IComparable<T>.CompareTo(T) 方法

定義

將目前的執行個體與相同型別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.

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

參數

other
T

與這個執行個體相互比較的物件。An object to compare with this instance.

傳回

值,表示所比較之物件的相對順序。A value that indicates the relative order of the objects being compared. 傳回值具有這些意義:The return value has these meanings:

Value 意義Meaning
小於零Less than zero 這個執行個體在排序次序中會在 other 之前。This instance precedes other in the sort order.
Zero 這個執行個體在排序次序中的位置和 other 相同。This instance occurs in the same position in the sort order as other.
大於零Greater than zero 這個執行個體在排序次序中會跟隨在 other 之後。This instance follows other in the sort order.

範例

下列IComparable<T>程式碼範例說明簡單Temperature物件的執行。The following code example illustrates the implementation of IComparable<T> for a simple Temperature object. 此範例會建立SortedList<TKey,TValue>含有Temperature物件索引鍵的字串集合,並將陣列溫度和字串加入順序中的清單。The example creates a SortedList<TKey,TValue> collection of strings with Temperature object keys, and adds several pairs of temperatures and strings to the list out of sequence. Add方法的呼叫中SortedList<TKey,TValue> ,集合會使用IComparable<T>執行來排序清單專案,然後以增加的溫度順序顯示。In the call to the Add method, the SortedList<TKey,TValue> collection uses the IComparable<T> implementation to sort the list entries, which are then displayed in order of increasing temperature.

#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(2017.15), "Boiling point of Lead");
   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");
   temps->Add(gcnew Temperature(600.65), "Melting point of Lead");

   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(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.
*/
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(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")

        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.
'

備註

CompareTo提供強型別的比較方法,以排序泛型集合物件的成員。CompareTo provides a strongly typed comparison method for ordering members of a generic collection object. 因此,通常不會直接從開發人員程式碼呼叫它。Because of this, it is usually not called directly from developer code. 相反地,它是由List<T>.Sort()Add之類的方法自動呼叫。Instead, it is called automatically by methods such as List<T>.Sort() and Add.

這個方法只是定義,必須由特定類別或實值型別實作用才會生效。This method is only a definition and must be implemented by a specific class or value type to have effect. 傳回值區段中所指定的比較意義("在" 之前 "、" 出現在與 "和" 後面的相同位置)取決於特定的執行。The meaning of the comparisons specified in the Return Values section ("precedes", "occurs in the same position as", and "follows) depends on the particular implementation.

根據定義,任何物件的比較都null大於,而兩個 null 參考的比較是否相等。By definition, any object compares greater than null, and two null references compare equal to each other.

給實施者的注意事項

若為 A、B 和 C 物件,下列條件必須成立:For objects A, B, and C, the following must be true: CompareTo (A)必須傳回零。A.CompareTo(A) is required to return zero.

如果. CompareTo (B)傳回零,則CompareTo (A)必須傳回零。If A.CompareTo(B) returns zero, then B.CompareTo(A) is required to return zero.

如果. CompareTo (B)傳回零和B,CompareTo (c)會傳回零,則CompareTo (c)必須傳回零。If A.CompareTo(B) returns zero and B.CompareTo(C) returns zero, then A.CompareTo(C) is required to return zero.

如果. CompareTo (B)傳回零以外的值,則需要CompareTo (A)來傳回相反正負號的值。If A.CompareTo(B) returns a value other than zero, then B.CompareTo(A) is required to return a value of the opposite sign.

如果. CompareTo (B) x傳回的值不等於零,而CompareTo (C)傳回yx值與相同的正負號,則需要CompareTo (c)來傳回相同正負號的值x和。yIf A.CompareTo(B) returns a value x that is not equal to zero, and B.CompareTo(C) returns a value y of the same sign as x, then A.CompareTo(C) is required to return a value of the same sign as x and y.

給呼叫者的注意事項

CompareTo(T)使用方法來判斷類別實例的順序。Use the CompareTo(T) method to determine the ordering of instances of a class.

適用於

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