Information Technology Reference
In-Depth Information
Example Using the IComparable Interface
To understand what this means and why it's useful, let's start by taking a look at the following
code, which takes an unsorted array of integers and sorts them in ascending order.
The first line creates an array of five integers that are in no particular order.
The second line uses the static
Sort
method of the
Array
class to sort the elements.
The
foreach
loop prints them out, showing that the integers are now in ascending order.
int[] MyInt = new int[5] { 20, 4, 16, 9, 2 }; // Create an array of ints.
Array.Sort(MyInt); // Sort elements by magnitude.
foreach (int i in MyInt) // Print them out.
Console.Write("{0} ", i);
This code produces the following output:
2 4 9 16 20
The
Sort
method works great on an array of
int
s, but what would happen if you were to try
to use it on one of your own classes, as shown here?
class MyClass // Declare a simple class.
{
public int TheValue;
}
...
MyClass[] mc= new MyClass[5]; // Create an array of five elements.
... // Create and initialize the elements.
Array.Sort(mc); // Try to use Sort--raises exception
When you try to run this code, it raises an exception. So why did it work for an array of
int
s,
but not for an array of
MyClass
objects?
The reason
Sort
doesn't work with the array of user-defined objects is that it relies on the
objects in the array to implement interface
IComparable
. When
Sort
is running, it compares
one element of the array to another by calling the element's
CompareTo
method and passing in
as a parameter a reference to the other element.
The
int
type implements
IComparable
, but
MyClass
does not, so when
Sort
tries to call the
nonexistent
CompareTo
method of
MyClass
, it raises an exception.
