Hashtable.Contains Method (System.Collections)

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Microsoft Visual Studio 2008/.NET Framework 3.5

Other versions are also available for the following:

.NET Framework Class Library

Hashtable..::.Contains Method

Determines whether the Hashtable contains a specific key.

Namespace: System.Collections
Assembly: mscorlib (in mscorlib.dll)

Syntax

Visual Basic (Declaration)

Public Overridable Function Contains ( _
    key As Object _
) As Boolean

Visual Basic (Usage)

Dim instance As Hashtable
Dim key As Object
Dim returnValue As Boolean

returnValue = instance.Contains(key)

public virtual bool Contains(
    Object key
)

Visual C++

public:
virtual bool Contains(
    Object^ key
)

JScript

public function Contains(
    key : Object
) : boolean

Parameters

key: Type: System..::.Object
The key to locate in the Hashtable.

Return Value

Type: System..::.Boolean
true if the Hashtable contains an element with the specified key; otherwise, false.

Implements

IDictionary..::.Contains(Object)

Exceptions

Exception	Condition
ArgumentNullException	key is nullNothingnullptra null reference (Nothing in Visual Basic).

Remarks

Contains implements IDictionary..::.Contains. It behaves exactly as ContainsKey.

This method is an O(1) operation.

Starting with the .NET Framework 2.0, this method uses the collection’s objects’ Equals and CompareTo methods on item to determine whether item exists. In the earlier versions of the .NET Framework, this determination was made by using the Equals and CompareTo methods of the item parameter on the objects in the collection.

Examples

The following example shows how to determine whether the Hashtable contains a specific element.

Visual Basic

Imports System
Imports System.Collections

Public Class SamplesHashtable

    Public Shared Sub Main()

        ' Creates and initializes a new Hashtable.
        Dim myHT As New Hashtable()
        myHT.Add(0, "zero")
        myHT.Add(1, "one")
        myHT.Add(2, "two")
        myHT.Add(3, "three")
        myHT.Add(4, "four")

        ' Displays the values of the Hashtable.
        Console.WriteLine("The Hashtable contains the following values:")
        PrintIndexAndKeysAndValues(myHT)

        ' Searches for a specific key.
        Dim myKey As Integer = 2
        Console.Write("The key ""{0}"" is ", myKey)
        If(myHT.ContainsKey(myKey))
           Console.WriteLine("in the Hashtable.")
        Else
           Console.WriteLine("NOT in the Hashtable.")
        End If

        myKey = 6
        Console.Write("The key ""{0}"" is ", myKey)
        If(myHT.ContainsKey(myKey))
           Console.WriteLine(" in the Hashtable.")
        Else
           Console.WriteLine(" NOT in the Hashtable.")
        End If

        ' Searches for a specific value.
        Dim myValue As String = "three"
        Console.Write("The value ""{0}"" is ", myValue)
        If(myHT.ContainsValue(myValue))
           Console.WriteLine(" in the Hashtable.")
        Else
           Console.WriteLine(" NOT in the Hashtable.")
        End If

        myValue = "nine"
        Console.Write("The value ""{0}"" is ", myValue)
        If(myHT.ContainsValue(myValue))
           Console.WriteLine(" in the Hashtable.")
        Else
           Console.WriteLine(" NOT in the Hashtable.")
        End If

    End Sub 'Main

    Public Shared Sub PrintIndexAndKeysAndValues(myHT As Hashtable)
        Dim i As Integer = 0
        Console.WriteLine(vbTab + "-INDEX-" + vbTab + "-KEY-" + vbTab + "-VALUE-")
        Dim de As DictionaryEntry
        For Each de In  myHT
            Console.WriteLine(vbTab + "[{0}]:" + vbTab + "{1}" + vbTab + "{2}", i, de.Key, de.Value)
            i = i + 1
        Next de
        Console.WriteLine()
    End Sub 'PrintIndexAndKeysAndValues

End Class 'SamplesHashtable 


' This code produces the following output.
' 
' The Hashtable contains the following values:
'         -INDEX- -KEY-   -VALUE-
'         [0]:    4       four
'         [1]:    3       three
'         [2]:    2       two
'         [3]:    1       one
'         [4]:    0       zero
'
' The key "2" is in the Hashtable.
' The key "6" is NOT in the Hashtable.
' The value "three" is in the Hashtable.
' The value "nine" is NOT in the Hashtable.

using System;
using System.Collections;
public class SamplesHashtable  {

   public static void Main()  {

      // Creates and initializes a new Hashtable.
      Hashtable myHT = new Hashtable();
      myHT.Add( 0, "zero" );
      myHT.Add( 1, "one" );
      myHT.Add( 2, "two" );
      myHT.Add( 3, "three" );
      myHT.Add( 4, "four" );

      // Displays the values of the Hashtable.
      Console.WriteLine( "The Hashtable contains the following values:" );
      PrintIndexAndKeysAndValues( myHT );

      // Searches for a specific key.
      int myKey = 2;
      Console.WriteLine( "The key \"{0}\" is {1}.", myKey, myHT.ContainsKey( myKey ) ? "in the Hashtable" : "NOT in the Hashtable" );
      myKey = 6;
      Console.WriteLine( "The key \"{0}\" is {1}.", myKey, myHT.ContainsKey( myKey ) ? "in the Hashtable" : "NOT in the Hashtable" );

      // Searches for a specific value.
      String myValue = "three";
      Console.WriteLine( "The value \"{0}\" is {1}.", myValue, myHT.ContainsValue( myValue ) ? "in the Hashtable" : "NOT in the Hashtable" );
      myValue = "nine";
      Console.WriteLine( "The value \"{0}\" is {1}.", myValue, myHT.ContainsValue( myValue ) ? "in the Hashtable" : "NOT in the Hashtable" );
   }


   public static void PrintIndexAndKeysAndValues( Hashtable myHT )  {
      int i = 0;
      Console.WriteLine( "\t-INDEX-\t-KEY-\t-VALUE-" );
      foreach ( DictionaryEntry de in myHT )
         Console.WriteLine( "\t[{0}]:\t{1}\t{2}", i++, de.Key, de.Value );
      Console.WriteLine();
   }

}


/* 
This code produces the following output.

The Hashtable contains the following values:
        -INDEX- -KEY-   -VALUE-
        [0]:    4       four
        [1]:    3       three
        [2]:    2       two
        [3]:    1       one
        [4]:    0       zero

The key "2" is in the Hashtable.
The key "6" is NOT in the Hashtable.
The value "three" is in the Hashtable.
The value "nine" is NOT in the Hashtable.

*/

Visual C++

using namespace System;
using namespace System::Collections;
void PrintIndexAndKeysAndValues( Hashtable^ myHT );
int main()
{

   // Creates and initializes a new Hashtable.
   Hashtable^ myHT = gcnew Hashtable;
   myHT->Add( (int^)0, "zero" );
   myHT->Add( 1, "one" );
   myHT->Add( 2, "two" );
   myHT->Add( 3, "three" );
   myHT->Add( 4, "four" );

   // Displays the values of the Hashtable.
   Console::WriteLine( "The Hashtable contains the following values:" );
   PrintIndexAndKeysAndValues( myHT );

   // Searches for a specific key.
   int myKey = 2;
   Console::WriteLine( "The key \"{0}\" is {1}.", myKey, myHT->ContainsKey( myKey ) ? (String^)"in the Hashtable" : "NOT in the Hashtable" );
   myKey = 6;
   Console::WriteLine( "The key \"{0}\" is {1}.", myKey, myHT->ContainsKey( myKey ) ? (String^)"in the Hashtable" : "NOT in the Hashtable" );

   // Searches for a specific value.
   String^ myValue = "three";
   Console::WriteLine( "The value \"{0}\" is {1}.", myValue, myHT->ContainsValue( myValue ) ? (String^)"in the Hashtable" : "NOT in the Hashtable" );
   myValue = "nine";
   Console::WriteLine( "The value \"{0}\" is {1}.", myValue, myHT->ContainsValue( myValue ) ? (String^)"in the Hashtable" : "NOT in the Hashtable" );
}

void PrintIndexAndKeysAndValues( Hashtable^ myHT )
{
   int i = 0;
   Console::WriteLine( "\t-INDEX-\t-KEY-\t-VALUE-" );
   IEnumerator^ myEnum = myHT->GetEnumerator();
   while ( myEnum->MoveNext() )
   {
      DictionaryEntry de =  *safe_cast<DictionaryEntry ^>(myEnum->Current);
      Console::WriteLine( "\t[{0}]:\t{1}\t{2}", i++, de.Key, de.Value );
   }

   Console::WriteLine();
}

/* 
 This code produces the following output.

 The Hashtable contains the following values:
         -INDEX- -KEY-   -VALUE-
         [0]:    4       four
         [1]:    3       three
         [2]:    2       two
         [3]:    1       one
         [4]:    0       zero

 The key "2" is in the Hashtable.
 The key "6" is NOT in the Hashtable.
 The value "three" is in the Hashtable.
 The value "nine" is NOT in the Hashtable.

 */

JScript

import System
import System.Collections
import Microsoft.VisualBasic

// Creates and initializes a new Hashtable.
var myHT : Hashtable = new Hashtable()
myHT.Add(0, "zero")
myHT.Add(1, "one")
myHT.Add(2, "two")
myHT.Add(3, "three")
myHT.Add(4, "four")

// Displays the values of the Hashtable.
Console.WriteLine("The Hashtable contains the following values:")
PrintIndexAndKeysAndValues(myHT)

// Searches for a specific key.
var msg : String
var myKey : int = 2
if(myHT.ContainsKey(myKey))
    msg = "in the Hashtable"
else
    msg = "NOT in the Hashtable"
Console.WriteLine("The key \"{0}\" is {1}.", myKey, msg)
myKey = 6
if(myHT.ContainsKey(myKey))
    msg = "in the Hashtable"
else
    msg = "NOT in the Hashtable"
Console.WriteLine("The key \"{0}\" is {1}.", myKey, msg)

// Searches for a specific value.
var myValue : String = "three"
if(myHT.ContainsValue(myValue))
    msg = "in the Hashtable"
else
    msg = "NOT in the Hashtable"
Console.WriteLine("The value \"{0}\" is {1}.", myValue, msg)
myValue = "nine"
if(myHT.ContainsValue(myValue))
    msg = "in the Hashtable"
else
    msg = "NOT in the Hashtable"
Console.WriteLine("The value \"{0}\" is {1}.", myValue, msg)

function PrintIndexAndKeysAndValues(myList : Hashtable){
    var myEnumerator : IDictionaryEnumerator = myList.GetEnumerator()
    var i : int = 0
    Console.WriteLine("\t-INDEX-\t-KEY-\t-VALUE-")
    while(myEnumerator.MoveNext()){
        Console.WriteLine("\t[{0}]:\t{1}\t{2}", i++, myEnumerator.Key,
            myEnumerator.Value)
    }
    Console.WriteLine()
}

// This code produces the following output.
// 
// The Hashtable contains the following values:
//     -INDEX-    -KEY-    -VALUE-
//     [0]:       4        four
//     [1]:       3        three
//     [2]:       2        two
//     [3]:       1        one
//     [4]:       0        zero
// 
// The key "2" is in the Hashtable.
// The key "6" is NOT in the Hashtable.
// The value "three" is in the Hashtable.
// The value "nine" is NOT in the Hashtable.

Platforms

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Version Information

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0, 1.0

XNA Framework

Supported in: 3.0, 2.0, 1.0

Reference

Hashtable Class

Hashtable Members

System.Collections Namespace

ContainsKey

IDictionary