IComparable.CompareTo(Object) Method

public:
 int CompareTo(System::Object ^ obj);

public int CompareTo(object obj);

public int CompareTo(object? obj);

abstract member CompareTo : obj -> int

Public Function CompareTo (obj As Object) As Integer

Parameters

Returns

A value that indicates the relative order of the objects being compared. The return value has these meanings:

Exceptions

Examples

The following example illustrates the use of CompareTo to compare a Temperature object implementing IComparable with another object. The Temperature object implements CompareTo by simply wrapping a call to the Int32.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

The CompareTo method is implemented by types whose values can be ordered or sorted. It is called automatically by methods of non-generic collection objects, such as Array.Sort, to order each member of the array. If a custom class or structure does not implement IComparable, its members cannot be ordered and the sort operation can throw an InvalidOperationException.

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 Value section ("precedes", "occurs in the same position as", and "follows") depends on the particular implementation.

By definition, any object compares greater than (or follows) null, and two null references compare equal to each other.

The parameter, obj, must be the same type as the class or value type that implements this interface; otherwise, an ArgumentException is thrown.

Notes to Implementers

For objects A, B and C, the following must be true:

A.CompareTo(A) must return zero.

If A.CompareTo(B) returns zero, then B.CompareTo(A) must return zero.

If A.CompareTo(B) returns zero and B.CompareTo(C) returns zero, then A.CompareTo(C) must return zero.

If A.CompareTo(B) returns a value other than zero, then B.CompareTo(A) must return a value of the opposite sign.

If A.CompareTo(B) returns a value "x" not equal to zero, and B.CompareTo(C) returns a value "y" of the same sign as "x", then A.CompareTo(C) must return a value of the same sign as "x" and "y".

Notes to Callers

Use the CompareTo(Object) method to determine the ordering of instances of a class.

See also

• Object