Module java.base
Package java.text

Class CollationKey

java.lang.Object
java.text.CollationKey
All Implemented Interfaces:
Comparable<CollationKey>

public abstract class CollationKey
extends Object
implements Comparable<CollationKey>
A CollationKey represents a String under the rules of a specific Collator object. Comparing two CollationKeys returns the relative order of the Strings they represent. Using CollationKeys to compare Strings is generally faster than using Collator.compare. Thus, when the Strings must be compared multiple times, for example when sorting a list of Strings. It's more efficient to use CollationKeys.

You can not create CollationKeys directly. Rather, generate them by calling Collator.getCollationKey. You can only compare CollationKeys 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 Strings 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 CollationKeys might be used to sort a list of Strings.


 // 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());
 

Since:
1.1
See Also:
Collator, RuleBasedCollator
  • Constructor Details

    • CollationKey

      protected CollationKey​(String source)
      CollationKey constructor.
      Parameters:
      source - the source string
      Throws:
      NullPointerException - if source is null
      Since:
      1.6
  • Method Details

    • compareTo

      public abstract int compareTo​(CollationKey target)
      Compare this CollationKey to the target CollationKey. The collation rules of the Collator object which created these keys are applied. Note: CollationKeys created by different Collators can not be compared.
      Specified by:
      compareTo in interface Comparable<CollationKey>
      Parameters:
      target - target CollationKey
      Returns:
      Returns an integer value. Value is less than zero if this is less than target, value is zero if this and target are equal and value is greater than zero if this is greater than target.
      See Also:
      Collator.compare(java.lang.String, java.lang.String)
    • getSourceString

      public String getSourceString()
      Returns the String that this CollationKey represents.
      Returns:
      the source string of this CollationKey
    • toByteArray

      public abstract byte[] toByteArray()
      Converts the CollationKey to a sequence of bits. If two CollationKeys could be legitimately compared, then one could compare the byte arrays for each of those keys to obtain the same result. Byte arrays are organized most significant byte first.
      Returns:
      a byte array representation of the CollationKey