ArrayLists - Building Java Programs: A Back to Basics Approach - page 674

13. Write a method called reverse3 that accepts an ArrayList of integer values as a parameter and reverses each suc-
cessive sequence of three values in the list. If the list has extra values that are not part of a sequence of three, those
values are unchanged. For example, if a list stores values [3, 8, 19, 42, 7, 26, 19, -8] , after the call the
list should store the values [19, 8, 3, 26, 7, 42, 19, -8] . The first sequence of three (3, 8, 19) has been
reversed to be (19, 8, 3) . The second sequence (42, 7, 26) has been reversed to be (26, 7, 42) , and so on.
Notice that 19 and -8 are unchanged because they were not part of a sequence of three values.
14. Write a method called removeShorterStrings that accepts an ArrayList of strings as a parameter and removes
from each pair of values the shorter string in the pair. If the list is of odd length, the final element is unchanged. For
example, suppose that a list contains ["four", "score", "and", ""seven", "years", "ago", "our"] . In
the first pair ( "four" and "score") the shorter string is "four" . In the second pair ("and" and "seven") the
shorter string is "and" . In the third pair ("years" and "ago" ) the shorter string is "ago" . Your method should
remove these shorter strings, changing the list to store ["score", "seven", "years", "our"] . If both strings
in a pair have the same length, remove the first string in the pair.
15. Write a method called clump that accepts an ArrayList of strings as a parameter and replaces each pair of strings
with a single string that consists of the two original strings in parentheses separated by a space. If the list is of odd
length, the final element is unchanged. For example, suppose that a list contains ["four", "score", "and",
"seven", "years", "ago", "our" ]. Your method should change the list to store ["(four score)", ("and
seven"), ("years ago"), "our"].
16. Write a method called interleave that accepts two ArrayList s of integers a1 and a2 as parameters and inserts
the elements of a2 into a1 at alternating indexes. If the lists are of unequal length, the remaining elements of the
longer list are left at the end of a1 . For example, if a1 stores [10, 20, 30] and a2 stores [4, 5, 6, 7, 8] , the
call of interleave(a1, a2); should change a1 to store [10, 4, 20, 5, 30, 6, 7, 8] . If a1 had stored
[10, 20, 30, 40, 50] and a2 had stored [6, 7, 8] , the call of interleave(a1, a2); would change a1 to
store [10, 6, 20, 7, 30, 8, 40, 50] .
17. Modify the Point class from Chapter 8 so that it defines a natural ordering by implementing the Comparable inter-
face. Compare the Points by y -major order; that is, points with smaller y -coordinate values should come before
those with higher y -coordinate values. Break ties by comparing x -coordinate values.
18. Modify the TimeSpan class from Chapter 8 to include a compareTo method that compares time spans by their
length. A time span that represents a shorter amount of time is considered to be “less than” one that represents a longer
amount of time. For example, a span of 3 hours and 15 minutes is greater than a span of 1 hour and 40 minutes.
19. Modify the CalendarDate class from this chapter to include a year field, and modify its compareTo method to
take years into account when making comparisons. Years take precedence over months, which take precedence over
days. For example, July 18, 1995 comes before March 2, 2001.
Programming Projects
1. Write classes to model a shopping list. Make an Item class that represents a grocery item's name and price, such as
tissues for $3. Also implement an ItemOrder class that represents a shopper's desire to purchase a given item in a
given quantity, such as five boxes of tissues. You might wish to implement bulk-discounted items, such as two boxes
of tissue for $4, which would bring the cost of the given item order of 2 + 2 + 1 boxes of tissues to $4 + $4 + $3, or
$11.00. Lastly, implement a ShoppingCart class that stores ItemOrder s in an ArrayList and allows item orders