CS 161 Assignment #5

Due Wednesday, February 28th by 11:59pm
(Not accepted after 3/1)

Introduction

The word is out! Your OrcaCard class became an overnight sensation. A copy found its way to a local startup company that figures they can make a fortune on web-based digital alarm clocks. They were so impressed with your OrcaCard that they want to pay you large sums of money to help them with a little problem: They need someone to write a Java class that models a clock display — one that shows hours, minutes, and seconds, and that can print an alarm message if the time hits a specified value. You figure it should be pretty easy to extend the clock display project from the "Objects First with Java" textbook, so you sign the contract and start writing Java code...

The Assignment

I've created a new project to get you started: Download and modify ClockAssignment instead of creating a new project via BlueJ or using the code from the book. The project contains the same two classes as the Clock project from the book that we looked at in class. As you'll recall, the book's Clock project represents a 24-hour clock that displays hours and minutes. It uses two instances of the NumberDisplay class to represent the time — one for hours and one for minutes. On this assignment you'll use a third NumberDisplay instance for seconds and modify the existing code as necessary so that the tick method increment's the clock's time by one second rather than one minute. You'll also add the ability to set an alarm time, and print a message when the clock reaches the specified time. (I suggest that you start by extending the current ClockDisplay code so that it keeps track of the time in hours, minutes, and seconds, and wait to implement the alarm until you get the basic clock working.) Your code must meet the following requirements for full credit:

The two-argument constructor should be changed so that it takes three arguments: the desired hour, minute, and second.
The setTime method should take three arguments as well, and set the clock to the specified hour, minute, and second.
The updateDisplay method should build a string showing the seconds as well as the hours and minutes. (See below for examples.)
The timeTick method should be changed so that it increments the seconds value each time it's called. The minutes field should increment each time the seconds field rolls over (and that might, in turn, increment the hours.)

If you only made these changes, you should have a ClockDisplay class that behaves as shown here. The codepad is being used in the example below to create a ClockDisplay object set to two seconds before midnight (23 hours, 59 minutes, and 58 seconds). The timeTick method is incrementing the seconds field, and it all rolls over as expected:

> ClockDisplay clock = new ClockDisplay(23, 59, 58);
> clock.getTime()
 "23:59:58"   (String)
> clock.timeTick();
> clock.getTime()
 "23:59:59"   (String)
> clock.timeTick();
> clock.getTime()
 "00:00:00"   (String)
> clock.timeTick();
> clock.getTime()
 "00:00:01"   (String)
> clock.setTime(0,0,59);
> clock.getTime()
 "00:00:59"   (String)
> clock.timeTick();
> clock.getTime()
 "00:01:00"   (String)

Your ClockDisplay must also implement an alarm function as well. The clock should remember a specified time (hour and minute), and print an alarm message if the clock's current time hits the alarm time. For full credit, you must do the following:

Implement a method called setAlarm that takes two integers as parameters, the hour and the minute (as integers) specifying the time that the alarm should go off. (You'll want to save these values for later use.) No alarms should go off unless this method has been called to set an alarm.
Implement a method called clearAlarm that takes no arguments and that "clears" the current alarm. That is, no alarm should go off after calling clearAlarm regardless of the number of times timeTick is called. (There are multiple ways to make this work, but the easiest is probably to set the alarm hour and minute to values that will never occur.)
Modify the timeTick method so that it prints Alarm! to the terminal window if the time, after incrementing the number of seconds, matches the alarm hour and minute. The message should only appear once though — we don't want it going off every second after that. (See interactions below for an example of the desired behavior.)
After verifying that the methods above work properly, add a second constructor — one that takes another ClockDisplay as its input. It should initialize the current ClockDisplay (the one whose constructor is running) so that its state is exactly like the ClockDisplay being passed in. You can see this constructor in use in the interactions below — we create a new ClockDisplay object called clone that's set to the same values as our original clock.
For full credit, your code should be well commented: Each and every method should have a "javadoc-style" comment above it (the ones that use /** ... */). For full credit, you should use the @param and @return tags as appropriate in these method comments. You should look for opportunities to use constants to tidy up your code, and each instance variable and constant should have a brief comment as well (using //). Don't forget the comments at the top of the classes either — I'm looking for more than just a sentence or two.

Some sample interactions are shown below. (To keep things tidy, the Alarm! lines are shown as part of the interactions in the codepad, but they should actually appear in the terminal window since they're being printed.) Notice that the alarm only goes off once, when the clock hits 9:00, even as additional timeTick() methods are called. Yours should do the same. Also, look carefully at the differences between my original clock and its clone. Asking one to tick does not change the time on the other, and yours should behave the same way. (If it doesn't, think about what's going on in your copy constructor. Draw a diagram of all of the objects and references involved.)

> ClockDisplay clock = new ClockDisplay(8,59,58);
> clock.getTime()
 "08:59:58"   (String)
> clock.setAlarm(9,0);
> clock.timeTick();
> clock.getTime()
 "08:59:59"   (String)
> ClockDisplay clone = new ClockDisplay(clock);
> clock.timeTick();
Alarm!
> clock.getTime()
 "09:00:00"   (String)
> clock.timeTick();
> clock.getTime()
 "09:00:01"   (String)
> clock.timeTick();
> clock.clearAlarm();
> clone.getTime()
 "08:59:59"   (String)
> clone.timeTick();
Alarm!
> clone.getTime()
 "09:00:00"   (String)
> clock.getTime()
 "09:00:02"   (String)

Extending the Assignment

There's no extra credit, but if you're looking for more of a challenge, consider implementing one or more of the following features:

Implement a "snooze" method that adds 10 minutes to the current alarm value.
Extend the updateDisplay method so that the display string includes the alarm time, but only if an alarm is set.
Add a minuteTick method that increments the minutes field without changing seconds. The hours should still increment if minutes roll over.

Grading

This assignment will be graded out of a total of 80 points.

[10pts] Appropriate fields have been declared.
[20pts] Constructors work properly.
[15pts] The timeTick() method works as described above.
[10pts] The setTime() and getTime() methods work as described.
[5pts] The updateDisplay() method works as described.
[10pts] The setAlarm() and clearAlarm() methods work properly.
[10pts] Commenting and style.

Submitting

Before submitting, make sure your code compiles and is commented properly, and test each of your methods thoroughly. When you're convinced that it's ready to go, submit the assignment using BlueJ's submission tool as described here.

Brad Richards, 2024