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RuleBasedCollator object.
Customized collation rules are contained in a String
object that is passed to the RuleBasedCollator
constructor. Here's a simple example:
String simpleRule = "< a < b < c < d"; RuleBasedCollator simpleCollator = new RuleBasedCollator(simpleRule);
For the simpleCollator object in the previous example,
a is less than b, which is less that
c, and so forth. The simpleCollator.compare
method references these rules when comparing strings. The full syntax
used to construct a collation rule is more flexible and complex than
this simple example. For a full description of the syntax, refer to the
API documentation for the
RuleBasedCollator class.
The example that follows sorts a list of Spanish words with two
collators. Full source code for this example is in
RulesDemo.java.
The RulesDemo program starts by defining collation rules
for English and Spanish. The program will sort the Spanish words in the
traditional manner. When sorting by the traditional rules, the letters
ch and ll and their uppercase equivalents each have their own positions
in the sort order. These character pairs compare as if they were one
character. For example, ch sorts as a single letter, following cz in
the sort order. Note how the rules for the two collators differ:
String englishRules =
("< a,A < b,B < c,C < d,D < e,E < f,F " +
"< g,G < h,H < i,I < j,J < k,K < l,L " +
"< m,M < n,N < o,O < p,P < q,Q < r,R " +
"< s,S < t,T < u,U < v,V < w,W < x,X " +
"< y,Y < z,Z");
String smallnTilde = new String("\u00F1"); // ñ
String capitalNTilde = new String("\u00D1"); // Ñ
String traditionalSpanishRules =
("< a,A < b,B < c,C " +
"< ch, cH, Ch, CH " +
"< d,D < e,E < f,F " +
"< g,G < h,H < i,I < j,J < k,K < l,L " +
"< ll, lL, Ll, LL " +
"< m,M < n,N " +
"< " + smallnTilde + "," + capitalNTilde + " " +
"< o,O < p,P < q,Q < r,R " +
"< s,S < t,T < u,U < v,V < w,W < x,X " +
"< y,Y < z,Z");
The following lines of code create the collators and invoke the sort routine:
try {
RuleBasedCollator enCollator =
new RuleBasedCollator(englishRules);
RuleBasedCollator spCollator =
new RuleBasedCollator(traditionalSpanishRules);
sortStrings(enCollator, words);
printStrings(words);
System.out.println();
sortStrings(spCollator, words);
printStrings(words);
} catch (ParseException pe) {
System.out.println("Parse exception for rules");
}
The sort routine, called sortStrings, is generic. It will
sort any array of words according to the rules of any
Collator object:
public static void sortStrings(Collator collator, String[] words) {
String tmp;
for (int i = 0; i < words.length; i++) {
for (int j = i + 1; j < words.length; j++) {
if (collator.compare(words[i], words[j]) > 0) {
tmp = words[i];
words[i] = words[j];
words[j] = tmp;
}
}
}
}
When sorted with the English collation rules, the array of words is as follows:
chalina curioso llama luz
Compare the preceding list with the following, which is sorted according to the traditional Spanish rules of collation:
curioso chalina luz llama
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