String.IsInterned Method

Parameters

• str
  Type: System.String
  The string to search for in the intern pool.

Return Value

Type: System.String
A reference to str if it is in the common language runtime intern pool; otherwise, nulla null reference (Nothing in Visual Basic).

Module Example
   Public Sub Demo(outputBlock As System.Windows.Controls.TextBlock)
      Dim str1 As String = "a"
      Dim str2 As String = str1 + "b"
      Dim str3 As String = str2 + "c"
      Dim strings() As String = { "value", "part1" + "_" + "part2", str3, 
                                  String.Empty, Nothing }
      For Each value In strings
         If value Is Nothing Then Continue For

         Dim interned As Boolean = (String.IsInterned(value) IsNot Nothing)
         If interned Then
            outputBlock.Text += String.Format("'{0}' is in the string intern pool.", 
                                              value) + vbCrLf
         Else
            outputBlock.Text += String.Format("'{0}' is not in the string intern pool.",
                                              value) + vbCrLf                      
         End If
      Next
   End Sub
End Module
' The example displays the following output:
'       'value' is in the string intern pool.
'       'part1_part2' is in the string intern pool.
'       'abc' is not in the string intern pool.
'       '' is in the string intern pool.

using System;

public class Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      string str1 = "a";
      string str2 = str1 + "b";
      string str3 = str2 + "c";
      string[] strings = { "value", "part1" + "_" + "part2", str3, 
                           String.Empty, null };
      foreach (var value in strings) {
         if (value == null) continue;

         bool interned = String.IsInterned(value) != null;
         if (interned)
            outputBlock.Text += String.Format("'{0}' is in the string intern pool.\n", 
                                              value);
         else
            outputBlock.Text += String.Format("'{0}' is not in the string intern pool.\n",
                                              value);                      
      }
   }
}
// The example displays the following output:
//       'value' is in the string intern pool.
//       'part1_part2' is in the string intern pool.
//       'abc' is not in the string intern pool.
//       '' is in the string intern pool.

' Sample for String.IsInterned(String)
Imports System.Text
Imports System.Runtime.CompilerServices

' In the .NET Framework 2.0 the following attribute declaration allows you to 
' avoid the use of the interning when you use NGEN.exe to compile an assembly 
' to the native image cache.
<Assembly: CompilationRelaxations(CompilationRelaxations.NoStringInterning)> 
Class Example
   Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
      ' 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()
      outputBlock.Text &= vbCrLf
      Test(outputBlock, 1, str1)
      Test(outputBlock, 2, str2)
   End Sub 'Main

   Public Shared Sub Test(ByVal outputBlock As System.Windows.Controls.TextBlock, ByVal sequence As Integer, ByVal str As [String])
      outputBlock.Text += String.Format("{0}) The string, '", sequence)
      Dim strInterned As [String] = [String].IsInterned(str)
      If strInterned Is Nothing Then
         outputBlock.Text += String.Format("{0}', is not interned.", str) & vbCrLf
      Else
         outputBlock.Text += String.Format("{0}', is interned.", strInterned) & vbCrLf
      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.

'If you use NGEN.exe to compile the assembly to the native image cache, this
'example produces the following results:

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

// Sample for String.IsInterned(String)
using System;
using System.Text;
using System.Runtime.CompilerServices;

// In the .NET Framework 2.0 the following attribute declaration allows you to 
// avoid the use of the interning when you use NGEN.exe to compile an assembly 
// to the native image cache.
[assembly: CompilationRelaxations(CompilationRelaxations.NoStringInterning)]
class Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      // 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();
      outputBlock.Text += "\n";
      Test(outputBlock, 1, str1);
      Test(outputBlock, 2, str2);
   }

   public static void Test(System.Windows.Controls.TextBlock outputBlock, int sequence, String str)
   {
      outputBlock.Text += String.Format("{0}) The string, '", sequence);
      String strInterned = String.IsInterned(str);
      if (strInterned == null)
         outputBlock.Text += String.Format("{0}', is not interned.", str) + "\n";
      else
         outputBlock.Text += String.Format("{0}', is interned.", strInterned) + "\n";
   }
}

//This example produces the following results:

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

//If you use NGEN.exe to compile the assembly to the native image cache, this
//example produces the following results:

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