C# 5.0 Programmer's Reference

636 ❘ APPENDIX A Solutions to Exercises
}
}
return true;
4. To define a method without providing any implementation, the method’s declaration must
include the abstract keyword. If the class contains an abstract method, its declaration
must also include the abstract keyword. The following code shows the Contactable class.
abstract class Contactable
{
abstract public bool Contact(string message);
}
5. The following code shows a Mailable class that inherits from Contactable and implements
the Contact method.
class Mailable : Contactable
{
public override bool Contact(string message)
{
return true;
}
}
6. The following code shows an implementation of the Root extension method.
static class DoubleExtensions
{
public static double Root(this double number)
{
return (Math.Sqrt(number));
}
}
7. The following code shows an overloaded version of the Root extension method. (In the same
DoubleExtensions class used in Exercise 6.)
public static double Root(this double number, int rootBase)
{
return (Math.Pow(number, 1.0 / rootBase));
}
8. If the program is going to use Piece variables to represent Pieces and Kings, the CanMoveTo
method must be virtual and the King class must override the method. Then if the program
uses a Piece variable to invoke CanMoveTo for a King object, it executes the King’s version of
the method.
The following code shows the Piece class.
class Piece
{
public virtual bool CanMoveTo(int row, int column)
{
return false;
}
}
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