Object.Equals 方法

定義

判斷兩種物件執行個體是否相同。

多載

Equals(Object)

判斷指定的物件是否等於目前的物件。

Equals(Object, Object)

判斷指定的物件執行個體是否視為相等。

Equals(Object)

判斷指定的物件是否等於目前的物件。

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

參數

obj
Object

要與目前物件比較的物件。

傳回

Boolean

若指定的物件等於目前的物件,則為 true;否則為 false

範例

下列範例顯示覆 PointEquals 方法以提供值相等的類別,以及 Point3D 衍生自 Point 的類別。 因為 PointObject.Equals(Object) 覆寫以測試值是否相等, Object.Equals(Object) 所以不會呼叫 方法。 不過, Point3D.Equals 由於 Point 會以提供值相等的方式來實 Object.Equals(Object) 作 ,因此會呼叫 Point.Equals

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

方法 Point.Equalsobj 檢查以確定引數不是 Null ,而且它參考與這個物件相同類型的實例。 如果任一檢查失敗,方法會傳 false 回 。

方法 Point.Equals 會呼叫 方法, GetType 以判斷兩個 物件的執行時間類型是否相同。 如果 方法在 C# 或 Visual Basic 中使用表單 obj is Point 的檢查,則即使 和 目前的實例不是相同的執行時間類型,也會傳 Point obj objtrue 檢查。 TryCast(obj, Point) 確認這兩個物件的類型都相同,方法會轉換成 obj 類型 Point ,並傳回比較兩個物件的實例欄位的結果。

在 中 Point3D.Equals ,會先叫用覆寫 Object.Equals(Object) 的繼承 Point.Equals 方法,再執行任何其他動作。 因為 Point3D 是 Visual Basic) 中的密封類別 (NotInheritable ,所以 C# 或 TryCast(obj, Point) Visual Basic 中的表單 obj is Point 簽入已足夠,以確保 objPoint3D 物件。 Point3D如果是 物件,則會轉換成 Point 物件,並傳遞至 的基類實作 Equals 。 只有在繼承 Point.Equals 的方法傳回 true 時,方法才會 z 比較衍生類別中導入的實例欄位。

下列範例會定義一個 Rectangle 類別,該類別會在內部實作矩形做為兩 Point 個物件。 類別 Rectangle 也會覆寫 Object.Equals(Object) 以提供值相等。

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

某些語言,例如 C# 和 Visual Basic 支援運算子多載。 當類型多載等號比較運算子時,也必須覆寫 Equals(Object) 方法以提供相同的功能。 這通常是藉由 Equals(Object) 以多載相等運算子撰寫 方法來完成,如下列範例所示。

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

因為 Complex 是實值型別,所以無法衍生自 。 因此,對 方法的覆寫 Equals(Object) 不需要呼叫 GetType 來判斷每個物件的精確執行時間類型,但可以改用 is C# 中的 運算子或 TypeOf Visual Basic 中的 運算子來檢查參數的類型 obj

備註

目前實例與 obj 參數之間的比較類型取決於目前的實例是參考型別還是實值型別。

  • 如果目前的實例是參考型別,則 Equals(Object) 方法會測試參考相等,而對 方法的呼叫相當於方法的呼叫 Equals(Object) ReferenceEquals 。 參考相等表示比較的物件變數會參考相同的物件。 下列範例說明這類比較的結果。 它會定義 Person 類別,這是參考型別,並呼叫 Person 類別建構函式來具現化兩個新 Person 物件, person1a 以及 person2 具有相同值的 。 它也會指派 person1a 給另一個物件變數 。 person1b 如範例的輸出所示, person1aperson1b 相等,因為它們參考相同的物件。 不過, person1aperson2 不相等,雖然它們具有相同的值。

    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
    
  • 如果目前的實例是實值型別,則方法會 Equals(Object) 測試值相等。 值相等表示下列各項:

    • 這兩個物件的類型相同。 如下列範例所示, Byte 值為 12 的物件不等於值為 12 的物件,因為兩個 Int32 物件有不同的執行時間類型。

      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
      
    • 兩個物件的公用和私用欄位的值相等。 下列範例會測試值相等。 它會定義 Person 結構,這是實值型別,並呼叫 Person 類別建構函式來具現化兩個新 Person 物件, person1 以及 person2 具有相同值的 。 如範例的輸出所示,雖然這兩個物件變數參考不同的物件,而且 person2 相等, person1 因為它們對私 personName 用欄位有相同的值。

      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
      

因為 類別 Object 是.NET Framework中所有型別的基類,所以 Object.Equals(Object) 方法會提供所有其他類型的預設相等比較。 不過,類型通常會覆寫 Equals 方法來實作值相等。 如需詳細資訊,請參閱呼叫端的附注和繼承者的附注一節。

Windows 執行階段注意事項

當您在Windows 執行階段類別上呼叫 Equals(Object) 方法多載時,它會為未覆寫 Equals(Object) 的類別提供預設行為。 這是.NET Framework為Windows 執行階段 (提供支援的一部分,請參閱.NET Framework Windows 市集應用程式和Windows 執行階段) 的支援。 Windows 執行階段中的類別不會繼承 Object ,而且目前不會實作 Equals(Object) 方法。 不過,當您在 C# 或Visual Basic程式碼中使用 、 和 方法時,它們似乎具有 ToStringEquals(Object)GetHashCode 方法,而.NET Framework會提供這些方法的預設行為。

注意

Windows 執行階段以 C# 或Visual Basic撰寫的類別可以覆寫 Equals(Object) 方法多載。

來電者的注意事項

衍生類別經常覆寫 Object.Equals(Object) 方法來實作值相等。 此外,類型也會經常透過實作 IEquatable<T> 介面,將額外的強型別多載 Equals 提供給 方法。 當您呼叫 Equals 方法來測試是否相等時,您應該知道目前的實例是否覆寫 Object.Equals 並瞭解如何解析方法的特定呼叫 Equals 。 否則,您可能會執行與預期不同之相等的測試,而且方法可能會傳回非預期的值。

下列範例提供說明。 它會具現化三 StringBuilder 個具有相同字串的物件,然後對方法進行四個呼叫 Equals 。 第一個方法呼叫會傳 true 回 ,其餘三個傳回 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

在第一種情況下,會呼叫測試值相等的強型別 StringBuilder.Equals(StringBuilder) 方法多載。 因為指派給兩 StringBuilder 個物件的字串相等,所以 方法會傳 true 回 。 不過, StringBuilder 不會覆寫 Object.Equals(Object) 。 因此,當 StringBuilder 物件轉換成 Object 時,當實例指派給 類型的 Object 變數時,以及當方法傳遞兩 StringBuilder 個物件時 Object.Equals(Object, Object) StringBuilder ,會呼叫預設 Object.Equals(Object) 方法。 因為 StringBuilder 是參考型別,這相當於將兩 StringBuilder 個物件傳遞至 ReferenceEquals 方法。 雖然這三個 StringBuilder 物件都包含相同的字串,但它們會參考三個不同的物件。 因此,這三個方法呼叫會傳回 false

您可以呼叫 ReferenceEquals 方法,將目前的 物件與另一個物件進行比較,以取得參考相等。 在Visual Basic中,您也可以使用 is 關鍵字 (例如 If Me Is otherObject Then ... ,) 。

繼承者的注意事項

當您定義自己的類型時,該類型會繼承其基底類型方法所 Equals 定義的功能。 下表列出.NET Framework中類型主要類別之 方法的預設實 Equals 作。

型別分類 所定義的相等 註解
直接衍生自 的類別 Object Object.Equals(Object) 參考相等;相當於呼叫 Object.ReferenceEquals
結構 ValueType.Equals 值相等;使用反映進行直接位元組位元組比較或欄位逐欄位比較。
列舉型別 Enum.Equals 值必須具有相同的列舉型別和相同的基礎值。
代理人 MulticastDelegate.Equals 委派必須具有相同調用清單的相同類型。
介面 Object.Equals(Object) 參考相等。

對於實數值型別,您應該一律覆寫 Equals ,因為測試依賴反映的相等可提供不佳的效能。 您也可以覆寫 的預設實 Equals 作,讓參考型別測試值相等,而不是參考相等,並定義值相等的精確意義。 如果兩個物件具有相同的值,則傳回 true 的這類實 Equals 作,即使它們不是相同的實例也一樣。 類型的實作器會決定構成物件值的內容,但通常是物件執行個體變數中儲存的部分或所有資料。 例如,物件的值是以字串的字元為基礎;此方法會 Object.Equals(Object) 覆寫 方法,以針對相同順序包含相同字元的任何兩個 String 字串實例傳回 trueString.Equals(Object)

下列範例示範如何覆寫 Object.Equals(Object) 方法來測試值相等。 它會覆寫 Equals 類別的 方法 Person 。 如果 Person 接受其相等的基類實作,則兩 Person 個物件只有在參考單一物件時才相等。 不過,在此情況下,如果兩個物件具有屬性的相同值 Person.Id ,則 Person 兩個物件相等。

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

除了覆寫 Equals 之外,您還可以實 IEquatable<T> 作 介面,以提供強型別測試以取得相等。

對於方法的所有實作 Equals(Object) ,下列語句必須成立。 在清單中, xyz 代表非 Null 的物件參考。

  • x.Equals(x) 會傳回 true

  • x.Equals(y) 會傳回與 y.Equals(x) 相同的值。

  • x.Equals(y)如果 和 y 都是 x ,則會 NaNtrue 回 。

  • 如果 (x.Equals(y) && y.Equals(z))true 回 ,則會 x.Equals(z)true 回 。

  • 只要 和 x y 所參考的物件未修改,後續呼叫就會 x.Equals(y) 傳回相同的值。

  • x.Equals(null) 會傳回 false

的實作 Equals 不得擲回例外狀況;它們應該一律傳回值。 例如,如果 obj 是 ,則 Equals 方法應該傳回 ,而不是擲 ArgumentNullExceptionfalse null

Equals(Object) 寫 時,請遵循下列指導方針:

  • IComparable 作的類型必須覆寫 Equals(Object)

  • 覆寫的類型也必須覆寫 Equals(Object) GetHashCode ;否則雜湊表可能無法正常運作。

  • 您應該考慮實作 IEquatable<T> 介面,以支援強型別測試是否相等。 您的 IEquatable<T>.Equals 實作應該會傳回與 Equals 一致的結果。

  • 如果您的程式設計語言支援運算子多載,而且多載指定類型的等號比較運算子,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。 這有助於確保使用 Equals (的類別庫程式碼,例如 ArrayListHashtable) 的行為,與應用程式程式碼使用等號比較運算子的方式一致。

參考型別的指導方針

下列指導方針適用于覆 Equals(Object) 寫參考型別:

  • 如果型別的語意是以類型代表某些值的事實為基礎,請考慮覆 Equals 寫 () 。

  • 大部分的參考型別不得多載等號比較運算子,即使它們覆寫 Equals 也一樣。 不過,如果您要實作要具有值語意的參考型別,例如複數類型,則必須覆寫等號比較運算子。

  • 您不應該覆寫 Equals 可變動的參考型別。 這是因為覆 Equals 寫需要您也覆寫 GetHashCode 方法,如上一節所述。 這表示可變動參考型別實例的雜湊碼在其存留期內可能會變更,這可能會導致物件在雜湊表中遺失。

實值型別的指導方針

下列指導方針適用于覆 Equals(Object) 寫實值型別:

  • 如果您要定義包含一或多個欄位的實值型別,其值為參考型別,您應該覆寫 Equals(Object)Equals(Object)所提供的 ValueType 實作會針對欄位為所有實值型別的實值型別執行位元組位元組比較,但會使用反映來執列欄位包含參考型別之實數值型別的逐欄位比較。

  • 如果您覆寫 Equals 和開發語言支援運算子多載,則必須多載等號比較運算子。

  • 您應該實作 IEquatable<T> 介面。 呼叫強型別 IEquatable<T>.Equals 方法可避免 Boxing 自 obj 變數。

另請參閱

適用於

Equals(Object, Object)

判斷指定的物件執行個體是否視為相等。

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

參數

objA
Object

要比較的第一個物件。

objB
Object

要比較的第二個物件。

傳回

Boolean

如果物件可視為相等則為 true,否則為 false。 如果 objAobjB 都是 null,則這個方法會傳回 true

範例

下列範例說明 Equals(Object, Object) 方法,並將其與 ReferenceEquals 方法進行比較。

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

備註

靜態 Equals(Object, Object) 方法會指出兩個 物件 objAobjB 是否相等。 它也可讓您測試其值為 Null 的相 等物件。 它會比較 objAobjB 是否相等,如下所示:

  • 它會判斷這兩個物件是否代表相同的物件參考。 如果這樣做,方法會傳 true 回 。 此測試相當於呼叫 ReferenceEquals 方法。 此外,如果 objAobjB 都是 null,方法會傳 true 回 。

  • 它會判斷 或 objB 是否 objANull。 如果是,則會傳 false 回 。

  • 如果兩個物件不代表相同的物件參考,而且兩者都不是 null,它會呼叫 objAEquals (objB) 並傳回結果。 這表示如果 objA 覆寫 Object.Equals(Object) 方法,則會呼叫這個覆寫。

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