/* SortedSet.java -- A set that makes guarantees about the order of its
   elements
   Copyright (C) 1998, 2001 Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.

GNU Classpath is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU Classpath; see the file COPYING.  If not, write to the
Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA.

As a special exception, if you link this library with other files to
produce an executable, this library does not by itself cause the
resulting executable to be covered by the GNU General Public License.
This exception does not however invalidate any other reasons why the
executable file might be covered by the GNU General Public License. */


package java.util;

/**
 * A set which guarantees its iteration order. The elements in the set
 * are related by the <i>natural ordering</i> if they are Comparable, or
 * by the provided Comparator.  Additional operations take advantage of
 * the sorted nature of the set.
 * <p>
 *
 * All elements entered in the set must be mutually comparable; in other words,
 * <code>k1.compareTo(k2)</code> or <code>comparator.compare(k1, k2)</code>
 * must not throw a ClassCastException. The ordering must be <i>consistent
 * with equals</i> (see {@link Comparator} for this definition), if the
 * map is to obey the general contract of the Set interface.  If not,
 * the results are well-defined, but probably not what you wanted.
 * <p>
 *
 * It is recommended that all implementing classes provide four constructors:
 * 1) one that takes no arguments and builds an empty set sorted by natural
 * order of the elements; 2) one that takes a Comparator for the sorting order;
 * 3) one that takes a Set and sorts according to the natural order of its
 * elements; and 4) one that takes a SortedSet and sorts by the same
 * comparator. Unfortunately, the Java language does not provide a way to
 * enforce this.
 *
 * @author Original author unknown
 * @author Eric Blake <ebb9@email.byu.edu>
 * @see Set
 * @see TreeSet
 * @see SortedMap
 * @see Collection
 * @see Comparable
 * @see Comparator
 * @see ClassCastException
 * @since 1.2
 * @status updated to 1.4
 */
public interface SortedSet extends Set
{
  /**
   * Returns the comparator used in sorting this set, or null if it is
   * the elements' natural ordering.
   *
   * @return the sorting comparator
   */
  Comparator comparator();

  /**
   * Returns the first (lowest sorted) element in the map.
   *
   * @return the first element
   */
  Object first();

  /**
   * Returns a view of the portion of the set strictly less than toElement. The
   * view is backed by this set, so changes in one show up in the other.
   * The subset supports all optional operations of the original.
   * <p>
   *
   * The returned set throws an IllegalArgumentException any time an element is
   * used which is out of the range of toElement. Note that the endpoint is not
   * included; if you want the endpoint, pass the successor object in to
   * toElement.  For example, for Strings, you can request
   * <code>headSet(limit + "\0")</code>.
   *
   * @param toElement the exclusive upper range of the subset
   * @return the subset
   * @throws ClassCastException if toElement is not comparable to the set
   *         contents
   * @throws IllegalArgumentException if this is a subSet, and toElement is out
   *         of range
   * @throws NullPointerException if toElement is null but the map does not
   *         allow null elements
   */
  SortedSet headSet(Object toElement);

  /**
   * Returns the last (highest sorted) element in the map.
   *
   * @return the last element
   */
  Object last();

  /**
   * Returns a view of the portion of the set greater than or equal to
   * fromElement, and strictly less than toElement. The view is backed by
   * this set, so changes in one show up in the other. The subset supports all
   * optional operations of the original.
   * <p>
   *
   * The returned set throws an IllegalArgumentException any time an element is
   * used which is out of the range of fromElement and toElement. Note that the
   * lower endpoint is included, but the upper is not; if you want to
   * change the inclusion or exclusion of an endpoint, pass the successor
   * object in instead.  For example, for Strings, you can request
   * <code>subSet(lowlimit + "\0", highlimit + "\0")</code> to reverse
   * the inclusiveness of both endpoints.
   *
   * @param fromElement the inclusive lower range of the subset
   * @param toElement the exclusive upper range of the subset
   * @return the subset
   * @throws ClassCastException if fromElement or toElement is not comparable
   *         to the set contents
   * @throws IllegalArgumentException if this is a subSet, and fromElement or
   *         toElement is out of range
   * @throws NullPointerException if fromElement or toElement is null but the
   *         set does not allow null elements
   */
  SortedSet subSet(Object fromElement, Object toElement);

  /**
   * Returns a view of the portion of the set greater than or equal to
   * fromElement. The view is backed by this set, so changes in one show up
   * in the other. The subset supports all optional operations of the original.
   * <p>
   *
   * The returned set throws an IllegalArgumentException any time an element is
   * used which is out of the range of fromElement. Note that the endpoint is
   * included; if you do not want the endpoint, pass the successor object in
   * to fromElement.  For example, for Strings, you can request
   * <code>tailSet(limit + "\0")</code>.
   *
   * @param fromElement the inclusive lower range of the subset
   * @return the subset
   * @throws ClassCastException if fromElement is not comparable to the set
   *         contents
   * @throws IllegalArgumentException if this is a subSet, and fromElement is
   *         out of range
   * @throws NullPointerException if fromElement is null but the set does not
   *         allow null elements
   */
  SortedSet tailSet(Object fromElement);
}