/* SortedSet.java -- A set that makes guarantees about the order of its
   elements
   Copyright (C) 1998, 2001, 2004, 2005 Free Software Foundation, Inc.

This file is part of GNU Classpath.

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permission to link this library with independent modules to produce an
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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
 * set 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<E> extends Set<E>
{
  /**
   * Returns the comparator used in sorting this set, or null if it is
   * the elements' natural ordering.
   *
   * @return the sorting comparator
   */
  Comparator<? super E> comparator();

  /**
   * Returns the first (lowest sorted) element in the set.
   *
   * @return the first element
   * @throws NoSuchElementException if the set is empty.
   */
  E 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, toElement,
   * is not included; if you want this value included, pass its successor object in to
   * toElement.  For example, for Integers, you could request
   * <code>headSet(new Integer(limit.intValue() + 1))</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 set does not
   *         allow null elements
   */
  SortedSet<E> headSet(E toElement);

  /**
   * Returns the last (highest sorted) element in the set.
   *
   * @return the last element
   * @throws NoSuchElementException if the set is empty.
   */
  E 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 its successor
   * object in instead.  For example, for Integers, you can request
   * <code>subSet(new Integer(lowlimit.intValue() + 1),
   * new Integer(highlimit.intValue() + 1))</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<E> subSet(E fromElement, E 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,
   * fromElement, is included; if you do not want this value to be included, pass its
   * successor object in to fromElement.  For example, for Integers, you could request
   * <code>tailSet(new Integer(limit.intValue() + 1))</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<E> tailSet(E fromElement);
}