Review Answers




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Review Answers



Module 1: Overview of the Microsoft .NET Platform
Module 2: Development Environment Features
Module 3: Language and Syntax Enhancements
Module 4: Object-Oriented Design for Visual Basic .NET
Module 5: Object-Oriented Programming in Visual Basic .NET
Module 6: Using Windows Forms
Module 7: Building Web Applications
Module 8: Using ADO.NET
Module 9: Developing Components in Visual Basic .NET
Module 10: Deploying Applications
Module 11: Upgrading to Visual Basic .NET










Module 1: Overview of the Microsoft .NET Platform

Review
What is the .NET Platform?


Answer
The .NET Platform is a set of technologies designed to transform the Internet into a full-scale distributed computing platform. It provides new ways to build applications from collections of Web Services. The .NET Platform fully supports the existing Internet infrastructure (HTTP, XML, SOAP).





What are the core technologies in the .NET Platform?


Answer
.NET Framework, .NET Enterprise Servers, .NET Building Block services, Visual Studio .NET, and Windows.





List the components of the .NET Framework.


Answer
Common language runtime, .NET Framework Class Library, data and XML, Web Services and Forms, and Windows Forms.





What is the purpose of common language runtime?


Answer
It provides an environment in which you can execute code.






What is the purpose of common language specification?


Answer
It defines a set of features that all .NET-compatible languages should support.





What is a Web Service?


Answer
A Web Service is a programmable Web component that can be shared between applications on the Internet or an intranet.





What is a managed environment?


Answer
A managed environment is one in which the environment provides services, such as garbage collection, security, and other similar features.














Module 2: Development Environment Features

Review
List the file extensions for the following Visual Basic .NET files:
Visual Basic .NET project files, classes, and modules.


Answer
.vbproj, .vb, and .vb





Describe the purpose of namespaces and the Imports keyword.


Answer
Namespaces organize the objects and items found in an assembly and prevent ambiguity when calling an object.
The Imports keyword allows you to access an object from within a namespace without using the object's fully qualified name.





Describe the purpose of Server Explorer.


Answer
Server Explorer allows you to view and manipulate databases and various server items, such as message queues, event logs, Windows services, and XML Web Services. You can also use Server Explorer to access these items from within your code.






The Object Browser is exactly the same as in previous versions of Visual Basic. True or false? If false, explain why.


Answer
False. The Object Browser has been enhanced to include inheritance and interfaces in the object hierarchy.





Describe the purpose of a conditional breakpoint and how to create one.


Answer
Conditional breakpoints halt execution when a particular condition is met, such as when a variable equals a certain value.
To set a conditional breakpoint, you add a standard breakpoint, and then use the Breakpoint Properties dialog box to modify the conditions.














Module 3: Language and Syntax Enhancements

Review
Declare and initialize an array that contains the following strings: "one", "two", "three", "four".


Answer
Dim myArray( ) As String = {"one", "two", "three", "four"}





What types of variables are created by the following declaration if Option Strict is off?
Dim a, b As Integer, c



Answer
The variables a and b are created as Integers; c is created as an Object.





What is the value of c after the following code executes:
Dim c As Integer
c = 1
CheckValue(c)
...
Sub CheckValue(ByVal iValue As Integer)
...
iValue = 13
End Sub



Answer
The variable c remains equal to 1 because the default passing mechanism is by value.





Assuming you have an open Recordset called rs and a TextBox control called txtData, which of the following statements will create a compiler or run-time error with Option Strict off? Why?
txtData.Text = rs(0)
txtData.Text = rs.Fields.Item(0)
txtData.Text = rs.Fields(0).Value



Answer
Statement (a) will fail because rs(0) returns a Field object; the Fields collection is the default property of the Recordset object. This cannot be assigned to the Text property of the txtData TextBox because the data types are not compatible.
Statement (b) will fail because Value is the default property of the Field object, and it does not take a parameter. This causes the compiler to attempt to assign the Field object to the txtData.Text property, resulting in an error.
Statement (c) will succeed because Item is the default property of the Fields object, and it does take a parameter.





What is the method or property of the System.Exception class that retrieves the most information about an exception?


Answer
The ToString method provides the fully qualified class name, and the error message (if available), the name of the inner exception, and the stack trace of the exception.














Module 4: Object-Oriented Design for Visual Basic .NET

Review
An actor must be a person that interacts with the system. True or false?


Answer
False. An actor can also be another system or a part of a system.





Define the object-oriented term encapsulation.


Answer
Encapsulation is the hiding of the details about how an object performs various operations.





Define the object-oriented term inheritance.


Answer
Inheritance is the reuse of the methods and attributes of a general class in more specialized classes.






Describe freeform modeling.


Answer
Freeform modeling is the ability to use UML and non-UML shapes in a Visio diagram.





In the following use case description, what are the likely classes and attributes?
A user requests a listing of grades from a school based on a particular student ID. The ID is validated by the database, and an error message appears if the student ID does not exist. If the ID matches a student, the student's name, address, and date of birth are retrieved, in addition to the grades. The user is prompted to verify the information, and the grades are displayed if the verification succeeds. An error message is displayed if the user is unable to verify the information. Three verification attempts are allowed before the user is automatically logged off. The user is automatically logged off after five minutes of inactivity.


Answer

Class
Attributes
User
<Unknown at this stage>
Student
StudentID
 
Name
 
Address
 
Date of Birth
 
Grades
Grades
ID













Module 5: Object-Oriented Programming in Visual Basic .NET

Review
Create code that defines multiple constructors for a Person class. The first constructor will not take any arguments. The second will take two string values: FirstName and LastName.


Answer
Class Person
Sub New( )
'Default constructor
End Sub
Sub New(ByVal FirstName As String, _
ByVal LastName As String)
'Second constructor
End Sub
End Class





Garbage collection occurs immediately after all references to an object are removed. True or false? If false, explain why.


Answer
False. Garbage collection may happen at any time after all object references have been removed.






Describe the functionality of the MyBase keyword.


Answer
MyBase is used in a derived class to access methods and properties in the immediate base class.





What is a potential problem that may result from the following class code sample? How can you rewrite the code to resolve the problem?
Class Person
Private Sub Save( )
'Save the local data in a database
End Sub

Sub Dispose( )
Save( )
End Sub

Protected Overrides Sub Finalize( )
Dispose( )
MyBase.Finalize( )
End Sub
End Class



Answer
The Dispose method can be called directly from a client and might be called again when the object is destroyed by garbage collection. This would result in the Save method being called twice, which may create data inconsistencies.
To avoid this, use the SuppressFinalize method of the GC class to stop the Finalize method being called after Dispose. Add the line "GC.SuppressFinalize()" in the Dispose method after the Save line as follows):
Sub Dispose()
Save()
GC.SuppressFinalize()
End Sub






You can create an interface explicitly in Visual Basic .NET. True or false? If false, explain why.


Answer
True. You can create an interface explicitly by using the Interface...End Interface statement block.





Will the following code compile correctly? If not, why?
Class Person
Event NameChanged( )
Private strName As String

Sub ChangeName(ByVal strNewName As String)
strName = strNewName
RaiseEvent NameChanged( )
End Sub
End Class

Module TestCode
Sub Main( )
Dim x As New Person( )
AddHandler x.NameChanged, AddressOf HandleIt
x.ChangeName("Jeff")
End Sub

Sub HandleIt(ByVal strValue As String)
MsgBox(strValue)
End Sub
End Module



Answer
The code will not compile correctly because the signature of the event does not match the signature of the delegate in the AddHandler statement.














Module 6: Using Windows Forms

Review
Identify some of the benefits of Windows Forms.


Answer
Rich set of controls, GDI+ support, advanced layout possibilities, accessibility support, advanced printing support, visual inheritance, extensibility.





The ContainerControl class is the fundamental base class for all other controls. True or false?


Answer
False. The Control class is the fundamental base class for all other controls.





Write the code to access the path from which an executable is running.


Answer
Dim strAppPath as String
strAppPath = Application.StartupPath





Describe an owned form.


Answer
An owned form is always displayed on top of its owner. It is minimized or closed when the owner is minimized or closed.






Write code to make the code behind a button called btnOK execute when a user presses RETURN.


Answer
Me.AcceptButton = btnOK





List two ways to provide Help to the user.


Answer
ErrorProvider, HelpProvider, or ToolTip controls.





Write code to create a Help menu with one menu item-About- at run time.


Answer
Dim mnuMain As New MainMenu( )
Dim mnuItem1 As New MenuItem( )
Dim mnuItem2 As New MenuItem( )

mnuItem1.Text = "Help"
mnuMain.MenuItems.Add(mnuItem1)

mnuItem2.Text = "About"
mnuMain.MenuItems(0).MenuItems.Add(mnuItem2)
AddHandler mnuItem2.Click, AddressOf AboutClick

Menu = mnuMain














Module 7: Building Web Applications

Review
Describe some of the features of ASP.NET.


Answer
Compiled code, multiple browser clients, session state that supports Web farms, and easy deployment.





Explain why updates to an ASP.NET application do not require you to restart IIS.


Answer
No items are locked by IIS, so updating does not require you to restart IIS.





Create a line of code that uses the Response object to retrieve a userCountersession variable and display it to the user.


Answer
Response.Write("Value: " & Session("userCounter").ToString)





Convert the following HTML control tag into a server-side control.
<input type=text id=mytext value="hello">



Answer
<input type=text id=mytext value="hello" runat=server>






What attribute do you add to class methods when creating a Web Service?


Answer
WebMethod.





Visual Basic .NET allows early binding to a Web Service. True or false?


Answer
True. Setting a Web reference to a discovery document allows Visual Basic .NET to create a proxy class that allows early binding in the client application.














Module 8: Using ADO.NET

Review
State three benefits that ADO.NET has over earlier data access technologies.


Answer
It is part of the .NET Framework, it is designed for disconnected data, and it is integrated with XML.





You have the following code in your application. What would you do to make the code more efficient? Why?
Dim sqlConn As New SqlClient.SqlConnection("Integrated Security=True;Data Source=LocalHost;Initial Catalog=Pubs;")
sqlConn.Open( )
Dim sqlAdapt As New SqlClient.SqlDataAdapter("Select au_lname from authors", sqlConn)
Dim sqlDataSet As New DataSet( )
sqlAdapt.Fill(sqlDataSet, "Authors")
Dim i As Integer
For i = 0 To sqlDataSet.Tables("Authors").Rows.Count - 1
MessageBox.Show(sqlDataSet.Tables("Authors").Rows(i).Item(0).ToString)
Next



Answer
You should replace the DataSet with a DataReader because a DataReader is more efficient for read-only, forward-only data access. This is because a DataReader only holds one record in memory at a time.






If you change the contents of a DataTable in a DataSet, will those changes be reflected in the underlying data source? Why, or why not?


Answer
The changes will only be reflected if you explicitly call the Update method of the DataAdapter. If you do not do this, the changes are made locally in the DataSet, which has no permanent connection to the source.





You have the following code in the Page_Load event of a Web Form, but the DataGrid does not appear. What is wrong, assuming all objects are correctly declared and instantiated?
sqlReader = sqlComm.ExecuteReader
DataGrid1.DataSource( ) = sqlReader



Answer
You have neglected to call the DataBind method of the DataGrid, as shown in the following line of code:
DataGrid1.DataBind( )





Write the code to load an XML document called Books.xml into a DataSet.


Answer
Dim ds As New DataSet( )
ds.ReadXml("books.xml")














Module 9: Developing Components in Visual Basic .NET

Review
An unmanaged client application uses a class created in Visual Basic .NET but cannot access any methods of the class. What is the likely cause of this problem, and how would you fix it?


Answer
The class may have public methods defined without using an interface or any class-level attributes. To solve this problem, create and implement methods in interfaces rather than classes, use the ClassInterface attribute, or use the COMClass attribute.






Modify the following code to use auto completion of transactions rather than the explicit SetAbort and SetComplete methods.
<Transaction(TransactionOption.Required)> _
Public Class TestClass
Public Sub MySub( )
Try
'Perform action
ContextUtil.SetComplete( )
Catch ex As Exception
ContextUtil.SetAbort( )
Throw ex
End Try
End Sub
End Class



Answer
<Transaction(TransactionOption.Required)> _
Public Class TestClass
<AutoComplete( )> Public Sub MySub( )
'Perform action
End Sub
End Class





Create assembly attributes so Component Services can automatically create an application named "TestComponents" that runs as server activation.


Answer
<Assembly: ApplicationName("TestComponents")>
<Assembly: ApplicationActivation(ActivationOption.Server )>





Why would you use the IComponent interface?


Answer
The interface enables component classes to site other components and enables the component class to be sited on other components.






The following code causes a compilation error. Explain what is causing the error and how it could be fixed.
Sub Main( )
Dim t As New Thread(AddressOf MySub)
t.Start(10)
End Sub

Sub MySub(ByVal x As Integer)
...
End Sub



Answer
The MySub procedure cannot be called directly because it expects an argument and the Start method of a Thread cannot accept parameters. To fix this error, you could create the following code:
Sub Main( )
Dim obj As New ThreadObj( )
Dim t As New Thread(AddressOf obj.MySub)
obj.x = 10
t.Start( )
End Sub

Class ThreadObj
Public x As Integer
Sub MySub( )
...
End Sub
End Class













Module 10: Deploying Applications

Review
Name the four ways of distributing a Visual Studio .NET project and describe what each is used for.


Answer
XCOPY deployment - for simple stand-alone applications
Copy Project deployment-for copying a Web project directly to the Web server
Windows Installer-for deploying Windows-based and Web-based applications
Merge Module-for packaging reusable, shared components





How do you create a strong-named assembly?


Answer
Use sn.exe to create a public-private key pair and apply it to the assembly by adding the AssemblyKeyFile attribute to the AssemblyInfo.vb file.





Describe the use of the Launch Conditions Editor.


Answer
The Launch Conditions Editor allows you to define certain conditions under which the installation of an application fails, for example, the absence of a required database on a server.














Module 11: Upgrading to Visual Basic .NET

Review
List two benefits of upgrading an application and how those benefits are gained.


Answer
Scalability can be gained through the use of ASP.NET. Performance can be improved through the use of ASP.NET and ADO.NET.





What is the most commonly followed upgrade path? Why?


Answer
Partial upgrade, because a complete rewrite is generally too expensive and a complete upgrade too impractical.





Which upgrade comments are not listed in the Task List? Why?


Answer
UPGRADE_NOTE comments are not listed because they only highlight potential problems, and the code will run without any modifications.











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