The Java TM Tutorial

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Trail: Internationalization
Lesson: Working with Text

## Improving Collation Performance

> Sorting long lists of strings is often time consuming. If your sort algorithm compares strings repeatedly, you can speed up the process by using the `CollationKey` class.

> A `CollationKey` object represents a sort key for a given `String` and `Collator`. Comparing two `CollationKey` objects involves a bitwise comparison of sort keys and is faster than comparing `String` objects with the `Collator.compare` method. However, generating `CollationKey` objects requires time. Therefore if a `String` is to be compared just once, `Collator.compare` offers better performance.

> The example that follows uses a `CollationKey` object to sort an array of words. Source code for this example is in `KeysDemo.java`.

> The `KeysDemo` program creates an array of `CollationKey` objects in the `main` method. To create a `CollationKey`, you invoke the `getCollationKey` method on a `Collator` object. You cannot compare two `CollationKey` objects unless they originate from the same `Collator`. The `main` method is as follows:

> >     static public void main(String[] args) {
> >         Collator enUSCollator =
> >                   Collator.getInstance (new Locale("en","US"));
> >         String [] words = {
> >     	"peach",
> >     	"apricot",
> >     	"grape",
> >     	"lemon"
> >         };

> >         CollationKey[] keys = new CollationKey[words.length];

> >         for (int k = 0; k < keys.length; k ++) {
> >     	keys[k] = enUSCollator.getCollationKey(words[k]);
> >         }

> >         sortArray(keys);
> >         printArray(keys);
> >     }

> The `sortArray` method invokes the `CollationKey.compareTo` method. The `compareTo` method returns an integer less than, equal to, or greater than zero if the `keys[i]` object is less than, equal to, or greater than the `keys[j]` object. Note that the program compares the `CollationKey` objects, not the `String` objects from the original array of words. Here is the code for the `sortArray` method:

> >     public static void sortArray(CollationKey[] keys) {

> >         CollationKey tmp;
> >         for (int i = 0; i < keys.length; i++) {
> >     	for (int j = i + 1; j < keys.length; j++) {
> >     	    if (keys[i].compareTo(keys[j]) > 0) {
> >     		tmp = keys[i];
> >     		keys[i] = keys[j];
> >     		keys[j] = tmp;
> >     	    }
> >     	}
> >         }
> >     }

> The `KeysDemo` program sorts an array of `CollationKey` objects, but the original goal was to sort an array of `String` objects. To retrieve the `String` representation of each `CollationKey`, the program invokes `getSourceString` in the `displayWords` method, as follows:

> >     static void displayWords(CollationKey[] keys) {

> >         for (int i = 0; i < keys.length; i++) {
> >     	System.out.println(keys[i].getSourceString());
> >         }
> >     }

> The `displayWords` method prints the following lines:

> >     apricot
> >     grape
> >     lemon
> >     peach

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