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Hashtable.Add Method

Adds an element with the specified key and value into the Hashtable.

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

public virtual void Add (
	Object key,
	Object value
)
public void Add (
	Object key, 
	Object value
)
public function Add (
	key : Object, 
	value : Object
)
Not applicable.

Parameters

key

The key of the element to add.

value

The value of the element to add. The value can be a null reference (Nothing in Visual Basic).

Exception typeCondition

ArgumentNullException

key is a null reference (Nothing in Visual Basic).

ArgumentException

An element with the same key already exists in the Hashtable.

NotSupportedException

The Hashtable is read-only.

-or-

The Hashtable has a fixed size.

A key cannot be a null reference (Nothing in Visual Basic), 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.

The following example shows how to add elements to 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( "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{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
*/ 

import System.*;
import System.Collections.*;

public class SamplesHashtable
{
    public static void main(String[] args)
    {
        // Creates and initializes a new Hashtable.
        Hashtable 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);
    } //main

    public static void PrintKeysAndValues(Hashtable myHT)
    {
        Console.WriteLine("\t-KEY-\t-VALUE-");
        IEnumerator myEnumerator = myHT.GetEnumerator();

		while (myEnumerator.MoveNext()) {
			DictionaryEntry de = (DictionaryEntry)myEnumerator.get_Current();
            Console.WriteLine("\t{0}:\t{1}", de.get_Key(), de.get_Value());
        }
        Console.WriteLine();
    } //PrintKeysAndValues
} //SamplesHashtable

/* 
 This code produces the following output.
 
 The Hashtable contains the following:
         -KEY-   -VALUE-
         two:    quick
         three:  brown
         four:   fox
         one:    The
 */

import System
import System.Collections

// Creates and initializes a new Hashtable.
var myHT : Hashtable = 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)
    
function PrintKeysAndValues(myList : Hashtable){
    var myEnumerator : IDictionaryEnumerator = myList.GetEnumerator()
    Console.WriteLine("\t-KEY-\t-VALUE-")
    while(myEnumerator.MoveNext())
        Console.WriteLine("\t{0}:\t{1}", myEnumerator.Key, myEnumerator.Value)
    Console.WriteLine()
}

// This code produces the following output.
// 
// The Hashtable contains the following:
//     -KEY-    -VALUE-
//     three:   brown
//     four:    fox
//     two:     quick
//     one:     The 

Windows 98, Windows Server 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0, 1.0

XNA Framework

Supported in: 1.0

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