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IComparable.CompareTo Method

Compares the current instance with another object of the same type.

Namespace: System
Assembly: mscorlib (in mscorlib.dll)

'Declaration
Function CompareTo ( _
	obj As Object _
) As Integer
'Usage
Dim instance As IComparable
Dim obj As Object
Dim returnValue As Integer

returnValue = instance.CompareTo(obj)
int CompareTo (
	Object obj
)
function CompareTo (
	obj : Object
) : int

Parameters

obj

An object to compare with this instance.

Return Value

A 32-bit signed integer that indicates the relative order of the objects being compared. The return value has these meanings:

Value

Meaning

Less than zero

This instance is less than obj.

Zero

This instance is equal to obj.

Greater than zero

This instance is greater than obj.

Exception typeCondition

ArgumentException

obj is not the same type as this instance.

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, "less than," "equal to," and "greater than," depends on the particular implementation.

By definition, any object compares greater than a null reference (Nothing in Visual Basic), 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) is required to return zero. If A.CompareTo(B) returns zero, then B.CompareTo(A) is required to return zero. If A.CompareTo(B) returns zero and B.CompareTo(C) returns zero, then A.CompareTo(C) is required to return zero. If A.CompareTo(B) returns a value other than zero, then B.CompareTo(A) is required to 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) is required to return a value of the same sign as x and y.

Notes to Callers Use the CompareTo method to determine the ordering of instances of a class.

The following code sample illustrates the use of CompareTo to compare a Temperature object implementing IComparable with another object.

Public Class Temperature
    Implements IComparable

    Public Overloads Function CompareTo(ByVal obj As Object) As Integer _
        Implements IComparable.CompareTo

        If TypeOf obj Is Temperature Then
            Dim temp As Temperature = CType(obj, Temperature)

            Return m_value.CompareTo(temp.m_value)
        End If

        Throw New ArgumentException("object is not a Temperature")
    End Function

    ' The value holder
    Protected m_value As Integer

    Public Property Value() As Integer
        Get
            Return m_value
        End Get
        Set(ByVal Value As Integer)
            m_value = Value
        End Set
    End Property

    Public Property Celsius() As Integer
        Get
            Return (m_value - 32) / 2
        End Get
        Set(ByVal Value As Integer)
            m_value = Value * 2 + 32
        End Set
    End Property
End Class

public class Temperature implements IComparable
{
    /// <summary>
    /// IComparable.CompareTo implementation.
    /// </summary>
    public int CompareTo(Object obj)
    {
        if (obj instanceof Temperature) {
            Temperature temp = (Temperature)obj;
            return ((Int32)mValue).CompareTo(temp.mValue);
        }
        throw new ArgumentException("object is not a Temperature");
    } //CompareTo

    // The value holder
    protected int mValue;

    /** @property
     */
    public int get_Value()
    {
        return mValue;
    }//get_Value

    /** @property
     */
    public void set_Value(int value)
    {
        mValue = value;
    }//set_Value

    /** @property
     */
    public int get_Celsius()
    {
        return (mValue - 32) / 2;
    }//get_Celsius

    /** @property 
     */
    public void set_Celsius(int value)
    {
        mValue = value * 2 + 32;
    }//set_Celsius
} //Temperature

Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.

.NET Framework

Supported in: 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0, 1.0

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