C# Chapter 9: Rectangle Class Quiz
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Questions and Answers

What is the purpose of the parameterized constructor in the Rectangle class?

  • To allow the user to set specific dimensions upon object creation. (correct)
  • To create copies of existing Rectangle objects.
  • To initialize length and width to zero.
  • To compute the area of the rectangle on creation.

    • Which method would you call to retrieve the width of a Rectangle object?

  • SetWidth
  • GetWidth (correct)
  • SetLength
  • GetLength

    • What does the GetArea method return for a Rectangle object?

  • The sum of length and width.
  • The value of the length field.
  • The total perimeter of the rectangle.
  • The product of length and width. (correct)

    • What is the role of the SetLength method in the Rectangle class?

    <p>To modify the length field with a new value.</p> Signup and view all the answers

    How many instances of the Rectangle class are created in the RoomAreas class's Main method?

    <p>Three</p> Signup and view all the answers

    Which statement about instance fields and methods in the Rectangle class is true?

    <p>They need an object instance to be utilized.</p> Signup and view all the answers

    What is the purpose of accessors (getters) and mutators (setters) in the Rectangle class?

    <p>To provide read and write access to private fields.</p> Signup and view all the answers

    What can be inferred about the width and length fields in the Rectangle class?

    <p>They are private and cannot be modified without methods.</p> Signup and view all the answers

    Which of the following statements correctly describes the GetArea method?

    <p>It calculates the area by multiplying length and width.</p> Signup and view all the answers

    What will happen if a negative value is assigned to the Length property?

    <p>The length will be set to zero.</p> Signup and view all the answers

    In the class definition of Rectangle, what keyword is used to define private fields?

    <p>private</p> Signup and view all the answers

    What role does the SetLength method serve in the Rectangle class?

    <p>It assigns a new value to the length field.</p> Signup and view all the answers

    What will the output be if the Width property is set to -10?

    <p>The width will be 0.</p> Signup and view all the answers

    What type of method is GetWidth in the Rectangle class?

    <p>An instance method that returns the width.</p> Signup and view all the answers

    How is an object of the Rectangle class instantiated in the Main method?

    <p>Rectangle box = new Rectangle();</p> Signup and view all the answers

    Which part of the Rectangle class is responsible for providing access to its private length field?

    <p>The Length property</p> Signup and view all the answers

    Which of the following accurately describes the fields of the Rectangle class?

    <p>They are private and can only be accessed through methods.</p> Signup and view all the answers

    In C#, what does it mean if a class has properties that include both 'get' and 'set' accessors?

    <p>The properties can be read and assigned new values.</p> Signup and view all the answers

    What is the purpose of the GetArea method in the Rectangle class?

    <p>To return the area of the rectangle as length multiplied by width.</p> Signup and view all the answers

    How is the Rectangle class instantiated in a given program?

    <p>By creating an instance with the new operator, such as new Rectangle().</p> Signup and view all the answers

    What concept is exemplified by the SetLength and SetWidth methods?

    <p>Mutator methods that modify the state of an object.</p> Signup and view all the answers

    What will happen if the Rectangle class is defined without any methods?

    <p>It will still allow for object creation, but functionality will be limited.</p> Signup and view all the answers

    Which of the following statements about the methods in the Rectangle class is correct?

    <p>GetLength is designed to return the value in the length field.</p> Signup and view all the answers

    Study Notes

    Chapter 9: Using Classes and Objects - Practice Example

    • Rectangle Class: A class representing a rectangle
    • Fields:
      • length: Stores the rectangle's length.
      • width: Stores the rectangle's width.
    • Methods:
      • SetLength(double len): Sets the rectangle's length.
      • SetWidth(double wid): Sets the rectangle's width.
      • GetLength(): Returns the rectangle's length.
      • GetWidth(): Returns the rectangle's width.
      • GetArea(): Returns the rectangle's area (length * width).

    Writing the Code for the Class Fields

    • Rectangle Class Definition: 
      public class Rectangle
{
    private double length;
    private double width;
}
    • Fields are declared as private
    • double data type for length and width

    Method Header for SetLength

    • Access Specifier: public
    • Return Type: void
    • Method Name: SetLength
    • Parameter: double len

    Writing and Demonstrating the SetLength Method

    • Method Body: 
      public void SetLength(double len)
{
    length = len;
}
    • Stores the value of len in the length field.

    Method Header for GetLength

    • Access Specifier: public
    • Return Type: double
    • Method Name: GetLength
    • No Parameters

    Writing and Demonstrating the GetLength Method

    • Method Body: 
      public double GetLength()
{
    return length;
}
    • Returns the value stored in the length field.

    Rectangle.cs (Version 1)

    • Contains SetLength and SetWidth methods, with comments explaining their purposes and parameters
    • private double length; and private double width; declare the instance fields for the rectangle's length and width

    Rectangle.cs (cont'd)

    • Contains GetLength, GetWidth, and GetArea methods, with comments explaining their purposes and return values
    • Uses multiplication length * width to calculate and return the area.

    RectangleDemo.cs

    • RectangleDemo class containing Main method, demonstrating how to use a Rectangle object
    • Rectangle box = new Rectangle(); creates a Rectangle object
    • box.SetLength(10.0); Sets the length of the box
    • box.SetWidth(20.0); Sets the width of the box
    • Outputs the length, width, and area of the box using Console.WriteLine()

    Create a Rectangle object

    • Rectangle box = new Rectangle(); creates a Rectangle object
    • The variable 'box' holds the address of the Rectangle object.

    Calling the SetLength Method

    • box.SetLength(10.0); sets the length of 'box'
    • 'box' variable now holds the address of rectangle object with length = 10, width = 0

    Accessors and Mutators of Rectangle Class

    • Setters (Mutators):
      • Modify object data
      • e.g., SetLength, SetWidth
    • Getters (Accessors):
      • Access object data
      • e.g., GetLength, GetWidth, GetArea

    Rectangle.cs (Version 2)

    • Includes parameterised constructor Rectangle(double len, double wid)
    • Parameterless constructor Rectangle()
    • Sets default values for length and width if no parameters are given

    Rectangle.cs (cont'd)

    • Contains SetLength, SetWidth, GetLength, GetWidth, and GetArea methods, with detailed comments

    Instance Fields and Methods

    • Instance fields and methods require an object to be created to be used.
    • Each object can have different values for its fields.

    RoomArea.cs

    • Creates 3 Rectangle objects (kitchen, bedroom, den) to hold area.
    • Prompts user for dimensions of each room
    • Calculates total area of the rooms.
    • Outputs the total area of the rooms

    RoomArea.cs (cont'd)

    • Contains code to get and store room dimensions using user input.
    • Implements calculations for total area.
    • Prints the total area to the console

    States of Three Different Rectangle Objects

    • Shows the state (length, width) of each of the three Rectangle objects created in the RoomArea class, after dimensions are entered.

    Rectangle.cs (Version 3)

    • Introduces properties for Length and Width to encapsulate the fields.
    • Methods use properties, instead of directly accessing the length and width fields.

    Rectangle.cs (cont'd)

    • Includes methods that use the properties Length and Width to get and set the values (getters & setters).

    PropertyTest.cs

    • Demonstrates the use of Rectangle class properties.
    • Sets length and width of a Rectangle object, calculates and displays the area of the object.

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    Chapter 9 • Using Classes and Objects PDF

    Description

    Test your understanding of object-oriented programming with a focus on the Rectangle class in C#. This quiz covers class fields, methods, and how to implement the SetLength method. Enhance your coding skills by practicing with this example!

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