# IComparable<T>.CompareTo(T) メソッド

## 定義

``````public:
int CompareTo(T other);``````
``public int CompareTo (T other);``
``public int CompareTo (T? other);``
``abstract member CompareTo : 'T -> int``
``Public Function CompareTo (other As T) As Integer``

#### パラメーター

other
T

このインスタンスと比較するオブジェクト。

#### 戻り値

Int32

[値] 説明
0 より小さい値 このインスタンスの位置が、並べ替え順序において `other` よりも前です。
ゼロ 並べ替え順序における、このインスタンスと `other` の位置が同じです。
0 より大きい値 このインスタンスの位置が、並べ替え順序において `other` よりも後ろです。

## 例

``````#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) >= 0;
}

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

// 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(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");

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) > 0;
}

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

// 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(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");

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.
*/
``````
``````open System
open System.Collections.Generic

type Temperature(kelvins: double) =
// The underlying temperature value.
let mutable kelvins = kelvins

do
if kelvins < 0. then
invalidArg (nameof kelvins) "Temperature cannot be less than absolute zero."

// Define the is greater than operator.
static member op_GreaterThan (operand1: Temperature, operand2: Temperature) =
operand1.CompareTo operand2 > 0

// Define the is less than operator.
static member op_LessThan (operand1: Temperature, operand2: Temperature) =
operand1.CompareTo operand2 < 0

// Define the is greater than or equal to operator.
static member op_GreaterThanOrEqual (operand1: Temperature, operand2: Temperature) =
operand1.CompareTo operand2 >= 0

// Define the is less than or equal to operator.
static member op_LessThanOrEqual (operand1: Temperature, operand2: Temperature) =
operand1.CompareTo operand2 <= 0

member _.Celsius =
kelvins - 273.15

member _.Kelvin
with get () =
kelvins
and set (value) =
if value < 0. then
invalidArg (nameof value) "Temperature cannot be less than absolute zero."
else
kelvins <- value

// Implement the generic CompareTo method with the Temperature
// class as the Type parameter.
member _.CompareTo(other: Temperature) =
// If other is not a valid object reference, this instance is greater.
match box other with
| null -> 1
| _ ->
// The temperature comparison depends on the comparison of
// the underlying Double values.
kelvins.CompareTo(other.Kelvin)

interface IComparable<Temperature> with
member this.CompareTo(other) = this.CompareTo other

let temps = SortedList()

// Add entries to the sorted list, out of order.
temps.Add(Temperature 0., "Absolute zero")
temps.Add(Temperature 273.15, "Freezing point of water")
temps.Add(Temperature 5100.15, "Boiling point of Carbon")
temps.Add(Temperature 373.15, "Boiling point of water")

for kvp in temps do
printfn \$"{kvp.Value} is {kvp.Key.Celsius} degrees 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) > 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

' 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(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")

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.
'
``````

## 注釈

CompareTo には、ジェネリック コレクション オブジェクトのメンバーを並べ替える厳密に型指定された比較メソッドが用意されています。 このため、通常は開発者コードから直接呼び出されません。 代わりに、次のようなList<T>.Sort()Addメソッドによって自動的に呼び出されます。

このメソッドは定義に過ぎません。影響を与えるためには、特定のクラスまたは値の型によって実装する必要があります。 戻り値セクションで指定された比較の意味 ("前"、"と同じ位置で発生"、および "フォロー) は、特定の実装によって異なります。

## 注意 (実装者)

オブジェクト A、B、C の場合は、次のことが該当する必要があります。 `A.CompareTo(A)` は 0 を返すために必要です。

`A.CompareTo(B) が` 0 を返す場合、`B.CompareTo(A)` は 0 を返す必要があります。

`A.CompareTo(B) が` 0 を返し、`B.CompareTo(C) が` 0 を返す場合、`A.CompareTo(C)` は 0 を返す必要があります。

`A.CompareTo(B) が` 0 以外の値を返す場合、`B.CompareTo(A)` は逆符号の値を返す必要があります。

`A.CompareTo(B) が` 0 以外の値`x`を返し、`B.CompareTo(C) が`同じ符号`x`の値`y`を返す場合は、`A.CompareTo(C)` が同じ符号と同じ符号`x``y`の値を返す必要があります。

## 注意 (呼び出し元)

このメソッドを CompareTo(T) 使用して、クラスのインスタンスの順序を決定します。