ITEC 120 2007spring ibarland, jpittges

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hw05
Objects containing objects
hw05

Due Mar.05 (Mon) 17:00;
30pts.

Reading: Chapter 3.
This problem is Exercise 3.30 from the textbook, However, some direction is provided here (as mentioned in 3.31), to help guide us toward a simple solution.

Take the class ClockDisplay from the book, and…

1. Make a project which includes class NumberDisplay and class ClockDisplay, from Chapter 3.
   On Blackboard¹, you can download the code which comes on the book's CD, as well as a version of that same code modified to look like the code this class is using in lecture. (You can work with either version; see below for how the lecture code style tends to differ from the book's code style.)
2. Add your name to the @author @return and @param as needed.
3. Rename getTime to be getTime24. Change its code as follows:

   String getTime24() { return hours.getDisplayValue() + ":" + minutes.getDisplayValue(); }

   (Note how the comment for the method is entirely unchanged, even though we are modifying the implementation.)
4. Delete the field displayString, the method updateDisplay, and all calls to updateDisplay. (Make sure your program compiles and works correctly.)
5. We will work towards writing getTime12, a ClockDisplay method which returns a string representing the time in a 12-hour format. Write a signature and a stub function, and (in BlueJ) record your test cases. Do not write the function yet.
6. Write a ClockDisplay method String amPmString(), which returns the correct suffix. (We'll use this string later, when computing the 12-hour display string; for now, we'll just write this small function to stand on its own.) Write test cases, before writing the function! Remember to use getters, as needed.
7. Write a helper method in ClockDisplay,

   /** Take a number, and wrap it to the interval [1,12] (inclusive). * @param n The number to wrap. * @return a number in 1,12. The number is usually * the remainder after dividing n by 12, except that * when n is a multiple of 12, we return 12 instead of 0. * Examples: * wrapTo1_12( 0 ) = 12 * wrapTo1_12( 1 ) = 1 * wrapTo1_12( 10 ) = 10 * wrapTo1_12( 12 ) = 12 * wrapTo1_12( 13 ) = 1 * wrapTo1_12( 144 ) = 1 12 * wrapTo1_12( 145 ) = 1 */

8. Finally, expand your stub-function for getTime12, so that it's a working function which passes your test cases. The two helper functions you just wrote will make your life easy!

Extra Credit

1. (3pts) Generalize wrapTo1_12(int) to wrapTo1(int, int) where the second input is the maximum value (instead of being hard-coded as 12).
2. (The homework page will have some extra-credit problems after this assignment is due.)

See differences between our code and the book.

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©2007, Ian Barland, Radford University Last modified 2007.Aug.27 (Mon)

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