Object.ReferenceEquals(Object, Object) 方法

定義

命名空間:
System
組件:
mscorlib.dll, System.Runtime.dll
組件:
mscorlib.dll
組件:
System.Runtime.dll
組件:
netstandard.dll

判斷指定的 Object 實例是否為同一實例。

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

第一個比較的對象。

objB
Object

第二個比較物件。

傳回

Boolean

true 若 objA 是 與 objB 相同的實例，或 兩者皆 為零;否則， false。

範例

以下範例用 ReferenceEquals 來判斷兩個物件是否為同一個實例。

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

與方法 Equals 及等號運算子不同，該 ReferenceEquals 方法無法被覆寫。 因此，如果你想測試兩個物件參考的相等性，且不確定方法的實作 Equals ，你可以呼叫該 ReferenceEquals 方法。

然而，在以下兩種情境中，該 ReferenceEquals 方法的返回值可能看起來異常：

  • 比較價值類型時， 若 objA 和 objB 是值型態，則在傳遞給 ReferenceEquals 方法前會先被框住。 這表示如果 和 objB 都objA代表同一值型態的實例，ReferenceEquals該方法仍會回傳 false，如下範例所示。

    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

    關於裝盒價值類型的資訊，請參見 「裝箱與開箱」。

  • 比較琴弦時， 若 objA 和 objB 是字串，則當字串被 interned 時，方法 ReferenceEquals 會回傳 true 。 它不會進行價值平等的檢驗。 以下範例中， s1 和 s2 相等，因為它們是同一個被包含字串的兩個實例。 然而， s3 和 s4 並不相等，因為雖然它們的字串值相同，但該字串並未被內化。

    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

    關於弦中介的更多資訊，請參見 String.IsInterned。

適用於

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