IEquatable<T>.Equals(T) 方法
定义
重要
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指示当前对象是否等于同一类型的另一个对象。
public:
bool Equals(T other);
public bool Equals (T other);
public bool Equals (T? other);
abstract member Equals : 'T -> bool
Public Function Equals (other As T) As Boolean
参数
- other
- T
一个与此对象进行比较的对象。
返回
如果当前对象等于 other
参数,则为 true
;否则为 false
。
示例
以下示例演示了实现 和 具有两个Person
属性LastName
和 SSN
的类IEquatable<T>的部分实现。 如果两个 对象的 属性相同,则Equals方法返回 ;否则返回 False
。True
Person
SSN
using System;
using System.Collections.Generic;
using System.Text.RegularExpressions;
public class Person : IEquatable<Person>
{
private string uniqueSsn;
private string lName;
public Person(string lastName, string ssn)
{
if (Regex.IsMatch(ssn, @"\d{9}"))
uniqueSsn = $"{ssn.Substring(0, 3)}-{ssn.Substring(3, 2)}-{ssn.Substring(5, 4)}";
else if (Regex.IsMatch(ssn, @"\d{3}-\d{2}-\d{4}"))
uniqueSsn = ssn;
else
throw new FormatException("The social security number has an invalid format.");
this.LastName = lastName;
}
public string SSN
{
get { return this.uniqueSsn; }
}
public string LastName
{
get { return this.lName; }
set {
if (String.IsNullOrEmpty(value))
throw new ArgumentException("The last name cannot be null or empty.");
else
this.lName = value;
}
}
public bool Equals(Person other)
{
if (other == null)
return false;
if (this.uniqueSsn == other.uniqueSsn)
return true;
else
return false;
}
public override bool Equals(Object obj)
{
if (obj == null)
return false;
Person personObj = obj as Person;
if (personObj == null)
return false;
else
return Equals(personObj);
}
public override int GetHashCode()
{
return this.SSN.GetHashCode();
}
public static bool operator == (Person person1, Person person2)
{
if (((object)person1) == null || ((object)person2) == null)
return Object.Equals(person1, person2);
return person1.Equals(person2);
}
public static bool operator != (Person person1, Person person2)
{
if (((object)person1) == null || ((object)person2) == null)
return ! Object.Equals(person1, person2);
return ! (person1.Equals(person2));
}
}
open System
open System.Text.RegularExpressions
type Person(lastName, ssn) =
let mutable lastName = lastName
let ssn =
if Regex.IsMatch(ssn, @"\d{9}") then
$"{ssn.Substring(0, 3)}-{ssn.Substring(3, 2)}-{ssn.Substring(5, 4)}"
elif Regex.IsMatch(ssn, @"\d{3}-\d{2}-\d{4}") then
ssn
else
raise (FormatException "The social security number has an invalid format.")
member _.SSN =
ssn
member _.LastName
with get () = lastName
and set (value) =
if String.IsNullOrEmpty value then
invalidArg (nameof value) "The last name cannot be null or empty."
else
lastName <- value
static member op_Equality (person1: Person, person2: Person) =
if box person1 |> isNull || box person2 |> isNull then
Object.Equals(person1, person2)
else
person1.Equals person2
static member op_Inequality (person1: Person, person2: Person) =
if box person1 |> isNull || box person2 |> isNull then
Object.Equals(person1, person2) |> not
else
person1.Equals person2 |> not
override _.GetHashCode() =
ssn.GetHashCode()
override this.Equals(obj: obj) =
match obj with
| :? Person as personObj ->
(this :> IEquatable<_>).Equals personObj
| _ -> false
interface IEquatable<Person> with
member this.Equals(other: Person) =
match box other with
| null -> false
| _ ->
this.SSN = other.SSN
Imports System.Collections.Generic
Imports System.Text.RegularExpressions
Public Class Person : Implements IEquatable(Of Person)
Private uniqueSsn As String
Private lName As String
Public Sub New(lastName As String, ssn As String)
If Regex.IsMatch(ssn, "\d{9}") Then
uniqueSsn = $"{ssn.Substring(0, 3)}-{ssn.Substring(3, 2)}-{ssn.Substring(5, 4)}"
ElseIf Regex.IsMatch(ssn, "\d{3}-\d{2}-\d{4}") Then
uniqueSsn = ssn
Else
Throw New FormatException("The social security number has an invalid format.")
End If
Me.LastName = lastName
End Sub
Public ReadOnly Property SSN As String
Get
Return Me.uniqueSsn
End Get
End Property
Public Property LastName As String
Get
Return Me.lName
End Get
Set
If String.IsNullOrEmpty(value) Then
Throw New ArgumentException("The last name cannot be null or empty.")
Else
lname = value
End If
End Set
End Property
Public Overloads Function Equals(other As Person) As Boolean _
Implements IEquatable(Of Person).Equals
If other Is Nothing Then Return False
If Me.uniqueSsn = other.uniqueSsn Then
Return True
Else
Return False
End If
End Function
Public Overrides Function Equals(obj As Object) As Boolean
If obj Is Nothing Then Return False
Dim personObj As Person = TryCast(obj, Person)
If personObj Is Nothing Then
Return False
Else
Return Equals(personObj)
End If
End Function
Public Overrides Function GetHashCode() As Integer
Return Me.SSN.GetHashCode()
End Function
Public Shared Operator = (person1 As Person, person2 As Person) As Boolean
If person1 Is Nothing OrElse person2 Is Nothing Then
Return Object.Equals(person1, person2)
End If
Return person1.Equals(person2)
End Operator
Public Shared Operator <> (person1 As Person, person2 As Person) As Boolean
If person1 Is Nothing OrElse person2 Is Nothing Then
Return Not Object.Equals(person1, person2)
End If
Return Not person1.Equals(person2)
End Operator
End Class
Person
然后,对象可以存储在 对象中 List<T> ,并由 方法标识 Contains
,如以下示例所示。
public class TestIEquatable
{
public static void Main()
{
// Create a Person object for each job applicant.
Person applicant1 = new Person("Jones", "099-29-4999");
Person applicant2 = new Person("Jones", "199-29-3999");
Person applicant3 = new Person("Jones", "299-49-6999");
// Add applicants to a List object.
List<Person> applicants = new List<Person>();
applicants.Add(applicant1);
applicants.Add(applicant2);
applicants.Add(applicant3);
// Create a Person object for the final candidate.
Person candidate = new Person("Jones", "199-29-3999");
if (applicants.Contains(candidate))
Console.WriteLine("Found {0} (SSN {1}).",
candidate.LastName, candidate.SSN);
else
Console.WriteLine("Applicant {0} not found.", candidate.SSN);
// Call the shared inherited Equals(Object, Object) method.
// It will in turn call the IEquatable(Of T).Equals implementation.
Console.WriteLine("{0}({1}) already on file: {2}.",
applicant2.LastName,
applicant2.SSN,
Person.Equals(applicant2, candidate));
}
}
// The example displays the following output:
// Found Jones (SSN 199-29-3999).
// Jones(199-29-3999) already on file: True.
// Create a Person object for each job applicant.
let applicant1 = Person("Jones", "099-29-4999")
let applicant2 = Person("Jones", "199-29-3999")
let applicant3 = Person("Jones", "299-49-6999")
// Add applicants to a List object.
let applicants = ResizeArray()
applicants.Add applicant1
applicants.Add applicant2
applicants.Add applicant3
// Create a Person object for the final candidate.
let candidate = Person("Jones", "199-29-3999")
if applicants.Contains candidate then
printfn $"Found {candidate.LastName} (SSN {candidate.SSN})."
else
printfn $"Applicant {candidate.SSN} not found."
// Call the shared inherited Equals(Object, Object) method.
// It will in turn call the IEquatable<T>.Equals implementation.
printfn $"{applicant2.LastName}({applicant2.SSN}) already on file: {Person.Equals(applicant2, candidate)}."
// The example displays the following output:
// Found Jones (SSN 199-29-3999).
// Jones(199-29-3999) already on file: True.
Module TestIEquatable
Public Sub Main()
' Create a Person object for each job applicant.
Dim applicant1 As New Person("Jones", "099-29-4999")
Dim applicant2 As New Person("Jones", "199-29-3999")
Dim applicant3 As New Person("Jones", "299-49-6999")
' Add applicants to a List object.
Dim applicants As New List(Of Person)
applicants.Add(applicant1)
applicants.Add(applicant2)
applicants.Add(applicant3)
' Create a Person object for the final candidate.
Dim candidate As New Person("Jones", "199-29-3999")
If applicants.Contains(candidate) Then
Console.WriteLine("Found {0} (SSN {1}).", _
candidate.LastName, candidate.SSN)
Else
Console.WriteLine("Applicant {0} not found.", candidate.SSN)
End If
' Call the shared inherited Equals(Object, Object) method.
' It will in turn call the IEquatable(Of T).Equals implementation.
Console.WriteLine("{0}({1}) already on file: {2}.", _
applicant2.LastName, _
applicant2.SSN, _
Person.Equals(applicant2, candidate))
End Sub
End Module
' The example displays the following output:
' Found Jones (SSN 199-29-3999).
' Jones(199-29-3999) already on file: True.
注解
方法的 Equals 实现旨在执行与当前对象相同类型的 T
另一个对象的相等性测试。 在 Equals(T) 以下情况下调用 方法:
Equals
当调用 方法并且other
参数是 类型的T
强类型对象时。 (如果other
不是 类型T
,则调用基 Object.Equals(Object) 方法。 在两种方法中, IEquatable<T>.Equals 性能稍好一些。)调用多个泛型集合对象的搜索方法时。 其中一些类型及其方法包括:
方法的一些泛型重载 BinarySearch 。
类的 List<T> 搜索方法,包括 List<T>.Contains(T)、 List<T>.IndexOf、 List<T>.LastIndexOf和 List<T>.Remove。
类的 Dictionary<TKey,TValue> 搜索方法,包括 ContainsKey 和 Remove。
泛型 LinkedList<T> 类的搜索方法,包括 LinkedList<T>.Contains 和 Remove。
换句话说,若要处理类的对象存储在数组或泛型集合对象中的可能性,最好实现 IEquatable<T> 以便可以轻松识别和操作对象。
实现 Equals 方法时,请适当地为泛型类型参数指定的类型定义相等性。 例如,如果类型参数为 ,则 Int32为比较两个 32 位带符号整数时适当定义相等性。
实施者说明
如果实现 Equals(T),还应重写 和 GetHashCode() 的Equals(Object)基类实现,使其行为与 方法的行为Equals(T)一致。 如果确实重写 Equals(Object),则还会在调用类上的静态 Equals(System.Object, System.Object)
方法时调用重写的实现。 此外,应重载 op_Equality
和 op_Inequality
运算符。 这可确保所有相等性测试返回一致的结果,如示例所示。