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IComparable.CompareTo Method

Compares the current object with another object of the same type.

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

'Declaration
Function CompareTo ( _
	other As T _
) As Integer
'Usage
Dim instance As IComparable(Of T)
Dim other As T
Dim returnValue As Integer

returnValue = instance.CompareTo(other)
int CompareTo (
	T other
)
function CompareTo (
	other : T
) : int
Not applicable.

Parameters

other

An object to compare with this object.

Return Value

A 32-bit signed integer that indicates the relative order of the objects being compared. The return value has the following meanings:

Value

Meaning

Less than zero

This object is less than the other parameter.

Zero

This object is equal to other.

Greater than zero

This object is greater than other.

This method is only a definition and must be implemented by a specific class or value type to have effect. The meaning of the comparisons, "less than," "equal to," and "greater than," depends on the particular implementation.

By definition, any object compares greater than a null reference (Nothing in Visual Basic), and two null references compare equal to each other.

Notes to Implementers: For objects A, B, and C, the following must be true: A.CompareTo(A) is required to return zero. If A.CompareTo(B) returns zero, then B.CompareTo(A) is required to return zero. If A.CompareTo(B) returns zero and B.CompareTo(C) returns zero, then A.CompareTo(C) is required to return zero. If A.CompareTo(B) returns a value other than zero, then B.CompareTo(A) is required to return a value of the opposite sign. If A.CompareTo(B) returns a value x that is not equal to zero, and B.CompareTo(C) returns a value y of the same sign as x, then A.CompareTo(C) is required to return a value of the same sign as x and y.

Notes to Callers: Use the CompareTo method to determine the ordering of instances of a class.

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
        Get
            Return m_value - 273.15
        End Get
    End Property

    Public Property Kelvin() As Double
        Get
            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.")
            Else
                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)
        Next
    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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