Adds an element with the specified key and value into the Hashtable.
public: virtual void Add(System::Object ^ key, System::Object ^ value);public virtual void Add (object key, object value);public virtual void Add (object key, object? value);abstract member Add : obj * obj -> unitoverride this.Add : obj * obj -> unitPublic Overridable Sub Add (key As Object, value As Object)Parameters
- key
- Object
The key of the element to add.
- value
- Object
The value of the element to add. The value can be null.
Implements
Exceptions
key is null.
An element with the same key already exists in the Hashtable.
Examples
The following example shows how to add elements to the Hashtable.
using namespace System;using namespace System::Collections;void PrintKeysAndValues( Hashtable^ myHT );int main(){ // Creates and initializes a new Hashtable. Hashtable^ myHT = gcnew Hashtable; myHT->Add( "one", "The" ); myHT->Add( "two", "quick" ); myHT->Add( "three", "brown" ); myHT->Add( "four", "fox" ); // Displays the Hashtable. Console::WriteLine( "The Hashtable contains the following:" ); PrintKeysAndValues( myHT );}void PrintKeysAndValues( Hashtable^ myHT ){ Console::WriteLine( "\t-KEY-\t-VALUE-" ); IEnumerator^ myEnum = myHT->GetEnumerator(); while ( myEnum->MoveNext() ) { DictionaryEntry de = *safe_cast<DictionaryEntry ^>(myEnum->Current); Console::WriteLine( "\t{0}:\t{1}", de.Key, de.Value ); } Console::WriteLine();}/* This code produces the following output. The Hashtable contains the following: -KEY- -VALUE- two: quick three: brown four: fox one: The */using System;using System.Collections;public class SamplesHashtable{ public static void Main() { // Creates and initializes a new Hashtable. var myHT = new Hashtable(); myHT.Add("one", "The"); myHT.Add("two", "quick"); myHT.Add("three", "brown"); myHT.Add("four", "fox"); // Displays the Hashtable. Console.WriteLine("The Hashtable contains the following:"); PrintKeysAndValues(myHT); } public static void PrintKeysAndValues( Hashtable myHT ) { Console.WriteLine("\t-KEY-\t-VALUE-"); foreach (DictionaryEntry de in myHT) Console.WriteLine($"\t{de.Key}:\t{de.Value}"); Console.WriteLine(); }}/*This code produces the following output.The Hashtable contains the following: -KEY- -VALUE- two: quick three: brown four: fox one: The*/Imports System.CollectionsPublic Class SamplesHashtable Public Shared Sub Main() ' Creates and initializes a new Hashtable. Dim myHT As New Hashtable() myHT.Add("one", "The") myHT.Add("two", "quick") myHT.Add("three", "brown") myHT.Add("four", "fox") ' Displays the Hashtable. Console.WriteLine("The Hashtable contains the following:") PrintKeysAndValues(myHT) End Sub Public Shared Sub PrintKeysAndValues(myHT As Hashtable) Console.WriteLine(vbTab + "-KEY-" + vbTab + "-VALUE-") For Each de As DictionaryEntry In myHT Console.WriteLine(vbTab + "{0}:" + vbTab + "{1}", de.Key, de.Value) Next Console.WriteLine() End SubEnd Class' This code produces the following output.' ' The Hashtable contains the following:' -KEY- -VALUE-' two: quick' one: The' three: brown' four: fox'Remarks
A key cannot be null, but a value can be.
An object that has no correlation between its state and its hash code value should typically not be used as the key. For example, String objects are better than StringBuilder objects for use as keys.
You can also use the Item[] property to add new elements by setting the value of a key that does not exist in the Hashtable; for example, myCollection["myNonexistentKey"] = myValue. However, if the specified key already exists in the Hashtable, setting the Item[] property overwrites the old value. In contrast, the Add method does not modify existing elements.
If Count is less than the capacity of the Hashtable, this method is an O(1) operation. If the capacity needs to be increased to accommodate the new element, this method becomes an O(n) operation, where n is Count.
