Object.Equals Object.Equals Object.Equals Object.Equals Method

定義

判斷兩個物件執行個體是否相等。 Determines whether two object instances are equal.

多載

Equals(Object) Equals(Object) Equals(Object) Equals(Object)

判斷指定的物件是否等於目前物件。 Determines whether the specified object is equal to the current object.

Equals(Object, Object) Equals(Object, Object) Equals(Object, Object) Equals(Object, Object)

判斷指定的物件執行個體是否視為相等。 Determines whether the specified object instances are considered equal.

Equals(Object) Equals(Object) Equals(Object) Equals(Object)

判斷指定的物件是否等於目前物件。 Determines whether the specified object is equal to the current object.

public:
 virtual bool Equals(System::Object ^ obj);
public virtual bool Equals (object obj);
abstract member Equals : obj -> bool
override this.Equals : obj -> bool
Public Overridable Function Equals (obj As Object) As Boolean
參數
obj
Object Object Object Object

要與目前物件比較的物件。 The object to compare with the current object.

傳回

如果指定的物件等於目前的物件,則為 true,否則為 false true if the specified object is equal to the current object; otherwise, false.

範例

下列範例所示Point類別會覆寫Equals方法,以提供實值相等,並Point3D類別衍生自PointThe following example shows a Point class that overrides the Equals method to provide value equality, and a Point3D class that is derived from Point. 因為Point會覆寫Object.Equals(Object)來測試值是否相等,Object.Equals(Object)不會呼叫方法。Because Point overrides Object.Equals(Object) to test for value equality, the Object.Equals(Object) method is not called. 不過,Point3D.Equals呼叫Point.Equals因為Point實作Object.Equals(Object)提供實值相等的方式。However, Point3D.Equals calls Point.Equals because Point implements Object.Equals(Object) in a manner that provides value equality.

using System;

class Point
{
   protected int x, y;

   public Point() : this(0, 0) 
   { }

   public Point(int x, int y) 
   {
      this.x = x;
      this.y = y;
   }
 
   public override bool Equals(Object obj) 
   {
      //Check for null and compare run-time types.
      if ((obj == null) || ! this.GetType().Equals(obj.GetType())) {
         return false;
      }
      else { 
         Point p = (Point) obj; 
         return (x == p.x) && (y == p.y);
      }   
   }

   public override int GetHashCode() 
   {
      return (x << 2) ^ y;
   }

    public override string ToString()
    {
        return String.Format("Point({0}, {1})", x, y);
    }
}

sealed class Point3D: Point 
{
   int z;

   public Point3D(int x, int y, int z) : base(x, y) 
   {
      this.z = z; 
   }

   public override bool Equals(Object obj) 
   {
      Point3D pt3 = obj as Point3D;
      if (pt3 == null)
         return false;
      else
         return base.Equals((Point)obj) && z == pt3.z;
   }

   public override int GetHashCode() 
   {
      return (base.GetHashCode() << 2) ^ z;
   }

   public override String ToString() 
   {
        return String.Format("Point({0}, {1}, {2})", x, y, z);
    }
}

class Example 
{
  public static void Main() 
  {
     Point point2D = new Point(5, 5);
     Point3D point3Da = new Point3D(5, 5, 2);
     Point3D point3Db = new Point3D(5, 5, 2);
     Point3D point3Dc = new Point3D(5, 5, -1);
     
     Console.WriteLine("{0} = {1}: {2}", 
                       point2D, point3Da, point2D.Equals(point3Da));
     Console.WriteLine("{0} = {1}: {2}", 
                       point2D, point3Db, point2D.Equals(point3Db));        
     Console.WriteLine("{0} = {1}: {2}", 
                       point3Da, point3Db, point3Da.Equals(point3Db));
     Console.WriteLine("{0} = {1}: {2}", 
                       point3Da, point3Dc, point3Da.Equals(point3Dc));
  } 
}
// The example displays the following output:
//       Point(5, 5) = Point(5, 5, 2): False
//       Point(5, 5) = Point(5, 5, 2): False
//       Point(5, 5, 2) = Point(5, 5, 2): True
//       Point(5, 5, 2) = Point(5, 5, -1): False
Class Point
    Protected x, y As Integer
    
    Public Sub New() 
        Me.x = 0
        Me.y = 0
    End Sub
    
    Public Sub New(x As Integer, y As Integer) 
        Me.x = x
        Me.y = y
    End Sub 

    Public Overrides Function Equals(obj As Object) As Boolean 
        ' Check for null and compare run-time types.
        If obj Is Nothing OrElse Not Me.GetType().Equals(obj.GetType()) Then
           Return False
        Else
           Dim p As Point = DirectCast(obj, Point)
           Return x = p.x AndAlso y = p.y
        End If
    End Function 

    Public Overrides Function GetHashCode() As Integer 
        Return (x << 2) XOr y
    End Function

    Public Overrides Function ToString() As String
        Return String.Format("Point({0}, {1})", x, y)
    End Function
End Class

Class Point3D : Inherits Point
    Private z As Integer
    
    Public Sub New(ByVal x As Integer, ByVal y As Integer, ByVal z As Integer) 
        MyBase.New(x, y) 
        Me.z = Z
    End Sub

    Public Overrides Function Equals(ByVal obj As Object) As Boolean 
        Dim pt3 As Point3D = TryCast(obj, Point3D)
        If pt3 Is Nothing Then
           Return False
        Else
           Return MyBase.Equals(CType(pt3, Point)) AndAlso z = pt3.Z  
        End If
    End Function
    
    Public Overrides Function GetHashCode() As Integer 
        Return (MyBase.GetHashCode() << 2) XOr z
    End Function 
    
    Public Overrides Function ToString() As String
        Return String.Format("Point({0}, {1}, {2})", x, y, z)
    End Function
End Class 

Module Example
    Public Sub Main() 
        Dim point2D As New Point(5, 5)
        Dim point3Da As New Point3D(5, 5, 2)
        Dim point3Db As New Point3D(5, 5, 2)
        Dim point3Dc As New Point3D(5, 5, -1)
        
        Console.WriteLine("{0} = {1}: {2}", 
                          point2D, point3Da, point2D.Equals(point3Da))
        Console.WriteLine("{0} = {1}: {2}", 
                          point2D, point3Db, point2D.Equals(point3Db))        
        Console.WriteLine("{0} = {1}: {2}", 
                          point3Da, point3Db, point3Da.Equals(point3Db))
        Console.WriteLine("{0} = {1}: {2}", 
                          point3Da, point3Dc, point3Da.Equals(point3Dc))
    End Sub  
End Module 
' The example displays the following output
'       Point(5, 5) = Point(5, 5, 2): False
'       Point(5, 5) = Point(5, 5, 2): False
'       Point(5, 5, 2) = Point(5, 5, 2): True
'       Point(5, 5, 2) = Point(5, 5, -1): False

Point.Equals方法會檢查並確定obj引數不是null和它所參考的這個物件與相同類型的執行個體。The Point.Equals method checks to make sure that the obj argument is not null and that it references an instance of the same type as this object. 如果其中一個檢查失敗,則方法會傳回falseIf either check fails, the method returns false.

Point.Equals方法呼叫GetType方法,以判斷兩個物件的執行階段類型是否相同。The Point.Equals method calls the GetType method to determine whether the run-time types of the two objects are identical. 如果使用表單的核取的方法obj is PointC# 中或TryCast(obj, Point)在 Visual Basic 中,檢查會傳回true萬一其中obj的衍生類別的執行個體Point,即使obj和目前執行個體不是相同的執行階段型別。If the method used a check of the form obj is Point in C# or TryCast(obj, Point) in Visual Basic, the check would return true in cases where obj is an instance of a derived class of Point, even though obj and the current instance are not of the same run-time type. 完成驗證,這兩個物件都是相同類型,也就是方法轉型obj輸入Point,並傳回比較兩個物件的執行個體欄位的結果。Having verified that both objects are of the same type, the method casts obj to type Point and returns the result of comparing the instance fields of the two objects.

Point3D.Equals,繼承Point.Equals方法,它會覆寫Object.Equals(Object),任何其他項目完成之前叫用。In Point3D.Equals, the inherited Point.Equals method, which overrides Object.Equals(Object), is invoked before anything else is done. 因為Point3D是密封的類別 (NotInheritable Visual Basic 中),在表單中的核取obj is Point在 C# 或TryCast(obj, Point)Visual Basic 中就已足夠,確保objPoint3D物件。Because Point3D is a sealed class (NotInheritable in Visual Basic), a check in the form obj is Point in C# or TryCast(obj, Point) in Visual Basic is adequate to ensure that obj is a Point3D object. 如果它是Point3D物件,它會轉換為Point物件,並傳遞至基底類別實作EqualsIf it is a Point3D object, it is cast to a Point object and passed to the base class implementation of Equals. 只有當繼承Point.Equals方法會傳回true沒有方法比較z執行個體的衍生類別中引進的欄位。Only when the inherited Point.Equals method returns true does the method compare the z instance fields introduced in the derived class.

下列範例會定義Rectangle類別在內部實作做為兩個矩形Point物件。The following example defines a Rectangle class that internally implements a rectangle as two Point objects. Rectangle類別也會覆寫Object.Equals(Object)提供的值是否相等。The Rectangle class also overrides Object.Equals(Object) to provide for value equality.

using System;

class Rectangle 
{
   private Point a, b;

   public Rectangle(int upLeftX, int upLeftY, int downRightX, int downRightY) {
      this.a = new Point(upLeftX, upLeftY);
      this.b = new Point(downRightX, downRightY);
   }

   public override bool Equals(Object obj) {
      // Perform an equality check on two rectangles (Point object pairs).
      if (obj == null || GetType() != obj.GetType()) 
          return false;
      Rectangle r = (Rectangle)obj;
      return a.Equals(r.a) && b.Equals(r.b);
   }

   public override int GetHashCode() {
      return Tuple.Create(a, b).GetHashCode();
   }

    public override String ToString() 
    {
       return String.Format("Rectangle({0}, {1}, {2}, {3})",
                            a.x, a.y, b.x, b.y); 
    }
}

class Point 
{
  internal int x;
  internal int y;

  public Point(int X, int Y) {
     this.x = X;
     this.y = Y;
  }

  public override bool Equals (Object obj) {
     // Performs an equality check on two points (integer pairs).
     if (obj == null || GetType() != obj.GetType()) return false;
     Point p = (Point)obj;
     return (x == p.x) && (y == p.y);
  }

  public override int GetHashCode() {
     return Tuple.Create(x, y).GetHashCode();
  }
}

class Example 
{
   public static void Main() 
   {
      Rectangle r1 = new Rectangle(0, 0, 100, 200);
      Rectangle r2 = new Rectangle(0, 0, 100, 200);
      Rectangle r3 = new Rectangle(0, 0, 150, 200);

      Console.WriteLine("{0} = {1}: {2}", r1, r2, r1.Equals(r2));
      Console.WriteLine("{0} = {1}: {2}", r1, r3, r1.Equals(r3));
      Console.WriteLine("{0} = {1}: {2}", r2, r3, r2.Equals(r3));
   }
}
// The example displays the following output:
//    Rectangle(0, 0, 100, 200) = Rectangle(0, 0, 100, 200): True
//    Rectangle(0, 0, 100, 200) = Rectangle(0, 0, 150, 200): False
//    Rectangle(0, 0, 100, 200) = Rectangle(0, 0, 150, 200): False
Class Rectangle 
    Private a, b As Point
    
    Public Sub New(ByVal upLeftX As Integer, ByVal upLeftY As Integer, _
                   ByVal downRightX As Integer, ByVal downRightY As Integer) 
        Me.a = New Point(upLeftX, upLeftY)
        Me.b = New Point(downRightX, downRightY)
    End Sub 
    
    Public Overrides Function Equals(ByVal obj As [Object]) As Boolean 
        ' Performs an equality check on two rectangles (Point object pairs).
        If obj Is Nothing OrElse Not [GetType]().Equals(obj.GetType()) Then
            Return False
        End If
        Dim r As Rectangle = CType(obj, Rectangle)
        Return a.Equals(r.a) AndAlso b.Equals(r.b)
    End Function

    Public Overrides Function GetHashCode() As Integer 
        Return Tuple.Create(a, b).GetHashCode()
    End Function 

    Public Overrides Function ToString() As String
       Return String.Format("Rectangle({0}, {1}, {2}, {3})",
                            a.x, a.y, b.x, b.y) 
    End Function
End Class 

Class Point
    Friend x As Integer
    Friend y As Integer
    
    Public Sub New(ByVal X As Integer, ByVal Y As Integer) 
        Me.x = X
        Me.y = Y
    End Sub 

    Public Overrides Function Equals(ByVal obj As [Object]) As Boolean 
        ' Performs an equality check on two points (integer pairs).
        If obj Is Nothing OrElse Not [GetType]().Equals(obj.GetType()) Then
            Return False
        Else
           Dim p As Point = CType(obj, Point)
           Return x = p.x AndAlso y = p.y
        End If
    End Function 
    
    Public Overrides Function GetHashCode() As Integer 
        Return Tuple.Create(x, y).GetHashCode()
    End Function 
End Class  

Class Example
    Public Shared Sub Main() 
        Dim r1 As New Rectangle(0, 0, 100, 200)
        Dim r2 As New Rectangle(0, 0, 100, 200)
        Dim r3 As New Rectangle(0, 0, 150, 200)
        
        Console.WriteLine("{0} = {1}: {2}", r1, r2, r1.Equals(r2))
        Console.WriteLine("{0} = {1}: {2}", r1, r3, r1.Equals(r3))
        Console.WriteLine("{0} = {1}: {2}", r2, r3, r2.Equals(r3))
    End Sub 
End Class 
' The example displays the following output:
'    Rectangle(0, 0, 100, 200) = Rectangle(0, 0, 100, 200): True
'    Rectangle(0, 0, 100, 200) = Rectangle(0, 0, 150, 200): False
'    Rectangle(0, 0, 100, 200) = Rectangle(0, 0, 150, 200): False

某些語言,例如 C# 和 Visual Basic 支援運算子多載。Some languages such as C# and Visual Basic support operator overloading. 當類型多載等號比較運算子時,它也必須覆寫Equals(Object)方法,以提供相同的功能。When a type overloads the equality operator, it must also override the Equals(Object) method to provide the same functionality. 這通常透過撰寫Equals(Object)方面的多載等號比較運算子,如下列範例所示的方法。This is typically accomplished by writing the Equals(Object) method in terms of the overloaded equality operator, as in the following example.

using System;

public struct Complex {
   public double re, im;

   public override bool Equals(Object obj) {
      return obj is Complex && this == (Complex)obj;
   }

   public override int GetHashCode() {
      return Tuple.Create(re, im).GetHashCode();
   }

   public static bool operator ==(Complex x, Complex y) {
      return x.re == y.re && x.im == y.im;
   }

   public static bool operator !=(Complex x, Complex y) {
      return !(x == y);
   }

    public override String ToString()
    {
       return String.Format("({0}, {1})", re, im);
    } 
}

class MyClass 
{
  public static void Main() 
  {
    Complex cmplx1, cmplx2;

    cmplx1.re = 4.0;
    cmplx1.im = 1.0;

    cmplx2.re = 2.0;
    cmplx2.im = 1.0;

    Console.WriteLine("{0} <> {1}: {2}", cmplx1, cmplx2, cmplx1 != cmplx2);        
    Console.WriteLine("{0} = {1}: {2}", cmplx1, cmplx2, cmplx1.Equals(cmplx2));        
      
    cmplx2.re = 4.0;
      
    Console.WriteLine("{0} = {1}: {2}", cmplx1, cmplx2, cmplx1 == cmplx2);        
    Console.WriteLine("{0} = {1}: {2}", cmplx1, cmplx2, cmplx1.Equals(cmplx2));          
  }
}
// The example displays the following output:
//       (4, 1) <> (2, 1): True
//       (4, 1) = (2, 1): False
//       (4, 1) = (4, 1): True
//       (4, 1) = (4, 1): True
Public Structure Complex
    Public re, im As Double
    
    Public Overrides Function Equals(ByVal obj As [Object]) As Boolean 
        Return TypeOf obj Is Complex AndAlso Me = CType(obj, Complex)
    End Function 
    
    Public Overrides Function GetHashCode() As Integer 
        Return Tuple.Create(re, im).GetHashCode()
    End Function 
    
    Public Shared Operator = (x As Complex, y As Complex) As Boolean
       Return x.re = y.re AndAlso x.im = y.im
    End Operator 
    
    Public Shared Operator <> (x As Complex, y As Complex) As Boolean
       Return Not (x = y)
    End Operator 
    
    Public Overrides Function ToString() As String
       Return String.Format("({0}, {1})", re, im)
    End Function 
End Structure

Class Example
   Public Shared Sub Main() 
      Dim cmplx1, cmplx2 As Complex
        
      cmplx1.re = 4.0
      cmplx1.im = 1.0
        
      cmplx2.re = 2.0
      cmplx2.im = 1.0

      Console.WriteLine("{0} <> {1}: {2}", cmplx1, cmplx2, cmplx1 <> cmplx2)        
      Console.WriteLine("{0} = {1}: {2}", cmplx1, cmplx2, cmplx1.Equals(cmplx2))        
      
      cmplx2.re = 4.0
        
      Console.WriteLine("{0} = {1}: {2}", cmplx1, cmplx2, cmplx1 = cmplx2)        
      Console.WriteLine("{0} = {1}: {2}", cmplx1, cmplx2, cmplx1.Equals(cmplx2))        
   End Sub
End Class 
' The example displays the following output:
'       (4, 1) <> (2, 1): True
'       (4, 1) = (2, 1): False
'       (4, 1) = (4, 1): True
'       (4, 1) = (4, 1): True

因為Complex是實值類型,它不能衍生自。Because Complex is a value type, it cannot be derived from. 因此,若要覆寫Equals(Object)方法實作不需要呼叫GetType若要判斷精確的執行階段輸入的每個物件,但可以改為使用isC# 中的運算子或TypeOf檢查類型的VisualBasic中的運算子obj參數。Therefore, the override to Equals(Object) method need not call GetType to determine the precise run-time type of each object, but can instead use the is operator in C# or the TypeOf operator in Visual Basic to check the type of the obj parameter.

備註

目前的執行個體之間的比較的類型和obj參數取決於目前的執行個體是否為參考型別或實值型別。The type of comparison between the current instance and the obj parameter depends on whether the current instance is a reference type or a value type.

  • 如果目前的執行個體是參考型別Equals(Object)方法會測試參考是否相等,並呼叫Equals(Object)方法就相當於呼叫ReferenceEquals方法。If the current instance is a reference type, the Equals(Object) method tests for reference equality, and a call to the Equals(Object) method is equivalent to a call to the ReferenceEquals method. 參考相等表示所比較的物件變數參考相同的物件。Reference equality means that the object variables that are compared refer to the same object. 下列範例說明這類比較的結果。The following example illustrates the result of such a comparison. 它會定義Person類別,這是參考型別,並呼叫Person類別建構函式產生兩個新Person物件person1aperson2,具有相同的值。It defines a Person class, which is a reference type, and calls the Person class constructor to instantiate two new Person objects, person1a and person2, which have the same value. 它也會指派person1a到另一個物件變數, person1bIt also assigns person1a to another object variable, person1b. 做為範例所示,從輸出person1aperson1b相等,因為它們參考相同的物件。As the output from the example shows, person1a and person1b are equal because they reference the same object. 不過,person1aperson2不相等,雖然它們有相同的值。However, person1a and person2 are not equal, although they have the same value.

    using System;
    
    // Define a reference type that does not override Equals.
    public class Person
    {
       private string personName;
       
       public Person(string name)
       {
          this.personName = name;
       }
       
       public override string ToString()
       {
          return this.personName;
       }
    }
    
    public class Example
    {
       public static void Main()
       {
          Person person1a = new Person("John");
          Person person1b = person1a;
          Person person2 = new Person(person1a.ToString());
          
          Console.WriteLine("Calling Equals:"); 
          Console.WriteLine("person1a and person1b: {0}", person1a.Equals(person1b));               
          Console.WriteLine("person1a and person2: {0}", person1a.Equals(person2));  
          
          Console.WriteLine("\nCasting to an Object and calling Equals:");
          Console.WriteLine("person1a and person1b: {0}", ((object) person1a).Equals((object) person1b));
          Console.WriteLine("person1a and person2: {0}", ((object) person1a).Equals((object) person2)); 
       }
    }
    // The example displays the following output:
    //       person1a and person1b: True
    //       person1a and person2: False
    //       
    //       Casting to an Object and calling Equals:
    //       person1a and person1b: True
    //       person1a and person2: False
    
    ' Define a reference type that does not override Equals.
    Public Class Person
       Private personName As String
       
       Public Sub New(name As String)
          Me.personName = name
       End Sub
       
       Public Overrides Function ToString() As String
          Return Me.personName
       End Function 
    End Class
    
    Module Example
       Public Sub Main()
          Dim person1a As New Person("John")
          Dim person1b As Person = person1a
          Dim person2 As New Person(person1a.ToString())
          
          Console.WriteLine("Calling Equals:") 
          Console.WriteLine("person1a and person1b: {0}", person1a.Equals(person1b))               
          Console.WriteLine("person1a and person2: {0}", person1a.Equals(person2))  
          Console.WriteLine()
          
          Console.WriteLine("Casting to an Object and calling Equals:")
          Console.WriteLine("person1a and person1b: {0}", CObj(person1a).Equals(CObj(person1b)))
          Console.WriteLine("person1a and person2: {0}", CObj(person1a).Equals(CObj(person2))) 
       End Sub
    End Module
    ' The example displays the following output:
    '       Calling Equals:
    '       person1a and person1b: True
    '       person1a and person2: False
    '       
    '       Casting to an Object and calling Equals:
    '       person1a and person1b: True
    '       person1a and person2: False
    
  • 如果目前的執行個體是實值類型,Equals(Object)方法測試值是否相等。If the current instance is a value type, the Equals(Object) method tests for value equality. 實值相等表示下列各項:Value equality means the following:

    • 兩個物件都屬於相同的類型。The two objects are of the same type. 如下列範例所示Byte不等於物件,其值為 12Int32有值為 12,,因為兩個物件具有不同的執行階段類型的物件。As the following example shows, a Byte object that has a value of 12 does not equal an Int32 object that has a value of 12, because the two objects have different run-time types.

      using System;
      
      public class Example
      {
         public static void Main()
         {
            byte value1 = 12;
            int value2 = 12;
            
            object object1 = value1;
            object object2 = value2;
            
            Console.WriteLine("{0} ({1}) = {2} ({3}): {4}",
                              object1, object1.GetType().Name,
                              object2, object2.GetType().Name,
                              object1.Equals(object2));
         }
      }
      // The example displays the following output:
      //        12 (Byte) = 12 (Int32): False
      
      Module Example
         Public Sub Main()
            Dim value1 As Byte = 12
            Dim value2 As Integer = 12
            
            Dim object1 As Object = value1
            Dim object2 As Object = value2
            
            Console.WriteLine("{0} ({1}) = {2} ({3}): {4}",
                              object1, object1.GetType().Name,
                              object2, object2.GetType().Name,
                              object1.Equals(object2))
         End Sub
      End Module
      ' The example displays the following output:
      '       12 (Byte) = 12 (Int32): False
      
    • 兩個物件的公用和私用欄位的值相等。The values of the public and private fields of the two objects are equal. 下列範例會測試值相等。The following example tests for value equality. 它會定義Person結構,也就是實值型別,並呼叫Person類別建構函式產生兩個新Person物件person1person2,具有相同的值。It defines a Person structure, which is a value type, and calls the Person class constructor to instantiate two new Person objects, person1 and person2, which have the same value. 範例輸出所示,兩個物件變數參考不同的物件,雖然person1person2相等,因為它們具有相同的值為私用personName欄位。As the output from the example shows, although the two object variables refer to different objects, person1 and person2 are equal because they have the same value for the private personName field.

      using System;
      
      // Define a value type that does not override Equals.
      public struct Person
      {
         private string personName;
         
         public Person(string name)
         {
            this.personName = name;
         }
         
         public override string ToString()
         {
            return this.personName;
         }
      }
      
      public struct Example
      {
         public static void Main()
         {
            Person person1 = new Person("John");
            Person person2 = new Person("John");
            
            Console.WriteLine("Calling Equals:"); 
            Console.WriteLine(person1.Equals(person2)); 
            
            Console.WriteLine("\nCasting to an Object and calling Equals:");
            Console.WriteLine(((object) person1).Equals((object) person2));  
         }
      }
      // The example displays the following output:
      //       Calling Equals:
      //       True
      //       
      //       Casting to an Object and calling Equals:
      //       True
      
      ' Define a value type that does not override Equals.
      Public Structure Person
         Private personName As String
         
         Public Sub New(name As String)
            Me.personName = name
         End Sub
         
         Public Overrides Function ToString() As String
            Return Me.personName
         End Function 
      End Structure
      
      Module Example
         Public Sub Main()
            Dim p1 As New Person("John")
            Dim p2 As New Person("John")
            
            Console.WriteLine("Calling Equals:") 
            Console.WriteLine(p1.Equals(p2))
            Console.WriteLine()
            
            Console.WriteLine("Casting to an Object and calling Equals:")
            Console.WriteLine(CObj(p1).Equals(p2))
         End Sub
      End Module
      ' The example displays the following output:
      '       Calling Equals:
      '       True
      '       
      '       Casting to an Object and calling Equals:
      '       True
      

因為Object類別是.NET Framework 中的所有類型的基底類別Object.Equals(Object)方法提供所有其他類型的預設相等比較。Because the Object class is the base class for all types in the .NET Framework, the Object.Equals(Object) method provides the default equality comparison for all other types. 不過,類型通常會覆寫Equals方法來實作實值相等。However, types often override the Equals method to implement value equality. 如需詳細資訊,請參閱 < 附註的呼叫端和注意事項繼承者區段。For more information, see the Notes for Callers and Notes for Inheritors sections.

資訊 Windows 執行階段Windows RuntimeNotes for the Windows 執行階段Windows Runtime

當您呼叫Equals(Object)中之類別的方法多載Windows 執行階段Windows Runtime,它不會覆寫的類別提供的預設行為Equals(Object)When you call the Equals(Object) method overload on a class in the Windows 執行階段Windows Runtime, it provides the default behavior for classes that don’t override Equals(Object). 這是.NET Framework 提供的支援之一Windows 執行階段Windows Runtime(請參閱 < .NET Framework 支援的 Windows 市集應用程式和 Windows 執行階段)。This is part of the support that the .NET Framework provides for the Windows 執行階段Windows Runtime (see .NET Framework Support for Windows Store Apps and Windows Runtime). 中的類別Windows 執行階段Windows Runtime不繼承Object,且不要只實作目前Equals(Object)方法。Classes in the Windows 執行階段Windows Runtime don’t inherit Object, and currently don’t implement an Equals(Object) method. 不過,它們似乎具有ToStringEquals(Object),和GetHashCode方法時您用於您的 C# 或 Visual Basic 程式碼,和.NET Framework 會提供這些方法中的預設行為。However, they appear to have ToString, Equals(Object), and GetHashCode methods when you use them in your C# or Visual Basic code, and the .NET Framework provides the default behavior for these methods.

注意

Windows 執行階段Windows Runtime 以 C# 或 Visual Basic 撰寫的類別可以覆寫Equals(Object)方法多載。 classes that are written in C# or Visual Basic can override the Equals(Object) method overload.

呼叫端資訊Notes for Callers

在衍生的類別經常覆寫Object.Equals(Object)方法來實作實值相等。Derived classes frequently override the Object.Equals(Object) method to implement value equality. 此外,型別也經常會提供額外的強型別多載,來Equals方法,通常是藉由實作IEquatable<T>介面。In addition, types also frequently provide an additional strongly typed overload to the Equals method, typically by implementing the IEquatable<T> interface. 當您呼叫Equals方法來測試是否相等,您應該知道是否會覆寫目前的執行個體Object.Equals,並了解如何以特定的呼叫Equals方法已解決。When you call the Equals method to test for equality, you should know whether the current instance overrides Object.Equals and understand how a particular call to an Equals method is resolved. 否則,您可能會執行測試不同的是您想要相等,而且方法可能會傳回未預期的值。Otherwise, you may be performing a test for equality that is different from what you intended, and the method may return an unexpected value.

下列範例提供一個實例。The following example provides an illustration. 它會將三個執行個體化StringBuilder物件具有相同的字串,並接著四個呼叫Equals方法。It instantiates three StringBuilder objects with identical strings, and then makes four calls to Equals methods. 第一個方法呼叫傳回true,並將其餘的三個傳回falseThe first method call returns true, and the remaining three return false.

using System;
using System.Text;

public class Example
{
   public static void Main()
   {
      StringBuilder sb1 = new StringBuilder("building a string...");
      StringBuilder sb2 = new StringBuilder("building a string...");
      
      Console.WriteLine("sb1.Equals(sb2): {0}", sb1.Equals(sb2));
      Console.WriteLine("((Object) sb1).Equals(sb2): {0}", 
                        ((Object) sb1).Equals(sb2));
      Console.WriteLine("Object.Equals(sb1, sb2): {0}",
                        Object.Equals(sb1, sb2));      
                        
      Object sb3 = new StringBuilder("building a string...");
      Console.WriteLine("\nsb3.Equals(sb2): {0}", sb3.Equals(sb2));                              
   }
}
// The example displays the following output:
//       sb1.Equals(sb2): True
//       ((Object) sb1).Equals(sb2): False
//       Object.Equals(sb1, sb2): False
//
//       sb3.Equals(sb2): False
Imports System.Text

Module Example
   Public Sub Main()
      Dim sb1 As New StringBuilder("building a string...")
      Dim sb2 As New StringBuilder("building a string...")
      
      Console.WriteLine("sb1.Equals(sb2): {0}", sb1.Equals(sb2))
      Console.WriteLine("CObj(sb1).Equals(sb2): {0}", 
                        CObj(sb1).Equals(sb2))
      Console.WriteLine("Object.Equals(sb1, sb2): {0}",
                        Object.Equals(sb1, sb2))                  
      
      Console.WriteLine()
      Dim sb3 As Object = New StringBuilder("building a string...")
      Console.WriteLine("sb3.Equals(sb2): {0}", sb3.Equals(sb2))                              
   End Sub
End Module
' The example displays the following output:
'       sb1.Equals(sb2): True
'       CObj(sb1).Equals(sb2): False
'       Object.Equals(sb1, sb2): False
'
'       sb3.Equals(sb2): False

在第一個案例中,強型別StringBuilder.Equals(StringBuilder)方法多載,測試值是否相等時,會呼叫。In the first case, the strongly typed StringBuilder.Equals(StringBuilder) method overload, which tests for value equality, is called. 因為字串指派給這兩個StringBuilder物件是否相等,則方法會傳回trueBecause the strings assigned to the two StringBuilder objects are equal, the method returns true. 不過,StringBuilder未覆寫Object.Equals(Object)However, StringBuilder does not override Object.Equals(Object). 因為這個緣故時,StringBuilder物件轉換成Object,當StringBuilder執行個體指派給變數的型別Object,和當Object.Equals(Object, Object)方法會傳遞兩個StringBuilder的物件,預設值Object.Equals(Object)呼叫方法。Because of this, when the StringBuilder object is cast to an Object, when a StringBuilder instance is assigned to a variable of type Object, and when the Object.Equals(Object, Object) method is passed two StringBuilder objects, the default Object.Equals(Object) method is called. 因為StringBuilder是參考型別,這相當於傳遞兩個StringBuilder物件到ReferenceEquals方法。Because StringBuilder is a reference type, this is equivalent to passing the two StringBuilder objects to the ReferenceEquals method. 雖然這三個StringBuilder物件包含相同的字串,它們參考三個不同的物件。Although all three StringBuilder objects contain identical strings, they refer to three distinct objects. 如此一來,這些三個方法會呼叫傳回falseAs a result, these three method calls return false.

您可以比較目前物件與另一個物件參考是否相等,藉由呼叫ReferenceEquals方法。You can compare the current object to another object for reference equality by calling the ReferenceEquals method. 在 Visual Basic 中,您也可以使用is關鍵字 (例如If Me Is otherObject Then ...)。In Visual Basic, you can also use the is keyword (for example, If Me Is otherObject Then ...).

繼承者注意事項Notes for Inheritors

當您定義自己的型別時,該類型會繼承所定義的功能Equals其基底類型的方法。When you define your own type, that type inherits the functionality defined by the Equals method of its base type. 下表列出的預設實作Equals方法主要的一種.NET Framework 中的型別。The following table lists the default implementation of the Equals method for the major categories of types in the .NET Framework.

型別分類Type category 所定義的相等Equality defined by 註解Comments
直接衍生自的類別 ObjectClass derived directly from Object Object.Equals(Object) 參考相等;相當於呼叫Object.ReferenceEqualsReference equality; equivalent to calling Object.ReferenceEquals.
結構Structure ValueType.Equals 值相等;直接的逐位元組比較或使用反映的欄位欄位比較。Value equality; either direct byte-by-byte comparison or field-by-field comparison using reflection.
列舉Enumeration Enum.Equals 值必須有相同的列舉型別與相同的基礎值。Values must have the same enumeration type and the same underlying value.
委派Delegate MulticastDelegate.Equals 委派必須具有相同的引動過程清單之相同類型。Delegates must have the same type with identical invocation lists.
介面Interface Object.Equals(Object) 參考相等。Reference equality.

對於實值類型,您應該一律覆寫Equals,因為依賴反映的等號比較測試會提供效能不佳。For a value type, you should always override Equals, because tests for equality that rely on reflection offer poor performance. 您也可以覆寫的預設實作Equals參考型別來測試值是否相等,而不是參考相等,並定義實值相等,就精確而言。You can also override the default implementation of Equals for reference types to test for value equality instead of reference equality and to define the precise meaning of value equality. 這類實作的Equals傳回true如果兩個物件有相同的值,即使它們不是相同的執行個體。Such implementations of Equals return true if the two objects have the same value, even if they are not the same instance. 類型的實作器會決定構成物件的值,但它通常是部分或所有儲存的資料物件的執行個體變數中。The type's implementer decides what constitutes an object's value, but it is typically some or all the data stored in the instance variables of the object. 例如,值String物件為基礎的字元字串;String.Equals(Object)方法覆寫Object.Equals(Object)方法,以傳回true任何兩個字串包含相同字元的相同順序的執行個體。For example, the value of a String object is based on the characters of the string; the String.Equals(Object) method overrides the Object.Equals(Object) method to return true for any two string instances that contain the same characters in the same order.

下列範例示範如何覆寫Object.Equals(Object)方法來測試值是否相等。The following example shows how to override the Object.Equals(Object) method to test for value equality. 它會覆寫Equals方法Person類別。It overrides the Equals method for the Person class. 如果Person接受等號比較,其基底類別實作兩個Person物件會參考單一物件,請將它們時,才。If Person accepted its base class implementation of equality, two Person objects would be equal only if they referenced a single object. 不過,在此情況下,兩個Person物件是否相等,如果它們有相同的值,如Person.Id屬性。However, in this case, two Person objects are equal if they have the same value for the Person.Id property.

public class Person
{
   private string idNumber;
   private string personName;
   
   public Person(string name, string id)
   {
      this.personName = name;
      this.idNumber = id;
   }
   
   public override bool Equals(Object obj)
   {
      Person personObj = obj as Person; 
      if (personObj == null)
         return false;
      else
         return idNumber.Equals(personObj.idNumber);
   }
   
   public override int GetHashCode()
   {
      return this.idNumber.GetHashCode(); 
   }
}

public class Example
{
   public static void Main()
   {
      Person p1 = new Person("John", "63412895");
      Person p2 = new Person("Jack", "63412895");
      Console.WriteLine(p1.Equals(p2));
      Console.WriteLine(Object.Equals(p1, p2));
   }
}
// The example displays the following output:
//       True
//       True
Public Class Person
   Private idNumber As String
   Private personName As String
   
   Public Sub New(name As String, id As String)
      Me.personName = name
      Me.idNumber = id
   End Sub
   
   Public Overrides Function Equals(obj As Object) As Boolean
      Dim personObj As Person = TryCast(obj, Person) 
      If personObj Is Nothing Then
         Return False
      Else
         Return idNumber.Equals(personObj.idNumber)
      End If   
   End Function
   
   Public Overrides Function GetHashCode() As Integer
      Return Me.idNumber.GetHashCode() 
   End Function
End Class

Module Example
   Public Sub Main()
      Dim p1 As New Person("John", "63412895")
      Dim p2 As New Person("Jack", "63412895")
      Console.WriteLine(p1.Equals(p2))
      Console.WriteLine(Object.Equals(p1, p2))
   End Sub
End Module
' The example displays the following output:
'       True
'       True

除了覆寫Equals,您可以實作IEquatable<T>介面,以提供強型別的測試是否相等。In addition to overriding Equals, you can implement the IEquatable<T> interface to provide a strongly typed test for equality.

下列陳述式必須為 true 的所有實作Equals(Object)方法。The following statements must be true for all implementations of the Equals(Object) method. 在清單中, xy,並z代表物件參考未nullIn the list, x, y, and z represent object references that are not null.

  • x.Equals(x) 傳回true,牽涉到浮點數類型的情況除外。x.Equals(x) returns true, except in cases that involve floating-point types. 請參閱 ISO/IEC/IEEE 60559:2011,資訊技術-微處理器系統-浮點算術。See ISO/IEC/IEEE 60559:2011, Information technology -- Microprocessor Systems -- Floating-Point arithmetic.

  • x.Equals(y) 會傳回與 y.Equals(x) 相同的值。x.Equals(y) returns the same value as y.Equals(x).

  • x.Equals(y) 會傳回true如果兩個xyNaNx.Equals(y) returns true if both x and y are NaN.

  • 如果(x.Equals(y) && y.Equals(z))會傳回true,然後x.Equals(z)傳回trueIf (x.Equals(y) && y.Equals(z)) returns true, then x.Equals(z) returns true.

  • 後續呼叫x.Equals(y)傳回相同的值,只要所參考的物件xy不會修改。Successive calls to x.Equals(y) return the same value as long as the objects referenced by x and y are not modified.

  • x.Equals(null) 傳回 falsex.Equals(null) returns false.

實作Equals不得擲回例外狀況; 它們應該一律會傳回值。Implementations of Equals must not throw exceptions; they should always return a value. 例如,如果objnull,則Equals方法應傳回false而非擲回ArgumentNullExceptionFor example, if obj is null, the Equals method should return false instead of throwing an ArgumentNullException.

覆寫時,請遵循下列指導方針Equals(Object):Follow these guidelines when overriding Equals(Object):

  • 型別都會實作IComparable必須覆寫Equals(Object)Types that implement IComparable must override Equals(Object).

  • 類型覆寫Equals(Object)也必須覆寫GetHashCode,否則雜湊表可能無法正常運作。Types that override Equals(Object) must also override GetHashCode; otherwise, hash tables might not work correctly.

  • 您應該考慮實作IEquatable<T>介面,以支援強型別測試是否相等。You should consider implementing the IEquatable<T> interface to support strongly typed tests for equality. IEquatable<T>.Equals實作應該會傳回與一致的結果EqualsYour IEquatable<T>.Equals implementation should return results that are consistent with Equals.

  • 如果您的程式語言支援運算子多載,而且您多載等號比較運算子,針對指定的型別,您也必須覆寫Equals(Object)方法,以傳回與等號比較運算子相同的結果。If your programming language supports operator overloading and you overload the equality operator for a given type, you must also override the Equals(Object) method to return the same result as the equality operator. 這有助於確保會使用該類別程式庫程式碼Equals(例如ArrayListHashtable) 行為與等號比較運算子由應用程式程式碼的方式一致的方式。This helps ensure that class library code that uses Equals (such as ArrayList and Hashtable) behaves in a manner that is consistent with the way the equality operator is used by application code.

參考類型的指導方針Guidelines for Reference Types

下列指導方針適用於覆寫Equals(Object)是參考型別:The following guidelines apply to overriding Equals(Object) for a reference type:

  • 請考慮覆寫Equals如果類型的語意是基礎類型所代表的某些值為基礎。Consider overriding Equals if the semantics of the type are based on the fact that the type represents some value(s).

  • 大部分的參考型別必須多載等號比較運算子,即使它們會覆寫EqualsMost reference types must not overload the equality operator, even if they override Equals. 不過,如果您要實作參考型別,要有值的語意,例如複雜數字 類型中,您必須覆寫等號比較運算子。However, if you are implementing a reference type that is intended to have value semantics, such as a complex number type, you must override the equality operator.

  • 您不應該覆寫Equals可變動參考類型。You should not override Equals on a mutable reference type. 這是因為覆寫Equals需要,您也會覆寫GetHashCode方法,如前一節所述。This is because overriding Equals requires that you also override the GetHashCode method, as discussed in the previous section. 這表示可變動參考類型的執行個體的雜湊碼,可以在其生命週期,這會導致遺失物件雜湊表中進行變更。This means that the hash code of an instance of a mutable reference type can change during its lifetime, which can cause the object to be lost in a hash table.

實值類型的指導方針Guidelines for Value Types

下列指導方針適用於覆寫Equals(Object)的實值型別:The following guidelines apply to overriding Equals(Object) for a value type:

  • 如果您要定義實值型別,其中包含一或多個欄位的值是參考型別,您應該覆寫Equals(Object)If you are defining a value type that includes one or more fields whose values are reference types, you should override Equals(Object). Equals(Object)所提供的實作ValueType執行逐位元組比較的值類型的欄位是所有實值型別,但它會使用反映來執行其欄位包含參考類型的實值型別的欄位的比較。The Equals(Object) implementation provided by ValueType performs a byte-by-byte comparison for value types whose fields are all value types, but it uses reflection to perform a field-by-field comparison of value types whose fields include reference types.

  • 如果您覆寫Equals和您的開發語言支援運算子多載,您必須多載等號比較運算子。If you override Equals and your development language supports operator overloading, you must overload the equality operator.

  • 您應該實作IEquatable<T>介面。You should implement the IEquatable<T> interface. 呼叫強型別IEquatable<T>.Equals方法可以避免 boxingobj引數。Calling the strongly typed IEquatable<T>.Equals method avoids boxing the obj argument.

另請參閱

Equals(Object, Object) Equals(Object, Object) Equals(Object, Object) Equals(Object, Object)

判斷指定的物件執行個體是否視為相等。 Determines whether the specified object instances are considered equal.

public:
 static bool Equals(System::Object ^ objA, System::Object ^ objB);
public static bool Equals (object objA, object objB);
static member Equals : obj * obj -> bool
Public Shared Function Equals (objA As Object, objB As Object) As Boolean
參數
objA
Object Object Object Object

要比較的第一個物件。 The first object to compare.

objB
Object Object Object Object

要比較的第二個物件。 The second object to compare.

傳回

如果物件被視為相等則為 true,否則為 false true if the objects are considered equal; otherwise, false. 如果 objAobjB 都是 null,則這個方法會傳回 true If both objA and objB are null, the method returns true.

範例

下列範例說明Equals(Object, Object)方法,並比較它與ReferenceEquals方法。The following example illustrates the Equals(Object, Object) method and compares it with the ReferenceEquals method.

using System;

public class Example
{
   public static void Main()
   {
      Dog m1 = new Dog("Alaskan Malamute");
      Dog m2 = new Dog("Alaskan Malamute");
      Dog g1 = new Dog("Great Pyrenees");
      Dog g2 = g1;
      Dog d1 = new Dog("Dalmation");
      Dog n1 = null;
      Dog n2 = null;
      
      Console.WriteLine("null = null: {0}", Object.Equals(n1, n2));
      Console.WriteLine("null Reference Equals null: {0}\n", Object.ReferenceEquals(n1, n2));
      
      Console.WriteLine("{0} = {1}: {2}", g1, g2, Object.Equals(g1, g2));
      Console.WriteLine("{0} Reference Equals {1}: {2}\n", g1, g2, Object.ReferenceEquals(g1, g2));
      
      Console.WriteLine("{0} = {1}: {2}", m1, m2, Object.Equals(m1, m2));
      Console.WriteLine("{0} Reference Equals {1}: {2}\n", m1, m2, Object.ReferenceEquals(m1, m2));
      
      Console.WriteLine("{0} = {1}: {2}", m1, d1, Object.Equals(m1, d1));  
      Console.WriteLine("{0} Reference Equals {1}: {2}", m1, d1, Object.ReferenceEquals(m1, d1));  
   }
}

public class Dog
{
   // Public field.
   public string Breed;
   
   // Class constructor.
   public Dog(string dogBreed)
   {
      this.Breed = dogBreed;
   }

   public override bool Equals(Object obj)
   {
      if (obj == null || !(obj is Dog))
         return false;
      else
         return this.Breed == ((Dog) obj).Breed;
   }
   
   public override int GetHashCode()
   {
      return this.Breed.GetHashCode();
   }
   
   public override string ToString()
   {
      return this.Breed;
   }
}
// The example displays the following output:
//       null = null: True
//       null Reference Equals null: True
//       
//       Great Pyrenees = Great Pyrenees: True
//       Great Pyrenees Reference Equals Great Pyrenees: True
//       
//       Alaskan Malamute = Alaskan Malamute: True
//       Alaskan Malamute Reference Equals Alaskan Malamute: False
//       
//       Alaskan Malamute = Dalmation: False
//       Alaskan Malamute Reference Equals Dalmation: False
Module Example
   Public Sub Main()
      Dim m1 As New Dog("Alaskan Malamute")
      Dim m2 As New Dog("Alaskan Malamute")
      Dim g1 As New Dog("Great Pyrenees")
      Dim g2 As Dog = g1
      Dim d1 As New Dog("Dalmation")
      Dim n1 As Dog = Nothing
      Dim n2 As Dog = Nothing
      
      Console.WriteLine("null = null: {0}", Object.Equals(n1, n2))
      Console.WriteLine("null Reference Equals null: {0}", Object.ReferenceEquals(n1, n2))
      Console.WriteLine()
      
      Console.WriteLine("{0} = {1}: {2}", g1, g2, Object.Equals(g1, g2))
      Console.WriteLine("{0} Reference Equals {1}: {2}", g1, g2, Object.ReferenceEquals(g1, g2))
      Console.WriteLine()
      
      Console.WriteLine("{0} = {1}: {2}", m1, m2, Object.Equals(m1, m2))
      Console.WriteLine("{0} Reference Equals {1}: {2}", m1, m2, Object.ReferenceEquals(m1, m2))
      Console.WriteLine()
      
      Console.WriteLine("{0} = {1}: {2}", m1, d1, Object.Equals(m1, d1))  
      Console.WriteLine("{0} Reference Equals {1}: {2}", m1, d1, Object.ReferenceEquals(m1, d1))  
   End Sub
End Module

Public Class Dog
   ' Public field.
   Public Breed As String
   
   ' Class constructor.
   Public Sub New(dogBreed As String)
      Me.Breed = dogBreed
   End Sub

   Public Overrides Function Equals(obj As Object) As Boolean
      If obj Is Nothing OrElse Not typeof obj Is Dog Then
         Return False
      Else
         Return Me.Breed = CType(obj, Dog).Breed
      End If   
   End Function
   
   Public Overrides Function GetHashCode() As Integer
      Return Me.Breed.GetHashCode()
   End Function
   
   Public Overrides Function ToString() As String
      Return Me.Breed
   End Function
End Class
' The example displays the following output:
'       null = null: True
'       null Reference Equals null: True
'       
'       Great Pyrenees = Great Pyrenees: True
'       Great Pyrenees Reference Equals Great Pyrenees: True
'       
'       Alaskan Malamute = Alaskan Malamute: True
'       Alaskan Malamute Reference Equals Alaskan Malamute: False
'       
'       Alaskan Malamute = Dalmation: False
'       Alaskan Malamute Reference Equals Dalmation: False

備註

靜態Equals(Object, Object)方法會指示是否兩個物件,objAobjB,相等。The static Equals(Object, Object) method indicates whether two objects, objA and objB, are equal. 它也可讓您測試其值的物件null是否相等。It also enables you to test objects whose value is null for equality. 它會比較objAobjB是否相等,如下所示:It compares objA and objB for equality as follows:

  • 它會判斷兩個物件是否代表相同的物件參考。It determines whether the two objects represent the same object reference. 如果沒有的話,則方法會傳回trueIf they do, the method returns true. 這項測試就相當於呼叫ReferenceEquals方法。This test is equivalent to calling the ReferenceEquals method. 此外,如果這兩個objAobjBnull,則方法會傳回trueIn addition, if both objA and objB are null, the method returns true.

  • 它會判斷是否可能objA或是objBnullIt determines whether either objA or objB is null. 如果,則會傳回falseIf so, it returns false.

  • 如果兩個物件不代表相同的物件參考,而且兩者都null,它會呼叫objAEquals(objB),並傳回結果。If the two objects do not represent the same object reference and neither is null, it calls objA.Equals(objB) and returns the result. 這表示,如果objA會覆寫Object.Equals(Object)方法,會呼叫此覆寫。This means that if objA overrides the Object.Equals(Object) method, this override is called.

另請參閱

適用於