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Lab Assignment 3 Classes

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 object 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 it will be a named constant.

 screenSize. The screenSize attribute will hold the size of the television screen. This cannot change once the television has been created so it will also 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.

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 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

-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

Data type returned

Class Name

Attributes or fields

Methods

+ public

– private

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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 named constant fields listed in the UML diagram. 4. Declare the 3 remaining private fields listed in the UML diagram. 5. Write a comment for each field indicating what it represents. 6. Save this class definition in a file named 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 name 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 named constant fields.

3. Initialize the powerOn field to false (power is off), the volume to 25, and the channel to 5.

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 values of their corresponding fields.

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 Documentation comments above each method header. 6. Compile and debug. Do not run.

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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 from Blackboard. Make sure it is in the same directory as Television.java.

2. Compile and run TelevisionDemo and follow the prompts. 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 58 inch Samsung has been turned on. What channel do you want? 56

Channel: 56 Volume: 25 Too loud! Lowering the volume.

Channel: 56 Volume: 20

Task #5 Creating another instance of a Television

1. Edit the TelevisionDemo.java file. 2. Declare another Television object called office. 3. Instantiate the office object to be a Sony 43-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 office

television. 8. Compile and debug this class. 9. Run TelevisionDemo again. 10. The output for Task #5 will appear after the output from Task #4 above, since

we added code to the bottom of the program. Sample output for Task #5 is shown below.

OUTPUT (boldface is user input)

A 43 inch Sony has been turned on. What channel do you want? 7

Channel: 7 Volume: 23

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