# Object.Equals 方法

## 多載

 Equals(Object) 判斷指定的物件是否等於目前的物件。 Equals(Object, Object) 判斷指定的物件執行個體是否視為相等。

## Equals(Object)

``````public:
virtual bool Equals(System::Object ^ obj);``````
``public virtual bool Equals (object obj);``
``public virtual bool Equals (object? obj);``
``````abstract member Equals : obj -> bool
override this.Equals : obj -> bool``````
``Public Overridable Function Equals (obj As Object) As Boolean``

obj
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
``````
``````type Point(x, y) =
new () = Point(0, 0)
member _.X = x
member _.Y = y

override _.Equals(obj) =
//Check for null and compare run-time types.
match obj with
| :? Point as p ->
x = p.X && y = p.Y
| _ ->
false

override _.GetHashCode() =
(x <<< 2) ^^^ y

override _.ToString() =
\$"Point({x}, {y})"

type Point3D(x, y, z) =
inherit Point(x, y)
member _.Z = z

override _.Equals(obj) =
match obj with
| :? Point3D as pt3 ->
base.Equals(pt3 :> Point) && z = pt3.Z
| _ ->
false

override _.GetHashCode() =
(base.GetHashCode() <<< 2) ^^^ z

override _.ToString() =
\$"Point({x}, {y}, {z})"

let point2D = Point(5, 5)
let point3Da = Point3D(5, 5, 2)
let point3Db = Point3D(5, 5, 2)
let point3Dc = Point3D(5, 5, -1)

printfn \$"{point2D} = {point3Da}: {point2D.Equals point3Da}"
printfn \$"{point2D} = {point3Db}: {point2D.Equals point3Db}"
printfn \$"{point3Da} = {point3Db}: {point3Da.Equals point3Db}"
printfn \$"{point3Da} = {point3Dc}: {point3Da.Equals point3Dc}"
// The example displays the following output:
//       Point(5, 5) = Point(5, 5, 2): False
//       Point(5, 5) = Point(5, 5, 2): False
//       Point(5, 5, 2) = Point(5, 5, 2): True
//       Point(5, 5, 2) = Point(5, 5, -1): False
``````
``````Class Point
Protected x, y As Integer

Public Sub New()
Me.x = 0
Me.y = 0
End Sub

Public Sub New(x As Integer, y As Integer)
Me.x = x
Me.y = y
End Sub

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

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

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

Class Point3D : Inherits Point
Private z As Integer

Public Sub New(ByVal x As Integer, ByVal y As Integer, ByVal z As Integer)
MyBase.New(x, y)
Me.z = Z
End Sub

Public Overrides Function Equals(ByVal obj As Object) As Boolean
Dim pt3 As Point3D = TryCast(obj, Point3D)
If pt3 Is Nothing Then
Return False
Else
Return MyBase.Equals(CType(pt3, Point)) AndAlso z = pt3.Z
End If
End Function

Public Overrides Function GetHashCode() As Integer
Return (MyBase.GetHashCode() << 2) XOr z
End Function

Public Overrides Function ToString() As String
Return String.Format("Point({0}, {1}, {2})", x, y, z)
End Function
End Class

Module Example
Public Sub Main()
Dim point2D As New Point(5, 5)
Dim point3Da As New Point3D(5, 5, 2)
Dim point3Db As New Point3D(5, 5, 2)
Dim point3Dc As New Point3D(5, 5, -1)

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

``````using System;

class Rectangle
{
private Point a, b;

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

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

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

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

class Point
{
internal int x;
internal int y;

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

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

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

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

Console.WriteLine("{0} = {1}: {2}", r1, r2, r1.Equals(r2));
Console.WriteLine("{0} = {1}: {2}", r1, r3, r1.Equals(r3));
Console.WriteLine("{0} = {1}: {2}", r2, r3, r2.Equals(r3));
}
}
// The example displays the following output:
//    Rectangle(0, 0, 100, 200) = Rectangle(0, 0, 100, 200): True
//    Rectangle(0, 0, 100, 200) = Rectangle(0, 0, 150, 200): False
//    Rectangle(0, 0, 100, 200) = Rectangle(0, 0, 150, 200): False
``````
``````type Point(x, y) =
member _.X = x
member _.Y = y

override _.Equals(obj) =
// Performs an equality check on two points (integer pairs).
match obj with
| :? Point as p ->
x = p.X && y = p.Y
| _ ->
false

override _.GetHashCode() =
(x, y).GetHashCode()

type Rectangle(upLeftX, upLeftY, downRightX, downRightY) =
let a = Point(upLeftX, upLeftY)
let b = Point(downRightX, downRightY)

member _.UpLeft = a
member _.DownRight = b

override _.Equals(obj) =
// Perform an equality check on two rectangles (Point object pairs).
match obj with
| :? Rectangle as r ->
a.Equals(r.UpLeft) && b.Equals(r.DownRight)
| _ ->
false

override _.GetHashCode() =
(a, b).GetHashCode()

override _.ToString() =
\$"Rectangle({a.X}, {a.Y}, {b.X}, {b.Y})"

let r1 = Rectangle(0, 0, 100, 200)
let r2 = Rectangle(0, 0, 100, 200)
let r3 = Rectangle(0, 0, 150, 200)

printfn \$"{r1} = {r2}: {r1.Equals r2}"
printfn \$"{r1} = {r3}: {r1.Equals r3}"
printfn \$"{r2} = {r3}: {r2.Equals r3}"
// The example displays the following output:
//    Rectangle(0, 0, 100, 200) = Rectangle(0, 0, 100, 200): True
//    Rectangle(0, 0, 100, 200) = Rectangle(0, 0, 150, 200): False
//    Rectangle(0, 0, 100, 200) = Rectangle(0, 0, 150, 200): False
``````
``````Class Rectangle
Private a, b As Point

Public Sub New(ByVal upLeftX As Integer, ByVal upLeftY As Integer, _
ByVal downRightX As Integer, ByVal downRightY As Integer)
Me.a = New Point(upLeftX, upLeftY)
Me.b = New Point(downRightX, downRightY)
End Sub

Public Overrides Function Equals(ByVal obj As [Object]) As Boolean
' Performs an equality check on two rectangles (Point object pairs).
If obj Is Nothing OrElse Not [GetType]().Equals(obj.GetType()) Then
Return False
End If
Dim r As Rectangle = CType(obj, Rectangle)
Return a.Equals(r.a) AndAlso b.Equals(r.b)
End Function

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

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

Class Point
Friend x As Integer
Friend y As Integer

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

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

Public Overrides Function GetHashCode() As Integer
Return Tuple.Create(x, y).GetHashCode()
End Function
End Class

Class Example
Public Shared Sub Main()
Dim r1 As New Rectangle(0, 0, 100, 200)
Dim r2 As New Rectangle(0, 0, 100, 200)
Dim r3 As New Rectangle(0, 0, 150, 200)

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

``````using System;

public struct Complex
{
public double re, im;

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

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

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

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

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

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

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

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

Console.WriteLine("{0} <> {1}: {2}", cmplx1, cmplx2, cmplx1 != cmplx2);
Console.WriteLine("{0} = {1}: {2}", cmplx1, cmplx2, cmplx1.Equals(cmplx2));

cmplx2.re = 4.0;

Console.WriteLine("{0} = {1}: {2}", cmplx1, cmplx2, cmplx1 == cmplx2);
Console.WriteLine("{0} = {1}: {2}", cmplx1, cmplx2, cmplx1.Equals(cmplx2));
}
}
// The example displays the following output:
//       (4, 1) <> (2, 1): True
//       (4, 1) = (2, 1): False
//       (4, 1) = (4, 1): True
//       (4, 1) = (4, 1): True
``````
``````[<Struct; CustomEquality; NoComparison>]
type Complex =
val mutable re: double
val mutable im: double

override this.Equals(obj) =
match obj with
| :? Complex as c when c = this -> true
| _ -> false

override this.GetHashCode() =
(this.re, this.im).GetHashCode()

override this.ToString() =
\$"({this.re}, {this.im})"

static member op_Equality (x: Complex, y: Complex) =
x.re = y.re && x.im = y.im

static member op_Inequality (x: Complex, y: Complex) =
x = y |> not

let mutable cmplx1 = Complex()
let mutable cmplx2 = Complex()

cmplx1.re <- 4.0
cmplx1.im <- 1.0

cmplx2.re <- 2.0
cmplx2.im <- 1.0

printfn \$"{cmplx1} <> {cmplx2}: {cmplx1 <> cmplx2}"
printfn \$"{cmplx1} = {cmplx2}: {cmplx1.Equals cmplx2}"

cmplx2.re <- 4.0

printfn \$"{cmplx1} = {cmplx2}: {cmplx1 = cmplx2}"
printfn \$"{cmplx1} = {cmplx2}: {cmplx1.Equals cmplx2}"

// The example displays the following output:
//       (4, 1) <> (2, 1): True
//       (4, 1) = (2, 1): False
//       (4, 1) = (4, 1): True
//       (4, 1) = (4, 1): True
``````
``````Public Structure Complex
Public re, im As Double

Public Overrides Function Equals(ByVal obj As [Object]) As Boolean
Return TypeOf obj Is Complex AndAlso Me = CType(obj, Complex)
End Function

Public Overrides Function GetHashCode() As Integer
Return Tuple.Create(re, im).GetHashCode()
End Function

Public Shared Operator = (x As Complex, y As Complex) As Boolean
Return x.re = y.re AndAlso x.im = y.im
End Operator

Public Shared Operator <> (x As Complex, y As Complex) As Boolean
Return Not (x = y)
End Operator

Public Overrides Function ToString() As String
Return String.Format("({0}, {1})", re, im)
End Function
End Structure

Class Example
Public Shared Sub Main()
Dim cmplx1, cmplx2 As Complex

cmplx1.re = 4.0
cmplx1.im = 1.0

cmplx2.re = 2.0
cmplx2.im = 1.0

Console.WriteLine("{0} <> {1}: {2}", cmplx1, cmplx2, cmplx1 <> cmplx2)
Console.WriteLine("{0} = {1}: {2}", cmplx1, cmplx2, cmplx1.Equals(cmplx2))

cmplx2.re = 4.0

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

### 備註

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

``````using System;

// Define a reference type that does not override Equals.
public class Person
{
private string personName;

public Person(string name)
{
this.personName = name;
}

public override string ToString()
{
return this.personName;
}
}

public class Example
{
public static void Main()
{
Person person1a = new Person("John");
Person person1b = person1a;
Person person2 = new Person(person1a.ToString());

Console.WriteLine("Calling Equals:");
Console.WriteLine("person1a and person1b: {0}", person1a.Equals(person1b));
Console.WriteLine("person1a and person2: {0}", person1a.Equals(person2));

Console.WriteLine("\nCasting to an Object and calling Equals:");
Console.WriteLine("person1a and person1b: {0}", ((object) person1a).Equals((object) person1b));
Console.WriteLine("person1a and person2: {0}", ((object) person1a).Equals((object) person2));
}
}
// The example displays the following output:
//       person1a and person1b: True
//       person1a and person2: False
//
//       Casting to an Object and calling Equals:
//       person1a and person1b: True
//       person1a and person2: False
``````
``````// Define a reference type that does not override Equals.
type Person(name) =
override _.ToString() =
name

let person1a = Person "John"
let person1b = person1a
let person2 = Person(string person1a)

printfn "Calling Equals:"
printfn \$"person1a and person1b: {person1a.Equals person1b}"
printfn \$"person1a and person2: {person1a.Equals person2}"

printfn "\nCasting to an Object and calling Equals:"
printfn \$"person1a and person1b: {(person1a :> obj).Equals(person1b :> obj)}"
printfn \$"person1a and person2: {(person1a :> obj).Equals(person2 :> obj)}"
// The example displays the following output:
//       person1a and person1b: True
//       person1a and person2: False
//
//       Casting to an Object and calling Equals:
//       person1a and person1b: True
//       person1a and person2: False
``````
``````' Define a reference type that does not override Equals.
Public Class Person
Private personName As String

Public Sub New(name As String)
Me.personName = name
End Sub

Public Overrides Function ToString() As String
Return Me.personName
End Function
End Class

Module Example
Public Sub Main()
Dim person1a As New Person("John")
Dim person1b As Person = person1a
Dim person2 As New Person(person1a.ToString())

Console.WriteLine("Calling Equals:")
Console.WriteLine("person1a and person1b: {0}", person1a.Equals(person1b))
Console.WriteLine("person1a and person2: {0}", person1a.Equals(person2))
Console.WriteLine()

Console.WriteLine("Casting to an Object and calling Equals:")
Console.WriteLine("person1a and person1b: {0}", CObj(person1a).Equals(CObj(person1b)))
Console.WriteLine("person1a and person2: {0}", CObj(person1a).Equals(CObj(person2)))
End Sub
End Module
' The example displays the following output:
'       Calling Equals:
'       person1a and person1b: True
'       person1a and person2: False
'
'       Casting to an Object and calling Equals:
'       person1a and person1b: True
'       person1a and person2: False
``````
• 如果目前的實例是實值型別，則方法會 Equals(Object) 測試值是否相等。 值相等表示下列各項：

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

``````byte value1 = 12;
int value2 = 12;

object object1 = value1;
object object2 = value2;

Console.WriteLine("{0} ({1}) = {2} ({3}): {4}",
object1, object1.GetType().Name,
object2, object2.GetType().Name,
object1.Equals(object2));

// The example displays the following output:
//        12 (Byte) = 12 (Int32): False
``````
``````let value1 = 12uy
let value2 = 12

let object1 = value1 :> obj
let object2 = value2 :> obj

printfn \$"{object1} ({object1.GetType().Name}) = {object2} ({object2.GetType().Name}): {object1.Equals object2}"

// The example displays the following output:
//        12 (Byte) = 12 (Int32): False
``````
``````Module Example
Public Sub Main()
Dim value1 As Byte = 12
Dim value2 As Integer = 12

Dim object1 As Object = value1
Dim object2 As Object = value2

Console.WriteLine("{0} ({1}) = {2} ({3}): {4}",
object1, object1.GetType().Name,
object2, object2.GetType().Name,
object1.Equals(object2))
End Sub
End Module
' The example displays the following output:
'       12 (Byte) = 12 (Int32): False
``````
• 兩個 物件的公用和私用欄位值相等。 下列範例會測試值相等。 它會定義 `Person` 結構，這是實值型別，並呼叫 `Person` 類別建構函式來具現化兩個新的 `Person` 物件， `person1` 以及 `person2` 具有相同值的 。 如範例的輸出所示，雖然兩個物件變數參考不同的物件， `person1` 但 相 `person2` 等，因為它們對私 `personName` 用欄位具有相同的值。

``````using System;

// Define a value type that does not override Equals.
public struct Person
{
private string personName;

public Person(string name)
{
this.personName = name;
}

public override string ToString()
{
return this.personName;
}
}

public struct Example
{
public static void Main()
{
Person person1 = new Person("John");
Person person2 = new Person("John");

Console.WriteLine("Calling Equals:");
Console.WriteLine(person1.Equals(person2));

Console.WriteLine("\nCasting to an Object and calling Equals:");
Console.WriteLine(((object) person1).Equals((object) person2));
}
}
// The example displays the following output:
//       Calling Equals:
//       True
//
//       Casting to an Object and calling Equals:
//       True
``````
``````// Define a value type that does not override Equals.
[<Struct>]
type Person(personName: string) =
override _.ToString() =
personName

let person1 = Person "John"
let person2 = Person "John"

printfn "Calling Equals:"
printfn \$"{person1.Equals person2}"

printfn \$"\nCasting to an Object and calling Equals:"
printfn \$"{(person1 :> obj).Equals(person2 :> obj)}"
// The example displays the following output:
//       Calling Equals:
//       True
//
//       Casting to an Object and calling Equals:
//       True
``````
``````' Define a value type that does not override Equals.
Public Structure Person
Private personName As String

Public Sub New(name As String)
Me.personName = name
End Sub

Public Overrides Function ToString() As String
Return Me.personName
End Function
End Structure

Module Example
Public Sub Main()
Dim p1 As New Person("John")
Dim p2 As New Person("John")

Console.WriteLine("Calling Equals:")
Console.WriteLine(p1.Equals(p2))
Console.WriteLine()

Console.WriteLine("Casting to an Object and calling Equals:")
Console.WriteLine(CObj(p1).Equals(p2))
End Sub
End Module
' The example displays the following output:
'       Calling Equals:
'       True
'
'       Casting to an Object and calling Equals:
'       True
``````

### Windows 執行階段注意事項

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

### 來電者的附注

``````using System;
using System.Text;

public class Example
{
public static void Main()
{
StringBuilder sb1 = new StringBuilder("building a string...");
StringBuilder sb2 = new StringBuilder("building a string...");

Console.WriteLine("sb1.Equals(sb2): {0}", sb1.Equals(sb2));
Console.WriteLine("((Object) sb1).Equals(sb2): {0}",
((Object) sb1).Equals(sb2));
Console.WriteLine("Object.Equals(sb1, sb2): {0}",
Object.Equals(sb1, sb2));

Object sb3 = new StringBuilder("building a string...");
Console.WriteLine("\nsb3.Equals(sb2): {0}", sb3.Equals(sb2));
}
}
// The example displays the following output:
//       sb1.Equals(sb2): True
//       ((Object) sb1).Equals(sb2): False
//       Object.Equals(sb1, sb2): False
//
//       sb3.Equals(sb2): False
``````
``````open System
open System.Text

let sb1 = StringBuilder "building a string..."
let sb2 = StringBuilder "building a string..."

printfn \$"sb1.Equals(sb2): {sb1.Equals sb2}"
printfn \$"((Object) sb1).Equals(sb2): {(sb1 :> obj).Equals sb2}"

printfn \$"Object.Equals(sb1, sb2): {Object.Equals(sb1, sb2)}"

let sb3 = StringBuilder "building a string..."
printfn \$"\nsb3.Equals(sb2): {sb3.Equals sb2}"
// The example displays the following output:
//       sb1.Equals(sb2): True
//       ((Object) sb1).Equals(sb2): False
//       Object.Equals(sb1, sb2): False
//
//       sb3.Equals(sb2): False
``````
``````Imports System.Text

Module Example
Public Sub Main()
Dim sb1 As New StringBuilder("building a string...")
Dim sb2 As New StringBuilder("building a string...")

Console.WriteLine("sb1.Equals(sb2): {0}", sb1.Equals(sb2))
Console.WriteLine("CObj(sb1).Equals(sb2): {0}",
CObj(sb1).Equals(sb2))
Console.WriteLine("Object.Equals(sb1, sb2): {0}",
Object.Equals(sb1, sb2))

Console.WriteLine()
Dim sb3 As Object = New StringBuilder("building a string...")
Console.WriteLine("sb3.Equals(sb2): {0}", sb3.Equals(sb2))
End Sub
End Module
' The example displays the following output:
'       sb1.Equals(sb2): True
'       CObj(sb1).Equals(sb2): False
'       Object.Equals(sb1, sb2): False
'
'       sb3.Equals(sb2): False
``````

### 繼承者注意事項

``````public class Person
{
private string idNumber;
private string personName;

public Person(string name, string id)
{
this.personName = name;
this.idNumber = id;
}

public override bool Equals(Object obj)
{
Person personObj = obj as Person;
if (personObj == null)
return false;
else
return idNumber.Equals(personObj.idNumber);
}

public override int GetHashCode()
{
return this.idNumber.GetHashCode();
}
}

public class Example
{
public static void Main()
{
Person p1 = new Person("John", "63412895");
Person p2 = new Person("Jack", "63412895");
Console.WriteLine(p1.Equals(p2));
Console.WriteLine(Object.Equals(p1, p2));
}
}
// The example displays the following output:
//       True
//       True
``````
``````open System

type Person(name, id) =
member _.Name = name
member _.Id = id

override _.Equals(obj) =
match obj with
| :? Person as personObj ->
id.Equals personObj.Id
| _ ->
false

override _.GetHashCode() =
id.GetHashCode()

let p1 = Person("John", "63412895")
let p2 = Person("Jack", "63412895")
printfn \$"{p1.Equals p2}"
printfn \$"{Object.Equals(p1, p2)}"
// The example displays the following output:
//       True
//       True
``````
``````Public Class Person
Private idNumber As String
Private personName As String

Public Sub New(name As String, id As String)
Me.personName = name
Me.idNumber = id
End Sub

Public Overrides Function Equals(obj As Object) As Boolean
Dim personObj As Person = TryCast(obj, Person)
If personObj Is Nothing Then
Return False
Else
Return idNumber.Equals(personObj.idNumber)
End If
End Function

Public Overrides Function GetHashCode() As Integer
Return Me.idNumber.GetHashCode()
End Function
End Class

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

• `x.Equals(x)` 會傳回 `true`

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

• `x.Equals(y)`如果 `x` 和 都是 `NaN``true``y` 傳回 。

• 如果 傳 `(x.Equals(y) && y.Equals(z))``true` 回 ，則 `x.Equals(z)``true` 回 。

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

• `x.Equals(null)` 會傳回 `false`

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

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

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

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

• 如果您的程式設計語言支援運算子多載，而且多載指定類型的相等運算子，您也必須覆寫 Equals(Object) 方法，以傳回與等號比較運算子相同的結果。 這有助於確保使用 Equals (的類別庫程式碼，例如 ArrayListHashtable) 的行為，與應用程式程式碼使用等號運算子的方式一致。

#### 參考類型的指導方針

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

• 大部分的參考型別不得多載相等運算子，即使它們覆寫 Equals 也一樣。 不過，如果您實作的參考型別是想要有值語意，例如複數類型，則必須覆寫相等運算子。

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

#### 實值型別的指導方針

• 如果您要定義值型別，其中包含一或多個其值為參考類型的欄位，您應該覆寫 Equals(Object) 。 所提供的 ValueTypeEquals(Object) 作會針對欄位為所有實值型別的值型別執行位元組位元組比較，但它會使用反映來執行包含參考型別之實數值型別的欄位逐欄位比較。

• 如果您覆寫 Equals 和開發語言支援運算子多載，則必須多載相等運算子。

• 您應該實作 IEquatable<T> 介面。 呼叫強型別 IEquatable<T>.Equals 方法可避免將引數方塊化 `obj`

## Equals(Object, Object)

``````public:
static bool Equals(System::Object ^ objA, System::Object ^ objB);``````
``public static bool Equals (object objA, object objB);``
``public static bool Equals (object? objA, object? objB);``
``static member Equals : obj * obj -> bool``
``Public Shared Function Equals (objA As Object, objB As Object) As Boolean``

objA
Object

objB
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
``````
``````open System

// Class constructor
type Dog(dogBreed) =
// Public property.
member _.Breed = dogBreed

override this.Equals(obj) =
match obj with
| :? Dog as dog when dog.Breed = this.Breed -> true
| _ -> false

override _.GetHashCode() =
dogBreed.GetHashCode()

override _.ToString() =
dogBreed

let m1 = Dog "Alaskan Malamute"
let m2 = Dog "Alaskan Malamute"
let g1 = Dog "Great Pyrenees"
let g2 = g1
let d1 = Dog "Dalmation"
let n1 = Unchecked.defaultof<Dog>
let n2 = Unchecked.defaultof<Dog>

printfn \$"null = null: {Object.Equals(n1, n2)}"
printfn \$"null Reference Equals null: {Object.ReferenceEquals(n1, n2)}\n"

printfn \$"{g1} = {g2}: {Object.Equals(g1, g2)}"
printfn \$"{g1} Reference Equals {g2}: {Object.ReferenceEquals(g1, g2)}\n"

printfn \$"{m1} = {m2}: {Object.Equals(m1, m2)}"
printfn \$"{m1} Reference Equals {m2}: {Object.ReferenceEquals(m1, m2)}\n"

printfn \$"{m1} = {d1}: {Object.Equals(m1, d1)}"
printfn \$"{m1} Reference Equals {d1}: {Object.ReferenceEquals(m1, d1)}"

// The example displays the following output:
//       null = null: True
//       null Reference Equals null: True
//
//       Great Pyrenees = Great Pyrenees: True
//       Great Pyrenees Reference Equals Great Pyrenees: True
//
//
//       Alaskan Malamute = 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

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

• 它會判斷 或 `objB` 是否 `objA`Null。 如果是，則會傳 `false` 回 。

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