Double.Equals Method (Object)
Returns a value indicating whether this instance is equal to a specified object.
Assembly: mscorlib (in mscorlib.dll)
Parameters
- obj
-
Type:
System.Object
An object to compare with this instance.
Return Value
Type: System.Booleantrue if obj is an instance of Double and equals the value of this instance; otherwise, false.
TheEquals method should be used with caution, because two apparently equivalent values can be unequal due to the differing precision of the two values. The following example reports that the Double value .3333 and the Double returned by dividing 1 by 3 are unequal.
' Initialize two doubles with apparently identical values Dim double1 As Double = .33333 Dim double2 As Object = 1/3 ' Compare them for equality Console.WriteLine(double1.Equals(double2)) ' displays False
For alternatives to calling the Equals method, see the documentation for the Equals(Double) overload.
Note |
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Because Epsilon defines the minimum expression of a positive value whose range is near zero, the margin of difference between two similar values must be greater than Epsilon. Typically, it is many times greater than Epsilon. |
The precision of floating-point numbers beyond the documented precision is specific to the implementation and version of the .NET Framework. Consequently, a comparison of two particular numbers might change between versions of the .NET Framework because the precision of the numbers' internal representation might change.
If two Double.NaN values are tested for equality by calling the Equals method, the method returns true. However, if two NaN values are tested for equality by using the equality operator, the operator returns false. When you want to determine whether the value of a Double is not a number (NaN), an alternative is to call the IsNaN method.
Notes to Callers:
Compiler overload resolution may account for an apparent difference in the behavior of the two Equals method overloads. If an implicit conversion between the obj argument and a Double is defined and the argument is not typed as an Object, compilers may perform an implicit conversion and call the Equals(Double) method. Otherwise, they call the Equals(Object) method, which always returns false if its obj argument is not a Double value. The following example illustrates the difference in behavior between the two method overloads. In the case of all primitive numeric types except for Decimal and in C#, the first comparison returns true because the compiler automatically performs a widening conversion and calls the Equals(Double) method, whereas the second comparison returns false because the compiler calls the Equals(Object) method.
Module Example Dim value As Double = 112 Public Sub Main() Dim byte1 As Byte = 112 Console.WriteLine("value = byte1: {0,16}", value.Equals(byte1)) TestObjectForEquality(byte1) Dim short1 As Short = 112 Console.WriteLine("value = short1: {0,16}", value.Equals(short1)) TestObjectForEquality(short1) Dim int1 As Integer = 112 Console.WriteLine("value = int1: {0,18}", value.Equals(int1)) TestObjectForEquality(int1) Dim long1 As Long = 112 Console.WriteLine("value = long1: {0,17}", value.Equals(long1)) TestObjectForEquality(long1) Dim sbyte1 As SByte = 112 Console.WriteLine("value = sbyte1: {0,16}", value.Equals(sbyte1)) TestObjectForEquality(sbyte1) Dim ushort1 As UShort = 112 Console.WriteLine("value = ushort1: {0,16}", value.Equals(ushort1)) TestObjectForEquality(ushort1) Dim uint1 As UInteger = 112 Console.WriteLine("value = uint1: {0,18}", value.Equals(uint1)) TestObjectForEquality(uint1) Dim ulong1 As ULong = 112 Console.WriteLine("value = ulong1: {0,17}", value.Equals(ulong1)) TestObjectForEquality(ulong1) Dim dec1 As Decimal = 112d Console.WriteLine("value = dec1: {0,20}", value.Equals(dec1)) TestObjectForEquality(dec1) Dim sng1 As Single = 112 Console.WriteLine("value = sng1: {0,19}", value.Equals(sng1)) TestObjectForEquality(sng1) End Sub Private Sub TestObjectForEquality(obj As Object) Console.WriteLine("{0} ({1}) = {2} ({3}): {4}", value, value.GetType().Name, obj, obj.GetType().Name, value.Equals(obj)) Console.WriteLine() End Sub End Module ' The example displays the following output: ' value = byte1: True ' 112 (Double) = 112 (Byte): False ' ' value = short1: True ' 112 (Double) = 112 (Int16): False ' ' value = int1: True ' 112 (Double) = 112 (Int32): False ' ' value = long1: True ' 112 (Double) = 112 (Int64): False ' ' value = sbyte1: True ' 112 (Double) = 112 (SByte): False ' ' value = ushort1: True ' 112 (Double) = 112 (UInt16): False ' ' value = uint1: True ' 112 (Double) = 112 (UInt32): False ' ' value = ulong1: True ' 112 (Double) = 112 (UInt64): False ' ' value = dec1: True ' 112 (Double) = 112 (Decimal): False ' ' value = sng1: True ' 112 (Double) = 112 (Single): False
Available since 8
.NET Framework
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
