# IComparable<T> Interface

## Definition

``````generic <typename T>
public interface class IComparable``````
``public interface IComparable<in T>``
``public interface IComparable<T>``
``type IComparable<'T> = interface``
``Public Interface IComparable(Of In T)``
``Public Interface IComparable(Of T)``

#### Type Parameters

T

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.
Derived

## Examples

``````#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 );
}

// Define the is greater than operator.
bool operator>=  (Temperature^ other)
{
return CompareTo(other) == 1;
}

// Define the is less than operator.
bool operator<  (Temperature^ other)
{
return CompareTo(other) == -1;
}

// Define the is greater than or equal to operator.
bool operator>  (Temperature^ other)
{
return CompareTo(other) >= 0;
}

// Define the is less than or equal to operator.
bool operator<=  (Temperature^ other)
{
return CompareTo(other) <= 0;
}

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(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");

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.
*/
``````
``````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);
}

// Define the is greater than operator.
public static bool operator >  (Temperature operand1, Temperature operand2)
{
return operand1.CompareTo(operand2) == 1;
}

// Define the is less than operator.
public static bool operator <  (Temperature operand1, Temperature operand2)
{
return operand1.CompareTo(operand2) == -1;
}

// Define the is greater than or equal to operator.
public static bool operator >=  (Temperature operand1, Temperature operand2)
{
return operand1.CompareTo(operand2) >= 0;
}

// Define the is less than or equal to operator.
public static bool operator <=  (Temperature operand1, Temperature operand2)
{
return operand1.CompareTo(operand2) <= 0;
}

// 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(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");

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.
*/
``````
``````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(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")

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.
'
``````

## Remarks

CompareTo(T) 方法的執行必須傳回具有三個值之一的 Int32，如下表所示。The implementation of the CompareTo(T) method must return an Int32 that has one of three values, as shown in the following table.

Value 意義Meaning

Zero 這個目前的實例在排序次序中的位置與 CompareTo 方法引數所指定的物件相同。This current instance occurs in the same position in the sort order as the object specified by the CompareTo method argument.

## Notes to Implementers

IComparable<T> 介面的型別參數取代為正在執行此介面的型別。Replace the type parameter of the IComparable<T> interface with the type that is implementing this interface.

## Methods

 將目前的執行個體與相同類型的另一個物件相比較，並傳回整數，這個整數表示目前的執行個體在排序次序中，位於另一個物件之前、之後或相同位置。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.