Solutions for those exercises.

Questions

1. What is the keyword used to call the constructor from the base class?

   • this.
   • the name of the base class.
   • base
   • over
   • inherits

2. Inheritance is …

   • … a way of implementing a class by re-using another class’ code.
   • … impossible to represent in a UML diagram.
   • … achieved using the ; (semicolon) symbol.
   • … a way of connecting a basic class with a derived class.

3. Suppose your are given an ElectricDevice class and a WallDecor class. You would like to write a Clock class that represents at the same time an electric device and a wall decor. This is possible only if the ElectricDevice and WallDecor classes are…

   • Sealed
   • Interfaces
   • Protected
   • Constructors

4. An abstract class…

   • … can be instantiated.
   • … can contain a constructor.
   • … can contain abstract and non-abstract methods.
   • … is represented in a UML diagram by prefixing its name with <<Abstract>>.

5. In a UML diagram, an abstract method is …

   • … underlined.
   • … impossible to distinguish from a non-abstract method.
   • … necessarily part of an abstract class.
   • … in italics.

6. A class Student inheriting from an abstract class Person …

   • … must override all of Person’s methods.
   • … must implement all the methods marked abstract in Student.
   • … can be instantiated.
   • … is connected to Person using an open triangle end and a continuous line (⇽) on the UML diagram.
   • … is connected to Person using an open triangle end and a dashed line (◁┈) on the UML diagram.

7. A method with header public virtual void Test(int a, out int b) will…

   • Return a value
   • Set the value of b
   • Require two arguments
   • Be overrideable

8. A method with header public abstract string Test() will…

   • Have an empty body
   • Need to be inside an abstract class
   • Not be overriden

9. A method …

   • … can be accessed from any class if it is marked protected.
   • … can be accessed from its derived classes if it is marked private.
   • … is recursive if it terminates.
   • … is recursive if it calls itself.
   • … must be overridden if it is marked abstract.
   • … cannot be overriden if it is marked sealed.

10. Give at least two differences between an abstract class and an interface.

Problems

1. Assume given the following class implementation:

   class Computer
   {
     private string brand;
    
     public void SetBrand(string brandP)
     {
       brand = brandP;
     }
    
     public Computer(string bP)
     {
       SetBrand(bP);
     }
    
     public override string ToString()
     {
       return $"Brand: {brand}";
     }
   }

   Write a Laptop class that

   1. Inherits from Computer,
   2. Has one single (automatic) property, called ScreenSize, of type int,
   3. Has a constructor that takes 2 parameters of appropriate datatypes, and use them to set brand and ScreenSize,
   4. Has a ToString method that returns a string containing the brand and screen size.

2. Consider the diagram representing the “Room”, “ClassRoom”, “Office” classes and their relations.

   

   Suppose you are given an implementation of the Room class, such that

       Room test = new Room("UH", 243);
       Console.WriteLine(test);

   displays

   UH 243

   1. Write an implementation of the ClassRoom class. Your ToString method should display the room’s building and number, in addition to whether it has AV set-up.

   2. Write a SameBuilding static method to be placed inside the Room class such that

      Office test1 = new Office("UH", 127, "706 737 1566");
      ClassRoom test2 = new ClassRoom("UH", 243, true);
      Office test3 = new Office("AH", 122, "706 729 2416");
      Console.WriteLine(Room.SameBuilding(test1, test2));
      Console.WriteLine(Room.SameBuilding(test2, test3));

      Would display “true” and “false”.

3. Consider the diagram representing the “Room”, “BedRoom”, “BathRoom” classes and their relations.

   

   1. Write an implementation of the SurfaceArea property for the Room class, assuming you are given an implementation of the Width and Length properties.

   2. Check the statements that would compile, assuming that rTest is a Room object, beTest is a BedRoom object, and baTest is a BathRoom object.

      • rTest.Capacity = 12;
      • baTest.Width = 12;
      • beTest.capacity = 3;
      • rTest.SurfaceArea = -2;
      • baTest.Capacity = 3;
      • beTest.Shower = true;
      • Console.WriteLine(baTest.ToString());

   3. Write a complete implementation of the BedRoom class.

      • Your Capacity property should use the capacity attribute, and throw an exception if the argument given is strictly less than 1.
      • Your ToString method should complement the Room’s ToString by appending to its string the capacity (in person) of the BedRoom object.

   4. Write the ToString method of the BathRoom class, knowing that a disclaimer should be part of the string returned if the BathRoom has a shower or a bathtub but no hot water.

4. Consider the diagram representing the “Article”, “Book” classes and their relations.

   

   1. Write a (partial) implementation of the Article abstract class:

      1. Write an implementation for the price attribute: you can either use a getter and a setter (as pictured in the UML diagram), or a property. However, in both cases, setting the price to a negative value should result in an ArgumentOutOfRangeException exception being thrown.
      2. Write an abstract ShippingCosts() method.

   2. Now, assume given a complete implementation of the Article abstract class. Write a complete implementation of the Book class (header included), containing:

      1. An implementation of the Title property using auto-properties.
      2. A Book constructor that passes the idP and priceP arguments to the Article constructor. The titleP argument should be assigned to the Title property.
      3. A ShippingCosts() method that returns either 5.0, or 10% of the Book’s price, whichever is smallest.

   3. Write statements that, if placed in a Main method, would

      1. Create a Book with Id “AAA001”, price $12.5, titled “What it’s like to be a bird”.
      2. Display (nicely) its shipping costs.
      3. Display its Id (as retrieved from the object).

5. Consider the diagram representing the “Shape”, “Circle” and “Rectangle” classes, as well as their relations.

   

   1. Write the complete implementation of the Shape abstract class. The ToString method should simply return the string "This shape is ".

   2. Write an implementation for the Radius property of the Circle class such that setting the radius to a negative value would result in an ArgumentOutOfRangeException (that you can shorten to AOORE) exception being thrown. Add an attribute if needed.

   3. Write the Diameter property for the Circle class, which should return $2$ times the radius. Only the get should be provided: briefly explain why the set is missing.

   4. Write an implementation for the ToString method of the Rectangle class that returns a string containing what was returned by the Shape’s ToString method, the width, length and area of the calling object. For example, for a Rectangle with width 10 and length 5, it should be of the form “This shape is a rectangle (W: 10, L: 5, Area: 50)“.

   5. Write the Equals method for the Rectangle class. It should return true if the calling object and the parameter have the same lengths and same widths, or if one can be obtained by rotating the other.

   6. Briefly explain how Shape could be converted into an interface and what would be the benefit(s) and disadvantage(s) of carrying out such a modification.