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1.2.4 - Object Oriented Programming Redo

  1. What attributes might be assigned to the following objects of the following classes?

    1. Cat
      • hunger
      • affection
      • name
      • age
      • fur_colour
      • eye_colour
    2. Rectangle
      • x1
      • y1
      • x2
      • y2
    3. HotelBooking
      • occupant
      • start
      • end
      • room
      • rate

  2. In the class definition for Radio (shown below) add the missing instance variables, and a procedure to set the volume.

    class Radio
    private volume
    private station
    private switch

    public procedure new(my_volume, my_station, my_switch)
        volume = my_volume
        station = my_station
        switch = my_switch
    endprocedure

    public procedure set_volume(new_volume)
        volume = new_volume
    endprocedure
endclass

  3. Write pseudocode statements to instantiate two new radio objects named roberts_radio and philips_radio.

    roberts_radio = new Radio(31.4, '88MHz', 'on')
philips_radio = new Radio(27.2, '42MHz', 'off')

  4. Inheritance diagram
    Class diagram involving inheritance

    All the animals in the superclass Animal share common attributes such as name and position. Animals may also have common procedures (methods), such as move_left, move_right. A Cat may have an extra attribute size, and an extra method pounce. A Rodent may have an extra method gnaw. A Beaver may have an extra method, make_dam.

    What extra methods might Mouse have?

    • squeak
    • scamper

  5. The class Animal may be defined like this:

    class Animal
    private name
    private position

    public procedure new(my_name, my_position)
        name = my_name
        position = my_position
    endprocedure

    public procedure move_left(steps)
        position = position = steps
    endprocedure

    public function get_position()
        return position
    endfunction
endclass

    Cat is a subclass of Animal (and has an extra attribute - size); here is its class definition:

    class Cat inherits Animal
    private size

    public procedure new(my_name, my_position, my_size)
        super.new(my_name, my_position)
        size = my_size
    endprocedure

    public procedure move_left(steps)
        position = position - (steps * 3)
    endprocedure
endclass

    A rodent has an extra attribute colour.
    Write the class definition for Rodent

    class Rodent inherits Animal
    private colour

    public procedure new(my_name, my_position, my_colour)
        super.new(my_name, my_position)
        colour = my_colour
    endprocedure
endclass

  6. All objects in the subclasses of Animal can execute the methods move_left and move_right, causing the animal to move left or right by one space.

    But the subclasses may decide that a Cat can move three spaces with a move_left or move_right message, and a Rodent moves two spaces. You would define different methods in each of the classes to implement these moves, but keeping the same method name. This would override the method in the superclass.

    Suppose that tom is an instance of the Cat class, and jerry is an instance of the Mouse class. What will happen when each of these statements is executed?

    1. tom.move_right()
      • tom's position will increase by 3
    2. jerry.move_right()
      • jerry's position will increase by 2

Exercises

  1. A sports club keeps details of its members. Each member has a unique membership number, first name, surname, and telephone number recorded. Three classes have been identified:

    • Member
    • JuniorMember
    • SeniorMember

    The classes JuniorMember and SeniorMember are related, by single inheritance, to the class Member.

    1. Draw an inheritance diagram for the given classes.

                Member
           ╱  ╲
JuniorMember  SeniorMember

    2. Programs that use objects of the class Member need to create a new member, edit a member's details, delete a member's details, and show a member's details. No other form of access is to be allowed.

      Complete the definition of the attributes and the procedure new for the Member class.

      class Member
    private number
    public forename
    public surname
    public tel

    public procedure new(my_number, my_forename, my_surname, my_tel)
        number = my_number
        forename = my_forename
        surname = my_surname
        tel = my_tel
    endprocedure
endclass

    3. In object-oriented programming, what is meant by encapsulation?

      • Encapsulation is where an object's state is protected, and all access and modifications are performed through the class' getters and setters, which can perform validation on the values assigned or calculation on the values retrieved