Exercise 04: Rock Around the Clock

Katarina Elevator in Stockholm, Foto by Arjan Richter

This week’s lab work is intended to get you to implement parts of a class that is given for you. You are also to begin to see the idea of modularization, that is, splitting up code into classes.

Pre-lab

P1. Which of the following expressions returns true? After writing your answers on paper, open the CodePad in BlueJ and try it out.

P2. Write an expression using boolean variables a and b that evaluates to true when either a and b are both true or both false.

P3. Write an expression using boolean variables a and b that evaluates to true when only one of a and b is true, and which is false if a and b are both true or both false. This is called the exclusive-or.

P4. Consider the expression (a && b). Write an equivalent expression (one that evaluates to true at exactly the same values for a and b) without using the && operator.

P5. Americans are kind of strange about numbers and units. They write the days backwards, they use pounds and inches instead of kilograms and centimeters, and they have this bizarre 12-hour clock they use with “am” and “pm”.

• What time is “12:00 am” on the German (24-hour) clock?
• What time is “12:00 pm”?
• What time is “03:00 am”?
• What time is “05:30 pm”?

Post-Lab, AKA What To Turn In

You need to upload 2 Files to Moodle:

• your Lab Report as PDF with the extension .pdf
• the source code folder containing the two BlueJ projects compressed with ZIP and the extension .zip

Your Lab Report should include:

• the names and roles of any collaborators in any parts of the exercise.

• a description of what you did during the lab, including a record of what worked, what problems you encountered.

• The discussion of which version was better, 1 or 2.

• A brief summary of what you learned

• A record of how long you needed for this lab

Lab assignments are due before your next lab at 23.00. They may, of course, be turned in earlier.

Assignment

Source Code for this exercise: https://github.com/htw-imi-info1/exercise04-ws2016

Clock time

1. Adapt the clock-display to display the time American-style (i.e. 12-hour clock and am / pm). You will have to include the am/pm in the time! As I will run automatic tests, make sure your displayString has exactly this format:

Also, if you want to introduce a new parameter to the setTime method, make sure that the old setTime method is still working using 24h-Format. Same goes for the constructor - add a third one if you want an alternative parameter list. 2. There are at least two ways in which you could have implemented exercise 1 - one keeps the time internally as a 24-hour clock and adapts the output, the other keeps the time internally as it is displayed. Whichever way you chose for exercise 1, implement the other in a new BlueJ project (I’ve provided a copy of the original clock-dispay in clock-display-alternative-implementation). Which one was better? Why? 3. Make your clock into an alarm clock by adding an alarm. You should be able to set the alarm time and turn the alarm on and off. When the clock reaches the alarm time, it should ring - writing “Riiiiiiiing!” to the terminal is sufficient. If you’ve completed Assignments 1-3, your ClockDisplay class should have these methods (possibly more):

public class ClockDisplay
{
    public ClockDisplay(){}
    public ClockDisplay(int hour, int minute){}
    public void timeTick(){}
    public void setTime(int hour, int minute){}
    public void setAlarmTime(int hour, int minute){}
    public String getTime(){return null;}
}

4. (For the bored - not obligatory) Research Threads and make the clock increment automatically every second.
5. (Kara Special - not obligatory) Open the kara-communicating project in Greenfoot. There are two Karas in the World, a MasterKara and a SlaveKara, which can communicate with each other as the MasterKara has a reference to the SlaveKara. Implement the copyRow method: MasterKara should move along a row to the left, have SlaveKara mirror its moves to the right, and have SlaveKara put down a leaf every time MasterKara encounters one.