IComparable Interface

Definition

public interface class IComparable

public interface IComparable

[System.Runtime.InteropServices.ComVisible(true)]
public interface IComparable

type IComparable = interface

[<System.Runtime.InteropServices.ComVisible(true)>]
type IComparable = interface

Public Interface IComparable

Derived

System.Boolean

System.Byte

System.Char

System.Data.OracleClient.OracleBinary

System.Data.OracleClient.OracleBoolean

More…

Attributes

ComVisibleAttribute

Examples

The following example illustrates the implementation of IComparable and the requisite CompareTo method.

using System;
using System.Collections;

public class Temperature : IComparable
{
 // The temperature value
 protected double temperatureF;

 public int CompareTo(object obj) {
 if (obj == null) return 1;

 Temperature otherTemperature = obj as Temperature;
 if (otherTemperature != null)
 return this.temperatureF.CompareTo(otherTemperature.temperatureF);
 else
 throw new ArgumentException("Object is not a Temperature");
 }

 public double Fahrenheit
 {
 get
 {
 return this.temperatureF;
 }
 set 
 {
 this.temperatureF = value;
 }
 }

 public double Celsius
 {
 get
 {
 return (this.temperatureF - 32) * (5.0/9);
 }
 set
 {
 this.temperatureF = (value * 9.0/5) + 32;
 }
 }
}

public class CompareTemperatures
{
 public static void Main()
 {
 ArrayList temperatures = new ArrayList();
 // Initialize random number generator.
 Random rnd = new Random();

 // Generate 10 temperatures between 0 and 100 randomly.
 for (int ctr = 1; ctr <= 10; ctr++)
 {
 int degrees = rnd.Next(0, 100);
 Temperature temp = new Temperature();
 temp.Fahrenheit = degrees;
 temperatures.Add(temp);
 }

 // Sort ArrayList.
 temperatures.Sort();

 foreach (Temperature temp in temperatures)
 Console.WriteLine(temp.Fahrenheit);
 }
}
// The example displays the following output to the console (individual
// values may vary because they are randomly generated):
// 2
// 7
// 16
// 17
// 31
// 37
// 58
// 66
// 72
// 95

open System
open System.Collections

type Temperature() =
 // The temperature value
 let mutable temperatureF = 0.

 interface IComparable with
 member _.CompareTo(obj) =
 match obj with 
 | null -> 1
 | :? Temperature as other -> 
 temperatureF.CompareTo other.Fahrenheit
 | _ ->
 invalidArg (nameof obj) "Object is not a Temperature"

 member _.Fahrenheit 
 with get () =
 temperatureF
 and set (value) = 
 temperatureF <- value

 member _.Celsius
 with get () =
 (temperatureF - 32.) * (5. / 9.)
 and set (value) =
 temperatureF <- (value * 9. / 5.) + 32.

let temperatures = ResizeArray()

// Initialize random number generator.
let rnd = Random()

// Generate 10 temperatures between 0 and 100 randomly.
for _ = 1 to 10 do
 let degrees = rnd.Next(0, 100)
 let temp = Temperature(Fahrenheit=degrees)
 temperatures.Add temp

// Sort ResizeArray.
temperatures.Sort()

for temp in temperatures do
 printfn $"{temp.Fahrenheit}"

// The example displays the following output to the console (individual
// values may vary because they are randomly generated):
// 2
// 7
// 16
// 17
// 31
// 37
// 58
// 66
// 72
// 95

Imports System.Collections

Public Class Temperature
 Implements IComparable
 ' The temperature value
 Protected temperatureF As Double

 Public Overloads Function CompareTo(ByVal obj As Object) As Integer _
 Implements IComparable.CompareTo
 
 If obj Is Nothing Then Return 1

 Dim otherTemperature As Temperature = TryCast(obj, Temperature)
 If otherTemperature IsNot Nothing Then
 Return Me.temperatureF.CompareTo(otherTemperature.temperatureF)
 Else
 Throw New ArgumentException("Object is not a Temperature")
 End If 
 End Function

 Public Property Fahrenheit() As Double
 Get
 Return temperatureF
 End Get
 Set(ByVal Value As Double)
 Me.temperatureF = Value
 End Set
 End Property

 Public Property Celsius() As Double
 Get
 Return (temperatureF - 32) * (5/9)
 End Get
 Set(ByVal Value As Double)
 Me.temperatureF = (Value * 9/5) + 32
 End Set
 End Property
End Class

Public Module CompareTemperatures
 Public Sub Main()
 Dim temperatures As New ArrayList
 ' Initialize random number generator.
 Dim rnd As New Random()
 
 ' Generate 10 temperatures between 0 and 100 randomly.
 For ctr As Integer = 1 To 10
 Dim degrees As Integer = rnd.Next(0, 100)
 Dim temp As New Temperature
 temp.Fahrenheit = degrees
 temperatures.Add(temp) 
 Next

 ' Sort ArrayList.
 temperatures.Sort()
 
 For Each temp As Temperature In temperatures
 Console.WriteLine(temp.Fahrenheit)
 Next 
 End Sub
End Module
' The example displays the following output to the console (individual
' values may vary because they are randomly generated):
' 2
' 7
' 16
' 17
' 31
' 37
' 58
' 66
' 72
' 95

Remarks

This interface is implemented by types whose values can be ordered or sorted. It requires that implementing types define a single method, CompareTo(Object), 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. The instance's IComparable implementation is called automatically by methods such as Array.Sort and ArrayList.Sort.

The implementation of the CompareTo(Object) method must return an Int32 that has one of three values, as shown in the following table.

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