Hashtable.ContainsKey(Object) Método

Definição

Namespace:

System.Collections

Assembly:

System.Runtime.dll

Origem:

Hashtable.cs

Determina se a Hashtable contém uma chave específica.

public:
 virtual bool ContainsKey(System::Object ^ key);

public virtual bool ContainsKey (object key);

abstract member ContainsKey : obj -> bool
override this.ContainsKey : obj -> bool

Public Overridable Function ContainsKey (key As Object) As Boolean

Parâmetros

key

Object

A chave a ser localizada no Hashtable.

Retornos

Boolean

true se o Hashtable contiver um elemento com a chave especificada; caso contrário, false.

Exceções

ArgumentNullException

key é null.

Exemplos

O exemplo a seguir mostra como determinar se o Hashtable contém um elemento específico.

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.

 */

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

   public static void Main()
   {
      // Creates and initializes a new Hashtable.
      var 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.
      var 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[{i++}]:\t{de.Key}\t{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.

*/

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 ""{myKey}"" is ")
        If (myHT.ContainsKey(myKey))
           Console.WriteLine("in the Hashtable.")
        Else
           Console.WriteLine("NOT in the Hashtable.")
        End If

        myKey = 6
        Console.Write($"The key ""{myKey}"" is ")
        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 ""{myValue}"" is ")
        If (myHT.ContainsValue(myValue))
           Console.WriteLine(" in the Hashtable.")
        Else
           Console.WriteLine(" NOT in the Hashtable.")
        End If

    End Sub

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

End Class


' 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.

Comentários

Esse método se comporta exatamente como Contains.

Esse método é uma O(1) operação.

A partir do .NET Framework 2.0, esse método usa os métodos e CompareTo objetos Equals da coleção em item para determinar se o item existe. Em versões anteriores do .NET Framework, essa decisão era tomada usando-se os métodos Equals e CompareTo do parâmetro item nos objetos na coleção.

Confira também

• Contains(Object)
• ContainsValue(Object)