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IComparable<T> Interface

Defines a generalized comparison method that a value type or class implements to create a type-specific comparison method for ordering instances.

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

public interface IComparable<T>

Type Parameters

T

The type of objects to compare.

This interface is implemented by types whose values can be ordered; for example, the numeric and string classes. A value type or class implements the CompareTo method to create a type-specific comparison method suitable for purposes such as sorting.

NoteNote:

The IComparable<T> interface defines the CompareTo method, which determines the sort order of instances of the implementing type. The IEquatable<T> interface defines the Equals method, which determines the equality of instances of the implementing type.

The IComparable<T> interface provides a strongly typed comparison method for ordering members of a generic collection object. Because of this, it is usually not called directly from developer code. Instead, it is called automatically by methods such as List<T>.Sort() and Add.

Notes to Implementers:

Replace the type parameter of the IComparable<T> interface with the type that is implementing this interface.

The following code example illustrates the implementation of IComparable for a simple Temperature object. The example creates a SortedList<TKey, TValue> collection of strings with Temperature object keys, and adds several pairs of temperatures and strings to the list out of sequence. In the call to the Add method, the SortedList<TKey, TValue> collection uses the IComparable<T> implementation to sort the list entries, which are then displayed in order of increasing temperature.

using System;
using System.Collections.Generic;

public class Temperature : IComparable<Temperature>
{
    // Implement the generic CompareTo method with the Temperature  
    // class as the Type parameter.  
    // 
    public int CompareTo(Temperature other)
    {
        // If other is not a valid object reference, this instance is greater. 
        if (other == null) return 1;

        // The temperature comparison depends on the comparison of  
        // the underlying Double values.  
        return m_value.CompareTo(other.m_value);
    }

    // The underlying temperature value. 
    protected double m_value = 0.0;

    public double Celsius    
    {
        get
        {
            return m_value - 273.15;
        }
    }

    public double Kelvin    
    {
        get
        {
            return m_value;
        }
        set
        {
            if (value < 0.0)
            {
                throw new ArgumentException("Temperature cannot be less than absolute zero.");
            }
            else
            {
                m_value = value;
            }
        }
    }

    public Temperature(double kelvins)
    {
        this.Kelvin = kelvins;
    }
}

public class Example
{
    public static void Main()
    {
        SortedList<Temperature, string> temps = 
            new SortedList<Temperature, string>();

        // Add entries to the sorted list, out of order.
        temps.Add(new Temperature(2017.15), "Boiling point of Lead");
        temps.Add(new Temperature(0), "Absolute zero");
        temps.Add(new Temperature(273.15), "Freezing point of water");
        temps.Add(new Temperature(5100.15), "Boiling point of Carbon");
        temps.Add(new Temperature(373.15), "Boiling point of water");
        temps.Add(new Temperature(600.65), "Melting point of Lead");

        foreach( KeyValuePair<Temperature, string> kvp in temps )
        {
            Console.WriteLine("{0} is {1} degrees Celsius.", kvp.Value, kvp.Key.Celsius);
        }
    }
}
/* This example displays the following output:
      Absolute zero is -273.15 degrees Celsius.
      Freezing point of water is 0 degrees Celsius.
      Boiling point of water is 100 degrees Celsius.
      Melting point of Lead is 327.5 degrees Celsius.
      Boiling point of Lead is 1744 degrees Celsius.
      Boiling point of Carbon is 4827 degrees Celsius.
*/

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0

.NET Compact Framework

Supported in: 3.5, 2.0

XNA Framework

Supported in: 3.0, 2.0, 1.0

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