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.NET Framework Class Library
IComparableT Interface

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

Namespace:   System
Assembly:  mscorlib (in mscorlib.dll)
Syntax
Public Interface IComparable(Of In T)
public interface IComparable<in T>
generic<typename T>
public interface class IComparable
type IComparable<'T> =  interface end
JScript does not support generic types or methods.

Type Parameters

T

The type of object to compare.

This type parameter is contravariant. That is, you can use either the type you specified or any type that is less derived. For more information about covariance and contravariance, see Covariance and Contravariance in Generics.

The IComparableT type exposes the following members.

Methods
  NameDescription
Public method Supported by the XNA Framework Supported by Portable Class Library CompareToCompares 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.
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Remarks

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, CompareTo(T), 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 ListTSort and Add.

Typically, types that provide an IComparableT implementation also implement the IEquatableT interface. The IEquatableT interface defines the Equals method, which determines the equality of instances of the implementing type.

The implementation of the CompareTo(T) method must return an 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 CompareTo method in the sort order.

Zero

This current instance occurs in the same position in the sort order as the object specified by the CompareTo method argument.

Greater than zero

This current instance follows the object specified by the CompareTo method argument in the sort order.

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

Notes to Implementers

Replace the type parameter of the IComparableT interface with the type that is implementing this interface.

If you implement IComparableT, you should overload the op_GreaterThan, op_GreaterThanOrEqual, op_LessThan, and op_LessThanOrEqual operators to return values that are consistent with CompareTo. In addition, you should also implement IEquatableT. See the IEquatableT article for complete information.

Examples

The following code example illustrates the implementation of IComparableT for a simple Temperature object. The example creates a SortedListTKey, 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 SortedListTKey, TValue collection uses the IComparableT 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 

    ' 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. 
'
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.
*/
#using <System.dll>

using namespace System;
using namespace System::Collections::Generic;

public ref class Temperature: public IComparable<Temperature^> {

protected:
   // The underlying temperature value.
   Double m_value;

public:
   // Implement the generic CompareTo method with the Temperature class  
   // as the Type parameter.  
   virtual Int32 CompareTo( Temperature^ other ) {

      // If other is not a valid object reference, this instance  
      // is greater. 
      if (other == nullptr) return 1;

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

   property Double Celsius {
      Double get() {
         return m_value + 273.15;
      }
   }

   property Double Kelvin {
      Double get() {
         return m_value;
      }
      void set( Double value ) {
         if (value < 0)
            throw gcnew ArgumentException("Temperature cannot be less than absolute zero.");
         else
            m_value = value;
      }
   }

   Temperature(Double kelvins) {
      this->Kelvin = kelvins;
   }
};

int main() {
   SortedList<Temperature^, String^>^ temps = 
      gcnew SortedList<Temperature^, String^>();

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

   for each( KeyValuePair<Temperature^, String^>^ kvp in temps )
   {
      Console::WriteLine("{0} is {1} degrees Celsius.", kvp->Value, kvp->Key->Celsius);
   }
}
/* The example displays the following output:
      Absolute zero is 273.15 degrees Celsius.
      Freezing point of water is 546.3 degrees Celsius.
      Boiling point of water is 646.3 degrees Celsius.
      Melting point of Lead is 873.8 degrees Celsius.
      Boiling point of Lead is 2290.3 degrees Celsius.
      Boiling point of Carbon is 5373.3 degrees Celsius.
*/
Version Information

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0, 2.0, 1.0

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8

Portable Class Library

Supported in: Portable Class Library