Comparer Class

Aug 26, 2008
by David Cumps

Part of my 2008 study notes for exam 70-536 (.NET Framework 2.0).

Overview

Used as the default comparer when sorting, for example with an ArrayList.
Implements the IComparer interface.

Good practice

When possible, use the generic version of IComparer<T> and Comparer<T>.

Examples

Compare Strings

// Returns 0 when equal, less than 0 when a < b and greater than 0 when a > b
Console.WriteLine("Is a equal to b? {0}", Comparer.DefaultInvariant.Compare("a", "b"));

Reverse Sort

public class Program
{
    static void Main(string[] args)
    {
        ArrayList a = new ArrayList();
        a.AddRange(new string[] { "Hello", "World", "Aloha" });
        a.Sort();
        foreach (object s in a) { Console.WriteLine(s); }
        a.Sort(new ReverseSort());
        foreach (object s in a) { Console.WriteLine(s); }
    }
}
 
public class ReverseSort : IComparer
{
    public int Compare(object x, object y)
    {
        return y.ToString().CompareTo(x.ToString());
    }
}