Hashtable.ContainsKey(Object) 方法
定义
重要
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确定 Hashtable 是否包含特定键。
public:
virtual bool ContainsKey(System::Object ^ key);public virtual bool ContainsKey (object key);abstract member ContainsKey : obj -> bool
override this.ContainsKey : obj -> boolPublic Overridable Function ContainsKey (key As Object) As Boolean参数
返回
如果 true 包含具有指定键的元素，则为 Hashtable；否则为 false。
例外
key 为 null。
示例
下面的示例演示如何确定 是否 Hashtable 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
此方法的行为与 Contains完全相同。
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 Equals 和 CompareTo 方法item来确定项是否存在。 在早期版本的 .NET Framework中，此确定是通过对集合中的 对象使用 Equals 参数的 item 和 CompareTo 方法做出的。
