REAL

   PUBLIC PROCEDURE NEW(GivenName : STRING, GivenPrice : REAL)

      PlanName ← GivenName

      BasePrice ← GivenPrice

   ENDPROCEDURE

   PUBLIC FUNCTION GetMonthlyCost() RETURNS REAL

      RETURN BasePrice

   ENDFUNCTION

ENDCLASS

The class FamilyPlan inherits from PhonePlan. Part of the class is shown.

CLASS FamilyPlan INHERITS PhonePlan

   PRIVATE ExtraUsers : INTEGER

   PUBLIC PROCEDURE NEW(GivenName : STRING, GivenPrice : REAL, GivenUsers : INTEGER)

      SUPER.NEW(GivenName, GivenPrice)

      ExtraUsers ← GivenUsers

   ENDPROCEDURE

ENDCLASS

The monthly cost of a family plan is the base price plus 8.50 for each extra user.

The method GetMonthlyCost() must be redefined in FamilyPlan to return this monthly cost.

Write pseudocode for the method GetMonthlyCost() in the class FamilyPlan.

A warehouse uses robots to move goods. The program is written using Object-Oriented Programming (OOP). The class Robot is shown.

CLASS Robot

   PRIVATE Position : INTEGER

   PRIVATE Battery : INTEGER

   PUBLIC PROCEDURE NEW()

      Position ← 0

      Battery ← 100

   ENDPROCEDURE

   PUBLIC FUNCTION GetPosition() RETURNS INTEGER

      RETURN Position

   ENDFUNCTION

   PUBLIC FUNCTION GetBattery() RETURNS INTEGER

      RETURN Battery

   ENDFUNCTION

   PUBLIC PROCEDURE SetBattery(NewBattery : INTEGER)

      Battery ← NewBattery

   ENDPROCEDURE

   PUBLIC PROCEDURE Move(Distance : INTEGER)

      Position ← Position + Distance

      Battery ← Battery - Distance

   ENDPROCEDURE

ENDCLASS

A robot uses 1 unit of battery for each metre it moves.

The class CarrierRobot inherits from Robot. A carrier robot can carry a load, measured in kilograms. Part of the class is shown.

CLASS CarrierRobot INHERITS Robot

   PRIVATE Load : INTEGER

   PUBLIC PROCEDURE NEW()

      SUPER.NEW()

      Load ← 0

   ENDPROCEDURE

   PUBLIC PROCEDURE SetLoad(NewLoad : INTEGER)

      Load ← NewLoad

   ENDPROCEDURE

ENDCLASS

The method Move() must be redefined in CarrierRobot so that:

• when Load is 0, the robot uses 1 unit of battery for each metre, in the same way as a Robot

• when Load is greater than 0, the robot uses 2 units of battery for each metre

• if the battery level is less than the battery needed for the whole move, the robot does not move and the method outputs "Battery too low".

The attributes of Robot are private, so they cannot be accessed directly from CarrierRobot.

Write pseudocode for the method Move() in the class CarrierRobot.