Object.ReferenceEquals(Object, Object) 方法

定義

判斷指定的 Object 執行個體是否為相同的執行個體。Determines whether the specified Object instances are the same instance.

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。The first object to compare.

objB
Object

要比較的第二個物件。The second object to compare.

傳回

如果 trueobjA 為相同的執行個體或兩者皆為 objBnull ,則為 ,否則為 falsetrue if objA is the same instance as objB or if both are null; otherwise, 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。The following example uses ReferenceEquals to determine if two objects are the same instance.

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
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

不同于 Equals 方法和等號比較運算子,無法覆寫 ReferenceEquals 方法。Unlike the Equals method and the equality operator, the ReferenceEquals method cannot be overridden. 因此,如果您想要測試兩個物件參考是否相等,而您不確定如何執行 Equals 方法,您可以呼叫 ReferenceEquals 方法。Because of this, if you want to test two object references for equality and you are unsure about the implementation of the Equals method, you can call the ReferenceEquals method.

不過,在這兩個案例中,ReferenceEquals 方法的傳回值可能會顯示為異常:However, the return value of the ReferenceEquals method may appear to be anomalous in these two scenarios:

  • 比較數值型別時。When comparing value types. 如果 objAobjB 是實值型別,則會在將它們傳遞至 ReferenceEquals 方法之前先將其裝箱。If objA and objB are value types, they are boxed before they are passed to the ReferenceEquals method. 這表示,如果 objAobjB 都代表實值型別的實例,ReferenceEquals 方法仍會傳回 false,如下列範例所示。This means that if both objA and objB represent the same instance of a value type, the ReferenceEquals method nevertheless returns false, as the following example shows.

    int int1 = 3;
    Console.WriteLine(Object.ReferenceEquals(int1, int1));
    Console.WriteLine(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
    

    如需實數值型別的相關資訊,請參閱裝箱和取消裝箱For information on boxing value types, see Boxing and Unboxing.

  • 比較字串時。When comparing strings. 如果 objAobjB 是字串,ReferenceEquals 方法會在字串暫留時傳回 trueIf objA and objB are strings, the ReferenceEquals method returns true if the string is interned. 它不會執行值相等的測試。It does not perform a test for value equality. 在下列範例中,s1s2 相等,因為它們是單一留用字串的兩個實例。In the following example, s1 and s2 are equal because they are two instances of a single interned string. 不過,s3s4 不相等,因為雖然它們具有相同的字串值,但不會暫留該字串。However, s3 and s4 are not equal, because although they are have identical string values, that string is not interned.

    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
    
    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
    

    如需有關字串暫留的詳細資訊,請參閱 String.IsInternedFor more information about string interning, see String.IsInterned.

適用於

另請參閱