Hashtable.Contains(Object) 方法

定义

确定 Hashtable 是否包含特定键。

public:
 virtual bool Contains(System::Object ^ key);
public virtual bool Contains (object key);
abstract member Contains : obj -> bool
override this.Contains : obj -> bool
Public Overridable Function Contains (key As Object) As Boolean

参数

key
Object

要在 Hashtable 中定位的键。

返回

Boolean

如果 true 包含具有指定键的元素,则为 Hashtable;否则为 false

实现

例外

keynull

示例

以下示例演示如何确定 Hashtable 是否包含特定元素。

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.

注解

Contains 可实现 IDictionary.Contains。 它的行为完全一样 ContainsKey

此方法是一个 O(1) 操作。

从 .NET Framework 2.0 开始,此方法使用集合的对象EqualsCompareTo方法item来确定项是否存在。 在早期版本的.NET Framework中,通过使用Equals集合中对象的参数和CompareTo方法item做出此决定。

适用于

另请参阅