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IComparer.Compare Method

Compares two objects and returns a value indicating whether one is less than, equal to, or greater than the other.

Namespace: System.Collections
Assembly: mscorlib (in mscorlib.dll)

int Compare (
	Object x,
	Object y
)
int Compare (
	Object x, 
	Object y
)
function Compare (
	x : Object, 
	y : Object
) : int
Not applicable.

Parameters

x

The first object to compare.

y

The second object to compare.

Return Value

Value

Condition

Less than zero

x is less than y.

Zero

x equals y.

Greater than zero

x is greater than y.

Exception typeCondition

ArgumentException

Neither x nor y implements the IComparable interface.

-or-

x and y are of different types and neither one can handle comparisons with the other.

The preferred implementation is to use the CompareTo method of one of the parameters.

Comparing a null reference (Nothing in Visual Basic) with any type is allowed and does not generate an exception when using IComparable. When sorting, a null reference (Nothing in Visual Basic) is considered to be less than any other object.

The following code example demonstrates the use of the IComparer interface to sort an ArrayList object. In this example, the IComparer interface is implemented using the CaseInsensitiveComparer class to reverse the order of the contents of the ArrayList.

using System;
using System.Collections;

public class SamplesArrayList  {
 
   public class myReverserClass : IComparer  {

      // Calls CaseInsensitiveComparer.Compare with the parameters reversed.
      int IComparer.Compare( Object x, Object y )  {
          return( (new CaseInsensitiveComparer()).Compare( y, x ) );
      }

   }

   public static void Main()  {
 
      // Creates and initializes a new ArrayList.
      ArrayList myAL = new ArrayList();
      myAL.Add( "The" );
      myAL.Add( "quick" );
      myAL.Add( "brown" );
      myAL.Add( "fox" );
      myAL.Add( "jumps" );
      myAL.Add( "over" );
      myAL.Add( "the" );
      myAL.Add( "lazy" );
      myAL.Add( "dog" );
 
      // Displays the values of the ArrayList.
      Console.WriteLine( "The ArrayList initially contains the following values:" );
      PrintIndexAndValues( myAL );
 
      // Sorts the values of the ArrayList using the default comparer.
      myAL.Sort();
      Console.WriteLine( "After sorting with the default comparer:" );
      PrintIndexAndValues( myAL );

      // Sorts the values of the ArrayList using the reverse case-insensitive comparer.
      IComparer myComparer = new myReverserClass();
      myAL.Sort( myComparer );
      Console.WriteLine( "After sorting with the reverse case-insensitive comparer:" );
      PrintIndexAndValues( myAL );

   }
 
   public static void PrintIndexAndValues( IEnumerable myList )  {
      int i = 0;
      foreach ( Object obj in myList )
         Console.WriteLine( "\t[{0}]:\t{1}", i++, obj );
      Console.WriteLine();
   }

}


/* 
This code produces the following output.
The ArrayList initially contains the following values:
        [0]:    The
        [1]:    quick
        [2]:    brown
        [3]:    fox
        [4]:    jumps
        [5]:    over
        [6]:    the
        [7]:    lazy
        [8]:    dog

After sorting with the default comparer:
        [0]:    brown
        [1]:    dog
        [2]:    fox
        [3]:    jumps
        [4]:    lazy
        [5]:    over
        [6]:    quick
        [7]:    the
        [8]:    The

After sorting with the reverse case-insensitive comparer:
        [0]:    the
        [1]:    The
        [2]:    quick
        [3]:    over
        [4]:    lazy
        [5]:    jumps
        [6]:    fox
        [7]:    dog
        [8]:    brown 
*/


import System.*;
import System.Collections.*;

public class SamplesArrayList
{
    public static class MyReverserClass implements IComparer
    {
        // Calls CaseInsensitiveComparer.Compare with the parameters reversed.
        public int Compare(Object x, Object y)
        {
            return(new CaseInsensitiveComparer()).Compare(y, x) ;
        } //IComparer.Compare
    } //MyReverserClass
    
    public static void main(String[] args) 
    {
        // Creates and initializes a new ArrayList.
        ArrayList myAL =  new ArrayList();
        myAL.Add("The");
        myAL.Add("quick");
        myAL.Add("brown");
        myAL.Add("fox");
        myAL.Add("jumps");
        myAL.Add("over");
        myAL.Add("the");
        myAL.Add("lazy");
        myAL.Add("dog");
          
        // Displays the values of the ArrayList.
        Console.WriteLine("The ArrayList initially contains the following"
            + " values:");
        PrintIndexAndValues(myAL); 
          
        // Sorts the values of the ArrayList using the default comparer.
        myAL.Sort();
        Console.WriteLine("After sorting with the default comparer:");
        PrintIndexAndValues(myAL);
          
        // Sorts the values of the ArrayList using the reverse case-insensitive
        // comparer.
        IComparer myComparer = new MyReverserClass();
        myAL.Sort(myComparer);
        Console.WriteLine("After sorting with the reverse case-insensitive"
            + " comparer:");
        PrintIndexAndValues(myAL);
    } //main
       
    public static void PrintIndexAndValues(IEnumerable myList) 
    {
        int i = 0;
        IEnumerator objEnum = myList.GetEnumerator();
        while (objEnum.MoveNext()) {
            Object obj = objEnum.get_Current();
            Console.WriteLine("\t[{0}]:\t{1}",(Int32)i++, obj);
        }
        Console.WriteLine();
    } //PrintIndexAndValues
} //SamplesArrayList
 
/* 
This code produces the following output.
The ArrayList initially contains the following values:
        [0]:    The
        [1]:    quick
        [2]:    brown
        [3]:    fox
        [4]:    jumps
        [5]:    over
        [6]:    the
        [7]:    lazy
        [8]:    dog

After sorting with the default comparer:
        [0]:    brown
        [1]:    dog
        [2]:    fox
        [3]:    jumps
        [4]:    lazy
        [5]:    over
        [6]:    quick
        [7]:    the
        [8]:    The

After sorting with the reverse case-insensitive comparer:
        [0]:    the
        [1]:    The
        [2]:    quick
        [3]:    over
        [4]:    lazy
        [5]:    jumps
        [6]:    fox
        [7]:    dog
        [8]:    brown 
*/

Windows 98, Windows Server 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0, 1.0

XNA Framework

Supported in: 1.0

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