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String.IsInterned Method

Retrieves a reference to a specified String.

[Visual Basic]
Public Shared Function IsInterned( _
   ByVal str As String _
) As String
[C#]
public static string IsInterned(
 string str
);
[C++]
public: static String* IsInterned(
 String* str
);
[JScript]
public static function IsInterned(
   str : String
) : String;

Parameters

str
A String.

Return Value

A String reference to str if it is in the common language runtime "intern pool"; otherwise a null reference (Nothing in Visual Basic).

Exceptions

Exception Type Condition
ArgumentNullException str is a null reference (Nothing in Visual Basic).

Remarks

The common language runtime automatically maintains a table, called the "intern pool", which contains a single instance of each unique literal string constant declared in a program, as well as any unique instance of String you add programmatically.

The intern pool conserves string storage. If you assign a literal string constant to several variables, each variable is set to reference the same constant in the intern pool instead of referencing several different instances of String that have identical values.

This method looks up str in the intern pool. If str has already been interned, a reference to that instance is returned; otherwise, a null reference (Nothing in Visual Basic) is returned.

Compare this method to the Intern method.

This method does not return a Boolean value, but can still be used where a Boolean is needed.

Example

[Visual Basic] 
' Sample for String.IsInterned(String)
Imports System
Imports System.Text

Class Sample
   Public Shared Sub Main()
      ' String str1 is known at compile time, and is automatically interned.
      Dim str1 As [String] = "abcd"
      
      ' Constructed string, str2, is not explicitly or automatically interned.
      Dim str2 As [String] = New StringBuilder().Append("wx").Append("yz").ToString()
      Console.WriteLine()
      Test(1, str1)
      Test(2, str2)
   End Sub 'Main
   
   Public Shared Sub Test(sequence As Integer, str As [String])
      Console.Write("{0}) The string, '", sequence)
      Dim strInterned As [String] = [String].IsInterned(str)
      If strInterned Is Nothing Then
         Console.WriteLine("{0}', is not interned.", str)
      Else
         Console.WriteLine("{0}', is interned.", strInterned)
      End If
   End Sub 'Test
End Class 'Sample '
'This example produces the following results:
'
'1) The string, 'abcd', is interned.
'2) The string, 'wxyz', is not interned.
'

[C#] 
// Sample for String.IsInterned(String)
using System;
using System.Text;

class Sample {
    public static void Main() {
// String str1 is known at compile time, and is automatically interned.
    String str1 = "abcd";

// Constructed string, str2, is not explicitly or automatically interned.
    String str2 = new StringBuilder().Append("wx").Append("yz").ToString();
    Console.WriteLine();
    Test(1, str1);
    Test(2, str2);
    }

    public static void Test(int sequence, String str) {
    Console.Write("{0}) The string, '", sequence);
    String strInterned = String.IsInterned(str);
    if (strInterned == null)
        Console.WriteLine("{0}', is not interned.", str);
    else
        Console.WriteLine("{0}', is interned.", strInterned);
    }
}
/*
This example produces the following results:

1) The string, 'abcd', is interned.
2) The string, 'wxyz', is not interned.
*/

[C++] 
// Sample for String::IsInterned(String)
#using <mscorlib.dll>

using namespace System;
using namespace System::Text;

void Test(int sequence, String* str) {
   Console::Write(S"{0} The string '",  __box(sequence));
   String*  strInterned = String::IsInterned(str);
   if (strInterned == 0)
      Console::WriteLine(S"{0}' is not interned.", str);
   else
      Console::WriteLine(S"{0}' is interned.", strInterned);
}

int main() {
   // String str1 is known at compile time, and is automatically interned.
   String*  str1 = S"abcd";

   // Constructed string, str2, is not explicitly or automatically interned.
   String* str2 = (new StringBuilder())->Append(S"wx")->Append(S"yz")->ToString();
   Console::WriteLine();
   Test(1, str1);
   Test(2, str2);
}
/*
This example produces the following results:

1) The string 'abcd' is interned.
2) The string 'wxyz' is not interned.
*/

[JScript] No example is available for JScript. To view a Visual Basic, C#, or C++ example, click the Language Filter button Language Filter in the upper-left corner of the page.

Requirements

Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family, .NET Compact Framework, Common Language Infrastructure (CLI) Standard

See Also

String Class | String Members | System Namespace | Intern

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