Answers to Self-Check Problems - Building Java Programs: A Back to Basics Approach - page 1079

10. for (String s : list) {
System.out.println(s.toUpperCase());
}
11. The code throws a ConcurrentModificationException because it is illegal to
modify the elements of an ArrayList while running a for-each over it.
12. The code doesn't compile because primitives cannot be specified as type parame-
ters for generic types. The solution is to use the “wrapper” type Integer instead
of int . Change the line declaring the ArrayList to the following lines:
ArrayList<Integer> numbers = new ArrayList<Integer>();
13. The main purpose of a wrapper class is to act as a bridge between primitive values
and objects. An Integer is an object that holds an int value. Wrappers are useful
in that they allow primitive values to be stored into collections.
14. To arrange an ArrayList into sorted order, call the Collections.sort method
on it. For example, if your ArrayList is stored in a variable named list , call the
following method:
Collections.sort(list);
In order for this to work, the type of the objects stored in the list must be Comparable .
15. A natural ordering is an order for objects of a class where “lesser” objects come
before “greater” ones, as determined by a procedure called the class's comparison
function. To give your own class a natural ordering, declare it to implement the
Comparable interface and define a comparison function for it by writing an appro-
priate compareTo method.
16. (a) n1.compareTo(n2) > 0
(b) n3.compareTo(n1) == 0
(c) n2.compareTo(n1) < 0
(d) s1.compareTo(s2) < 0
(e) s3.compareTo(s1) > 0
(f) s2.compareTo(s2) == 0
17. Scanner console = new Scanner(System.in);
System.out.print("Type a name: ");
String name1 = console.nextLine();
System.out.print("Type a name: ");
String name2 = console.nextLine();
if (name1.compareTo(name2) < 0) {
System.out.println(name1 + " goes before " + name2);
} else if (name1.compareTo(name2) > 0) {
System.out.println(name1 + " goes after " + name2);
} else { // equal
System.out.println(name1 + " is the same as " + name2);
}