# Object.EqualsObject.EqualsObject.EqualsObject.Equals Method

## 多載

 Equals(Object) Equals(Object) Equals(Object) Equals(Object) 判斷指定的物件是否等於目前的物件。Determines whether the specified object is equal to the current object. Equals(Object, Object) Equals(Object, Object) Equals(Object, Object) Equals(Object, Object) 判斷指定的物件執行個體是否視為相等。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``

#### 參數

obj
Object Object Object Object

### 範例

``````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`方法會檢查並確定`obj`引數不是null和它所參考的這個物件與相同類型的執行個體。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. 如果其中一個檢查失敗，則方法會傳回`false`If either check fails, the method returns `false`.

`Point.Equals`方法呼叫GetType方法，以判斷兩個物件的執行階段類型是否相同。The `Point.Equals` method calls the GetType method to determine whether the run-time types of the two objects are identical. 如果使用表單的核取的方法`obj is Point`C# 中或`TryCast(obj, Point)`在 Visual Basic 中，檢查會傳回`true`萬一其中`obj`的衍生類別的執行個體`Point`，即使`obj`和目前執行個體不是相同的執行階段型別。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. 完成驗證，這兩個物件都是相同類型，也就是方法轉型`obj`輸入`Point`，並傳回比較兩個物件的執行個體欄位的結果。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`，繼承`Point.Equals`方法，它會覆寫Object.Equals(Object)，任何其他項目完成之前叫用。In `Point3D.Equals`, the inherited `Point.Equals` method, which overrides Object.Equals(Object), is invoked before anything else is done. 因為`Point3D`是密封的類別 (`NotInheritable` Visual Basic 中)，在表單中的核取`obj is Point`在 C# 或`TryCast(obj, Point)`Visual Basic 中就已足夠，確保`obj``Point3D`物件。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`物件，它會轉換為`Point`物件，並傳遞至基底類別實作EqualsIf it is a `Point3D` object, it is cast to a `Point` object and passed to the base class implementation of Equals. 只有當繼承`Point.Equals`方法會傳回`true`沒有方法比較`z`執行個體的衍生類別中引進的欄位。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
``````

### 備註

• 如果目前的執行個體是參考型別Equals(Object)方法會測試參考是否相等，並呼叫Equals(Object)方法就相當於呼叫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. 參考相等表示所比較的物件變數參考相同的物件。Reference equality means that the object variables that are compared refer to the same object. 下列範例說明這類比較的結果。The following example illustrates the result of such a comparison. 它會定義`Person`類別，這是參考型別，並呼叫`Person`類別建構函式產生兩個新`Person`物件`person1a``person2`，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. 它也會指派`person1a`到另一個物件變數， `person1b`It also assigns `person1a` to another object variable, `person1b`. 做為範例所示，從輸出`person1a``person1b`相等，因為它們參考相同的物件。As the output from the example shows, `person1a` and `person1b` are equal because they reference the same object. 不過，`person1a``person2`不相等，雖然它們有相同的值。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
``````
• 如果目前的執行個體是實值類型，Equals(Object)方法測試值是否相等。If the current instance is a value type, the Equals(Object) method tests for value equality. 實值相等表示下列各項：Value equality means the following:

• 兩個物件都屬於相同的類型。The two objects are of the same type. 如下列範例所示Byte不等於物件，其值為 12Int32有值為 12，，因為兩個物件具有不同的執行階段類型的物件。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
``````
• 兩個物件的公用和私用欄位的值相等。The values of the public and private fields of the two objects are equal. 下列範例會測試值相等。The following example tests for value equality. 它會定義`Person`結構，也就是實值型別，並呼叫`Person`類別建構函式產生兩個新`Person`物件`person1``person2`，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. 範例輸出所示，兩個物件變數參考不同的物件，雖然`person1``person2`相等，因為它們具有相同的值為私用`personName`欄位。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
``````

### 資訊 Windows 執行階段Windows RuntimeNotes for the Windows 執行階段Windows Runtime

Windows 執行階段Windows Runtime 以 C# 或 Visual Basic 撰寫的類別可以覆寫Equals(Object)方法多載。classes that are written in C# or Visual Basic can override the Equals(Object) method overload.

### 呼叫端資訊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
``````

### 繼承者注意事項Notes for Inheritors

Delegate - 委派Delegate MulticastDelegate.Equals 委派必須具有相同的引動過程清單之相同類型。Delegates must have the same type with identical invocation lists.

``````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)` 傳回`true`，牽涉到浮點數類型的情況除外。`x.Equals(x)` returns `true`, except in cases that involve floating-point types.

• `x.Equals(y)` 會傳回與 `y.Equals(x)` 相同的值。`x.Equals(y)` returns the same value as `y.Equals(x)`.

• `x.Equals(y)` 會傳回`true`如果兩個`x``y``NaN``x.Equals(y)` returns `true` if both `x` and `y` are `NaN`.

• 如果`(x.Equals(y) && y.Equals(z))`會傳回`true`，然後`x.Equals(z)`傳回`true`If `(x.Equals(y) && y.Equals(z))` returns `true`, then `x.Equals(z)` returns `true`.

• 後續呼叫`x.Equals(y)`傳回相同的值，只要所參考的物件`x``y`不會修改。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)` 會傳回 `false``x.Equals(null)` returns `false`.

• 型別都會實作IComparable必須覆寫Equals(Object)Types that implement IComparable must override Equals(Object).

• 類型覆寫Equals(Object)也必須覆寫GetHashCode，否則雜湊表可能無法正常運作。Types that override Equals(Object) must also override GetHashCode; otherwise, hash tables might not work correctly.

• 您應該考慮實作IEquatable<T>介面，以支援強型別測試是否相等。You should consider implementing the IEquatable<T> interface to support strongly typed tests for equality. IEquatable<T>.Equals實作應該會傳回與一致的結果EqualsYour IEquatable<T>.Equals implementation should return results that are consistent with Equals.

• 如果您的程式語言支援運算子多載，而且您多載等號比較運算子，針對指定的型別，您也必須覆寫Equals(Object)方法，以傳回與等號比較運算子相同的結果。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. 這有助於確保會使用該類別程式庫程式碼Equals(例如ArrayListHashtable) 行為與等號比較運算子由應用程式程式碼的方式一致的方式。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.

#### 參考類型的指導方針Guidelines for Reference Types

• 請考慮覆寫Equals如果類型的語意是基礎類型所代表的某些值為基礎。Consider overriding Equals if the semantics of the type are based on the fact that the type represents some value(s).

• 大部分的參考型別必須多載等號比較運算子，即使它們會覆寫EqualsMost reference types must not overload the equality operator, even if they override Equals. 不過，如果您要實作參考型別，要有值的語意，例如複雜數字 類型中，您必須覆寫等號比較運算子。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.

• 您不應該覆寫Equals可變動參考類型。You should not override Equals on a mutable reference type. 這是因為覆寫Equals需要，您也會覆寫GetHashCode方法，如前一節所述。This is because overriding Equals requires that you also override the GetHashCode method, as discussed in the previous section. 這表示可變動參考類型的執行個體的雜湊碼，可以在其生命週期，這會導致遺失物件雜湊表中進行變更。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.

#### 實值類型的指導方針Guidelines for Value Types

• 如果您要定義實值型別，其中包含一或多個欄位的值是參考型別，您應該覆寫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)所提供的實作ValueType執行逐位元組比較的值類型的欄位是所有實值型別，但它會使用反映來執行其欄位包含參考類型的實值型別的欄位的比較。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.

• 您應該實作IEquatable<T>介面。You should implement the IEquatable<T> interface. 呼叫強型別IEquatable<T>.Equals方法可以避免 boxing`obj`引數。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``

#### 參數

objA
Object Object Object Object

objB
Object Object Object Object

### 範例

``````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
``````

### 備註

• 它會判斷兩個物件是否代表相同的物件參考。It determines whether the two objects represent the same object reference. 如果沒有的話，則方法會傳回`true`If they do, the method returns `true`. 這項測試就相當於呼叫ReferenceEquals方法。This test is equivalent to calling the ReferenceEquals method. 此外，如果這兩個`objA``objB`null，則方法會傳回`true`In addition, if both `objA` and `objB` are null, the method returns `true`.

• 它會判斷是否可能`objA`或是`objB`nullIt determines whether either `objA` or `objB` is null. 如果，則會傳回`false`If so, it returns `false`.

• 如果兩個物件不代表相同的物件參考，而且兩者都null，它會呼叫`objA``Equals`(`objB`)，並傳回結果。If the two objects do not represent the same object reference and neither is null, it calls `objA`.`Equals`(`objB`) and returns the result. 這表示，如果`objA`會覆寫Object.Equals(Object)方法，會呼叫此覆寫。This means that if `objA` overrides the Object.Equals(Object) method, this override is called.