# Object.Equals 方法

## 多載

 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) 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)

``````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``

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
``````
``````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` 方法會進行檢查，以確定 `obj` 引數不是null ，而且它參考的實例與此物件屬於相同的類型。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，此方法會傳回 `false`If either check fails, the method returns `false`.

`Point.Equals` 方法會呼叫 GetType 方法，以判斷兩個物件的執行時間類型是否相同。The `Point.Equals` method calls the GetType method to determine whether the run-time types of the two objects are identical. 如果方法在 Visual Basic 中C#使用 `obj is Point` 的格式檢查或 `TryCast(obj, Point)`，則當 `obj` 和目前的實例不是相同的執行時間類型時，檢查就會傳回 `true` `Point`的衍生類別實例。`obj`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. 確認兩個物件都屬於相同類型，方法會將 `obj` 轉換為類型 `Point`，並傳回比較這兩個物件之實例欄位的結果。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`中，會在任何其他專案完成之前叫用覆寫 Object.Equals(Object)的繼承 `Point.Equals` 方法。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（在 Visual Basic 中`NotInheritable`），所以 `TryCast(obj, Point)``obj is Point` 的簽C#入或 Visual Basic 就足以確保 `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，它會轉換成 `Point` 物件，並傳遞至 Equals的基類執行。If it is a `Point3D` object, it is cast to a `Point` object and passed to the base class implementation of Equals. 只有當繼承的 `Point.Equals` 方法傳回 `true` 時，方法才會比較衍生類別中所引進的 `z` 實例欄位。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

• 如果目前的實例是參考型別，則 Equals(Object) 方法會測試參考是否相等，而 Equals(Object) 方法的呼叫相當於對 ReferenceEquals 方法的呼叫。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. 參考相等表示比較的物件變數會參考相同的物件。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，也就是參考型別，並呼叫 `Person` 類別的函式來具現化兩個新的 `Person` 物件，`person1a``person2`，其具有相同的值。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. 它也會將 `person1a` 指派給另一個物件變數，`person1b`It also assigns `person1a` to another object variable, `person1b`. 如範例的輸出所示，`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
``````
• 如果目前的實例是實值型別，則 Equals(Object) 方法會測試值是否相等。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:

• 這兩個物件具有相同的類型。The two objects are of the same type. 如下列範例所示，值為12的 Byte 物件不等於值為12的 Int32 物件，因為這兩個物件有不同的執行時間類型。As the following example shows, a Byte object that has a value of 12 does not equal an Int32 object that has a value of 12, because the two objects have different run-time types.

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

object object1 = value1;
object object2 = value2;

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

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

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

Console.WriteLine("{0} ({1}) = {2} ({3}): {4}",
object1, object1.GetType().Name,
object2, object2.GetType().Name,
object1.Equals(object2))
End Sub
End Module
' The example displays the following output:
'       12 (Byte) = 12 (Int32): False
``````
• 兩個物件的公用和私用欄位值相等。The values of the public and private fields of the two objects are equal. 下列範例會測試值是否相等。The following example tests for value equality. 它會定義一個 `Person` 結構，也就是實值型別，並呼叫 `Person` 類別的函式來具現化兩個新的 `Person` 物件，`person1``person2`，其具有相同的值。It defines a `Person` structure, which is a value type, and calls the `Person` class constructor to instantiate two new `Person` objects, `person1` and `person2`, which have the same value. 如範例的輸出所示，雖然兩個物件變數參考不同的物件，但 `person1``person2` 相等，因為它們的私用 `personName` 欄位具有相同的值。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
``````

### Windows 執行階段Windows Runtime 的注意事項Notes for the Windows 執行階段Windows Runtime

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

### 呼叫者的注意事項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 委派的類型必須與相同的調用清單相同。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
``````

Equals(Object) 方法的所有執行中，下列語句都必須為 true。The following statements must be true for all implementations of the Equals(Object) method. 在清單中，`x``y``z` 代表不是null的物件參考。In the list, `x`, `y`, and `z` represent object references that are not null.

• `x.Equals(x)` 會傳回 `true`，但牽涉到浮點類型的情況除外。`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)`.

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

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

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

Equals 的執行不能擲回例外狀況;它們應該一律會傳回值。Implementations of Equals must not throw exceptions; they should always return a value. 例如，如果 `null``obj`Equals 方法應該會傳回 `false`，而不是擲回 ArgumentNullExceptionFor example, if `obj` is `null`, the Equals method should return `false` instead of throwing an ArgumentNullException.

• 執行 IComparable 的類型必須覆寫 Equals(Object)Types that implement IComparable must override 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。Types that override Equals(Object) must also override GetHashCode; otherwise, hash tables might not work correctly.

• 您應該考慮執行 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. 您的 IEquatable<T>.Equals 執行應該會傳回與 Equals一致的結果。Your IEquatable<T>.Equals implementation should return results that are consistent with Equals.

• 如果您的程式設計語言支援運算子多載，而且您多載給定類型的等號比較運算子，您也必須覆寫 Equals(Object) 方法，使其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. 這有助於確保使用 Equals 的類別庫程式碼（例如 ArrayListHashtable）的運作方式，與應用程式程式碼使用等號比較運算子的方式一致。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.

#### 參考型別的指導方針Guidelines for Reference Types

• 如果類型的語義是根據該類型代表一些值的事實，請考慮覆寫 EqualsConsider overriding Equals if the semantics of the type are based on the fact that the type represents some value(s).

• 大部分的參考型別都不能多載等號比較運算子，即使它們覆寫 Equals也一樣。Most reference types must not overload the equality operator, even if they override Equals. 不過，如果您要執行的參考型別必須要有值的語義，例如複數型別，您就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.

• 您不應該覆寫可變參考型別上的 EqualsYou should not override Equals on a mutable reference type. 這是因為覆寫 Equals 需要您同時覆寫 GetHashCode 方法，如上一節中所述。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。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.

#### 實數值型別的指導方針Guidelines for Value Types

• 如果您定義的實數值型別包含一或多個值為參考類型的欄位，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). ValueType 所提供的 Equals(Object) 實作為其欄位全都是實值型別之值型別的逐位元組比較，但它會使用反映來對欄位包含參考型別的實值型別執行逐欄位比較。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.

• 您應該執行 IEquatable<T> 介面。You should implement the IEquatable<T> interface. 呼叫強型別 IEquatable<T>.Equals 方法可避免將 `obj` 引數裝箱。Calling the strongly typed IEquatable<T>.Equals method avoids boxing the `obj` argument.

## 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``

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
``````
``````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. 如果有的話，方法會傳回 `true`If they do, the method returns `true`. 這項測試相當於呼叫 ReferenceEquals 方法。This test is equivalent to calling the ReferenceEquals method. 此外，如果 `objA``objB` 都是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 `objA``objB` 是否為nullIt determines whether either `objA` or `objB` is null. 若是如此，它會傳回 `false`If so, it returns `false`.

• 如果兩個物件不代表相同的物件參考，而且兩者都不是null，則會呼叫 `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` 覆寫 Object.Equals(Object) 方法，則會呼叫此覆寫。This means that if `objA` overrides the Object.Equals(Object) method, this override is called.