Lab: Experience with the Programming Process

1. Understanding the Problem Domain: This part of the lab will help you realize how important it is to understand the problem domain at the start of the programming process (and long before you start writing code).

Read and understand the document describing different techniques for representing the time of day.
What character is used to delimit the hours, minutes, and seconds in a time of day?
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A colon (i.e., the : character).
How is "midnight" represented in military time and civilian time?
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00:00:00 in military time and 12:00:00AM in civilian time.
How is "noon" represented in military time and civilian time?
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12:00:00 in military time and 12:00:00PM in civilian time.
What is the last time of day in military time and civilian time?
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23:59:59 in military time and 11:59:59PM in civilian time.
What important difference is there in the way the 1-digit hours are presented in military time and civilian time?
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Though they both are presented in a 2-character field, the leading character in military time is a 0 whereas it is a space in civilian time.

2. Decompose the Problem into Parts: This part of the lab will help you understand why it is important to decompose a problem into parts and give you some experience doing so.

Read and understand the Software Requirements Specification (SRS) for TimeOut
What are the important functions that TimeOut must perform?
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1. It must determine the current time.

2. It must print the current time using a civilian representation.

3. It must print the current time using a military representation.

4. It must convert String command-line parameters to int values.

5. It must print the command-line parameters.

6. It must calculate the time in the future/past.

7. It must print the future/past time using a civilian representation.

8. It must print the future/past time using a military representation.
Break the problem of formatting a time into subproblems.
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1. It must determine if the hour/minute/second has 1 or 2 digits.

2. It must pad 1-digit numbers with either a leading space or a leading 0.

3. Solve Each Part of the Problem by Hand: This part of the lab will help you understand why it is important to solve each part of the problem by hand before writing code in a particular language.

Suppose the current time is 11:05:28AM. What is the time +22min in the past/future.
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This one is pretty easy: 11:27:28AM.
Suppose the current time is 11:05:28AM. What is the time +57min in the past/future.
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This one is a little harder. Proceeding as in the previous example yields 11:62:28AM. But, we know that the minutes must be in the interval [0, 59] so we have to "carry" into the hour. 62/60 is 1 and 62%60 is 2, so we must increase the hour by 1 and set the minute to 2. But, increasing the hour by 1 also changes AM to PM. So, the answer is 12:02:28PM.
Suppose the current time is 11:05:28AM. What is the time +1hr, -6min, +5sec in the past/future.
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This one is harder still. Blindly adding/subtracting yields 12:-01:33PM which doesn't make sense and I'm a little worried about using the / and % operators with a negative number. However, it looks like it should be 11:59:33AM.
Could you come up with even more complicated examples?
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Yes, have the signs be different, and the absolute value of the hours, minutes, and seconds be be more than 24, 60 and 60 respectively.
Should you start writing code in a programming language yet?
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No, it would be a disaster. If you can't solve the problem by hand you can't even give instructions to another person, let alone to a computer.
How should you proceed at this point?
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There are two possibilities. You can either work harder on this approach or you can consider a different approach. We're going to try a different approach.
Rather than working with times represented as hours, minutes and seconds, we're instead going to work with times represented as seconds since midnight. With that in mind, how many seconds since midnight is 11:05:28AM?
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11hr * 3600sec/hr + 5min * 60sec/min + 28sec = 39928
Working backwards, what hour, minute and second of the day (in military time) correspond to 39928 seconds since midnight?
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The hour is 39928sec / 3600sec/hr = 11hr

For the minute we first must calculate the seconds remaining after this division (i.e., 39928sec % 3600sec/hr = 328sec) and then divide this by 60sec/min. Hence, the minute is 328sec / 60sec/min = 5min.

For the second we need the seconds remaining after this division. Hence, the second is 328sec % 60sec/min = 28sec.
How many seconds are in +1hr, -6min, +5sec?
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This is easy: 1hr * 3600sec/hr - 6min * 60sec/min + 5sec = 3245.
Using the previous answers, how many seconds since midnight is 11:05:28AM changed by +1hr, -6min, +5sec?
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39928 + 3245 = 43173
Working backwards, what hour, minute and second of the day (in military time) correspond to your answer to the previous question?
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43173sec / 3600sec/hr = 11

(43173sec % 3600sec/hr) / 60sec/min = 3573sec / 60sec/min = 59

3573sec % 60sec/min = 33
Which approach seems easier and less error-prone?
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The second approach, so that's what we'll use.
Is it time to start writing Java code?
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No (we're not even close to ready).
Consider the civilian time 11:05:28AM. What is the equivalent military time?
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This one is easy: 11:05:28
Consider the civilian time 3:05:28PM. What is the equivalent military time?
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We have to add 12 to the hour, so 15:05:28
Consider the military time 09:05:28. What is the equivalent civilian time?
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Since the hour is greater than 12 we know that the time is before noon (i.e., AM). So, the answer is 9:05:28AM.
Consider the military time 16:05:28. What is the equivalent civilian time?
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Since the hour is greater than 12 we know that the time is after noon (i.e., PM) and we have to subtract 12 from the hour. So, the answer is 4:05:28PM.
Consider the military time 00:05:28. What is the equivalent civilian time?
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Since the hour is less than 12 we know that the time is before noon (i.e., AM). However, since the hour is exactly 0 we know that we are in the hour immediately after midnight. So, the answer is 12:05:28AM.
In general, when the military hour is less than 12, what is the civilian hour? Is it during the AM or PM half of the day?
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The civilian hour is the same as the military hour. It is during the AM half of the day.
There is one exception to the answer to the previous question. What is it?
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When the military hour is 0 then the civilian hour is 12 (still in the AM half of the day).
In general, when the military hour is greater than or equal to 12, what is the civilian hour? Is it during the AM or PM half of the day?
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The civilian hour is the military hour minus 12. It is during the PM half of the day.
There is one exception to the answer to the previous question. What is it?
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When the military hour is 12 then the civilian hour is also 12 (still in the PM half of the day).
Is it time to start writing Java code?
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No. Look back at the different problems we have to solve and you'll see that there are two we haven't considered yet.
How many digits are in the number -11, -6, 0, 6, 11, and 22 respectively?
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2, 1, 1, 1, 2 and 2.
Mathematically, what is true of numbers with exactly one digit?
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Their absolute value is in the interval [0, 9].
Mathematically, what is true of numbers with exactly two digits?
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Their absolute value is in the interval [10, 99].
Is it time to start writing Java code?
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If you were proficient Java programmers you could start writing code now. However, since you're not, its important that you first understand the language features that you will be making use of.

4. Understand the Relevant Features of the Language: This part of the lab will help you review the relevant features of the Java programming language that you will need to understand when you start writing code.

What are the two kinds of members in a class?
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Attributes and methods.
What does it mean when we say that a member of a class is static?
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It means it belongs to the class, not to individual objects in that class. Hence, it can be referred to using the class name and not the identifier for a particular object.
When should an attribute be declared final?
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When it can't be the left-side operand of an assignment operator more than once.
What is the advantage of declaring an attribute final?
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The compiler will prevent you from mistakenly assigning a value to the attribute.
Why is it better to include a method in a class and call it from multiple locations rather than duplicate the code in each of those locations?
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Code often contains defects. So, duplicate code often duplicates defects. Then, even if you correct a defect in one copy of the code, you're likely to forget about the existence of the the other copies, and the defects in those copies will remain.
Also, smaller components are easier to understand than larger components, and methods result in smaller components.
What does 11 / 3 evaluate to?
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3
What does 11 % 3 evaluate to?
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2 (because 11 / 3 is 3 with a remainder of 2).
Are you overconfident?
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Probably!
What does -4 / 3 evaluate to? Why?
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-1 because Java rounds to 0 (i.e., the result is closer to 0 than the quotient). This is sometimes referred to as truncation.
What does 4 / -3 evaluate to? Why?
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-1 because Java rounds to 0 (i.e., the result is closer to 0 than the quotient).
What does -4 / -3 evaluate to? Why?
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1 because Java rounds to 0 (i.e., the result is closer to 0 than the quotient).
What does -4 % 3 evaluate to? Why?
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-1 because -4 / 3 evaluates to -1 and the quotient is -1 1/3 (meaning there is negative one 3s remaining).
What does 4 % -3 evaluate to? Why?
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1 because 4 / -3 evaluates to -1 and the quotient is -1 1/3 (meaning there is one -3s remaining).
What does -4 % -3 evaluate to? Why?
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-1 because -4 / -3 evaluates to 1 and the quotient is 1 1/3 (meaning there is negative one -3s remaining).
Suppose the current time is exactly 11:00:00. What time will it be 15 hours from now using the seconds since midnight representation?
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11:00:00 corresponds to 11hr * 3600sec/hr = 39600sec since midnight. 15 hours forward corresponds to 15hr * 3600sec/hr = 54000sec. Adding yields 93600 which is, unfortunately, bigger than the 86400 seconds we know are in a day.
We could subtract, but what happens if we then add 30hr or 60hr? So, instead, we should use the % operator. Specifically, the number of seconds since midnight is (39600 + 54000) % 86400 = 93600 % 86400 = 7200 (i.e., 02:00:00).
Suppose the current time is exactly 11:00:00. What time was it 15 hours ago using the seconds since midnight representation?
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11:00:00 corresponds to 11hr * 3600sec/hr = 39600sec since midnight. 15 hours backward corresponds to -15hr * 3600sec/hr = -54000sec. Using the same algorithm as in the previous question, the number of seconds since midnight is (39600 - 54000) % 86400 = -14400 % 86400 = -14400. In other words, 14400 seconds before midnight. So, to figure out the number of seconds since midnight we must add 86400 to get 72000 (i.e., 20:00:00).
Look at the documentation for the Calendar class in the package java.util. Is the method getInstance() static or not?
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static
Look at the documentation for the Calendar class in the package java.util. Is the method get() static or not?
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It is not static.

Using what you now know, how can you find the current time in Java?

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        Calendar       today;
        int            hour, minute, second;
        
        today  = Calendar.getInstance();
        hour   = today.get(Calendar.HOUR_OF_DAY);
        minute = today.get(Calendar.MINUTE);
        second = today.get(Calendar.SECOND);

How can you convert String representations of integers to int values?
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Using the static method named parseInt() in the Integer class.
How are command line parameters passed into the main() method of an application?
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As a String[].
How can you print an unformatted String?
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There are many ways. The easiest is to use the static attribute named out in the System class and call it's print() or println() methods.

5. Understanding any Existing Designs and Components: This part of the lab will help you appreciate the importance/value of UML and why you need to understand existing designs and components before you start writing code.

Read and understand the high-level design for TimeOut.
How many classes are included in the design and what are they?
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Three, the TimeOut, TimeOfDay, and Numerical classes.
In UML, what does it mean when a member is underlined?
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It is static.
All of the methods in Numerical are underlined. What term is often used to describe such a class?
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Classes that have only static methods are often called utility classes.
What tasks are going to be performed by the main() method in the TimeOut class?
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Input and output.
What tasks are going to be performed by the methods in the Numerical class?
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Tasks related to formatting the one-digit and two-digit numbers.
What tasks are going to be performed by TimeOfDay objects.
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TimeOfDay objects will know how to construct themselves, how to change themselves, and how to create String representations of themselves.
Though it isn't made explicit, you should be able to infer the purpose of the boolean parameter of the toString() method by its name. How should the returned String be formatted when the actual parameter is false?
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When it is true it should use the civilian format so, when it is false it should use the military format (since those are only two options).
Have you been given any existing components for TimeOut?
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No. But, if we had, now would be the time to understand them.
Is it time to start writing Java code?
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No (but we're getting closer).

6. Create a Detailed Design: This part of the lab will help you understand how you go from software requirements specifications and a high-level design to a detailed design.

Using the "seconds since midnight" approach, what attribute should the TimeOfDay class have?
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A private int named elapsed.
What "constants" should the TimeOfDay class have?
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It should certainly have the int "constants" SECONDS_PER_MINUTE, MINUTES_PER_HOUR, and HOURS_PER_DAY. It may also need the String constants AM and PM.
Should the "constants" be static as well as final?
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Yes because they are not attributes of individual objects.
Before actually constructing the String, what calculations will the toString() method in the TimeOfDay class need to perform?
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It will need to calculate the hour, minute, and second from the elapsed attribute.
What two methods could be included in the TimeOfDay class that would simplify the toString() method?
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Methods named formatAsMilitary() and formatAsCivilian(), both of which are passed an hour, minute, and second and return a String.
Should those two methods be static or not?
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They should be static because they only use parameters and local variables (no attributes of TimeOfDay objects).
Should those two methods be private or public?
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This is a harder question. They might be useful to other classes, which would argue for making them public. However, if they are public they will need to validate the parameters and handle invalid parameters somehow.
Let's make them public and, just for the purposes of this lab, not worry about validating the parameters.
Draw the UML class diagram look like for this detailed design.
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7. Conclusion: This part of the lab will, hopefully, help you learn the most important lesson of this lab.

You still haven't written a single line of code. Would you be "farther along" if you had started writing code sooner?
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No. You've probably only devoted about an hour to this lab and the understanding that you have gained will save you far more than an hour when you start writing code.
In the past, have you been told that you were wasting a lot of time on programming assignments?
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Yes. I've spent 8-10 hours on assignments that I've been told should take half that time or less. (I've never believed those claims, though.)
Given that you were unable to solve the examples above by hand, do you really think that you could have completed TimeOut without any help?
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I do, but I probably couldn't convince anybody else.
In the future, should you think before you start writing code?
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I should.
In the future, should you break problems up into pieces before you start writing code?
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I should. Small problems are much easier to solve.
In the future, should you think about multiple ways to solve the problem before you start writing code?
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I should. In this case, I probably would have used the first approach (i.e., working with the hour, minute and second) but the second approach (i.e., using the elapsed seconds since midnight) is much better.
In the future, will you you think about these things before you start writing code?
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Only time will tell.