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IComparable<T> インターフェイス

 

公開日: 2016年10月

インスタンスの並べ替えなどを目的とし、型固有の比較メソッドを作成するために値型またはクラスで実装する、汎用の比較メソッドを定義します。

名前空間:   System
アセンブリ:  mscorlib (mscorlib.dll 内)

public interface IComparable<in T>

型パラメーター

inT

比較するオブジェクトの型。

名前説明
System_CAPS_pubmethodCompareTo(T)

現在のインスタンスを同じ型の別のオブジェクトと比較し、現在のインスタンスの並べ替え順序での位置が、比較対象のオブジェクトと比べて前か、後か、または同じかを示す整数を返します。

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, M:System.IComparable`1.CompareTo(`0), 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 M:System.Collections.Generic.List`1.Sort and M:System.Collections.Generic.SortedList`2.Add(`0,`1).

Typically, types that provide an T:System.IComparable`1 implementation also implement the T:System.IEquatable`1 interface. The T:System.IEquatable`1 interface defines the M:System.IEquatable`1.Equals(`0) method, which determines the equality of instances of the implementing type.

The implementation of the M:System.IComparable`1.CompareTo(`0) method must return an T:System.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 M:System.IComparable`1.CompareTo(`0) method in the sort order.

Zero

This current instance occurs in the same position in the sort order as the object specified by the M:System.IComparable`1.CompareTo(`0) method argument.

Greater than zero

This current instance follows the object specified by the M:System.IComparable`1.CompareTo(`0) method argument in the sort order.

All numeric types (such as T:System.Int32 and T:System.Double) implement T:System.IComparable`1, as do T:System.String, T:System.Char, and T:System.DateTime. Custom types should also provide their own implementation of T:System.IComparable`1 to enable object instances to be ordered or sorted.

実装時の注意:

Replace the type parameter of the T:System.IComparable`1 interface with the type that is implementing this interface.

If you implement T:System.IComparable`1, you should overload the op_GreaterThan, op_GreaterThanOrEqual, op_LessThan, and op_LessThanOrEqual operators to return values that are consistent with M:System.IComparable`1.CompareTo(`0). In addition, you should also implement T:System.IEquatable`1. See the T:System.IEquatable`1 article for complete information.

The following code example illustrates the implementation of T:System.IComparable`1 for a simple Temperature object. The example creates a T:System.Collections.Generic.SortedList`2 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 M:System.Collections.Generic.SortedList`2.Add(`0,`1) method, the T:System.Collections.Generic.SortedList`2 collection uses the T:System.IComparable`1 implementation to sort the list entries, which are then displayed in order of increasing temperature.

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(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.
*/

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8 以降で使用可能
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