While watching this course from K. Scott Allen I’ve re-learned some things about Object Oriented Programming, namely this ..
If you have a class…
public class GradeBook
{
public List<int> ListOfNumbers { get; set; }
public int ReturnLowest()
{
int lowest = int.MaxValue;
foreach (int number in ListOfNumbers)
{
lowest = Math.Min(lowest, number);
}
return lowest;
}
}
and a derived class…
public class AugmentedGradeBook : GradeBook
{
public int ReturnLowest()
{
int lowest = int.MaxValue;
foreach (var number in ListOfNumbers)
{
lowest = Math.Min(lowest, number);
}
ListOfNumbers.Remove(lowest);
return base.ReturnLowest();
}
}
The c# compiler will choose the method to run based on the type of the variable.
[Theory]
[InlineData(new int[] { 1, 2, 3, 4, 5 })]
[InlineData(new int[] { 5, 4, 3, 2, 1 })]
[InlineData(new int[] { 5, 4, 1, 3, 2 })]
public void ReturnsLowestBaseClass(int[] listInts)
{
GradeBook gradeBook = new AugmentedGradeBook();
gradeBook.ListOfNumbers = listInts.ToList();
var lowest = gradeBook.ReturnLowest();
Assert.Equal(1, lowest);
}
Since we have a variable of type GradeBook gradeBook it will execute the method GradeBook.ReturnLowest();
On the other hand, if we have a variable of type AugmentedGradeBook gradeBook
[Theory]
[InlineData(new int[] { 1, 2, 3, 4, 5 })]
[InlineData(new int[] { 5, 4, 3, 2, 1 })]
[InlineData(new int[] { 5, 4, 1, 3, 2 })]
public void ReturnsLowestOwnClass(int[] listInts)
{
AugmentedGradeBook gradeBook = new AugmentedGradeBook();
gradeBook.ListOfNumbers = listInts.ToList();
var lowest = gradeBook.ReturnLowest();
Assert.Equal(2, lowest);
}
it will execute AugmentedGradeBook.ReturnLowest();
To achieve polymorphism we can change the class GradeBook to use a virtual method and then override the behavior in another class.
public class GradeBook
{
public List<int> ListOfNumbers { get; set; }
public virtual int ReturnLowest()
{
int lowest = int.MaxValue;
foreach (int number in ListOfNumbers)
{
lowest = Math.Min(lowest, number);
}
return lowest;
}
}
and the new derived class
public class AugmentedVirtualGradeBook : GradeBook
{
public override int ReturnLowest()
{
int lowest = int.MaxValue;
foreach (var number in ListOfNumbers)
{
lowest = Math.Min(lowest, number);
}
ListOfNumbers.Remove(lowest);
return base.ReturnLowest();
}
}
this way we can have a variable of type GradeBook gradeBook and the executed method will be AugmentedVirtualGradeBook.ReturnLowest
[Theory]
[InlineData(new int[] { 1, 2, 3, 4, 5 })]
[InlineData(new int[] { 5, 4, 3, 2, 1 })]
[InlineData(new int[] { 5, 4, 1, 3, 2 })]
public void ReturnsLowestVirtualAugmentedClass(int[] listInts)
{
GradeBook gradeBook = new AugmentedVirtualGradeBook();
gradeBook.ListOfNumbers = listInts.ToList();
var lowest = gradeBook.ReturnLowest();
Assert.Equal(2, lowest);
}
Hope it helps…
Cheers!
Rambling about .NET 