Methods Lab

Learning Goals

• Implement instance methods that change object state

Introduction

The starter code provides a TV class along with a Junit TVTest class.

public class TV {
    // Instance variables
    private boolean on;
    private int volume = MIN_VOLUME;
    private int channel = MIN_CHANNEL;
    
    // Class constants
    public static final int MIN_VOLUME = 0;
    public static final int MAX_VOLUME = 10;
    public static final int MIN_CHANNEL = 1;
    public static final int MAX_CHANNEL = 100;
    
    // Getters are used by Junit tests
    public boolean isOn() {return on;}
    public int getVolume() {return volume;}
    public int getChannel() {return channel;}

    // Implement the following methods

    public void toggleOnOff() {

    }

    public void volumeUp() {

    }

    public void volumeDown() {

    }

    public void setChannel(int channel) {

    }

}

The instance variables store the state of each TV object:

• on : a value of true indicates the tv is turned on, while false indicates tv is turned off.
• volume : initialized to MIN_VOLUME and should range between MIN_VOLUME and MAX_VOLUME, inclusive. The tv must be on to change the volume.
• channel : initialized to MIN_CHANNEL and should range between MIN_CHANNEL and MAX_CHANNEL, inclusive. The tv must be on to change the channel.

Task Instructions

• Do not add/delete/change the TV fields (instance variables or static constants).
• Edit the TV methods to implement the functionality described in each task below.
• Do not modify the TV method signatures.
• Do not modify the TVTest methods, except to remove the @Disabled annotation.

Note: Screen prints for tasks 1-4 are missing the Junit test multipleTVsDifferentState, which will be implemented in task5.

Task #1 - Turn the TV on and off

The setUp method in class TVTest creates an instance of TV that will be used to test the TV instance methods.

class TVTest {
    
    private TV tv;

    @BeforeEach
    void setUp() {
        tv = new TV();  //tv not on
    }

    //Test methods
    ...
}

The test methods in class TVTest are all disabled using @Disabled except for the first method toggleOnOff(), which fails if you run it.

Edit the toggleOnOff() method in the TV class:

• The method should toggle the value stored in the on instance variable between true and false.
• Can you do this without an if-else statement? (HINT: use a logical operator)

Run the Junit toggleOnOff() test to confirm your implementation.

Task #2 - Turn the volume up

Edit the volumeUp() method in the TV class to increase the volume by 1. The following two conditions must be true to increase the volume. Do not change the volume if either condition is false.

• The tv must be on.
• The current volume must be less than MAX_VOLUME.

Remove @Disabled from the following Junit tests:

• volumeUpTvNotOn
• volumeUpTvOn
• volumeUpMaxThreshold

Run the tests to confirm your implementation:

Task #3 - Turn the volume down

Edit the volumeDown() method in the TV class to decrease the volume by 1. The following two conditions must be true to decrease the volume. Do not change the volume if either condition is false.

• The tv must be on.
• The current volume must be greater than MIN_VOLUME.

Remove @Disabled from the following Junit tests:

• volumeDownTvNotOn
• volumeDownTvOn
• volumeDownMinThreshold

Run the tests to confirm your implementation:

Task #4 - Set the channel

Edit the setChannel(int channel) method in the TV class to assign the instance variable named channel to the value passed as a parameter variable named channel.

The following two conditions must be true to set the channel. Do not set the channel if either condition is false.

• The tv must be on.
• The channel parameter value must be within the range of MIN_CHANNEL and MAX_CHANNEL, inclusive.

Note the parameter name channel shadows the instance variable channel. Do not alter the method signature. Your parameter must be named channel. Consider how to use a qualified name in the method body to refer to the instance variable named channel versus the parameter named channel.

Remove @Disabled from the following Junit tests:

• setChannelTVNotOn
• setChannelTVOn

Run the tests to confirm your implementation:

Task #5 - Complete the Junit test method named multipleTVsDifferentState

Now you are going to get some practice implementing Junit test methods.

Remove @Disabled from the following Junit test:

• multipleTVsDifferentState

Although the method passes if you run the test, you will need to implement the code for each comment to pass the tests when you submit this assignment.

Add the appropriate method call and/or assertion below each comment. The method is testing two TV objects referenced by variables sony and vizio, so take care to use the correct variable.