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<h1>Language: Use Scoping-Overriding-Overloading</h1>
Shows how to allow various levels of access to the members of a class,
including Public, Private, Protected and otherwise. To demonstrate how to
extend derived classes with features like Overloading and Overriding.
<h2>Featured Highlights:</h2>
<p>This application simulates a simple hiring system, allowing for the
hiring of full-time, part-time and temporary employees. Each kind of employee
has specific features that set them apart from the other kinds. For
example, only full-time employees get annual leave, and only temporary
employees have an expected termination date when they are hired. Part-time
employees are required to work at least 20 hours per week. However, all
employees have many things in common: they all get hired, all have salaries,
each has a name, etc.</p>
<p>The application utilizes a base class called Employee, from which the classes
FullTimeEmployee, PartTimeEmployee and TempEmployee are derived. Each derived
class extends the base class in some way: by overriding methods of the base
class, by implementing new methods or properties of its own, or by replacing
(shadowing) members of the base class. There is also a Friend class called
EmployeeDataManager which simulates reading and writing employee data to and
from a database.</p>
<p>The application demonstrates the use of these statements and modifiers in
classes and their members:</p>
<ul>
<li>
<strong>Inherits:</strong>
Specifies the class (also known as the base class) from which the current class
inherits.
<li>
<strong>NotInheritable:</strong>
Prevents programmers from using the class as a base class.
<li>
<strong>MustInherit:</strong>
Specifies that instances of the given class cannot be created. The only way to
use the class is to inherit from it.
<li>
<strong>Overridable:</strong>
Allows a property or a method to be overridden in an inheriting class. Public
methods are NotOverridable by default.
<li>
<strong>Overrides:</strong>
Allows you to override a property or method that is defined in the base class.
<li>
<strong>NotOverridable (default):</strong>
Prevents a property or method from being overridden in an inheriting class.
<li>
<strong>MustOverride:</strong>
Requires the inheriting class to override the property or method.
<li>
<strong>Shadows:</strong> Allows reuse of the names of inherited class members,
making all of the inherited type members unavailable in the derived
class. </li></ul>
<p>It also demonstrates scoping with the use of these keywords:</p>
<ul>
<li>
<strong>Public:</strong>
Classes and procedures declared with the Public keyword have public access.
There are no restrictions on their accessibility.
<li>
<strong>Protected:</strong>
Class members declared with the Protected keyword are accessible only from
within their own class or from a derived class.
<li>
<strong>Friend:</strong>
Classes and procedures declared with the Friend keyword are accessible from
within the program where they are declared and from anywhere else in the same
assembly.
<li>
<strong>Private:</strong>
Class members declared with the Private keyword are accessible only from within
the class where they are declared.
<li>
<strong>Shared:</strong> Procedures declared with the Shared keyword can be
used without necessarily having to create an instance of the class they belong
to. You can call a shared procedure either by qualifying it with the class name
(EmployeeDataManager.WriteEmployeeData), or with the variable name of a
specific instance of the class (edmManager.WriteEmployeeData).
</li>
</ul>
<h2>Requirements:</h2>
<ul>
<li>
There is no database access, since this is a simulation. All data is in memory.
<li>
Set breakpoints at strategic places throughout the classes to observe the
interaction between base class and inherited class.</li></ul>
<H2>Running the Sample:</H2>
<P>Simply press <STRONG>F5</STRONG>.</P>
<H3>See Also</H3>
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VB_NET_Framework_Scoping_Overloading.rar （21个子文件） 
VB.NET - Framework - Scoping, Overloading, Overriding 
VB.NET How-To Use Scoping-Overriding-Overloading.suo 13KB bin 
VB.NET How-To Use Scoping-Overriding-Overloading.exe 136KB VB.NET How-To Use Scoping-Overriding-Overloading.pdb 90KB Employee.vb 6KB obj Debug temp VBNET.HowTo.UseScopingOverridingOverloading.frmAbout.resources 2KB TempPE VBNET.HowTo.UseScopingOverridingOverloading.frmMain.resources 66KB VB.NET How-To Use Scoping-Overriding-Overloading.exe 136KB VB.NET How-To Use Scoping-Overriding-Overloading.pdb 90KB frmAbout.vb 6KB VB.NET How-To Use Scoping-Overriding-Overloading.sln 992B VB.NET How-To Use Scoping-Overriding-Overloading.vbproj.user 2KB VB.NET How-To Use Scoping-Overriding-Overloading.vbproj 6KB frmMain.vb 52KB frmAbout.resx 7KB EmployeeDataManager.vb 3KB FullTimeEmployee.vb 3KB TempEmployee.vb 3KB ReadMe.htm 5KB frmMain.resx 84KB PartTimeEmployee.vb 3KB AssemblyInfo.vb 3KB资源评论
