Object.ReferenceEquals(Object, Object) 方法

定義

命名空間:

System

組件:

System.Runtime.dll

來源:

Object.cs

判斷指定的 Object 執行個體是否為相同的執行個體。

public:
 static bool ReferenceEquals(System::Object ^ objA, System::Object ^ objB);

public static bool ReferenceEquals (object? objA, object? objB);

static member ReferenceEquals : obj * obj -> bool

Public Shared Function ReferenceEquals (objA As Object, objB As Object) As Boolean

參數

objA

Object

要比較的第一個物件。

objB

Object

要比較的第二個物件。

傳回

Boolean

如果 objA 與 objB 為相同的執行個體或兩者皆為 null，則為 true，否則為 false。

範例

下列範例會使用 ReferenceEquals 來判斷兩個物件是否為相同的實例。

using namespace System;
int main()
{
   Object^ o = nullptr;
   Object^ p = nullptr;
   Object^ q = gcnew Object;
   Console::WriteLine( Object::ReferenceEquals( o, p ) );
   p = q;
   Console::WriteLine( Object::ReferenceEquals( p, q ) );
   Console::WriteLine( Object::ReferenceEquals( o, p ) );
}

/*

This code produces the following output.

True
True
False

*/

object o = null;
object p = null;
object q = new Object();

Console.WriteLine(Object.ReferenceEquals(o, p));
p = q;
Console.WriteLine(Object.ReferenceEquals(p, q));
Console.WriteLine(Object.ReferenceEquals(o, p));

// This code produces the following output:
//   True
//   True
//   False

let o: obj = null
let mutable p: obj = null
let q = obj ()

printfn $"{Object.ReferenceEquals(o, p)}"
p <- q
printfn $"{Object.ReferenceEquals(p, q)}"
printfn $"{Object.ReferenceEquals(o, p)}"

// This code produces the following output:
//   True
//   True
//   False

Public Class App
    Public Shared Sub Main() 
        Dim o As Object = Nothing
        Dim p As Object = Nothing
        Dim q As New Object
        Console.WriteLine(Object.ReferenceEquals(o, p))
        p = q
        Console.WriteLine(Object.ReferenceEquals(p, q))
        Console.WriteLine(Object.ReferenceEquals(o, p))
    End Sub 
End Class 
' This code produces the following output:
'
' True
' True
' False
'

備註

Equals不同于 方法和等號比較運算子， ReferenceEquals 無法覆寫 方法。 因此，如果您想要測試兩個物件參考是否相等，而且不確定方法的實作 Equals ，您可以呼叫 ReferenceEquals 方法。

不過，在下列兩個案例中，方法的 ReferenceEquals 傳回值可能會異常：

• 比較實值型別時。 如果 objA 和 objB 是實值型別，則會先進行 Box 處理，再將它們傳遞至 ReferenceEquals 方法。 這表示，如果 和 objB 都 objA 代表實值型別的相同實例， ReferenceEquals 方法仍會傳 false 回 ，如下列範例所示。

  int int1 = 3;
  Console.WriteLine(Object.ReferenceEquals(int1, int1));
  Console.WriteLine(int1.GetType().IsValueType);
  
  // The example displays the following output:
  //       False
  //       True
  

  let int1 = 3
  printfn $"{Object.ReferenceEquals(int1, int1)}"
  printfn $"{int1.GetType().IsValueType}"
  
  // The example displays the following output:
  //       False
  //       True
  

  Public Module Example
     Public Sub Main
        Dim int1 As Integer = 3
        Console.WriteLine(Object.ReferenceEquals(int1, int1))
        Console.WriteLine(int1.GetType().IsValueType)
     End Sub
  End Module
  ' The example displays the following output:
  '       False
  '       True
  

  如需 Boxing 實值型別的資訊，請參閱 Boxing 和 Unboxing。

• 比較字串時。 如果 objA 和 objB 是字串，則如果字串為terned，則 ReferenceEquals 方法會傳回 true 。 它不會針對值相等執行測試。 在下列範例中， s1 和 s2 相等，因為它們是單一三元字串的兩個實例。 不過， s3 和 s4 不相等，因為雖然它們具有相同的字串值，但該字串不是三元。

  String s1 = "String1";
  String s2 = "String1";
  Console.WriteLine("s1 = s2: {0}", Object.ReferenceEquals(s1, s2));
  Console.WriteLine("{0} interned: {1}", s1,
                    String.IsNullOrEmpty(String.IsInterned(s1)) ? "No" : "Yes");
  
  String suffix = "A";
  String s3 = "String" + suffix;
  String s4 = "String" + suffix;
  Console.WriteLine("s3 = s4: {0}", Object.ReferenceEquals(s3, s4));
  Console.WriteLine("{0} interned: {1}", s3,
                    String.IsNullOrEmpty(String.IsInterned(s3)) ? "No" : "Yes");
  
  // The example displays the following output:
  //       s1 = s2: True
  //       String1 interned: Yes
  //       s3 = s4: False
  //       StringA interned: No
  

  open System
  
  let s1 = "String1"
  let s2 = "String1"
  printfn $"s1 = s2: {Object.ReferenceEquals(s1, s2)}"
  printfn $"""{s1} interned: {if String.IsNullOrEmpty(String.IsInterned s1) then "No" else "Yes"}"""
  
  let suffix = "A"
  let s3 = "String" + suffix
  let s4 = "String" + suffix
  printfn $"s3 = s4: {Object.ReferenceEquals(s3, s4)}"
  printfn $"""{s3} interned: {if String.IsNullOrEmpty(String.IsInterned s3) then "No" else "Yes"}"""
  
  // The example displays the following output:
  //       s1 = s2: True
  //       String1 interned: Yes
  //       s3 = s4: False
  //       StringA interned: No
  

  Module Example
     Public Sub Main()
        Dim s1 As String = "String1"
        Dim s2 As String = "String1"
        Console.WriteLine("s1 = s2: {0}", Object.ReferenceEquals(s1, s2))
        Console.WriteLine("{0} interned: {1}", s1, 
                          If(String.IsNullOrEmpty(String.IsInterned(s1)), "No", "Yes"))
  
        Dim suffix As String = "A"
        Dim s3 = "String" + suffix
        Dim s4 = "String" + suffix
        Console.WriteLine("s3 = s4: {0}", Object.ReferenceEquals(s3, s4))
        Console.WriteLine("{0} interned: {1}", s3, 
                          If(String.IsNullOrEmpty(String.IsInterned(s3)), "No", "Yes"))
     End Sub
  End Module
  ' The example displays the following output:
  '       s1 = s2: True
  '       String1 interned: Yes
  '       s3 = s4: False
  '       StringA interned: No
  

  如需字串插播的詳細資訊，請參閱 String.IsInterned 。

另請參閱

• Equals(Object)