# Object.EqualsObject.EqualsObject.EqualsObject.Equals Method

## 重载

 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)

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

### 示例

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.

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

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

### 注解

• 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.

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

• 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

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

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

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

### 对继承者的说明Notes for Inheritors

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

• 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.

• 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.

• 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

• 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

• 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.

• 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.

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

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

objB
Object Object Object Object

### 示例

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 = 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 = Dalmation: False
'       Alaskan Malamute Reference Equals Dalmation: False

### 注解

• 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.