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:

  • Constructor Summary

    Constructors
    Modifier
    Constructor
    Description
    protected
    CollationKey(String source)
    CollationKey constructor.

  • Method Summary

    Modifier and Type
    Method
    Description
    abstract int
    compareTo(CollationKey target)
    Compare this CollationKey to the target CollationKey.
    String
    getSourceString()
    Returns the String that this CollationKey represents.
    abstract byte[]
    toByteArray()
    Converts the CollationKey to a sequence of bits.

    Methods declared in class Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
    Modifier and Type
    Method
    Description
    protected Object
    clone()
    Answers a new instance of the same class as the receiver, whose slots have been filled in with the values in the slots of the receiver.
    boolean
    equals(Object o)
    Compares the argument to the receiver, and answers true if they represent the same object using a class specific comparison.
    protected void
    finalize()
    Deprecated, for removal: This API element is subject to removal in a future version.
    May cause performance issues, deadlocks and hangs.
    final Class<? extends Object>
    getClass()
    Answers the unique instance of java.lang.Class which represents the class of the receiver.
    int
    hashCode()
    Answers an integer hash code for the receiver.
    final void
    notify()
    Causes one thread which is waiting on the receiver to be made ready to run.
    final void
    notifyAll()
    Causes all threads which are waiting on the receiver to be made ready to run.
    String
    toString()
    Answers a string containing a concise, human-readable description of the receiver.
    final void
    wait()
    Causes the thread which sent this message to be made not ready to run pending some change in the receiver (as indicated by notify or notifyAll).
    final void
    wait(long time)
    Causes the thread which sent this message to be made not ready to run either pending some change in the receiver (as indicated by notify or notifyAll) or the expiration of the timeout.
    final void
    wait(long time, int frac)
    Causes the thread which sent this message to be made not ready to run either pending some change in the receiver (as indicated by notify or notifyAll) or the expiration of the timeout.

  • 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:

    • 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