A
CollationKey
represents a
String
under the
rules of a specific
Collator
object. Comparing two
CollationKey
s returns the relative order of the
String
s they represent. Using
CollationKey
s
to compare
String
s is generally faster than using
Collator.compare
. Thus, when the
String
s
must be compared multiple times, for example when sorting a list
of
String
s. It's more efficient to use
CollationKey
s.
You can not create CollationKey
s directly. Rather,
generate them by calling Collator.getCollationKey
.
You can only compare CollationKey
s generated from
the same Collator
object.
Generating a CollationKey
for a String
involves examining the entire String
and converting it to series of bits that can be compared bitwise. This
allows fast comparisons once the keys are generated. The cost of generating
keys is recouped in faster comparisons when String
s need
to be compared many times. On the other hand, the result of a comparison
is often determined by the first couple of characters of each String
.
Collator.compare
examines only as many characters as it needs which
allows it to be faster when doing single comparisons.
The following example shows how CollationKey
s might be used
to sort a list of String
s.
// Create an array of CollationKeys for the Strings to be sorted.
Collator myCollator = Collator.getInstance();
CollationKey[] keys = new CollationKey[3];
keys[0] = myCollator.getCollationKey("Tom");
keys[1] = myCollator.getCollationKey("Dick");
keys[2] = myCollator.getCollationKey("Harry");
sort( keys );
//...
// Inside body of sort routine, compare keys this way
if( keys[i].compareTo( keys[j] ) > 0 )
// swap keys[i] and keys[j]
//...
// Finally, when we've returned from sort.
System.out.println( keys[0].getSourceString() );
System.out.println( keys[1].getSourceString() );
System.out.println( keys[2].getSourceString() );