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

Definition

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

Overloads

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

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

Returns

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

Examples

下面的示例演示Point类,并重写Equals方法以提供值相等性和一个Point3D类派生自PointThe following example shows a Point class that overrides the Equals method to provide value equality, and a Point3D class that is derived from Point. 因为Point重写Object.Equals(Object)来测试值相等性Object.Equals(Object)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.Equals因为Point实现Object.Equals(Object)提供值相等性的方式。However, Point3D.Equals calls Point.Equals because Point implements Object.Equals(Object) in a manner that provides value equality.

using System;

class Point
{
   protected int x, y;

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

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

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

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

sealed class Point3D: Point 
{
   int z;

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

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

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

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

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

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

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

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

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

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

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

Point.Equals方法检查,确保obj参数不是null和它引用此对象与相同类型的实例。The Point.Equals method checks to make sure that the obj argument is not null and that it references an instance of the same type as this object. 如果任一检查失败,该方法返回falseIf either check fails, the method returns false.

Point.Equals方法调用GetType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. 如果使用的方法的窗体复选obj is PointC# 中或TryCast(obj, Point)在 Visual Basic 中,检查将返回true情况下在其中obj是派生的类的实例Point,即使obj和当前实例不属于相同的运行时类型。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. 验证这两个对象是否相同的类型,方法强制转换obj键入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.

在中Point3D.Equals,继承Point.Equals方法,这会重写Object.Equals(Object),任何其他操作完成之前调用。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 (NotInheritable在 Visual Basic 中),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Point3D对象,它被强制转换为Point对象,并传递到基类实现的EqualsIf 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方法将返回true没有方法比较z实例在派生类中引入的字段。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Rectangle类,该类在内部实现为两个矩形Point对象。The following example defines a Rectangle class that internally implements a rectangle as two Point objects. Rectangle类还重写Object.Equals(Object)提供的值是否相等。The Rectangle class also overrides Object.Equals(Object) to provide for value equality.

using System;

class Rectangle 
{
   private Point a, b;

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

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

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

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

class Point 
{
  internal int x;
  internal int y;

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

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

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

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

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

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

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

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

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

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

C# 和 Visual Basic 等某些语言支持运算符重载。Some languages such as C# and Visual Basic support operator overloading. 当某个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. 这通常通过编写实现Equals(Object)方面重载的相等运算符,如以下示例所示的方法。This is typically accomplished by writing the Equals(Object) method in terms of the overloaded equality operator, as in the following example.

using System;

public struct Complex {
   public double re, im;

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

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

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

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

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

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

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

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

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

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

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

因为Complex是值类型,不能从派生。Because Complex is a value type, it cannot be derived from. 因此,对重写Equals(Object)方法无需调用GetType若要确定精确的运行时键入的每个对象,但可以改为使用isC# 中的运算符或TypeOf运算符在 Visual Basic 中检查的类型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.

Remarks

当前实例比较的类型和obj参数取决于当前实例是引用类型或值类型。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,Equals(Object)方法测试的引用相等性,并调用Equals(Object)方法相当于调用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. 引用相等性指进行比较的对象变量引用同一对象。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. 它定义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,person1aperson2,其中具有相同的值。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. 它还会将分配person1a到另一个对象变量, person1bIt also assigns person1a to another object variable, person1b. 如示例所示,输出person1aperson1b因为它们引用同一个对象是否相等。As the output from the example shows, person1a and person1b are equal because they reference the same object. 但是,person1aperson2是否不相等,尽管它们具有相同的值。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,Equals(Object)方法测试的值相等性。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:

    • 两个对象都属于同一类型。The two objects are of the same type. 如下面的示例所示,Byte的值为 12 的对象不等于Int32的值为 12,因为两个对象具有不同的运行时类型的对象。As the following example shows, a Byte object that has a value of 12 does not equal an Int32 object that has a value of 12, because the two objects have different run-time types.

      using System;
      
      public class Example
      {
         public static void Main()
         {
            byte value1 = 12;
            int value2 = 12;
            
            object object1 = value1;
            object object2 = value2;
            
            Console.WriteLine("{0} ({1}) = {2} ({3}): {4}",
                              object1, object1.GetType().Name,
                              object2, object2.GetType().Name,
                              object1.Equals(object2));
         }
      }
      // The example displays the following output:
      //        12 (Byte) = 12 (Int32): False
      
      Module Example
         Public Sub Main()
            Dim value1 As Byte = 12
            Dim value2 As Integer = 12
            
            Dim object1 As Object = value1
            Dim object2 As Object = value2
            
            Console.WriteLine("{0} ({1}) = {2} ({3}): {4}",
                              object1, object1.GetType().Name,
                              object2, object2.GetType().Name,
                              object1.Equals(object2))
         End Sub
      End Module
      ' The example displays the following output:
      '       12 (Byte) = 12 (Int32): False
      
    • 两个对象的公共和私有字段的值相等。The values of the public and private fields of the two objects are equal. 下面的示例测试值相等。The following example tests for value equality. 它定义Person结构,它是值类型,并调用Person类构造函数来实例化两个新Person对象,person1person2,其中具有相同的值。It defines a Person structure, which is a value type, and calls the Person class constructor to instantiate two new Person objects, person1 and person2, which have the same value. 如示例输出所示,虽然两个对象变量引用不同的对象,但person1person2相等,因为它们具有相同的值为私有personName字段。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Object类是.NET Framework 中的所有类型的基类Object.Equals(Object)方法对于所有其他类型提供默认的相等性比较。Because the Object class is the base class for all types in the .NET Framework, the Object.Equals(Object) method provides the default equality comparison for all other types. 但是,类型通常覆盖Equals方法来实现值相等性。However, types often override the Equals method to implement value equality. 有关详细信息,请参阅说明调用方和说明的继承者节。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

当您调用Equals(Object)中的类上的方法重载Windows 运行时Windows Runtime,它不替代的类提供的默认行为Equals(Object)When 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 提供了有关支持的一部分Windows 运行时Windows Runtime(请参阅.NET Framework 支持的 Windows 应用商店应用程序和 Windows 运行时)。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). 中的类Windows 运行时Windows Runtime不继承Object,并不实现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,它们显示为具有ToStringEquals(Object),和GetHashCode方法在 C# 或 Visual Basic 代码中,使用它们以及.NET Framework 提供的默认行为,这些方法时。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 在 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.

调用方的说明Notes for Callers

经常重写派生的类Object.Equals(Object)方法来实现值相等性。Derived classes frequently override the Object.Equals(Object) method to implement value equality. 此外,类型也经常提供到另一个强类型的重载Equals方法,通常通过实现IEquatable<T>接口。In addition, types also frequently provide an additional strongly typed overload to the Equals method, typically by implementing the IEquatable<T> interface. 当您调用Equals方法来测试相等性,您应该知道的当前实例是否重写Object.Equals,并了解如何为特定的调用Equals方法得到解决。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. 否则为你可能要为确定相等性不同于您的预期,执行测试,该方法可能返回意外的值。Otherwise, you may be performing a test for equality that is different from what you intended, and the method may return an unexpected value.

下面的示例进行了这方面的演示。The following example provides an illustration. 它实例化三StringBuilder具有相同的字符串对象,并将对四个调用Equals方法。It instantiates three StringBuilder objects with identical strings, and then makes four calls to Equals methods. 第一种方法调用返回true,和剩余的三个返回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

在第一个的情况下,强类型化StringBuilder.Equals(StringBuilder)方法重载,它的值相等性测试,名为。In the first case, the strongly typed StringBuilder.Equals(StringBuilder) method overload, which tests for value equality, is called. 因为这些字符串分配到两个StringBuilder对象是否相等,则该方法返回trueBecause the strings assigned to the two StringBuilder objects are equal, the method returns true. 但是,StringBuilder不重写Object.Equals(Object)However, StringBuilder does not override Object.Equals(Object). 正因为如此,当StringBuilder对象强制转换为Object,当StringBuilder实例分配给类型的变量Object,以及何时Object.Equals(Object, Object)方法传递两个StringBuilder的对象,默认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. 因为StringBuilder是引用类型,这相当于将传递两个StringBuilder对象添加到ReferenceEquals方法。Because StringBuilder is a reference type, this is equivalent to passing the two StringBuilder objects to the ReferenceEquals method. 虽然所有这三个StringBuilder对象包含相同的字符串,它们是指三个不同的对象。Although all three StringBuilder objects contain identical strings, they refer to three distinct objects. 因此,以下三个方法调用返回falseAs a result, these three method calls return false.

您可以通过调用比较当前对象与另一个对象引用相等性ReferenceEquals方法。You can compare the current object to another object for reference equality by calling the ReferenceEquals method. 在 Visual Basic 中,您还可以使用is关键字 (例如, If Me Is otherObject Then ...)。In Visual Basic, you can also use the is keyword (for example, If Me Is otherObject Then ...).

继承者说明Notes for Inheritors

在定义您自己的类型时,该类型继承定义的功能Equals其基类型的方法。When you define your own type, that type inherits the functionality defined by the Equals method of its base type. 下表列出的默认实现Equals主要类别的.NET Framework 中的类型的方法。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 所定义的相等Equality defined by 注释Comments
直接从派生类 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;直接逐字节比较或使用反射的逐个字段比较。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相同的基础值。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的相同类型。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,则应始终重写Equals,这是因为依赖反射的相等性测试产品/服务性能不佳。For a value type, you should always override Equals, because tests for equality that rely on reflection offer poor performance. 此外可以重写的默认实现Equals对于引用类型的值是否相等,而不是引用相等性测试并定义值相等性的精确意义。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. 此类实现Equals返回true如果两个对象具有相同的值,即使它们不是同一个实例。Such implementations of Equals return true if the two objects have the same value, even if they are not the same instance. 该类型的实施者决定什么构成对象的值,但通常某些或所有存储的数据对象的实例变量中。The type's implementer decides what constitutes an object's value, but it is typically some or all the data stored in the instance variables of the object. 例如,值String对象所基于的; 在字符串的字符String.Equals(Object)方法重写Object.Equals(Object)方法以返回true对于任何两个字符串包含相同的字符顺序相同的实例。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)方法来测试值相等性。The following example shows how to override the Object.Equals(Object) method to test for value equality. 它将替代Equals方法Person类。It overrides the Equals method for the Person class. 如果Person接受的相等性,其基本类实现两个Person对象会引用单个对象,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. 但是,在这种情况下,两个Person对象是否相等,如果它们具有相同的值为Person.Id属性。However, in this case, two Person objects are equal if they have the same value for the Person.Id property.

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

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

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

除了重写Equals,可以实现IEquatable<T>接口,以提供强类型化的测试相等性。In addition to overriding Equals, you can implement the IEquatable<T> interface to provide a strongly typed test for equality.

下面的语句必须为 true 的所有实现Equals(Object)方法。The following statements must be true for all implementations of the Equals(Object) method. 在列表中, xy,并z表示对象引用了不nullIn the list, x, y, and z represent object references that are not null.

  • x.Equals(x) 返回true,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) 返回true如果这两个xyNaNx.Equals(y) returns true if both x and y are NaN.

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

  • 后续调用x.Equals(y)返回相同的值,只要引用的对象xy不会被修改。Successive calls to x.Equals(y) return the same value as long as the objects referenced by x and y are not modified.

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

实现Equals不得引发异常; 它们应始终返回一个值。Implementations of Equals must not throw exceptions; they should always return a value. 例如,如果objnull,则Equals方法应返回false而不是引发ArgumentNullExceptionFor example, if obj is null, the Equals method should return false instead of throwing an ArgumentNullException.

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

  • 类型实现IComparable必须重写Equals(Object)Types that implement IComparable must override Equals(Object).

  • 类型重写Equals(Object)还必须重写GetHashCode; 否则为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.

  • 您应该考虑实施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实现应返回与一致的结果EqualsYour 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,并且重载相等运算符对于给定的类型,还必须重写Equals(Object)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. 这有助于确保使用该类库代码Equals(如ArrayListHashtable) 的行为方式与应用程序代码使用相等运算符的方法一致。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.

对于引用类型的指导原则Guidelines for Reference Types

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

  • 考虑重写Equals如果类型的语义是基于对的这一事实,该类型表示某些值。Consider overriding Equals if the semantics of the type are based on the fact that the type represents some value(s).

  • 大多数引用类型必须不能重载相等运算符,即使它们重写EqualsMost reference types must not overload the equality operator, even if they override Equals. 但是,如果要实现一个引用类型,用于具有值的语义,如复杂的数字类型,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.

  • 不应重写Equals可变引用类型上。You should not override Equals on a mutable reference type. 这是因为在重写Equals需要,还可以覆盖GetHashCode方法,如在上一部分中所述。This is because overriding Equals requires that you also override the GetHashCode method, as discussed in the previous section. 这意味着在其生存期内,这可能导致丢失的对象的哈希表中可以更改可变引用类型的实例的哈希代码。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.

对于值类型的指导原则Guidelines for Value Types

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

  • 如果您要定义包含一个或多个字段的值类型的值是引用类型,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). Equals(Object)提供实现ValueType执行逐字节比较,对于值类型,它的字段都是值类型,但它使用反射来执行的字段包含引用类型的值类型按字段比较。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和您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.

  • 应实现IEquatable<T>接口。You should implement the IEquatable<T> interface. 调用强类型化IEquatable<T>.Equals方法可避免装箱obj参数。Calling the strongly typed IEquatable<T>.Equals method avoids boxing the obj argument.

See Also

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

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 Object Object Object

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

objB
Object Object Object Object

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

Returns

如果认为对象相等,则为 true;否则为 false true if the objects are considered equal; otherwise, false. 如果 objAobjB 均为 null,此方法返回 true If both objA and objB are null, the method returns true.

Examples

下面的示例阐释Equals(Object, Object)方法并将其与比较ReferenceEquals方法。The following example illustrates the Equals(Object, Object) method and compares it with the ReferenceEquals method.

using System;

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

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

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

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

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

Remarks

静态Equals(Object, Object)方法指示是否两个对象,objAobjB,是否相等。The static Equals(Object, Object) method indicates whether two objects, objA and objB, are equal. 它还使您要测试其值为的对象null是否相等。It also enables you to test objects whose value is null for equality. 它将进行比较objAobjB为确定相等性,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. 如果这样,该方法返回trueIf they do, the method returns true. 此测试是否等效于调用ReferenceEquals方法。This test is equivalent to calling the ReferenceEquals method. 此外,如果这两个objAobjBnull,该方法将返回trueIn addition, if both objA and objB are null, the method returns true.

  • 它确定是否是objAobjBnullIt determines whether either objA or objB is null. 如果有,则返回falseIf so, it returns false.

  • 如果两个对象不表示相同的对象引用,并且二者均null,它将调用objAEquals(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重写Object.Equals(Object)方法,调用此重写。This means that if objA overrides the Object.Equals(Object) method, this override is called.

See Also

Applies to