gcc/libjava/java/text/CollationKey.java

/* CollationKey.java -- Precomputed collation value
   Copyright (C) 1998, 1999, 2000, 2003  Free Software Foundation, Inc.

This file is part of GNU Classpath.

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it under the terms of the GNU General Public License as published by
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As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
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package java.text;

/* Written using "Java Class Libraries", 2nd edition, plus online
 * API docs for JDK 1.2 from http://www.javasoft.com.
 * Status: Believed complete and correct.
 */

/**
 * This class represents a pre-computed series of bits representing a
 * <code>String</code> for under a particular <code>Collator</code>.  This
 * value may be compared bitwise against another <code>CollationKey</code>
 * representing a different <code>String</code> under the same
 * <code>Collator</code> in a manner than is usually more efficient than
 * using the raw <code>Collator</code> compare methods.  There is overhead
 * associated with calculating this value, so it is generally not
 * advisable to compute <code>CollationKey</code>'s unless multiple 
 * comparisons against a <code>String</code> will be done.  (For example,
 * in a sort routine).
 * <p>
 * This class cannot be instantiated directly.  Instead, a 
 * <code>CollationKey</code> is created by calling the
 * <code>getCollationKey</code> method on an instance of <code>Collator</code>.
 *
 * @author Aaron M. Renn <arenn@urbanophile.com>
 * @author Tom Tromey <tromey@cygnus.com>
 * @date March 25, 1999
 */
public final class CollationKey implements Comparable
{
  /**
   * This is the <code>Collator</code> this object was created from.
   */
  private Collator collator;

  /**
   * This is the <code>String</code> this object represents.
   */
  private String originalText;

  /**
   * This is the bit value for this key.
   */
  private byte[] key;

  CollationKey (Collator collator, String originalText, byte[] key)
  {
    this.collator = collator;
    this.originalText = originalText;
    this.key = key;
  }

  /**
   * This method compares the specified object to this one.  An integer is 
   * returned which indicates whether the specified object is less than, 
   * greater than, or equal to this object.
   *
   * @param ck The <code>CollationKey</code> to compare against this one.
   *
   * @return A negative integer if this object is less than the specified object, 0 if it is equal or a positive integer if it is greater than the specified object.
   */
  public int compareTo (CollationKey ck)
  {
    int max = Math.min (key.length, ck.key.length);

    for (int i = 0; i < max; ++i)
      {
	if (key[i] != ck.key[i])
	  return key[i] - ck.key[i];
      }

    return key.length - ck.key.length;
  }

  /**
   * This method compares the specified object to this one.  The specified
   * object must be an instance of <code>CollationKey</code> or an exception
   * will be thrown.  An integer is returned which indicates whether the
   * specified object is less than, greater than, or equal to this object.
   *
   * @param obj The <code>Object</code> to compare against this one.
   *
   * @return A negative integer if this object is less than the specified object, 0 if it is equal or a positive integer if it is greater than the specified object.
   */
  public int compareTo (Object obj)
  {
    return compareTo ((CollationKey) obj);
  }

  /**
   * This method tests the specified <code>Object</code> for equality with
   * this object.  This will be true if and only if:
   * <p>
   * <ul>
   * <li>The specified object must not be <code>null</code></li>
   * <li>The specified object is an instance of <code>CollationKey</code>.</li>
   * <li>The specified object was created from the same <code>Collator</code>
   * as this object.</li>
   * <li>The specified object has the same source string and bit key as
   * this object.</li>
   * </ul>
   *
   * @param obj The <code>Object</code> to test for equality.
   *
   * @return <code>true</code> if the specified object is equal to this one, <code>false</code> otherwise.
   */
  public boolean equals (Object obj)
  {
    if (! (obj instanceof CollationKey))
      return false;

    CollationKey ck = (CollationKey) obj;

    if (ck.collator != collator)
      return false;

    if (!ck.getSourceString ().equals (getSourceString ()))
      return false;

    if (!ck.toByteArray ().equals (toByteArray ()))
      return false;

    return true;
  }

  /**
   * This method returns the <code>String</code> that this object was created
   * from.
   *
   * @return The source <code>String</code> for this object.
   */
  public String getSourceString()
  {
    return originalText;
  }

  /**
   * This method returns a hash value for this object.  The hash value
   * returned will be the hash code of the bit key so that identical bit
   * keys will return the same value.
   *
   * @return A hash value for this object.
   */
  public int hashCode()
  {
    // We just follow BitSet instead of thinking up something new.
    long h = originalText.hashCode();
    for (int i = key.length - 1; i >= 0; --i)
      h ^= key[i] * (i + 1);
    return (int) ((h >> 32) ^ h);
  }
  
  /**
   * This method returns the collation bit sequence as a byte array.
   *
   * @param A byte array containing the collation bit sequence.
   */
  public byte[] toByteArray()
  {
    return key;
  }
}