The Java Tutorials have been written for JDK 8. Examples and practices described in this page don't take advantage of improvements introduced in later releases and might use technology no longer available.
See Java Language Changes for a summary of updated language features in Java SE 9 and subsequent releases.
See JDK Release Notes for information about new features, enhancements, and removed or deprecated options for all JDK releases.
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