IComparable(Of T).CompareTo Method (T)
Compares the current instance with another object of the same type and returns an integer that indicates whether the current instance precedes, follows, or occurs in the same position in the sort order as the other object.
Assembly: mscorlib (in mscorlib.dll)
Parameters
- other
-
Type:
T
An object to compare with this instance.
Return Value
Type: System.Int32A value that indicates the relative order of the objects being compared. The return value has these meanings:
Value | Meaning |
|---|---|
Less than zero | This instance precedes other in the sort order. |
Zero | This instance occurs in the same position in the sort order as other. |
Greater than zero | This instance follows other in the sort order. |
CompareTo 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(Of T).Sort() and Add.
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 specified in the Return Values section ("precedes", "occurs in the same position as", and "follows) depends on the particular implementation.
By definition, any object compares greater than null, 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(Of 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(Of TKey, TValue) collection uses the IComparable(Of T) implementation to sort the list entries, which are then displayed in order of increasing temperature.
Imports System.Collections.Generic Public Class Temperature Implements IComparable(Of Temperature) ' Implement the generic CompareTo method with the Temperature class ' as the type parameter. ' Public Overloads Function CompareTo(ByVal other As Temperature) As Integer _ Implements IComparable(Of Temperature).CompareTo ' If other is not a valid object reference, this instance is greater. If other Is Nothing Then Return 1 ' The temperature comparison depends on the comparison of the ' the underlying Double values. Return m_value.CompareTo(other.m_value) End Function ' Define the is greater than operator. Public Shared Operator > (operand1 As Temperature, operand2 As Temperature) As Boolean Return operand1.CompareTo(operand2) = 1 End Operator ' Define the is less than operator. Public Shared Operator < (operand1 As Temperature, operand2 As Temperature) As Boolean Return operand1.CompareTo(operand2) = -1 End Operator ' Define the is greater than or equal to operator. Public Shared Operator >= (operand1 As Temperature, operand2 As Temperature) As Boolean Return operand1.CompareTo(operand2) >= 0 End Operator ' Define the is less than operator. Public Shared Operator <= (operand1 As Temperature, operand2 As Temperature) As Boolean Return operand1.CompareTo(operand2) <= 0 End Operator ' 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 kelvins As Double) Me.Kelvin = kelvins 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 ' The 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. '
Available since 8
.NET Framework
Available since 2.0
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1