Programming Exercise (Ungraded): Inheritance

Implement the following class hierarchy:


Description of each class and its members:

• Phone - an abstract class
  
• Type - an abstract readonly property that identifies the type of phone. Implemented by subclasses
  
• Number - an abstract property that sets and gets the phone number. Implemented by subclasses
  
• Ring - an abstract method that will output the message "Ringing phone-type" when invoked. Implemented by subclasses
  
• Telephone - an implementation of the Phone abstract class that represents all landline-based phones
• Telephone - constructor that accepts a phone number as parameter
  
• Type - returns "Telephone"
  
• Number - gets or sets the phone number. This property should also validate the assigned phone number using this format: nnn-nnnn
  
• Ring - displays the message "Ringing Telephone" when invoked
  
• CellularPhone - an implementation of the Phone abstract class that represents all mobile-based phones
• CellularPhone - constructor that accepts a phone number parameter
  
• Type - returns "CellularPhone"
  
• Number - gets or sets the phone number. This property should also validate the assigned phone number using this format: nnnn-nnnnnnn
• Ring - displays the message "Ringing CellularPhone" when invoked
  

After implementing, you should be able to use your classes as follows:

class Program
{
static void Main(string[] args)
{
    Telephone telephone = new Telephone("233-1234");
    CellularPhone cellphone = new CellularPhone("0920-1234567");

    Console.WriteLine(telephone.Type);   // displays "Telephone"
    Console.WriteLine(cellphone.Type);   // displays "CellularPhone"

    telephone.Number = "233-123";        // displays error
    Console.WriteLine(telephone.Number); // displays "233-1234"
    cellphone.Number = "0920-123x567";   // displays error
    Console.WriteLine(cellphone.Number); // displays
"0920-1234567"
    Phone phone = cellphone;
    Console.WriteLine(phone.Number);     // displays
                                         // "0920-1234567"

    phone = telephone;
    phone.Ring();                        // displays "Ringing Telephone"

    Console.ReadLine();
}
}