Object.Equals 方法

定义

确定两个对象实例是否相等。Determines whether two object instances are equal.

重载

Equals(Object)

确定指定的对象是否等于当前对象。Determines whether the specified object is equal to the current object.

Equals(Object, Object)

确定指定的对象实例是否被视为相等。Determines whether the specified object instances are considered equal.

Equals(Object)

确定指定的对象是否等于当前对象。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

参数

obj
Object

要与当前对象进行比较的对象。The object to compare with the current object.

返回

如果指定的对象等于当前对象,则为 true;否则为 falsetrue if the specified object is equal to the current object; otherwise, false.

示例

下面的示例演示一个Point Equals重写方法以提供值相等性的类,以及Point3D一个派生自Point的类。The following example shows a Point class that overrides the Equals method to provide value equality, and a Point3D class that is derived from Point. 因为PointObject.Equals(Object)写可测试值相等性, Object.Equals(Object)所以不会调用方法。Because Point overrides Object.Equals(Object) to test for value equality, the Object.Equals(Object) method is not called. 但是, Point3D.Equals调用Point.EqualsPoint因为实现Object.Equals(Object)方式可提供值相等性。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

方法将进行检查以确保obj参数不为null ,并且它引用与此对象相同的类型的实例。 Point.EqualsThe 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. 如果任一检查失败,则该方法false将返回。If either check fails, the method returns false.

Point.Equals 方法GetType调用方法来确定两个对象的运行时类型是否相同。The Point.Equals method calls the GetType method to determine whether the run-time types of the two objects are identical. obj is Point如果该方法在C#或TryCast(obj, Point) Visual Basic 中使用了窗体的检查,则在的派生true类的实例objPoint情况下,检查将返回,即使obj和当前实例的运行时类型不相同。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. 验证两个对象的类型是否相同,方法强制转换obj为类型Point并返回比较两个对象的实例字段的结果。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中,将Point.Equals在执行其他操作Object.Equals(Object)之前调用继承的方法(重写)。In Point3D.Equals, the inherited Point.Equals method, which overrides Object.Equals(Object), is invoked before anything else is done. 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。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. 如果它是一个Point3D对象,则会将其强制Point转换为对象,并传递给的基类Equals实现。If it is a Point3D object, it is cast to a Point object and passed to the base class implementation of Equals. 仅当继承Point.Equals的方法返回true时,方法才会z比较派生类中引入的实例字段。Only when the inherited Point.Equals method returns true does the method compare the z instance fields introduced in the derived class.

下面的示例定义了Rectangle一个类,该类在内部实现一个Point矩形作为两个对象。The following example defines a Rectangle class that internally implements a rectangle as two Point objects. 类还将重Object.Equals(Object)写以提供值相等性。 RectangleThe 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

某些语言(如C#和) Visual Basic 支持运算符重载。Some languages such as C# and Visual Basic support operator overloading. 当类型重载相等运算符时,它还必须重写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. 这通常通过使用重载的相等Equals(Object)运算符编写方法来完成,如以下示例中所示。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

由于Complex是值类型,因此不能从派生。Because Complex is a value type, it cannot be derived from. 因此Equals(Object) ,对方法的重写不需要GetType调用来确定每个对象的确切运行时类型,但可以改为使用is中C#的运算符或TypeOf Visual Basic 中的运算符来检查obj参数。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.

注解

当前实例和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。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.

  • 如果当前实例是引用类型,则Equals(Object)方法会测试引用相等性,并调用Equals(Object)方法等效于调用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. 引用相等性意味着比较的对象变量引用相同的对象。Reference equality means that the object variables that are compared refer to the same object. 下面的示例说明了此类比较的结果。The following example illustrates the result of such a comparison. Person定义了一个类,该类是一个引用类型,它Person调用类构造函数来实例化Person person2两个person1a新的对象,这些对象具有相同的值。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. 它还分配person1a给另一个对象person1b变量。It also assigns person1a to another object variable, person1b. 如示例的输出所示,和person1a person1b相等,因为它们引用相同的对象。As the output from the example shows, person1a and person1b are equal because they reference the same object. 但是, person1aperson2不相等,但它们具有相同的值。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
    
  • 如果当前实例是值类型,则Equals(Object)方法会测试值是否相等。If the current instance is a value type, the Equals(Object) method tests for value equality. 值相等性意味着:Value equality means the following:

    • 这两个对象属于同一类型。The two objects are of the same type. 如下面的示例所示, Byte值为12的对象不Int32等于值为12的对象,因为这两个对象具有不同的运行时类型。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.

      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
      
    • 这两个对象的公共字段和私有字段的值相等。The values of the public and private fields of the two objects are equal. 下面的示例测试值是否相等。The following example tests for value equality. Person定义结构(值类型),并Person调用类构造函数来person1实例化两个具有相同Person值的新person2对象和。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. 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person1person2但它们相等,因为它们对于私有personName字段具有相同的值。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
      

因为该类是 .NET Framework 中所有类型的基类Object.Equals(Object) ,所以方法为所有其他类型提供默认的相等比较。 ObjectBecause 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. 但类型通常会重写Equals方法以实现值相等性。However, types often override the Equals method to implement value equality. 有关详细信息,请参阅调用方的说明和对继承者的说明部分。For more information, see the Notes for Callers and Notes for Inheritors sections.

说明Windows 运行时Windows RuntimeNotes for the Windows 运行时Windows Runtime

当对Equals(Object) Equals(Object)中的类调用方法重载时,它将为不重写的类提供默认行为。Windows 运行时Windows RuntimeWhen you call the Equals(Object) method overload on a class in the Windows 运行时Windows Runtime, it provides the default behavior for classes that don't override Equals(Object). 这是 .NET Framework 为Windows 运行时Windows Runtime提供的支持的一部分(请参阅Windows 应用商店应用和 Windows 运行时的 .NET Framework 支持)。This is part of the support that the .NET Framework provides for the Windows 运行时Windows Runtime (see .NET Framework Support for Windows Store Apps and Windows Runtime). 中的Windows 运行时Windows Runtime类不会Object继承,当前无法实现Equals(Object)方法。Classes in the Windows 运行时Windows Runtime don't inherit Object, and currently don't implement an Equals(Object) method. 但是,当ToString你在C#或 Visual Basic Equals(Object)代码中GetHashCode使用它们时,它们看起来具有、和方法,而 .NET Framework 提供这些方法的默认行为。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.

备注

Windows 运行时Windows Runtime用C#或 Visual Basic 编写的类可以重写Equals(Object)方法重载。classes that are written in C# or Visual Basic can override the Equals(Object) method overload.

调用方说明Notes for Callers

派生类经常重写Object.Equals(Object)方法以实现值相等性。Derived classes frequently override the Object.Equals(Object) method to implement value equality. 此外,类型通常还向Equals方法提供附加的强类型重载,这通常是通过IEquatable<T>实现接口来实现的。In addition, types also frequently provide an additional strongly typed overload to the Equals method, typically by implementing the IEquatable<T> interface. 当调用Equals方法来测试相等性时,应知道当前实例是否会重写Object.Equals ,并了解对Equals方法的特定调用的解析方式。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. 否则,你可能会执行与预期不同的相等性测试,方法可能会返回意外值。Otherwise, you may be performing a test for equality that is different from what you intended, and the method may return an unexpected value.

下面的示例进行了这方面的演示。The following example provides an illustration. 它用相同StringBuilder的字符串实例化三个对象,然后对Equals方法进行四次调用。It instantiates three StringBuilder objects with identical strings, and then makes four calls to Equals methods. 第一个方法调用返回true,其余三个返回。 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

在第一种情况下,将StringBuilder.Equals(StringBuilder)调用强类型化方法重载,该重载用于测试值相等性。In the first case, the strongly typed StringBuilder.Equals(StringBuilder) method overload, which tests for value equality, is called. 由于分配给这两个StringBuilder对象的字符串相等,因此该方法返回。 trueBecause the strings assigned to the two StringBuilder objects are equal, the method returns true. 但是, StringBuilder不会重Object.Equals(Object)写。However, StringBuilder does not override Object.Equals(Object). StringBuilder因此,当对象被强制转换Object为时,如果StringBuilder将实例分配给类型Object的变量,并且Object.Equals(Object, Object)方法传递两个StringBuilder对象,则默认值Object.Equals(Object)调用方法。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. 由于StringBuilder是引用类型,因此这等效于将两个StringBuilder对象传递给ReferenceEquals方法。Because StringBuilder is a reference type, this is equivalent to passing the two StringBuilder objects to the ReferenceEquals method. 尽管所有三StringBuilder个对象都包含相同的字符串,但是它们引用三个不同的对象。Although all three StringBuilder objects contain identical strings, they refer to three distinct objects. 因此,这三个方法调用返回falseAs a result, these three method calls return false.

通过调用ReferenceEquals方法,可以将当前的对象与另一个对象进行比较以便引用相等性。You can compare the current object to another object for reference equality by calling the ReferenceEquals method. 在 Visual Basic 中,还可以使用is关键字( If Me Is otherObject Then ...例如)。In Visual Basic, you can also use the is keyword (for example, If Me Is otherObject Then ...).

对继承者的说明Notes for Inheritors

定义自己的类型时,该类型将继承其基类型的Equals方法所定义的功能。When you define your own type, that type inherits the functionality defined by the Equals method of its base type. 下表列出了Equals方法的默认实现,该方法适用于 .NET Framework 中的类型的主要类别。The following table lists the default implementation of the Equals method for the major categories of types in the .NET Framework.

类型类别Type category 定义的相等Equality defined by 注释Comments
直接从派生的类ObjectClass derived directly from Object Object.Equals(Object) 引用相等性;等效于调用Object.ReferenceEqualsReference equality; equivalent to calling Object.ReferenceEquals.
结构Structure ValueType.Equals 值相等性;使用反射直接进行逐字节比较或逐字段比较。Value equality; either direct byte-by-byte comparison or field-by-field comparison using reflection.
枚举Enumeration Enum.Equals 值必须具有相同的枚举类型和基础值。Values must have the same enumeration type and the same underlying value.
委托Delegate MulticastDelegate.Equals 委托必须具有相同的调用列表类型。Delegates must have the same type with identical invocation lists.
接口Interface Object.Equals(Object) 引用相等性。Reference equality.

对于值类型,应始终重写Equals,因为依赖于反射的相等性测试会降低性能。For a value type, you should always override Equals, because tests for equality that rely on reflection offer poor performance. 您还可以重写引用类型的Equals的默认实现,以测试值相等性而不是引用相等性,并定义值相等性的精确含义。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. 如果两个Equals对象true具有相同的值,则此类实现将返回,即使它们不是相同的实例。Such implementations of Equals return true if the two objects have the same value, even if they are not the same instance. 类型的实施器决定对象的值是什么,但它通常是存储在对象的实例变量中的部分或全部数据。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, String对象的值基于字符串的字符String.Equals(Object) ; 方法会重写Object.Equals(Object)方法,以便为任意两个包含相同字符true的字符串实例返回相同的顺序。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.

下面的示例演示如何重写Object.Equals(Object)方法,以测试值是否相等。The following example shows how to override the Object.Equals(Object) method to test for value equality. 它重写Equals Person类的方法。It overrides the Equals method for the Person class. 如果Person接受其相等的基类实现,则只有Person当两个对象引用单个对象时,它们才相等。If Person accepted its base class implementation of equality, two Person objects would be equal only if they referenced a single object. 但在这种情况下, Person如果两个对象具有相同的Person.Id属性值,则这两个对象相等。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

除了重写Equals外,还可以IEquatable<T>实现接口,以提供相等的强类型测试。In addition to overriding Equals, you can implement the IEquatable<T> interface to provide a strongly typed test for equality.

对于Equals(Object)方法的所有实现,以下语句必须为 true。The following statements must be true for all implementations of the Equals(Object) method. 在列表中, x y、和z表示不为 null的对象引用。In the list, x, y, and z represent object references that are not null.

  • x.Equals(x)返回true,但涉及浮点类型的情况除外。x.Equals(x) returns true, except in cases that involve floating-point types. 请参阅ISO/IEC/IEEE 60559:2011,信息技术--微处理器系统-浮点运算See ISO/IEC/IEEE 60559:2011, Information technology -- Microprocessor Systems -- Floating-Point arithmetic.

  • x.Equals(y) 返回与 y.Equals(x) 相同的值。x.Equals(y) returns the same value as y.Equals(x).

  • x.Equals(y)如果和均为y trueNaN则返回。 xx.Equals(y) returns true if both x and y are NaN.

  • 如果(x.Equals(y) && y.Equals(z))返回true,则x.Equals(z)返回。trueIf (x.Equals(y) && y.Equals(z)) returns true, then x.Equals(z) returns true.

  • 如果不修改x.Equals(y) x和引用的对象, y则连续调用将返回相同的值。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) 返回 falsex.Equals(null) returns false.

Equals实现不得引发异常; 它们应始终返回值。Implementations of Equals must not throw exceptions; they should always return a value. 例如obj ,如果ArgumentNullExceptionnull,则该Equals方法应返回false ,而不是引发。For example, if obj is null, the Equals method should return false instead of throwing an ArgumentNullException.

重写Equals(Object)时,请遵循以下准则:Follow these guidelines when overriding Equals(Object):

  • 实现IComparable的类型必须重Equals(Object)写。Types that implement IComparable must override Equals(Object).

  • 重写Equals(Object)的类型还必须GetHashCode重写; 否则,哈希表可能无法正常工作。Types that override Equals(Object) must also override GetHashCode; otherwise, hash tables might not work correctly.

  • 应考虑实现IEquatable<T>接口,以支持强类型化测试是否相等。You should consider implementing the IEquatable<T> interface to support strongly typed tests for equality. IEquatable<T>.Equals的实现应返回与Equals一致的结果。Your IEquatable<T>.Equals implementation should return results that are consistent with Equals.

  • 如果您的编程语言支持运算符重载,而您为给定类型重载了相等运算符,则您还必须Equals(Object)重写方法以返回与相等运算符相同的结果。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. 这有助于确保使用EqualsArrayList如和Hashtable)的类库代码的行为与应用程序代码使用相等运算符的方式一致。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.

引用类型的准则Guidelines for Reference Types

以下准则适用于替代Equals(Object)引用类型:The following guidelines apply to overriding Equals(Object) for a reference type:

  • 如果类型Equals的语义基于该类型表示某个值的情况,请考虑重写。Consider overriding Equals if the semantics of the type are based on the fact that the type represents some value(s).

  • 大多数引用类型不得重载相等运算符(即使它们重写Equals)。Most reference types must not overload the equality operator, even if they override Equals. 但是,如果要实现的引用类型应具有值语义(如复数类型),则必须重写相等运算符。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.

  • 不应覆盖Equals可变引用类型。You should not override Equals on a mutable reference type. 这是因为, Equals重写要求你还GetHashCode重写方法,如前一部分中所述。This is because overriding Equals requires that you also override the GetHashCode method, as discussed in the previous section. 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,这可能会导致对象在哈希表中丢失。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.

值类型的准则Guidelines for Value Types

以下准则适用于重写Equals(Object)值类型:The following guidelines apply to overriding Equals(Object) for a value type:

  • 如果要定义的值类型包括一个或多个字段的值为引用类型,则应重写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). 提供的Equals(Object)实现对其字段为所有值类型的值类型执行逐字节的比较,但它使用反射来执行字段中包含引用类型的值类型的ValueType逐字段比较。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.

  • 如果重写Equals ,并且你的开发语言支持运算符重载,则必须重载相等运算符。If you override Equals and your development language supports operator overloading, you must overload the equality operator.

  • 应该实现IEquatable<T>接口。You should implement the IEquatable<T> interface. 调用强类型IEquatable<T>.Equals方法可避免对obj参数进行装箱。Calling the strongly typed IEquatable<T>.Equals method avoids boxing the obj argument.

另请参阅

Equals(Object, Object)

确定指定的对象实例是否被视为相等。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

参数

objA
Object

要比较的第一个对象。The first object to compare.

objB
Object

要比较的第二个对象。The second object to compare.

返回

如果对象被视为相等,则为 true,否则为 falsetrue if the objects are considered equal; otherwise, false. 如果 objAobjB 均为 null,此方法返回 trueIf both objA and objB are null, the method returns true.

示例

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

注解

静态Equals(Object, Object)方法指示两个objA对象objB是否相等。The static Equals(Object, Object) method indicates whether two objects, objA and objB, are equal. 它还使你能够测试值为null的对象是否相等。It also enables you to test objects whose value is null for equality. 它比较objAobjB以确定是否相等,如下所示:It compares objA and objB for equality as follows:

  • 它确定两个对象是否表示相同的对象引用。It determines whether the two objects represent the same object reference. 如果是这样,则该方法true返回。If they do, the method returns true. 此测试等效于调用ReferenceEquals方法。This test is equivalent to calling the ReferenceEquals method. 此外,如果objAobjB均为null,则该方法返回trueIn addition, if both objA and objB are null, the method returns true.

  • 它确定objAobjB是否为nullIt determines whether either objA or objB is null. 如果是,则返回falseIf so, it returns false.

  • 如果两个对象不表示相同的对象引用,并且两者都不为nullobjAEquals调用。(objB)并返回结果。If the two objects do not represent the same object reference and neither is null, it calls objA.Equals(objB) and returns the result. 这意味着,如果objA Object.Equals(Object)重写方法,则将调用此重写。This means that if objA overrides the Object.Equals(Object) method, this override is called.

另请参阅

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