LAB 9 : EXPERIMENTING WITH SPECIALIZATION

Getting Ready: Before going any further you should:

1. Make a directory on your N: drive for this lab.

2. Setup your development environment.

3. Download Clock.class and icon.gif, and put them in your working directory.

The documentation for the Clock class is available at javadocs/Clock.html.

Part I: In this part of the lab you will use an existing class.

1. Write a driver that constructs two clocks, one for Harrisonburg and one for Paris. (Some others you can try are London, Rome, Chicago.)
2. Be sure that you test each of the get methods and the beep. IMPORTANT: if you do not hear the beep it is because the computers have had their sounds turned off. You can modify the code so that the color changes as an alarm instead. NOTE: You do not need to test the update method as it is likely called by the Constructor. (You will see it in operation as soon as you display the clock.)
3. Compile and execute your driver.

Part II: In this part of the lab you will specialize an existing class. (Or in java terms, extend the class.)

1. Create a file named AlarmClock.java that contains the following:

/**

* A GUI window that contains an alarm clock

* with a digital display

*

* @author

* @version 1.0

*/

public class AlarmClock extends Clock

{

private boolean on;

private int hour, minute, second;

private String ampm;

/**

* Default Constructor

*/

public AlarmClock()

{

// call parent default constructor

}

/**

* Explicit Value Constructor

*

* Constructs a clock for a particular city, setting

* the time zone appropriately – think about what the parent does

*

* @param city The city

*/

public AlarmClock(String city)

{

}

}

2. Modify the two constructors in the AlarmClock class so that they call the appropriate constructors in the Clock class.
3. Modify your driver so that the clock for Harrisonburg is actually an AlarmClock object.
4. Compile and execute your driver.

See worksheet

5. Add the following to your AlarmClock.java class:

/**

* Set the alarm

*

* @param hour The hour of the alarm

* @param minute The minute of the alarm

* @param second The second of the alarm

* @param ampm "AM" for before noon, "PM" for noon and after

*/

public void setAlarm(int hour, int minute, int second, String ampm)

{

}

/**

* Turn the alarm off

*/

public void turnAlarmOff()

{

on = false;

}

/**

* Turn the alarm on

*/

public void turnAlarmOn()

{

on = true;

}

and complete the setAlarm() method (i.e., set the attributes appropriately).

6. Add the following to your AlarmClock.java class:

/**

* Update the time displayed on the clock

*/

public void updateTime()

{

int hourNow, minuteNow, secondNow;

String ampmNow;

// Call the parent's version of updateTime()

// If the alarm is on, get the current hour, minute

// second, and ampm and check to see if the alarm

// should sound now

}

and complete the udpateTime() method.

7. Modify your driver so that it sets the alarm (for a time about a minute in the future) and turns the alarm on.
8. Compile and execute your driver.

See worksheet

9. What happens (or doesn't happen) if you comment out the call to the parent's updateTime() method?

See worksheet

Part III: In this part of the lab you will think about specialization in Java, and what kinds of errors you might encounter when you compile classes that you develop.

1. Create a file named Tester1.java that contains the following:

/**

* A Driver for testing the Clock and AlarmClock classes

*/

public class Tester1

{

/**

* The enty point of the application

*

* @param args The command line arguments

*/

public static void main(String[] args)

{

AlarmClock home;

Clock paris;

home = new AlarmClock();

paris = new Clock("Paris");

setup(home);

setup(paris);

}

/**

* Setup a Clock

*

* @param clock The clock to setup

*/

private static void setup(Clock clock)

{

clock.reverseColors();

}

}

2. The setup() method has a Clock as a formal parameter but is actually passed an AlarmClock. Will this class compile? If so, why? If not, why not?

3. Create a file named Tester2.java that contains the following:

/**

* A Driver for testing the Clock and AlarmClock classes

*/

public class Tester2

{

/**

* The enty point of the application

*

* @param args The command line arguments

*/

public static void main(String[] args)

{

AlarmClock home;

Clock paris;

home = new AlarmClock();

paris = new Clock("Paris");

setup(home);

setup(paris);

}

/**

* Setup a clock

*

* @param clock The clock to setup

*/

private static void setup(Clock clock)

{

clock.reverseColors();

clock.turnAlarmOn();

}

}

4. Will this class compile? If so, why? If not, why not?

5. Create a file named Tester3.java that contains the following:

/**

* A Driver for testing the Clock and AlarmClock classes

*/

public class Tester3

{

/**

* The enty point of the application

*

* @param args The command line arguments

*/

public static void main(String[] args)

{

AlarmClock home;

Clock paris;

home = new AlarmClock();

paris = new Clock("Paris");

setup(home);

setup(paris);

}

/**

* Setup a clock

*

* @param clock The clock to setup

*/

private static void setup(AlarmClock clock)

{

clock.reverseColors();

clock.turnAlarmOn();

}

}

6. Will this class compile? If so, why? If not, why not?

7. Create a file named Tester4.java that contains the following:

/**

* A Driver for testing the Clock and AlarmClock classes

*/

public class Tester4

{

/**

* The enty point of the application

*

* @param args The command line arguments

*/

public static void main(String[] args)

{

Clock home, paris;

home = createClock("Harrisonburg");

paris = createClock("Paris");

}

/**

* Create and setup a Clock

*

* @param clock The clock to setup

*/

private static AlarmClock createClock(String city)

{

AlarmClock temp;

temp = new AlarmClock(city);

temp.reverseColors();

return temp;

}

}

8. The createClock() method creates and returns AlarmClock objects that main assigns to Clock objects. Will this class compile? If so, why? If not, why not?

9. Create a file named Tester5.java that contains the following:

/**

* A Driver for testing the Clock and AlarmClock classes

*/

public class Tester5

{

/**

* The enty point of the application

*

* @param args The command line arguments

*/

public static void main(String[] args)

{

Clock home, paris;

home = createClock("Harrisonburg");

paris = createClock("Paris");

home.setAlarm(1, 39, 45, "PM");

home.turnAlarmOn();

}

/**

* Create and setup a Clock

*

* @param clock The clock to setup

*/

private static AlarmClock createClock(String city)

{

AlarmClock temp;

temp = new AlarmClock(city);

temp.reverseColors();

return temp;

}

}

10. Will this class compile? If so, why? If not, why not?