C# 4 and .NET 4

array Class ❘ 137
The output of the application shows the sorted result of the array:
Beyonce
Christina Aguilera
Gwen Stefani
Shakira
If you are using custom classes with the array, you must implement the interface IComparable. This
interface defines just one method, CompareTo(), that must return 0 if the objects to compare are equal, a
value smaller than 0 if the instance should go before the object from the parameter, and a value larger than
0 if the instance should go after the object from the parameter.
Change the Person class to implement the interface IComparable. The comparison is done on the
value of the LastName. Because the LastName is of type string, and the String class already implements
the IComparable interface, with the implementation you can rely on the CompareTo() method of the
String class. If the LastName has the same value, the FirstName is compared:
public class Person: IComparable
{
public int CompareTo(Person other)
{
if (other == null) throw new ArgumentNullException("other");
int result = this.LastName.CompareTo(
other.LastName);
if (result == 0)
{
result = this.FirstName.CompareTo(
other.FirstName);
}
return result;
}
//...
code snippet SortingSample/Person.cs
Now it is possible to sort an array of Person objects by the last name:
Person[] persons = {
new Person { FirstName="Damon", LastName="Hill" },
new Person { FirstName="Niki", LastName="Lauda" },
new Person { FirstName="Ayrton", LastName="Senna" },
new Person { FirstName="Graham", LastName="Hill" }
};
Array.Sort(persons);
foreach (var p in persons)
{
Console.WriteLine(p);
}
Using the sort of the Person class, the output returns the names sorted by the last name:
Damon Hill
Graham Hill
Niki Lauda
Ayrton Senna
code snippet SortingSample/Program.cs
If the Person object should be sorted differently, or if you don’t have the option to change the class that
is used as an element in the array, you can implement the interface IComparer or IComparer. These
interfaces define the method Compare(). One of these interfaces must be implemented by the class that
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