Lesson 23: Inheritance with this base Class

Inheritance With the Base Class

Inheriting the Base Object

After creating a derived class, to let you access the parent class, the C# language provides a keyword named base that gives a child class access to public and protected members of its parent class.

Practical Learning: Accessing the Base Object from a Child Class

Save the following picture somewhere on your computer:
Start Microsoft Visual Studio
On the main menu, click File -> New -> Project...
In the middle list, click ASP.NET Application (.NET Framework) and, in the Name text box, replace the name with Geometry09
Click OK
In the New ASP.NET Web Application dialog box, click Empty and click OK
In the Solution Explorer, right-click Geometry09, position the mouse on Add, position the mouse on Add ASP.NET Folder, and click App_Code
In the Solution Explorer, right-click Geometry09 -> Add -> Folder
Type images and press Enter
Add the above picture to the images folder
In the Solution Explorer, right-click App_Code -> Add -> Class...
Change the name of the file to Trapezoid
Click Add

Fill the class as follows:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace Geometry09.App_Code
{
    public class Trapezoid
    {
        public double TopBase { get; set; }
        public double BottomBase { get; set; }
        public double Height { get; set; }

        public double Area
        {
            get
            {
                return Height * (TopBase + BottomBase) / 2.00;
            }
        }
    }
}

In the Solution Explorer, right-click App_Code -> Add -> Class...
Change the name of the class as TrapezoidalPrism
Click Add

Fill the class as follows:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace Geometry09.App_Code
{
    public class TrapezoidalPrism : Trapezoid
    {
        private double len;

        public double Length
        {
            get
            {
                return len;
            }

            set
            {
                len = value;
            }
        }

        public double BaseArea
        {
            get
            {
                // "base" refers to a parent's property
                return base.Area;
            }
        }

        public double TopArea
        {
            get
            {
                // "base" TopBase refers to a parent's property
                return base.TopBase * Length;
            }
        }

        public double BottomArea
        {
            get
            {
                // "base" BottomBase refers to a parent's property
                return base.BottomBase * Length;
            }
        }

        public double Volume
        {
            get
            {
                // "base" Area refers to a parent's property
                return base.Area * Length;
            }
        }
    }
}

In the Solution Explorer, right-click the name of the project -> Add -> New Item...
In the left list, expand Web, and click Razor
In the middle list, click Web Page (Razor)
Change the name to Index
Press Enter

Change the code as follows:

<!DOCTYPE html>
<html>
<head>
<style>
.container {
    margin: auto;
    width: 600px;
}
</style>
<title>Geometry - Trapezoidal Prism</title>
</head>
<body>
@{ 
    Geometry09.App_Code.TrapezoidalPrism tp = new Geometry09.App_Code.TrapezoidalPrism();

    double top    = 0.00;
    double bottom = 0.00;
    double height = 0.00;
    double length = 0.00;

    if (IsPost)
    {
        top    = Convert.ToDouble(Request["txtTopBase"]);
        bottom = Convert.ToDouble(Request["txtBottomBase"]);
        height = Convert.ToDouble(Request["txtHeight"]);
        length = Convert.ToDouble(Request["txtLength"]);

        tp.TopBase = top;
        tp.BottomBase = bottom;
        tp.Height = height;
        tp.Length = length;
    }
}

<div class="container">
    <h2 style="text-align: center">Geometry - Trapezoidal Prism</h2>

   <form name="frmGeometry" method="post">
      <table>
          <tr>
              <td style="width: 300px" rowspan="9">
                  <img src="~/images/tp.png" width="289" height="230" alt="Geometry - Trapezoidal Prism">
              </td>
              <td style="width: 110px">Top Base:</td>
              <td><input type="text" name="txtTopBase" value="@tp.TopBase" /></td>
          </tr>
          <tr>
              <td>Bottom Base:</td>
              <td><input type="text" name="txtBottomBase" value="@tp.BottomBase" /></td>
          </tr>
          <tr>
              <td>Height:</td>
              <td><input type="text" name="txtHeight" value="@tp.Height" /></td>
          </tr>
          <tr>
              <td>Length:</td>
              <td><input type="text" name="txtLength" value="@tp.Length" /></td>
          </tr>
          <tr>
              <td>&nbsp;</td>
              <td style="text-align: center"><input type="submit" name="btnSubmit" value="Calculate" /></td>
          </tr>
          <tr>
              <td>Base Area:</td>
              <td><input type="text" name="txt>BaseArea" value="@tp.BaseArea" /></td>
          </tr>
          <tr>
              <td>Top Area:</td>
              <td><input type="text" name="txtTopArea" value="@tp.TopArea" /></td>
          </tr>
          <tr>
              <td>Bottom Area:</td>
              <td><input type="text" name="txtBottomArea" value="@tp.BottomArea" /></td>
          </tr>
          <tr>
              <td>Volume:</td>
              <td><input type="text" name="txtVolume" value="@tp.Volume" /></td>
          </tr>
      </table>
  </form>
</div>
</body>
</html>

To execute the project, on the main menu, click Debug -> Start Without Debugging:
In the Top Base text box, enter a number such as 137.96
In the Bottom Base text box, enter a number such as 209.73
In the Height text box, enter a number such as 87.59
In the Length text box, enter a number such as 142.46
Click the Calculate button:
Close the browser and return to your programming environment

Inheriting the Base Constructors

If a parent class has a constructor, you can call that constructor in the child class. The constructor is accessed using the base keyword preceded by a colon. The keyword is accessed as when calling a method but after the parentheses of a constructor in the child class. That is, it must use parentheses. The primary formula to follow is:

class class-name : parent-name
{
    access-level class-name(parameter(s)) : base(parameter(s))
}

To call the base() constructor in a constructor of a child class, there are a few rules you must follow:

To start, once at least one construtor exists in the parent class and that constructor uses at least one parameter, any class derived from it must have at least one explicit constructor (this means that you must create that constructor) that has either the same number and types of parameters or more parameters than the constructor(s) in the parent class. This means that once a parent class has at least one constructor, every one of its child classes also must have at least one constructor. As a retult, the following code produces an error:
```
public class Person
{
    public string FirstName { get; set; }
    public string LastName  { get; set; }

    public Person(string fName, string lName)
    {
        FirstName = fName;
        LastName  = lName;
    }
}

public class Employee : Person
{
    public double HourlySalary { get; set; }
}
```
The error is because the Employee class must have at least one constructor (a constructor you must create). One way to avoid this error is to create a parameter-less constructor in the parent class. Here is an example:
```
public class Person
{
    public string FirstName { get; set; }
    public string LastName { get; set; }

    public Person()
    {
    }

    public Person(string fName, string lName)
    {
        FirstName = fName;
        LastName = lName;
    }
}

public class Employee : Person
{
    public double HourlySalary { get; set; }
}
```
The base() constructor must be called immediately after the parentheses of the child constructor, using the formula we reviewed

To use the base() constructor, the constructor on it is applied in the child class and must use more than or the same number of parameters and same type(s) of parameter(s) as the constructor of the parent class.

To call a constructor of the parent class from the derived class, if you are calling a constructor that doesn't use any parameter, leave the parentheses empty. Here is an example:

public class Circle
{
    private double _radius;

    public Circle()
    {
        _radius = 0.00;
    }
}

public class Cone : Circle
{
    private double _height;

    public Cone() : base()
    {
        _height = 0.00;
    }
}

If you are calling a constructor that uses one parameter, in the parentheses of base(), type the name of the parameter. Here is an example:

using System;

public class Circle
{
    private double _radius;

    public Circle(double rad)
    {
        _radius = rad;
    }
}

public class Cone : Circle
{
    private double _height;

    public Cone(double rad, double hgt) : base(rad)
    {
        _height = hgt;
    }
}

If the constructor of the parent class uses more than one parameter, in the parentheses of base, enter the names of the parameters of the child contructor that is calling it. Here is an example:

public class Person
{
    public string FirstName { get; set; }
    public string LastName  { get; set; }

    public Person(string fName, string lName)
    {
        FirstName = fName;
        LastName  = lName;
    }
}

public class Employee : Person
{
    public Employee(string fName, string lName) : base(fName, lName)
    {
    }
}

To make your code easy to read, you can call the base() constructor on the next line. Here is an example:

public class Person
{
    public string FirstName { get; set; }
    public string LastName  { get; set; }

    public Person(string fName, string lName)
    {
        FirstName = fName;
        LastName  = lName;
    }
}

public class Employee : Person
{
    public Employee(string fName, string lName)
        : base(fName, lName)
    {
    }
}

If the child construtor uses more parameters than the parent constructor, you can initialize the extra parameter(s) in the body of the (child) constructor. Here is an example:

public class Person
{
    public string FirstName { get; set; }
    public string LastName  { get; set; }

    public Person(string fName, string lName)
    {
        FirstName = fName;
        LastName  = lName;
    }
}

public class Employee : Person
{
    public Employee(string fName, string lName, double salary)
        : base(fName, lName)
    {
        HourlySalary = salary;
    }

    public double HourlySalary { get; set; }
}

Practical Learning: Inheriting A Base Constructor

Access the Trapezoid.cs file and add a constructor to the class as follows:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace Geometry09.App_Code
{
    public class Trapezoid
    {
        public double TopBase { get; set; }
        public double BottomBase { get; set; }
        public double Height { get; set; }

        public Trapezoid(double top, double bottom, double height)
        {
            TopBase = top;
            BottomBase = bottom;
            Height = height;
        }

        public double Area
        {
            get
            {
                return Height * (TopBase + BottomBase) / 2.00;
            }
        }
    }
}

Access the TrapezoidalPrism.cs file and create a constructor in the class as follows:

namespace Geometry09.App_Code
{
    public class TrapezoidalPrism: Trapezoid
    {
        private double len;

        public TrapezoidalPrism(double top, double bottom, double height, double length)
            : base(top, bottom, height)
        {
            Length = length;
        }

        . . . No Change
    }
}

To execute the application and test the webpage, press Ctrl + F5
Close the browser and return to your programming environment

Inheritance With this Class

Inheritance With this Object

We already know that every non-static class is equipped with an object named this. If you derive a class from a parent class, the child class has direct access to all public and protected members of the parent class. As an alternative to indicate that you are accessing a local member or a member of the parent class, in the child class, you can start the name of the member with .this.

Practical Learning: Inheriting this Parent

Access the TrapezoidalPrism.cs file and change its class as follows:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace Geometry09.App_Code
{
    public class TrapezoidalPrism: Trapezoid
    {
        private double len;

        public TrapezoidalPrism(double top, double bottom, double height, double length)
            : base(top, bottom, height)
        {
            // "this" refers to a local property
            this.Length = length;
        }

        public double Length
        {
            get
            {
                // "this" refers to a local field
                return this.len;
            }

            set
            {
                // "this" refers to a local field
                this.len = value;
            }
        }

        public double BaseArea
        {
            get
            {
                // "base" refers to a parent
                return base.Area;
            }
        }

        public double TopArea
        {
            get
            {
                // "this" TopBase refers to a parent's property
                // "this" refers to a local property
                return this.TopBase * this.Length;
            }
        }

        public double BottomArea
        {
            get
            {
                // "this" BottomBase refers to a parent's property
                // "this" refers to a local property
                return this.BottomBase * this.Length;
            }
        }

        public double Volume
        {
            get
            {
                // "base" Area refers to a parent's property
                // "this" refers to a local property
                return base.Area * this.Length;
            }
        }
    }
}

To execute the application and test the form, press Ctrl + F5
Close the browser and return to your programming environment
Save the following picture somewhere on your computer:
On the main menu of Microsoft Visual Studio, click File -> New -> Project...
In the middle list, click ASP.NET Application (.NET Framework) and, in the Name text box, replace the name with Geometry10
Click OK
In the New ASP.NET Web Application dialog box, click Empty and click OK
In the Solution Explorer, right-click Geometry10, position the mouse on Add, position the mouse on Add ASP.NET Folder, and click App_Code
In the Solution Explorer, right-click Geometry10 -> Add -> Folder
Type Images and press Enter
Add the above picture to the images folder
In the Solution Explorer, right-click App_Code -> Add -> Class...
Set the name of the class as Cylinder
Click Add

Fill the class as follows:

using static System.Math;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace Geometry10.App_Code
{
    public class Cylinder
    {
        public double Length { get; set; }
        public double Radius { get; set; }

        public double Diameter      => this.Radius * 2.00;
        public double Circumference => this.Diameter * PI;
        public double CrossArea     => this.Radius * this.Radius * PI;
        public double LateralArea   => this.Circumference * this.Length;
        public double CentralVolume => this.CrossArea * this.Length;
    }
}

In the Solution Explorer, right-click the name of the project -> Add -> New Item...
In the left list, expand Web, and click Razor
In the middle list, click Web Page (Razor)
Change the name to Index
Press Enter

Change the code as follows:

<!DOCTYPE html>
<html>
<head>
<style>
.container {
    margin: auto;
    width: 420px;
}
</style>

<title>Geometry - Cylinder</title>
</head>
<body>
@{
    double radius = 0.00;
    double length = 0.00;
    Geometry10.App_Code.Cylinder body = new Geometry10.App_Code.Cylinder();

    if (IsPost)
    {
        radius = Convert.ToDouble(Request["txtRadius"]);
        length = Convert.ToDouble(Request["txtLength"]);

        body.Radius = radius;
        body.Length = length;
    }
}

    <div align="center">
        <h2>Geometry - Cylinder</h2>

        <form name="frmTank" method="post">
            <table>
                <tr>
                    <td colspan="2" style="text-align: center"><img src="~/Images/cylinder3.png" alt="Geometry - Cylinder" width="373" height="298" /></td>
                </tr>
                <tr>
                    <td style="width: 150px; font-weight: bold">Radius:</td>
                    <td><input type="text" name="txtRadius" value="@radius" /></td>
                </tr>
                <tr>
                    <td style="font-weight: bold">Length:</td>
                    <td><input type="text" name="txtLength" value=@length /></td>
                </tr>
                <tr>
                    <td>&nbsp;</td>
                    <td><input type="submit" name="btnCalculate" value="Calculate" style="width: 70px;" /></td>
                </tr>
                <tr>
                    <td style="font-weight: bold">Diameter:</td>
                    <td><input type="text" name="txtDiameter" value=@body.Diameter /></td>
                </tr>
                <tr>
                    <td style="font-weight: bold">Circumference:</td>
                    <td><input type="text" name="txtCircumference" value=@body.Circumference /></td>
                </tr>
                <tr>
                    <td style="font-weight: bold">Cross Area:</td>
                    <td><input type="text" name="txtCrossArea" value=@body.CrossArea /></td>
                </tr>
                <tr>
                    <td style="font-weight: bold">Lateral Area:</td>
                    <td><input type="text" name="txtLateralArea" value=@body.LateralArea /></td>
                </tr>
                <tr>
                    <td style="font-weight: bold">Volume:</td>
                    <td><input type="text" name="txtVolume" value=@body.CentralVolume /></td>
                </tr>
            </table>
        </form>
    </div>
</body>
</html>

To execute the project, on the main menu, click Debug -> Start Without Debugging:
In the Radius text box, enter a number such as 79.84
In the Length text box, type a number such as 258.93
Click the Calculate button:
Close the browser and return to your programming environment
Save the following picture somewhere on your computer:
Add this picture to the images folder
In the Solution Explorer, right-click App_Code -> Add -> Class...
Change the name of the class as Tank
Click Add

Fill the class as follows:

using static System.Math;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace Geometry10.App_Code
{
    public class Tank : Cylinder
    {
        public double Width
        {
            get
            {
                return this.Diameter;
            }
        }

        public double TotalLength
        {
            get
            {
                return this.Length + this.Radius + this.Radius;
            }
        }

        public double TotalArea
        {
            get
            {
                // Area on one side (half sphere) = Area of Sphere / 2
                // Areas on both sides = area of a sphere = radius * radius * 4 * PI
                // Total External Area = lateral area (of the central cylinder) + areas on both sides
                return this.LateralArea + (this.Radius * this.Radius * PI * 4.00);
            }
        }

        public double TotalVolume
        {
            get
            {
                // Volume on one side (half sphere) = Volue of Sphere / 2
                // Volumes on both sides = volume of a sphere = radius * radius * radius * PI * 4 / 3
                // Total Volume = central volume + volumes on both sides (which is the volume of a sphere)
                return this.CentralVolume + (this.Radius * this.Radius * this.Radius * PI * 4.00 / 3.00);
            }
        }
    }
}

Access the Index.cshtml file and change its document as follows:

<!DOCTYPE html>
<html>
<head>
<style>
.container {
    margin: auto;
    width: 420px;
}
</style>
<title>Geometry - Cylinder</title>
</head>
<body>
@{
    double radius = 0.00;
    double length = 0.00;
    Geometry10.App_Code.Tank whole = new Geometry10.App_Code.Tank();

    if (IsPost)
    {
        radius = Convert.ToDouble(Request["txtRadius"]);
        length = Convert.ToDouble(Request["txtLength"]);

        whole.Radius = radius;
        whole.Length = length;
    }
}

<div align="center">
    <h2>Geometry - Tank</h2>

    <p style="text-align: center"><img src="~/images/tank.png" alt="Geometry - Tank" width="428" height="235" /></p>
    <form name="frmTank" method="post">
        <table border="6">
            <tr>
                <td>
                    <table>
                        <tr>
                            <td style="width: 150px; font-weight: bold">Radius:</td>
                            <td><input type="text" name="txtRadius" value="@radius" /></td>
                        </tr>
                        <tr>
                            <td style="font-weight: bold">Cylinder Length:</td>
                            <td><input type="text" name="txtLength" value=@length /></td>
                        </tr>
                        <tr>
                            <td>&nbsp;</td>
                            <td><input type="submit" name="btnCalculate" value="Calculate" style="width: 70px;" /></td>
                        </tr>
                    </table>
                    <table>
                        <tr>
                            <td style="font-weight: bold; text-decoration: underline">Each Side (Half Sphere)</td>
                        </tr>
                    </table>
                    <table>
                        <tr>
                            <td style="width: 150px; font-weight: bold">Diameter:</td>
                            <td><input type="text" name="txtDiameter" value=@whole.Diameter /></td>
                        </tr>
                        <tr>
                            <td style="font-weight: bold">Circumference:</td>
                            <td><input type="text" name="txtCircumference" value=@whole.Circumference /></td>
                        </tr>
                        <tr>
                            <td style="font-weight: bold">Base Area:</td>
                            <td><input type="text" name="txtCrossArea" value=@whole.CrossArea /></td>
                        </tr>
                    </table>
                    <table>
                        <tr>
                            <td style="font-weight: bold; text-decoration: underline">The Central Cylinder</td>
                        </tr>
                    </table>
                    <table>
                        <tr>
                            <td style="width: 150px; font-weight: bold">Lateral Area:</td>
                            <td><input type="text" name="txtLateralArea" value=@whole.LateralArea /></td>
                        </tr>
                        <tr>
                            <td style="font-weight: bold">Central Volume:</td>
                            <td><input type="text" name="txtCentralVolume" value=@whole.CentralVolume /></td>
                        </tr>
                    </table>
                    <table>
                        <tr>
                            <td style="font-weight: bold; text-decoration: underline">The Tank as a Whole</td>
                        </tr>
                    </table>
                    <table>
                        <tr>
                            <td style="width: 150px; font-weight: bold">Through Width:</td>
                            <td><input type="text" name="txtWidth" value=@whole.Width /></td>
                        </tr>
                        <tr>
                            <td style="font-weight: bold">Total Length:</td>
                            <td><input type="text" name="txtLateralLength" value=@whole.TotalLength /></td>
                        </tr>
                        <tr>
                            <td style="font-weight: bold">Total Area:</td>
                            <td><input type="text" name="txtTotalArea" value=@whole.TotalArea /></td>
                        </tr>
                        <tr>
                            <td style="font-weight: bold">Total Volume:</td>
                            <td><input type="text" name="txtTotalVolume" value=@whole.TotalVolume /></td>
                        </tr>
                    </table>
                </td>
            </tr>
        </table>
        
    </form>
</div>
</body>
</html>

To execute the project, on the main menu, click Debug -> Start Without Debugging:
In the Radius text box, enter a number such as 79.84
In the Length text box, type a number such as 258.93
Click the Calculate button:
Close the browser and return to your programming environment

Returning this Object

You may remember that a method of a class can return this object that represents the class itself. Here is an example:

public class Triangle
{
    public void Examine()
    {
        Triangle inside = this;
    }
}

Practical Learning: Returning this Object

Save the following picture somewhere on your computer and return to your programming environment:
On the main menu, click File -> New -> Project...
In the middle list, click ASP.NET Application (.NET Framework) and, in the Name text box, replace the name with Geometry11
Click OK
In the New ASP.NET Web Application dialog box, click Empty and click OK
In the Solution Explorer, right-click Geometry11, position the mouse on Add, position the mouse on Add ASP.NET Folder, and click App_Code
In the Solution Explorer, right-click Geometry11 -> Add -> Folder
Type images and press Enter
Add the above picture to the images folder
In the Solution Explorer, right-click App_Code -> Add -> Class...
Set the name of the class as Circle
Click Add

Change the document as follows:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace Geometry11.App_Code
{
    public class Circle
    {
        public double Radius { get; set; }

        public Circle(double radius)
        {
            Radius = radius;
        }

        public double Diameter => Radius * 2.00;
        public double Circumference => Diameter * Math.PI;
        public double Area => Radius * Radius * Math.PI;

        public Circle Encircle()
    	 {
            return this;
       }
    }
}

In the Solution Explorer, right-click App_Code -> Add -> Class...
Change the name of the class to Cone
Click Add

Change the document as follows:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace Geometry11.App_Code
{
    public class Cone : Circle
    {
        public double Height { get; set; }

        public Cone(double radius, double height) : base(radius)
        {
            Height = height;
        }

        public double BaseArea => Area;
        public double Volume   => Radius * Radius * Height * Math.PI / 3.00;
    }
}

Getting this Parent

A method of an inherited class can return this. You must then identify the role of this object as it is used in a derived class.

Practical Learning: Getting this Parent

In the Cone class, create two methods as follows:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace Geometry11.App_Code
{
    public class Cone : Circle
    {
        public double Height { get; set; }

        public Cone(double radius, double height) : base(radius)
        {
            Height = height;
        }

        public double BaseArea => Area;
        public double Volume   => Radius * Radius * Height * Math.PI / 3.00;

        public Circle Create()
        {
            return this;
        }

        public Cone Surround()
        {
            return this;
        }
    }
}

In the Solution Explorer, right-click the name of the project -> Add -> New Item...
In the left list, expand Web, and click Razor
In the middle list, click Web Page (Razor)
Change the name to Index
Press Enter

Change the code as follows:

<!DOCTYPE html>
<html>
<head>
<title>Geometry - Cone</title>
<style>
.container {
    margin: auto;
    width: 500px;
}
.col-empty {
    width: 40px
}
.col-format {
    width: 120px
}
</style>
</head>
<body>
<h2 style="text-align: center">Geometry - Cone</h2>

@{ 
    double radius = 0.00;
    double height = 0.00;

    Geometry11.App_Code.Cone dongle = new Geometry11.App_Code.Cone(0.00, 0.00);

    Geometry11.App_Code.Circle c = dongle.Create();

    if (IsPost)
    {
        radius = Convert.ToDouble(Request["txtBaseRadius"]);
        height = Convert.ToDouble(Request["txtHeight"]);

        Geometry11.App_Code.Circle round = new Geometry11.App_Code.Circle(radius);
        dongle = new Geometry11.App_Code.Cone(radius, height);

        c = dongle.Create();
    }
}

<div class="container">
    <form name="frmCone" method="post">
        <table>
            <tr>
                <td style="width: 170px; vertical-align: top"><img src="~/Images/cone.png" alt="Geometry - Cone" width="163" height="185" /></td>
                <td>
                    <table>
                        <tr>
                            <td class="col-empty">&nbsp;</td>
                            <td class="col-format">Base Radius:</td>
                            <td><input type="text" name="txtBaseRadius" value="@radius" /></td>
                        </tr>
                        <tr>
                            <td>&nbsp;</td>
                            <td>Height:</td>
                            <td><input type="text" name="txtHeight" value="@height" /></td>
                        </tr>
                        <tr>
                            <td>&nbsp;</td>
                            <td>&nbsp;</td>
                            <td><input type="submit" name="btnCalculate" value="Calculate" /></td>
                        </tr>
                    </table>

                    <p><span style="font-weight: bold; text-decoration: underline">Base</span></p>

                    <table>
                        <tr>
                            <td class="col-empty">&nbsp;</td>
                            <td class="col-format">Diameter:</td>
                            <td><input type="text" name="txtDiameter" value="@c.Diameter" /></td>
                        </tr>
                        <tr>
                            <td>&nbsp;</td>
                            <td>Circumference:</td>
                            <td><input type="text" name="txtCircumference" value="@c.Circumference" /></td>
                        </tr>
                        <tr>
                            <td>&nbsp;</td>
                            <td>Base Area:</td>
                            <td><input type="text" name="txtBaseArea" value="@c.Area" /></td>
                        </tr>
                    </table>

                    <p><span style="font-weight: bold; text-decoration: underline;">Cone</span></p>

                    <table>
                        <tr>
                            <td class="col-empty">&nbsp;</td>
                            <td class="col-format">Volume:</td>
                            <td><input type="text" name="txtVolume" value="0" /></td>
                        </tr>
                    </table>
                </td>
            </tr>
        </table>
    </form>
</div>
</body>
</html>

To execute the application, press Ctrl + F5:
In the Base Radius text box, type a number such as 84.79
In the Height text box, type a number such as 375.67
Click the Calculate button:
Close the browser and return to your programming environment

Change the Index.cshtml file as follows:

<!DOCTYPE html>
<html>
<head>
<title>Geometry - Cone</title>
<style>
.container {
    margin: auto;
    width: 500px;
}
.col-empty {
    width: 40px
}
.col-format {
    width: 120px
}
</style>
</head>
<body>
<h2 style="text-align: center">Geometry - Cone</h2>

@{ 
    double radius = 0.00;
    double height = 0.00;

    Geometry11.App_Code.Cone dongle = new Geometry11.App_Code.Cone(0.00, 0.00);
    Geometry11.App_Code.Cone fancy = new Geometry11.App_Code.Cone(0.00, 0.00);

    if (IsPost)
    {
        radius = Convert.ToDouble(Request["txtBaseRadius"]);
        height = Convert.ToDouble(Request["txtHeight"]);

        dongle = new Geometry11.App_Code.Cone(radius, height);
        fancy = dongle.Surround();
    }
}

<div class="container">
    <form name="frmCone" method="post">
        <table>
            <tr>
                <td style="width: 170px; vertical-align: top"><img src="~/Images/cone.png" alt="Geometry - Cone" width="163" height="185" /></td>
                <td>
                    <table>
                        <tr>
                            <td class="col-empty">&nbsp;</td>
                            <td class="col-format">Base Radius:</td>
                            <td><input type="text" name="txtBaseRadius" value="@radius" /></td>
                        </tr>
                        <tr>
                            <td>&nbsp;</td>
                            <td>Height:</td>
                            <td><input type="text" name="txtHeight" value="@height" /></td>
                        </tr>
                        <tr>
                            <td>&nbsp;</td>
                            <td>&nbsp;</td>
                            <td><input type="submit" name="btnCalculate" value="Calculate" /></td>
                        </tr>
                    </table>

                    <p><span style="font-weight: bold; text-decoration: underline">Base</span></p>

                    <table>
                        <tr>
                            <td class="col-empty">&nbsp;</td>
                            <td class="col-format">Diameter:</td>
                            <td><input type="text" name="txtDiameter" value="@fancy.Diameter" /></td>
                        </tr>
                        <tr>
                            <td>&nbsp;</td>
                            <td>Circumference:</td>
                            <td><input type="text" name="txtCircumference" value="@fancy.Circumference" /></td>
                        </tr>
                        <tr>
                            <td>&nbsp;</td>
                            <td>Base Area:</td>
                            <td><input type="text" name="txtBaseArea" value="@fancy.Area" /></td>
                        </tr>
                    </table>

                    <p><span style="font-weight: bold; text-decoration: underline;">Cone</span></p>

                    <table>
                        <tr>
                            <td class="col-empty">&nbsp;</td>
                            <td class="col-format">Volume:</td>
                            <td><input type="text" name="txtVolume" value="@fancy.Volume" /></td>
                        </tr>
                    </table>
                </td>
            </tr>
        </table>
    </form>
</div>
</body>
</html>

Execute the application to test the form:
In the Base Radius text box, type a number such as 84.79
In the Height text box, type a number such as 375.67
Click the Calculate button:
Close the browser and return to your programming environment

Comparing an Object to this Parent

Remember that you can compare an object to this to find out what that object represents. This operation can be used to find out if an object refers to a parent, grand-parent, etc, of the object.

The new Modifier

Introduction

Imagine you create a class, such as one for a geometric shape such as a trapezoid. As we saw above, you can use such a class as the base class for a prism. Both the trapezoid and its related prism have an area but their areas are different.

If you create or declare a new member in a derived class and that member has the same name as a member of the base class, when creating the new member, you may want to indicate to the compiler that you want to create a brand new and independent version of that method. When doing this, you would be asking the compiler to hide the member of the base class that has the same name, when the member of the current class is invoked.

Creating a New Version of a Member

To create a new version of a member, type the new keyword to its left.

Practical Learning: Creating a New Version of a Member

Open the Geometry09 project created earlier

Access the TrapezoidalPrism file and add a new method in the class as follows:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace Geometry09.App_Code
{
    public class TrapezoidalPrism : Trapezoid
    {
        private double len;

        public TrapezoidalPrism(double top, double bottom, double height, double length)
            : base(top, bottom, height)
        {
            Length = length;
        }

        public double Length
        {
            get
            {
                // "this" refers to a local field
                return this.len;
            }

            set
            {
                // "this" refers to a local field
                this.len = value;
            }
        }

        public double BaseArea
        {
            get
            {
                // "base" refers to the parent
                return base.Area;
            }
        }

        public double TopArea
        {
            get
            {
                // "base" refers to the parent
                // "this" Length refers to a local property
                return this.TopBase * this.Length;
            }
        }

        public double BottomArea
        {
            get
            {
                // "base" refers to the parent
                // "this" Length refers to a local property
                return this.BottomBase * this.Length;
            }
        }

        public new double Area
        {
            get
            {
                return BaseArea + TopArea + BottomArea + BaseArea;
            }
        }

        public double Volume
        {
            get
            {
                // "base" refers to the parent
                // "this" Length refers to a local property
                return base.Area * this.Length;
            }
        }
    }
}

Access the Index.cshtml file and change its document as follows:

<!DOCTYPE html>
<html>
<head>
<style>
.container {
    margin: auto;
    width: 590px;
}
</style>

<title>Geometry - Trapezoidal Prism</title>
</head>
<body>
    @{
        Geometry09.App_Code.TrapezoidalPrism tp = new Geometry09.App_Code.TrapezoidalPrism(0, 0, 0, 0);

        double top = 0.00;
        double bottom = 0.00;
        double height = 0.00;
        double length = 0.00;

        if (IsPost)
        {
            top = Convert.ToDouble(Request["txtTopBase"]);
            bottom = Convert.ToDouble(Request["txtBottomBase"]);
            height = Convert.ToDouble(Request["txtHeight"]);
            length = Convert.ToDouble(Request["txtLength"]);

            tp = new Geometry09.App_Code.TrapezoidalPrism(top, bottom, height, length);
        }
    }

    <div class="container">
        <h2 style="text-align: center">Geometry - Trapezoidal Prism</h2>

        <form name="frmGeometry" method="post">
            <table>
                <tr>
                    <td style="width: 300px" rowspan="10">
                        <img src="~/images/tp.png" width="289" height="230" alt="Geometry - Trapezoidal Prism">
                    </td>
                    <td style="width: 110px">Top Base:</td>
                    <td><input type="text" name="txtTopBase" value="@tp.TopBase" /></td>
                </tr>
                <tr>
                    <td>Bottom Base:</td>
                    <td><input type="text" name="txtBottomBase" value="@tp.BottomBase" /></td>
                </tr>
                <tr>
                    <td>Height:</td>
                    <td><input type="text" name="txtHeight" value="@tp.Height" /></td>
                </tr>
                <tr>
                    <td>Length:</td>
                    <td><input type="text" name="txtLength" value="@tp.Length" /></td>
                </tr>
                <tr>
                    <td>&nbsp;</td>
                    <td style="text-align: center"><input type="submit" name="btnSubmit" value="Calculate" /></td>
                </tr>
                <tr>
                    <td>Base Area:</td>
                    <td><input type="text" name="txt>BaseArea" value="@tp.BaseArea" /></td>
                </tr>
                <tr>
                    <td>Top Area:</td>
                    <td><input type="text" name="txtTopArea" value="@tp.TopArea" /></td>
                </tr>
                <tr>
                    <td>Bottom Area:</td>
                    <td><input type="text" name="txtBottomArea" value="@tp.BottomArea" /></td>
                </tr>
                <tr>
                    <td>Total Area:</td>
                    <td><input type="text" name="txtTotalArea" value="@tp.Area" /></td>
                </tr>
                <tr>
                    <td>Volume:</td>
                    <td><input type="text" name="txtVolume" value="@tp.Volume" /></td>
                </tr>
            </table>
        </form>
    </div>
</body>
</html>

To execute the application, on the menu, click Debug -> Start Without Debugging:
In the Top Base text box, enter a number such as 137.96
In the Bottom Base text box, enter a number such as 209.73
In the Height text box, enter a number such as 87.59
In the Length text box, enter a number such as 142.46
Click the Calculate button:
Close the browser and return to your programming environment
Close your programming environment


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