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Metodo Single.Equals (Object)

 

Data di pubblicazione: ottobre 2016

Restituisce un valore che indica se questa istanza è uguale a un oggetto specificato.

Spazio dei nomi:   System
Assembly:  mscorlib (in mscorlib.dll)

public override bool Equals(
	object obj
)

Parametri

obj
Type: System.Object

Oggetto da confrontare con l'istanza.

Valore restituito

Type: System.Boolean

true se obj è un'istanza di Single ed è uguale al valore dell'istanza; in caso contrario, false.

TheM:System.Single.Equals(System.Single) 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 T:System.Single value .3333 and the T:System.Single returned by dividing 1 by 3 are unequal.

// Initialize two floats with apparently identical values
float float1 = .33333f;
object float2 = 1/3;
// Compare them for equality
Console.WriteLine(float1.Equals(float2));    // displays false

Rather than comparing for equality, one recommended technique involves defining an acceptable margin of difference between two values (such as .01% of one of the values). If the absolute value of the difference between the two values is less than or equal to that margin, the difference is likely to be due to differences in precision and, therefore, the values are likely to be equal. The following example uses this technique to compare .33333 and 1/3, the two T:System.Single values that the previous code example found to be unequal.

// Initialize two floats with apparently identical values
float float1 = .33333f;
object float2 = (float) 1/3;
// Define the tolerance for variation in their values
float difference = Math.Abs(float1 * .0001f);

// Compare the values
// The output to the console indicates that the two values are equal
if (Math.Abs(float1 - (float) float2) <= difference)
   Console.WriteLine("float1 and float2 are equal.");
else
   Console.WriteLine("float1 and float2 are unequal.");

In this case, the values are equal.

System_CAPS_noteNota

Because F:System.Single.Epsilon defines the minimum expression of a positive value whose range is near zero, the margin of difference must be greater than F:System.Single.Epsilon. Typically, it is many times greater than F:System.Single.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.

Note per i chiamanti:

Compiler overload resolution may account for an apparent difference in the behavior of the two M:System.Single.Equals(System.Object) method overloads. If an implicit conversion between the obj argument and a T:System.Single is defined and the argument is not typed as an T:System.Object, compilers may perform an implicit conversion and call the M:System.Single.Equals(System.Single) method. Otherwise, they call the M:System.Single.Equals(System.Object) method, which always returns false if its obj argument is not a T:System.Single value. The following example illustrates the difference in behavior between the two method overloads. In the case of all primitive numeric types except for T:System.Double in Visual Basic and except for T:System.Decimal and T:System.Double in C#, the first comparison returns true because the compiler automatically performs a widening conversion and calls the M:System.Single.Equals(System.Single) method, whereas the second comparison returns false because the compiler calls the M:System.Single.Equals(System.Object) method.

using System;

public class Example
{
   static float value = 112;

   public static void Main()
   {
      byte byte1= 112;
      Console.WriteLine("value = byte1: {0,16}", value.Equals(byte1));
      TestObjectForEquality(byte1);

      short short1 = 112;
      Console.WriteLine("value = short1: {0,16}", value.Equals(short1));
      TestObjectForEquality(short1);

      int int1 = 112;
      Console.WriteLine("value = int1: {0,18}", value.Equals(int1));
      TestObjectForEquality(int1);

      long long1 = 112;
      Console.WriteLine("value = long1: {0,17}", value.Equals(long1));
      TestObjectForEquality(long1);

      sbyte sbyte1 = 112;
      Console.WriteLine("value = sbyte1: {0,16}", value.Equals(sbyte1));
      TestObjectForEquality(sbyte1);

      ushort ushort1 = 112;
      Console.WriteLine("value = ushort1: {0,16}", value.Equals(ushort1));
      TestObjectForEquality(ushort1);

      uint uint1 = 112;
      Console.WriteLine("value = uint1: {0,18}", value.Equals(uint1));
      TestObjectForEquality(uint1);

      ulong ulong1 = 112;
      Console.WriteLine("value = ulong1: {0,17}", value.Equals(ulong1));
      TestObjectForEquality(ulong1);

      decimal dec1 = 112m;
      Console.WriteLine("value = dec1: {0,21}", value.Equals(dec1));
      TestObjectForEquality(dec1);

      double dbl1 = 112;
      Console.WriteLine("value = dbl1: {0,20}", value.Equals(dbl1));
      TestObjectForEquality(dbl1);
   }

   private static void TestObjectForEquality(Object obj)
   {
      Console.WriteLine("{0} ({1}) = {2} ({3}): {4}\n",
                        value, value.GetType().Name,
                        obj, obj.GetType().Name,
                        value.Equals(obj));
   }
}
// The example displays the following output:
//       value = byte1:             True
//       112 (Single) = 112 (Byte): False
//
//       value = short1:             True
//       112 (Single) = 112 (Int16): False
//
//       value = int1:               True
//       112 (Single) = 112 (Int32): False
//
//       value = long1:              True
//       112 (Single) = 112 (Int64): False
//
//       value = sbyte1:             True
//       112 (Single) = 112 (SByte): False
//
//       value = ushort1:             True
//       112 (Single) = 112 (UInt16): False
//
//       value = uint1:               True
//       112 (Single) = 112 (UInt32): False
//
//       value = ulong1:              True
//       112 (Single) = 112 (UInt64): False
//
//       value = dec1:                 False
//       112 (Single) = 112 (Decimal): False
//
//       value = dbl1:                False
//       112 (Single) = 112 (Double): False

The following code example demonstrates the M:System.Single.Equals(System.Object) method.

obj1 = (Single)500;
if (a.Equals(obj1)) {
    Console.WriteLine("The value type and reference type values are equal.");
}

Universal Windows Platform
Disponibile da 8
.NET Framework
Disponibile da 1.1
Libreria di classi portabile
Supportato in: piattaforme .NET portabili
Silverlight
Disponibile da 2.0
Windows Phone Silverlight
Disponibile da 7.0
Windows Phone
Disponibile da 8.1
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