Object.Equals 方法

定义

确定两个对象实例是否相等。

重载

Equals(Object)

确定指定对象是否等于当前对象。

Equals(Object, Object)

确定指定的对象实例是否被视为相等。

Equals(Object)

确定指定对象是否等于当前对象。

public:
 virtual bool Equals(System::Object ^ obj);
public virtual bool Equals (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

参数

obj
Object

要与当前对象进行比较的对象。

返回

Boolean

如果指定的对象等于当前对象,则为 true;否则为 false

示例

下面的示例演示一个 Point 类,该类重写 Equals 方法以提供值相等性,以及 Point3D 派生自 Point的类。 由于 Point 重写 Object.Equals(Object) 用于测试值相等性, Object.Equals(Object) 因此不调用该方法。 但是, Point3D.Equals 调用 Point.Equals 是因为 Point 以提供值相等性的方式实现 Object.Equals(Object)

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
type Point(x, y) =
    new () = Point(0, 0)
    member _.X = x
    member _.Y = y

    override _.Equals(obj) =
        //Check for null and compare run-time types.
        match obj with
        | :? Point as p ->
            x = p.X && y = p.Y
        | _ -> 
            false

    override _.GetHashCode() =
        (x <<< 2) ^^^ y

    override _.ToString() =
        $"Point({x}, {y})"

type Point3D(x, y, z) =
    inherit Point(x, y)
    member _.Z = z

    override _.Equals(obj) =
        match obj with
        | :? Point3D as pt3 ->
            base.Equals(pt3 :> Point) && z = pt3.Z
        | _ -> 
            false

    override _.GetHashCode() =
        (base.GetHashCode() <<< 2) ^^^ z

    override _.ToString() =
        $"Point({x}, {y}, {z})"

let point2D = Point(5, 5)
let point3Da = Point3D(5, 5, 2)
let point3Db = Point3D(5, 5, 2)
let point3Dc = Point3D(5, 5, -1)

printfn $"{point2D} = {point3Da}: {point2D.Equals point3Da}"
printfn $"{point2D} = {point3Db}: {point2D.Equals point3Db}"
printfn $"{point3Da} = {point3Db}: {point3Da.Equals point3Db}"
printfn $"{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

该方法 Point.Equals 检查以确保 obj 参数不 为 null ,并且它引用与此对象相同的类型的实例。 如果任一检查失败,该方法将 false返回 。

该方法 Point.Equals 调用 GetType 该方法来确定两个对象的运行时类型是否相同。 如果该方法在 C# 或 TryCast(obj, Point) Visual Basic 中使用了窗体obj is Point的检查,则检查将在派生类Point的实例的情况下obj返回true,即使obj当前实例不是相同的运行时类型。 验证这两个对象的类型相同后,该方法将 obj 转换为类型 Point 并返回比较两个对象的实例字段的结果。

Point.EqualsPoint3D.Equals继承的方法(替代)Object.Equals(Object)在完成任何其他操作之前调用。 因为Point3D是一个密封的类 (在 Visual Basic 中为 NotInheritable),签入窗体obj is PointC# 中或TryCast(obj, Point)在 Visual Basic 中是足以确保objPoint3D对象。 如果它是一个Point3D对象,则将其强制转换为Point对象,并传递给基类实现。Equals 仅当继承 Point.Equals 的方法返回 true 时,该方法才会比较 z 派生类中引入的实例字段。

以下示例定义一个 Rectangle 类,该类在内部将矩形实现为两 Point 个对象。 该 Rectangle 类还会重写 Object.Equals(Object) 以提供值相等性。

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
type Point(x, y) =
    member _.X = x
    member _.Y = y

    override _.Equals(obj) =
        // Performs an equality check on two points (integer pairs).
        match obj with
        | :? Point as p ->
            x = p.X && y = p.Y
        | _ ->
            false
    
    override _.GetHashCode() =
        (x, y).GetHashCode()

type Rectangle(upLeftX, upLeftY, downRightX, downRightY) =
    let a = Point(upLeftX, upLeftY)
    let b = Point(downRightX, downRightY)
    
    member _.UpLeft = a
    member _.DownRight = b

    override _.Equals(obj) =
        // Perform an equality check on two rectangles (Point object pairs).
        match obj with
        | :? Rectangle as r ->
            a.Equals(r.UpLeft) && b.Equals(r.DownRight)
        | _ -> 
            false
        
    override _.GetHashCode() =
        (a, b).GetHashCode()

    override _.ToString() =
       $"Rectangle({a.X}, {a.Y}, {b.X}, {b.Y})"

let r1 = Rectangle(0, 0, 100, 200)
let r2 = Rectangle(0, 0, 100, 200)
let r3 = Rectangle(0, 0, 150, 200)

printfn $"{r1} = {r2}: {r1.Equals r2}"
printfn $"{r1} = {r3}: {r1.Equals r3}"
printfn $"{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

某些语言(如 C# 和 Visual Basic)支持运算符重载。 当类型重载相等运算符时,还必须重写 Equals(Object) 方法以提供相同的功能。 这通常通过编写 Equals(Object) 重载相等运算符的方法来实现,如以下示例所示。

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
[<Struct; CustomEquality; NoComparison>]
type Complex =
    val mutable re: double
    val mutable im: double

    override this.Equals(obj) =
        match obj with 
        | :? Complex as c when c = this -> true
        | _ -> false 

    override this.GetHashCode() =
        (this.re, this.im).GetHashCode()

    override this.ToString() =
        $"({this.re}, {this.im})"

    static member op_Equality (x: Complex, y: Complex) =
        x.re = y.re && x.im = y.im

    static member op_Inequality (x: Complex, y: Complex) =
        x = y |> not

let mutable cmplx1 = Complex()
let mutable cmplx2 = Complex()

cmplx1.re <- 4.0
cmplx1.im <- 1.0

cmplx2.re <- 2.0
cmplx2.im <- 1.0

printfn $"{cmplx1} <> {cmplx2}: {cmplx1 <> cmplx2}"
printfn $"{cmplx1} = {cmplx2}: {cmplx1.Equals cmplx2}"

cmplx2.re <- 4.0

printfn $"{cmplx1} = {cmplx2}: {cmplx1 = cmplx2}"
printfn $"{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

由于 Complex 是值类型,因此无法从中派生它。 因此,重写方法Equals(Object)不需要调用GetType来确定每个对象的精确运行时类型,但可以改用 is C# 中的运算符或TypeOfVisual Basic中的运算符来检查参数的类型obj

注解

当前实例与 obj 参数之间的比较类型取决于当前实例是引用类型还是值类型。

  • 如果当前实例是引用类型,则 Equals(Object) 方法测试引用相等性,对该方法的调用 Equals(Object) 等效于对方法的 ReferenceEquals 调用。 引用相等性表示比较的对象变量引用同一对象。 以下示例演示了此类比较的结果。 它定义一个 Person 类,该类是引用类型,并调用 Person 类构造函数来实例化两个新 Person 对象, person1a 以及 person2具有相同值的类。 它还分配给person1a另一个对象变量。 person1b 如示例的输出所示, person1a 并且 person1b 相等,因为它们引用了同一对象。 但是, person1a 并且 person2 不相等,尽管它们具有相同的值。

    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.
    type Person(name) =
        override _.ToString() =
            name
    
    let person1a = Person "John"
    let person1b = person1a
    let person2 = Person(string person1a)
    
    printfn "Calling Equals:"
    printfn $"person1a and person1b: {person1a.Equals person1b}"
    printfn $"person1a and person2: {person1a.Equals person2}"
    
    printfn "\nCasting to an Object and calling Equals:"
    printfn $"person1a and person1b: {(person1a :> obj).Equals(person1b :> obj)}"
    printfn $"person1a and person2: {(person1a :> obj).Equals(person2 :> obj)}"
    // 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
    
  • 如果当前实例是值类型,则 Equals(Object) 该方法会测试值相等性。 值相等性表示:

    • 这两个对象的类型相同。 如以下示例所示,一个 Byte 值为 12 的对象不等于值为 12 的对象,因为两个 Int32 对象具有不同的运行时类型。

      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
      
      let value1 = 12uy
      let value2 = 12
      
      let object1 = value1 :> obj
      let object2 = value2 :> obj
      
      printfn $"{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
      
    • 两个对象的公共字段和专用字段的值相等。 以下示例测试值相等性。 它定义一个结构,它是一 Person 个值类型,并调用 Person 类构造函数来实例化两个新 Person 对象, person1 并且 person2具有相同的值。 如示例中的输出所示,尽管这两个对象变量引用不同的对象, person1 并且 person2 相等,因为它们对专用 personName 字段具有相同的值。

      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.
      [<Struct>]
      type Person(personName: string) =
          override _.ToString() =
              personName
      
      let person1 = Person "John"
      let person2 = Person "John"
      
      printfn "Calling Equals:"
      printfn $"{person1.Equals person2}"
      
      printfn $"\nCasting to an Object and calling Equals:"
      printfn $"{(person1 :> obj).Equals(person2 :> obj)}"
      // 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
      

由于该Object类是.NET Framework中所有类型的基类,因此该方法Object.Equals(Object)为所有其他类型提供默认的相等比较。 但是,类型通常重写 Equals 方法以实现值相等性。 有关详细信息,请参阅“调用方备注”和“继承者备注”部分。

Windows 运行时说明

在Windows 运行时中对类调用Equals(Object)方法重载时,它会为不重写Equals(Object)的类提供默认行为。 这是.NET Framework为Windows 运行时 (提供的支持的一部分,请参阅.NET Framework对 Windows 应用商店应用的支持和Windows 运行时) 。 Windows 运行时中的类不会继承Object,并且当前不实现方法Equals(Object)。 但是,在 C# 或Visual Basic代码中使用它们时,它们似乎具有ToStringEquals(Object)GetHashCode方法,.NET Framework为这些方法提供默认行为。

备注

Windows 运行时用 C# 或Visual Basic编写的类可以替代Equals(Object)方法重载。

对调用者的说明

派生类经常重写 Object.Equals(Object) 方法以实现值相等性。 此外,类型还经常通过实现IEquatable<T>接口向方法提供额外的强类型重载Equals。 调用 Equals 该方法以测试相等性时,应知道当前实例是否重写 Object.Equals 并了解如何解析对方法的特定调用 Equals 。 否则,可能会对与预期值不同的相等性执行测试,该方法可能会返回意外值。

下面的示例进行了这方面的演示。 它实例化三 StringBuilder 个具有相同字符串的对象,然后对方法进行四次 Equals 调用。 第一个方法调用返回 true,其余三个返回 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
open System
open System.Text

let sb1 = StringBuilder "building a string..."
let sb2 = StringBuilder "building a string..."

printfn $"sb1.Equals(sb2): {sb1.Equals sb2}"
printfn $"((Object) sb1).Equals(sb2): {(sb1 :> obj).Equals sb2}"
                  
printfn $"Object.Equals(sb1, sb2): {Object.Equals(sb1, sb2)}"

let sb3 = StringBuilder "building a string..."
printfn $"\nsb3.Equals(sb2): {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

在第一种情况下,将调用强类型 StringBuilder.Equals(StringBuilder) 方法重载,该重载测试值相等性。 由于分配给这两 StringBuilder 个对象的字符串相等,因此该方法返回 true。 但是, StringBuilder 不重写 Object.Equals(Object)。 因此,当对象被强制转换为某个对象时StringBuilder,当实例被赋给类型Object变量时,以及当该方法传递两StringBuilderStringBuilder对象时Object.Equals(Object, Object),将调用默认Object.Equals(Object)方法。Object 因为 StringBuilder 是引用类型,这等效于将两 StringBuilder 个对象传递给 ReferenceEquals 该方法。 尽管所有三 StringBuilder 个对象都包含相同的字符串,但它们引用三个不同的对象。 因此,这三个方法调用返回 false

可以通过调用 ReferenceEquals 方法将当前对象与另一个对象进行比较,以便引用相等。 在Visual Basic中,还可以使用is关键字 (, If Me Is otherObject Then ... 例如,) 。

继承者的注释

定义自己的类型时,该类型将继承其 Equals 基类型方法定义的功能。 下表列出了.NET Framework中主要类型类别的方法的默认实现Equals

类型类别 Equality defined by 注释
从中直接派生的类 Object Object.Equals(Object) 引用相等性;等效于调用 Object.ReferenceEquals
结构 ValueType.Equals 值相等性;使用反射进行直接字节字节比较或逐字段比较。
枚举 Enum.Equals 值必须具有相同的枚举类型和相同的基础值。
委托 MulticastDelegate.Equals 委托必须具有具有相同调用列表的相同类型。
接口 Object.Equals(Object) 引用相等性。

对于值类型,应始终重写 Equals,因为对依赖反射的相等性测试的性能不佳。 还可以重写引用类型的默认实现 Equals ,以测试值相等性而不是引用相等性,并定义值相等的精确含义。 如果两个对象具有相同的值,则返回trueEquals此类实现,即使它们不是相同的实例也是如此。 该类型的实现程序决定构成对象的值,但通常是对象实例变量中存储的部分或全部数据。 例如,对象的值 String 基于字符串的字符;该方法 String.Equals(Object) 重写该方法 Object.Equals(Object) ,以返回 true 以相同顺序包含相同字符的任何两个字符串实例。

下面的示例演示如何重写 Object.Equals(Object) 方法来测试值相等性。 它会替代 Equals 类的方法 Person 。 如果 Person 接受其基类实现相等,则仅当两 Person 个对象引用单个对象时才相等。 但是,在这种情况下,如果两个 Person 对象具有 Person.Id 属性的相同值,则两个对象相等。

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
open System

type Person(name, id) =
    member _.Name = name
    member _.Id = id

    override _.Equals(obj) =
        match obj with
        | :? Person as personObj ->
            id.Equals personObj.Id
        | _ -> 
            false

    override _.GetHashCode() =
        id.GetHashCode()

let p1 = Person("John", "63412895")
let p2 = Person("Jack", "63412895")
printfn $"{p1.Equals p2}"
printfn $"{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

除了重写 Equals之外,还可以实现 IEquatable<T> 接口以提供强类型测试以实现相等性。

对于该方法的所有实现 Equals(Object) ,以下语句必须为 true。 在列表中,x``y表示znull 的对象引用。

  • x.Equals(x) 返回 true

  • x.Equals(y) 返回与 y.Equals(x) 相同的值。

  • x.Equals(y)``true返回这两个值x,并且yNaN

  • 如果 (x.Equals(y) && y.Equals(z)) 返回 true,则 x.Equals(z) 返回 true

  • 只要引用的对象且未修改,x``y连续调用以x.Equals(y)返回相同的值。

  • x.Equals(null) 返回 false

实现 Equals 不得引发异常;它们应始终返回值。 例如,如果是obj``null,则Equals该方法应返回false而不是引发 。ArgumentNullException

重写 Equals(Object)时,请遵循以下准则:

  • 实现 IComparable 的类型必须重写 Equals(Object)

  • 重写 Equals(Object) 的类型还必须重写 GetHashCode;否则,哈希表可能无法正常工作。

  • 应考虑实现 IEquatable<T> 接口以支持强类型测试以实现相等性。 IEquatable<T>.Equals 实现应返回与 Equals 一致的结果。

  • 如果编程语言支持运算符重载,并且重载给定类型的相等运算符,则还必须重写 Equals(Object) 该方法以返回与相等运算符相同的结果。 这有助于确保使用 Equals ((如 ArrayListHashtable) )的类库代码的行为方式与应用程序代码使用相等运算符的方式一致。

参考类型的指南

以下准则适用于重写 Equals(Object) 引用类型:

  • 如果类型的语义基于类型表示某些值 () 的事实,请考虑重写 Equals

  • 大多数引用类型不得重载相等运算符,即使它们重写 Equals也是如此。 但是,如果要实现旨在具有值语义的引用类型(例如复数类型),则必须重写相等运算符。

  • 不应在可变引用类型上重写 Equals 。 这是因为重写 Equals 要求你也重写 GetHashCode 该方法,如上一部分所述。 这意味着可变引用类型的实例的哈希代码在其生存期内可能会更改,这可能导致对象在哈希表中丢失。

值类型的指南

以下准则适用于重写 Equals(Object) 值类型:

  • 如果要定义一个值类型,其中包含一个或多个字段,其值是引用类型,则应重写 Equals(Object)。 提供的 Equals(Object) 实现对 ValueType 字段均为值类型的值类型执行字节字节比较,但它使用反射对字段包含引用类型的值类型执行逐字段比较。

  • 如果重写 Equals 并且开发语言支持运算符重载,则必须重载相等运算符。

  • 应实现 IEquatable<T> 接口。 调用强类型 IEquatable<T>.Equals 方法可避免将 obj 参数装箱。

另请参阅

适用于

Equals(Object, Object)

确定指定的对象实例是否被视为相等。

public:
 static bool Equals(System::Object ^ objA, System::Object ^ objB);
public static bool Equals (object objA, 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

参数

objA
Object

要比较的第一个对象。

objB
Object

要比较的第二个对象。

返回

Boolean

如果对象被视为相等,则为 true,否则为 false。 如果 objAobjB 均为 null,此方法返回 true

示例

下面的示例演示了该方法 Equals(Object, Object) ,并将其与 ReferenceEquals 方法进行比较。

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
open System

// Class constructor
type Dog(dogBreed) =
    // Public property.
    member _.Breed = dogBreed

    override this.Equals(obj) =
        match obj with
        | :? Dog as dog when dog.Breed = this.Breed -> true
        | _ -> false

    override _.GetHashCode() =
        dogBreed.GetHashCode()

    override _.ToString() =
        dogBreed

let m1 = Dog "Alaskan Malamute"
let m2 = Dog "Alaskan Malamute"
let g1 = Dog "Great Pyrenees"
let g2 = g1
let d1 = Dog "Dalmation"
let n1 = Unchecked.defaultof<Dog>
let n2 = Unchecked.defaultof<Dog>

printfn $"null = null: {Object.Equals(n1, n2)}"
printfn $"null Reference Equals null: {Object.ReferenceEquals(n1, n2)}\n"

printfn $"{g1} = {g2}: {Object.Equals(g1, g2)}"
printfn $"{g1} Reference Equals {g2}: {Object.ReferenceEquals(g1, g2)}\n"

printfn $"{m1} = {m2}: {Object.Equals(m1, m2)}"
printfn $"{m1} Reference Equals {m2}: {Object.ReferenceEquals(m1, m2)}\n"

printfn $"{m1} = {d1}: {Object.Equals(m1, d1)}"
printfn $"{m1} Reference Equals {d1}: {Object.ReferenceEquals(m1, d1)}"

// 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

注解

静态 Equals(Object, Object) 方法指示两个对象 objA objB是否相等。 它还使你能够测试其值为 null 的相等性对象。 它比较 objAobjB 相等,如下所示:

  • 它确定这两个对象是否表示相同的对象引用。 如果这样做,该方法将 true返回 。 此测试等效于调用 ReferenceEquals 该方法。 此外,如果同时为 objA objB null,则该方法返回 true

  • 它确定是 null 还是 objA objB 为 null。 如果是,则返回 false

  • 如果两个对象不表示相同的对象引用,并且两个对象都不为 null,则调用 objA.Equals (objB) 并返回结果。 这意味着,如果 objA 重写 Object.Equals(Object) 该方法,将调用此替代。

另请参阅

适用于