Chapter 6 Lab: Classes

This practical assignment is a Java programming lab focusing on the concept of classes and objects. Students are tasked with creating a `Television` class with attributes like manufacturer, screen size, power status, channel, and volume. The assignment involves defining a constructor, accessor methods (getters), and mutator methods (setters) to manage the television's state. Students are guided through several tasks: creating the class, writing the constructor, implementing methods to control the television's attributes (e.g., changing channels, adjusting volume), and testing the class using a provided driver program (`TelevisionDemo.java`). The final task involves creating another `Television` object and manipulating its attributes. The assignment includes sample output to verify the correctness of the code. The website provides past papers and solved assignments to help students complete this lab.

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Chapter 6 Lab: Classes
Lab Submission Instructions
1) Indicate which tasks you completed:
2) Copy screen shots of your program execution for tasks 4 and 5 and paste them below.
Upload this file to Canvas under this assignment DropBox.
3) Upload a text file containing a copy of your completed code for Task5 (or the last task you
have completed a working program) to Canvas under this assignment DropBox.
Lab Objectives
 Be able to declare a new class
 Be able to write a constructor
 Be able to write instance methods that return a value
 Be able to instantiate an object
 Be able to use calls to instance methods to access a change the state of an object
Introduction
Everyone is familiar with a television. It is the class we are going to create in this lab.
First we need a blueprint. All manufacturers have the same basic elements in the
televisions they produce as well as many options. We are going to work with a few basic
elements that are common to all televisions. Think about a television in general. It has a
brand name (i.e. it is made by a specific manufacturer). The television screen has a
specific size. It has some basic controls. There is a control to turn the power on and off.
There is a control to change the channel. There is also a control for the volume. At any
point in time, the television’s state can be described by how these controls are set.
We will write the Television class. Each object that is created from the
Television class must be able to hold information about that instance of a
Television in fields. So a Television object will have the following attributes:
 manufacturer. The manufacturer attribute will hold the brand name.
This cannot change once the television is created, so will be a named constant.
 screenSize. The screenSize attribute will hold the size of the television
screen.

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This cannot change once the television has been created so will be a named
constant.
 powerOn. The powerOn attribute will hold the value true if the power is on
and false if the power is off.
 channel. The channel attribute will hold the value of the station that the
television is showing.
 volume. The volume attribute will hold a number value representing the
loudness (0 being no sound).

These attributes become fields in our class.
The Television object will also be able to control the state of its attributes. These
controls become methods in our class.
 setChannel. The setChannel method will store the desired station in the
channel field.
 power. The power method will toggle the power between on and off, changing
the value stored in the powerOn field from true to false or from false
to true.
 increaseVolume. The increaseVolume method will increase the value
stored in the volume field by 1.
 decreaseVolume. The decreaseVolume method will decrease the value
stored in the volume field by 1.
 getChannel. The getChannel method will return the value stored in the
channel field.
 getVolume. The getVolume method will return the value stored in the
volume field.
 getManufacturer. The getManufacturer method will return the
constant value stored in the MANUFACTURER field.
 getScreenSize. The getScreenSize method will return the constant
value stored in the SCREEN_SIZE field.
We will also need a constructor method that will be used to create an instance of a
Television.
These ideas can be brought together to form a UML (Unified Modeling Language)
diagram for this class, as shown below.
Television

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-MANUFACTURER: String
-SCREEN_SIZE: int
-powerOn: boolean
-channel: int
-volume: int
+Television(brand: String, size: int):
+setChannel (station: int): void
+power( ): void
+increaseVolume( ): void
+decreaseVolume( ): void
+getChannel( ): int
+getVolume( ): int
+getManufacturer( ): String
+getScreenSize( ): int
Task #1 Creating a New Class
1. In a new file, create a class definition called Television.
2. Put a program header (comments or documentation) at the top of the file
// The purpose of this class is to model a television
// Your name and today’s date
3. Declare the 2 constant fields MANUFACTURER and SCREEN_SIZE listed in the
UML diagram.
4. Declare the 3 remaining fields listed in the UML diagram.
5. Write a comment for each field indicating what it represents.
6. Save this file as Television.java.
7. Compile and debug. Do not run.
Task #2 Writing a Constructor
1. Create a constructor definition that has two parameters, a manufacturer’s brand
and a screen size. These parameters will bring in information.
2. Inside the constructor, assign the values taken in from the parameters to the
corresponding fields.
3. Initialize the powerOn field to false (power is off), the volume to 20, and the

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channel to 2.
4. Write comments describing the purpose of the constructor above the method
header.
5. Compile and debug. Do not run.
Task #3 Methods
1. Define accessor methods called getVolume, getChannel,
getManufacturer, and getScreenSize that return the value of the
corresponding field.
2. Define a mutator method called setChannel that accepts a value to be stored
in the channel field.
3. Define a mutator method called power that changes the state from true to
false or from false to true. This can be accomplished by using the NOT
operator (!). If the boolean variable powerOn is true, then !powerOn is
false and vice versa.
Use the assignment statement
powerOn = !powerOn;
to change the state of powerOn and then store it back into powerOn
(remember assignment statements evaluate the right hand side first, then assign
the result to the left hand side variable.
4. Define two mutator methods to change the volume. One method should be
called increaseVolume and will increase the volume by 1. The other
method should be called decreaseVolume and will decrease the volume by
1.
5. Write javadoc comments above each method header.
6. Compile and debug. Do not run.
Task #4 Running the Application
1. You can only execute (run) a program that has a main method, so there is a
driver program that is already written to test out your Television class. Copy
the file TelevisionDemo.java (attached) to the same directory as Television.java.
2. Compile and run TelevisionDemo and follow the prompts.

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3. If your output matches the output below, Television.java is complete
and correct. You will not need to modify it further for this lab.
OUTPUT (boldface is user input)
A 55 inch Toshiba has been turned on.
What channel do you want? 56
Channel: 56 Volume: 21
Too loud! Lowering the volume.
Channel: 56 Volume: 15
Task #5 Creating another instance of a Television
1. Edit the TelevisionDemo.java file.
2. Declare another Television object called portable.
3. Instantiate portable to be a Sharp 19 inch television.
4. Use a call to the power method to turn the power on.
5. Use calls to the accessor methods to print what television was turned on.
6. Use calls to the mutator methods to change the channel to the user’s
preference and decrease the volume by two.
7. Use calls to the accessor methods to print the changed state of the portable.
8. Compile and debug this class.
9. Run TelevisionDemo again.
10. The output for Task #5 will appear after the output from above, since we added
onto the bottom of the program. The output for Task #5 is shown below.
OUTPUT (boldface is user input)
A 19 inch Sharp has been turned on.
What channel do you want? 7
Channel: 7 Volume: 18

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Code Listing 6.1 (TelevisionDemo.java)
import java.util.Scanner; // Needed for the Scanner class
/**
This class demonstrates the Television class.
*/
public class TelevisionDemo
{
public static void main(String[] args)
{
// Create a Scanner object to read from the keyboard
Scanner keyboard = new Scanner (System.in);
// Declare variables
int station; // The user's channel choice
// Declare and instantiate a television object
Television bigScreen = new Television("Toshiba", 55);
// Turn the power on
bigScreen.power();
// Display the state of the television
System.out.println("A " +
bigScreen.getScreenSize() +
" inch " +
bigScreen.getManufacturer() +
" has been turned on.");
// Prompt the user for input and store into station
System.out.print("What channel do you want? ");
station = keyboard.nextInt();
// Change the channel on the television
bigScreen.setChannel(station);
// Increase the volume of the television
bigScreen.increaseVolume();
// Display the the current channel and
// volume of the television
System.out.println("Channel: " +
bigScreen.getChannel() +
" Volume: " +
bigScreen.getVolume());

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System.out.println("Too loud! Lowering the volume.");
// Decrease the volume of the television
bigScreen.decreaseVolume();
bigScreen.decreaseVolume();
bigScreen.decreaseVolume();
bigScreen.decreaseVolume();
bigScreen.decreaseVolume();
bigScreen.decreaseVolume();
// Display the the current channel and
// volume of the television
System.out.println("Channel: " +
bigScreen.getChannel() +
" Volume: " +
bigScreen.getVolume());
System.out.println(); // For a blank line
// HERE IS WHERE YOU DO TASK #5
}
}