Hash table using ASP.NET 2.0 and VB

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This example illustrates how to create and use a hash table. Each element of hash table is a key/value pair stored in a DictionaryEntry object. A key cannot be a null reference (Nothing in Visual Basic), but a value can be.

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This example illustrates how to create and use a hash table. Each element of hash table is a key/value pair stored in a DictionaryEntry object. A key cannot be a null reference (Nothing in Visual Basic), but a value can be.

First, you will need to import the using System.Collections and System.IO namespace.

Imports System.Collection
Imports System.IO

The System.Collections namespace contains interfaces and classes that define various collections of objects, such as lists, queues, bit arrays, hash tables and dictionaries.
The System.IO namespace contains types that allow reading and writing to files and data streams, and types that provide basic file and directory support.

The following example shows how to determine whether the Hashtable contains a specific element. We can search a hash table either by the keys, or by the associated values; But search by key will make an excellent search efficiency. We use the btnID_Click and btnName_click event to do the work. We then call the Hashtable.Contains Method to use the collection’s objects’ Equals and CompareTo methods on item to determine whether item exists. In the earlier versions of the .NET Framework, this determination was made by using the Equals and CompareTo methods of the item parameter on the objects in the collection.

Public Sub btnID_Click([source] As [Object], e As EventArgs)

output.Text = "<PRE>" + HashTableSample.FindEntry(empID.Text, Nothing) + "</PRE>"
btnClear.Visible = True

End Sub

Public Sub btnName_Click([source] As [Object], e As EventArgs)

output.Text = "<PRE>" + HashTableSample.FindEntry(0, empName.Text) + "</PRE>"
btnClear.Visible = True

End Sub

Sub ResetList()

HashTableSample.table.Clear()

HashTableSample.table.Add(5123, "Jay")
HashTableSample.table.Add(2569, "Brad")
HashTableSample.table.Add(1254, "Brian")
HashTableSample.table.Add(6839, "Seth")
HashTableSample.table.Add(3948, "Rajesh")
HashTableSample.table.Add(1930, "Lakshan")
HashTableSample.table.Add(9341, "Kristian")
HashTableSample.table.Add(7921, "Stephen")
HashTableSample.table.Add(2839, "Tom")
HashTableSample.table.Add(1829, "Kit")

MakeList()

End Sub

Public Sub MakeList()

lstNames.Items.Clear()
Dim o As [Object]
For Each o In HashTableSample.table.Keys

lstNames.Items.Add((o.ToString() + ": " + HashTableSample.table(o)))

Next o

End Sub

Class HashTableSample

Public Shared table As New Hashtable()

Public Shared Function FindEntry(inKey As [Object], value As [Object]) As String

Dim strWriter As New StringWriter()
Console.SetOut(strWriter)
Console.WriteLine()
If inKey Is Nothing OrElse inKey = "" Then

inKey = 0

End If
Dim key As Int32
Try

key = Int32.Parse(inKey.ToString)

Catch generatedExceptionVariable0 As Exception

key = 0

End Try
If Not (value Is Nothing) Then

If table.ContainsValue(value) Then

Console.WriteLine("Yes, Value '{0}' was found in the list!", value)

Else

Console.WriteLine("Sorry, Employee '{0}' could not be found.", value)

End If

Else

If table.Contains(key) Then

Console.WriteLine("Yes, ID '{0}' was found in the list!", key)

Else

Console.WriteLine("Sorry, Employee ID '{0}' could not be found.", key)

End If

End If

Console.WriteLine()
Console.WriteLine("Now we will print out the entire list of employees.")
Console.WriteLine("ID" + ControlChars.Tab + "Name")
Console.WriteLine("----" + ControlChars.Tab + "-----------")

Dim d As DictionaryEntry
For Each d In table

Console.WriteLine("{0}" + ControlChars.Tab + "{1}", d.Key, d.Value)

Next d
Return strWriter.ToString()

End Function

The front end HashtableDemoCsharp.aspx page looks something like this:

<table width=800 align="center">
<tr><td width=350><b>Find an existing Entry</b></td>
<td width=150></td>
<td width=150></td>

<td><b>Hashtable Entries</b></td>
<td style="width: 147px"><b>New Entry</b></td>
</tr>

<tr><td width=400>Enter a value (employee name) to find:</td>
<td align=right><asp:textbox width="60px" id="empName" runat="server"/></td>
<td width=200><asp:button width="80px" Text="Find Value" id="btnName" onclick="btnName_Click" runat="server"/>
</td>

<td rowspan=3><asp:ListBox id="lstNames" width="150px" rows="7" runat="server"/></td>

<td align=right style="width: 147px">Key:<asp:textbox width="100px" id="txtAddKey" runat="server"/></td>
</tr>

<tr><td>Enter a key (employee id) to find:</td>
<td align=right><asp:textbox width="60px" id="empID" runat="server"/></td>
<td><asp:button width="80px" Text="Find Key" id="btnID" onclick="btnID_Click" runat="server"/></td>
<td align=right style="width: 147px">Value:<asp:textbox width="100px" id="txtAddVal" runat="server"/></td>
</tr>

<tr><td></td>
<td></td>
<td></td>
<td align=right style="width: 147px">
<asp:button width="120px" Text="Add Entry" id="btnAdd" onclick="btnAdd_Click" runat="server"/>
</td>
</tr>

<tr><td></td>
<td></td>
<td></td>
<td>
<asp:button width="120px" Text="Reset List" id="btnReset" onclick="btnReset_Click" runat="server"/>
</td>
</tr>
</table>

The flow for the code behind page is as follows.

Imports System
Imports System.Data
Imports System.Configuration
Imports System.Web
Imports System.Web.Security
Imports System.Web.UI
Imports System.Web.UI.WebControls
Imports System.Web.UI.WebControls.WebParts
Imports System.Web.UI.HtmlControls
Imports System.Collections
Imports System.IO

Class _Default

Inherits System.Web.UI.Page

Protected Sub Page_Load(sender As Object, e As EventArgs)

If Not Page.IsPostBack Then

ResetList()

End If

End Sub 'Page_Load

Sub ResetList()

End Sub

Public Sub MakeList()

lstNames.Items.Clear()
Dim o As [Object]
For Each o In HashTableSample.table.Keys

lstNames.Items.Add((o.ToString() + ": " + HashTableSample.table(o)))

Next o

End Sub

Class HashTableSample

Public Shared table As New Hashtable()

Public Shared Function FindEntry(inKey As [Object], value As [Object]) As String

Dim strWriter As New StringWriter()
Console.SetOut(strWriter)
Console.WriteLine()

If inKey Is Nothing OrElse inKey = "" Then

inKey = 0

End If
Dim key As Int32
Try

key = Int32.Parse(inKey.ToString)

Catch generatedExceptionVariable0 As Exception

key = 0

End Try

If Not (value Is Nothing) Then

If table.ContainsValue(value) Then

Console.WriteLine("Yes, Value '{0}' was found in the list!", value)

Else

Console.WriteLine("Sorry, Employee '{0}' could not be found.", value)

End If

Else

If table.Contains(key) Then

Console.WriteLine("Yes, ID '{0}' was found in the list!", key)

Else

Console.WriteLine("Sorry, Employee ID '{0}' could not be found.", key)

End If

Console.WriteLine("{0}" + ControlChars.Tab + "{1}", d.Key, d.Value)

Next d
Return strWriter.ToString()

End Function

Public Shared Function AddEntry(key As String, value As String) As Boolean

Try

Dim i As Int32 = Convert.ToInt32(key)
table.Add(i, value)
Return True

Catch generatedExceptionVariable0 As Exception

Return False

End Try

End Function

End Class

Public Sub btnID_Click([source] As [Object], e As EventArgs)

output.Text = "<PRE>" + HashTableSample.FindEntry(empID.Text, Nothing) + "</PRE>"
btnClear.Visible = True

End Sub

Public Sub btnName_Click([source] As [Object], e As EventArgs)

output.Text = "<PRE>" + HashTableSample.FindEntry(0, empName.Text) + "</PRE>"
btnClear.Visible = True

End Sub

Public Sub btnClear_Click([source] As [Object], e As EventArgs)

output.Text = ""
empName.Text = ""
empID.Text = ""
btnClear.Visible = False

End Sub

Public Sub btnReset_Click([source] As [Object], e As EventArgs)

ResetList()

End Sub

Public Sub btnAdd_Click([source] As [Object], e As EventArgs)

If txtAddKey.Text = "" OrElse txtAddVal.Text = "" Then

output.Text = "ADD FAILED: Please ensure you enter both a key, and value entry"
btnClear.Visible = True

Else

If HashTableSample.AddEntry(txtAddKey.Text, txtAddVal.Text) Then

MakeList()
btnClear_Click(Nothing, Nothing)

Else

output.Text = "ADD FAILED: Please ensure the following:<br>" + "1) The key is a valid integer<br>" + "2) The key does not already exist in the list"
btnClear.Visible = True

End If

End Sub

End Class

Download the Full Working Version of this Project written with Visual Studio.NET VB.NET 2005 Here!

Looking for the C# 2005 Version? Click Here!

Looking for more ASP.NET Tutorials? Click Here!