Internationalization and Localization - The Java Programming Language - page 1053

Determining collation factors for a string can be expensive. A Colla-
tionKey object examines a string once, so you can compare precomputed
keys instead of comparing strings with a Collator . The method Collat-
or.getCollationKey returns a key for a string. For example, because Col-
lator implements the interface Comparator , you could use a Collator to
maintain a sorted set of strings:
class CollatorSorting {
private TreeSet<String> sortedStrings;
CollatorSorting(Collator collator) {
sortedStrings = new TreeSet<String>(collator);
}
void add(String str) {
sortedStrings.add(str);
}
Iterator<String> strings() {
return sortedStrings.iterator();
}
}
Each time a new string is inserted in sortedStrings , the Collator is used
as a Comparator , with its compare method invoked on various elements
of the set until the TReeSet finds the proper place to insert the string.
This results in several comparisons. You can make this quicker at the
cost of space by creating a treeMap that uses a CollationKey to map to
the original string. CollationKey implements the interface Comparable with
a compareTo method that can be much more efficient than using Collat-
or.compare .
class CollationKeySorting {
private TreeMap<CollationKey, String> sortedStrings;
private Collator collator;