IComparable Generic 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(Of T)
Dim instance As IComparable(Of T)

J# supports the use of generic types and methods, but not the declaration of new ones.
JScript does not support generic types and methods.
Not applicable.

Type Parameters


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.


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

Notes to Implementers: Replace the type parameter of the IComparable 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 collection of strings with Temperature object keys, and adds several pairs of temperatures and strings to the list out of sequence. The SortedList collection uses the IComparable implementation to sort the list entries, which are then displayed in order of increasing temperature.

Imports System
Imports System.Collections.Generic

Public Class Temperature
    Implements IComparable(Of Temperature)

    ' Implement the generic CompareTo method. In the Implements statement,
    ' specify the Temperature class for the type parameter of the
    ' generic IComparable interface. Use that type for the parameter
    ' of the CompareTo method.
    Public Overloads Function CompareTo(ByVal other As Temperature) As Integer _
        Implements IComparable(Of Temperature).CompareTo

        ' The temperature comparison depends on the comparison of the
        ' the underlying Double values. Because the CompareTo method is
        ' strongly typed, it is not necessary to test for the correct
        ' object type.
        Return m_value.CompareTo(other.m_value)
    End Function

    ' The underlying temperature value.
    Protected m_value As Double = 0.0

    Public ReadOnly Property Celsius() As Double
            Return m_value - 273.15
        End Get
    End Property

    Public Property Kelvin() As Double
            Return m_value
        End Get
        Set(ByVal Value As Double)
            If value < 0.0 Then 
                Throw New ArgumentException("Temperature cannot be less than absolute zero.")
                m_value = Value
            End If
        End Set
    End Property

    Public Sub New(ByVal degreesKelvin As Double)
        Me.Kelvin = degreesKelvin 
    End Sub
End Class

Public Class Example
    Public Shared Sub Main()
        Dim temps As New SortedList(Of 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")

        For Each kvp As KeyValuePair(Of Temperature, String) In temps
            Console.WriteLine("{0} is {1} degrees Celsius.", kvp.Value, kvp.Key.Celsius)
    End Sub
End Class

' This code example produces 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 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

.NET Compact Framework

Supported in: 2.0

XNA Framework

Supported in: 1.0

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