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IComparable(Of T)-Schnittstelle

 

Veröffentlicht: Oktober 2016

Definiert eine allgemeine Vergleichsmethode, die von einem Werttyp oder einer Klasse für die Erstellung einer typspezifischen Vergleichsmethode zum Ordnen oder Sortieren von Instanzen implementiert wird.

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

Public Interface IComparable(Of In T)

Typparameter

InT

Der Typ der zu vergleichenden Objekte.

NameBeschreibung
System_CAPS_pubmethodCompareTo(T)

Vergleicht die aktuelle Instanz mit einem anderen Objekt vom selben Typ und gibt eine ganze Zahl zurück, die angibt, ob die aktuelle Instanz in der Sortierreihenfolge vor oder nach dem anderen Objekt oder an derselben Position auftritt.

This interface is implemented by types whose values can be ordered or sorted and provides a strongly typed comparison method for ordering members of a generic collection object. For example, one number can be larger than a second number, and one string can appear in alphabetical order before another. It requires that implementing types define a single method, M:System.IComparable`1.CompareTo(`0), that indicates whether the position of the current instance in the sort order is before, after, or the same as a second object of the same type. Typically, the method is not called directly from developer code. Instead, it is called automatically by methods such as M:System.Collections.Generic.List`1.Sort and M:System.Collections.Generic.SortedList`2.Add(`0,`1).

Typically, types that provide an T:System.IComparable`1 implementation also implement the T:System.IEquatable`1 interface. The T:System.IEquatable`1 interface defines the M:System.IEquatable`1.Equals(`0) method, which determines the equality of instances of the implementing type.

The implementation of the M:System.IComparable`1.CompareTo(`0) method must return an T:System.Int32 that has one of three values, as shown in the following table.

Value

Meaning

Less than zero

This object precedes the object specified by the M:System.IComparable`1.CompareTo(`0) method in the sort order.

Zero

This current instance occurs in the same position in the sort order as the object specified by the M:System.IComparable`1.CompareTo(`0) method argument.

Greater than zero

This current instance follows the object specified by the M:System.IComparable`1.CompareTo(`0) method argument in the sort order.

All numeric types (such as T:System.Int32 and T:System.Double) implement T:System.IComparable`1, as do T:System.String, T:System.Char, and T:System.DateTime. Custom types should also provide their own implementation of T:System.IComparable`1 to enable object instances to be ordered or sorted.

Hinweise für Implementierer:

Replace the type parameter of the T:System.IComparable`1 interface with the type that is implementing this interface.

If you implement T:System.IComparable`1, you should overload the op_GreaterThan, op_GreaterThanOrEqual, op_LessThan, and op_LessThanOrEqual operators to return values that are consistent with M:System.IComparable`1.CompareTo(`0). In addition, you should also implement T:System.IEquatable`1. See the T:System.IEquatable`1 article for complete information.

The following code example illustrates the implementation of T:System.IComparable`1 for a simple Temperature object. The example creates a T:System.Collections.Generic.SortedList`2 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 M:System.Collections.Generic.SortedList`2.Add(`0,`1) method, the T:System.Collections.Generic.SortedList`2 collection uses the T:System.IComparable`1 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.
'

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