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  package java.util;
  
  /**
   * A {@link Map} that further provides a <em>total ordering</em> on its keys.
   * The map is ordered according to the {@linkplain Comparable natural
   * ordering} of its keys, or by a {@link Comparator} typically
   * provided at sorted map creation time.  This order is reflected when
   * iterating over the sorted map's collection views (returned by the
   * {@code entrySet}, {@code keySet} and {@code values} methods).
   * Several additional operations are provided to take advantage of the
   * ordering.  (This interface is the map analogue of {@link SortedSet}.)
   *
   * <p>All keys inserted into a sorted map must implement the {@code Comparable}
   * interface (or be accepted by the specified comparator).  Furthermore, all
   * such keys must be <em>mutually comparable</em>: {@code k1.compareTo(k2)} (or
   * {@code comparator.compare(k1, k2)}) must not throw a
   * {@code ClassCastException} for any keys {@code k1} and {@code k2} in
   * the sorted map.  Attempts to violate this restriction will cause the
   * offending method or constructor invocation to throw a
   * {@code ClassCastException}.
   *
   * <p>Note that the ordering maintained by a sorted map (whether or not an
   * explicit comparator is provided) must be <em>consistent with equals</em> if
   * the sorted map is to correctly implement the {@code Map} interface.  (See
   * the {@code Comparable} interface or {@code Comparator} interface for a
   * precise definition of <em>consistent with equals</em>.)  This is so because
   * the {@code Map} interface is defined in terms of the {@code equals}
   * operation, but a sorted map performs all key comparisons using its
   * {@code compareTo} (or {@code compare}) method, so two keys that are
   * deemed equal by this method are, from the standpoint of the sorted map,
   * equal.  The behavior of a tree map <em>is</em> well-defined even if its
   * ordering is inconsistent with equals; it just fails to obey the general
   * contract of the {@code Map} interface.
   *
   * <p>All general-purpose sorted map implementation classes should provide four
   * "standard" constructors. It is not possible to enforce this recommendation
   * though as required constructors cannot be specified by interfaces. The
   * expected "standard" constructors for all sorted map implementations are:
   * <ol>
   *   <li>A void (no arguments) constructor, which creates an empty sorted map
   *   sorted according to the natural ordering of its keys.</li>
   *   <li>A constructor with a single argument of type {@code Comparator}, which
   *   creates an empty sorted map sorted according to the specified comparator.</li>
   *   <li>A constructor with a single argument of type {@code Map}, which creates
   *   a new map with the same key-value mappings as its argument, sorted
   *   according to the keys' natural ordering.</li>
   *   <li>A constructor with a single argument of type {@code SortedMap}, which
   *   creates a new sorted map with the same key-value mappings and the same
   *   ordering as the input sorted map.</li>
   * </ol>
   *
   * <p><strong>Note</strong>: several methods return submaps with restricted key
   * ranges. Such ranges are <em>half-open</em>, that is, they include their low
   * endpoint but not their high endpoint (where applicable).  If you need a
   * <em>closed range</em> (which includes both endpoints), and the key type
   * allows for calculation of the successor of a given key, merely request
   * the subrange from {@code lowEndpoint} to
   * {@code successor(highEndpoint)}.  For example, suppose that {@code m}
   * is a map whose keys are strings.  The following idiom obtains a view
   * containing all of the key-value mappings in {@code m} whose keys are
   * between {@code low} and {@code high}, inclusive:<pre>
   *   SortedMap&lt;String, V&gt; sub = m.subMap(low, high+"\0");</pre>
   *
   * A similar technique can be used to generate an <em>open range</em>
   * (which contains neither endpoint).  The following idiom obtains a
   * view containing all of the key-value mappings in {@code m} whose keys
   * are between {@code low} and {@code high}, exclusive:<pre>
   *   SortedMap&lt;String, V&gt; sub = m.subMap(low+"\0", high);</pre>
   *
   * <p>This interface is a member of the
   * <a href="{@docRoot}/../technotes/guides/collections/index.html">
   * Java Collections Framework</a>.
   *
   * @param <K> the type of keys maintained by this map
   * @param <V> the type of mapped values
   *
   * @author  Josh Bloch
   * @see Map
   * @see TreeMap
   * @see SortedSet
   * @see Comparator
   * @see Comparable
   * @see Collection
   * @see ClassCastException
   * @since 1.2
   */
  
  public interface SortedMap<K,V> extends Map<K,V> {
      /**
       * Returns the comparator used to order the keys in this map, or
       * {@code null} if this map uses the {@linkplain Comparable
       * natural ordering} of its keys.
       *
       * @return the comparator used to order the keys in this map,
       *         or {@code null} if this map uses the natural ordering
       *         of its keys
       */
      Comparator<? super K> comparator();
  
      /**
       * Returns a view of the portion of this map whose keys range from
       * {@code fromKey}, inclusive, to {@code toKey}, exclusive.  (If
       * {@code fromKey} and {@code toKey} are equal, the returned map
       * is empty.)  The returned map is backed by this map, so changes
       * in the returned map are reflected in this map, and vice-versa.
       * The returned map supports all optional map operations that this
       * map supports.
       *
       * <p>The returned map will throw an {@code IllegalArgumentException}
       * on an attempt to insert a key outside its range.
       *
       * @param fromKey low endpoint (inclusive) of the keys in the returned map
       * @param toKey high endpoint (exclusive) of the keys in the returned map
       * @return a view of the portion of this map whose keys range from
       *         {@code fromKey}, inclusive, to {@code toKey}, exclusive
       * @throws ClassCastException if {@code fromKey} and {@code toKey}
       *         cannot be compared to one another using this map's comparator
       *         (or, if the map has no comparator, using natural ordering).
       *         Implementations may, but are not required to, throw this
       *         exception if {@code fromKey} or {@code toKey}
       *         cannot be compared to keys currently in the map.
       * @throws NullPointerException if {@code fromKey} or {@code toKey}
       *         is null and this map does not permit null keys
       * @throws IllegalArgumentException if {@code fromKey} is greater than
       *         {@code toKey}; or if this map itself has a restricted
       *         range, and {@code fromKey} or {@code toKey} lies
       *         outside the bounds of the range
       */
      SortedMap<K,V> subMap(K fromKey, K toKey);
  
      /**
       * Returns a view of the portion of this map whose keys are
       * strictly less than {@code toKey}.  The returned map is backed
       * by this map, so changes in the returned map are reflected in
       * this map, and vice-versa.  The returned map supports all
       * optional map operations that this map supports.
       *
       * <p>The returned map will throw an {@code IllegalArgumentException}
       * on an attempt to insert a key outside its range.
       *
       * @param toKey high endpoint (exclusive) of the keys in the returned map
       * @return a view of the portion of this map whose keys are strictly
       *         less than {@code toKey}
       * @throws ClassCastException if {@code toKey} is not compatible
       *         with this map's comparator (or, if the map has no comparator,
       *         if {@code toKey} does not implement {@link Comparable}).
       *         Implementations may, but are not required to, throw this
       *         exception if {@code toKey} cannot be compared to keys
       *         currently in the map.
       * @throws NullPointerException if {@code toKey} is null and
       *         this map does not permit null keys
       * @throws IllegalArgumentException if this map itself has a
       *         restricted range, and {@code toKey} lies outside the
       *         bounds of the range
       */
      SortedMap<K,V> headMap(K toKey);
  
      /**
       * Returns a view of the portion of this map whose keys are
       * greater than or equal to {@code fromKey}.  The returned map is
       * backed by this map, so changes in the returned map are
       * reflected in this map, and vice-versa.  The returned map
       * supports all optional map operations that this map supports.
       *
       * <p>The returned map will throw an {@code IllegalArgumentException}
       * on an attempt to insert a key outside its range.
       *
       * @param fromKey low endpoint (inclusive) of the keys in the returned map
       * @return a view of the portion of this map whose keys are greater
       *         than or equal to {@code fromKey}
       * @throws ClassCastException if {@code fromKey} is not compatible
       *         with this map's comparator (or, if the map has no comparator,
       *         if {@code fromKey} does not implement {@link Comparable}).
       *         Implementations may, but are not required to, throw this
       *         exception if {@code fromKey} cannot be compared to keys
       *         currently in the map.
       * @throws NullPointerException if {@code fromKey} is null and
       *         this map does not permit null keys
       * @throws IllegalArgumentException if this map itself has a
       *         restricted range, and {@code fromKey} lies outside the
       *         bounds of the range
       */
      SortedMap<K,V> tailMap(K fromKey);
  
      /**
       * Returns the first (lowest) key currently in this map.
       *
       * @return the first (lowest) key currently in this map
       * @throws NoSuchElementException if this map is empty
       */
      K firstKey();
  
      /**
       * Returns the last (highest) key currently in this map.
       *
       * @return the last (highest) key currently in this map
       * @throws NoSuchElementException if this map is empty
       */
      K lastKey();
  
      /**
       * Returns a {@link Set} view of the keys contained in this map.
       * The set's iterator returns the keys in ascending order.
       * The set is backed by the map, so changes to the map are
       * reflected in the set, and vice-versa.  If the map is modified
       * while an iteration over the set is in progress (except through
       * the iterator's own {@code remove} operation), the results of
       * the iteration are undefined.  The set supports element removal,
       * which removes the corresponding mapping from the map, via the
       * {@code Iterator.remove}, {@code Set.remove},
       * {@code removeAll}, {@code retainAll}, and {@code clear}
       * operations.  It does not support the {@code add} or {@code addAll}
       * operations.
       *
       * @return a set view of the keys contained in this map, sorted in
       *         ascending order
       */
      Set<K> keySet();
  
      /**
       * Returns a {@link Collection} view of the values contained in this map.
       * The collection's iterator returns the values in ascending order
       * of the corresponding keys.
       * The collection is backed by the map, so changes to the map are
       * reflected in the collection, and vice-versa.  If the map is
       * modified while an iteration over the collection is in progress
       * (except through the iterator's own {@code remove} operation),
       * the results of the iteration are undefined.  The collection
       * supports element removal, which removes the corresponding
       * mapping from the map, via the {@code Iterator.remove},
       * {@code Collection.remove}, {@code removeAll},
       * {@code retainAll} and {@code clear} operations.  It does not
       * support the {@code add} or {@code addAll} operations.
       *
       * @return a collection view of the values contained in this map,
       *         sorted in ascending key order
       */
      Collection<V> values();
  
      /**
       * Returns a {@link Set} view of the mappings contained in this map.
       * The set's iterator returns the entries in ascending key order.
       * The set is backed by the map, so changes to the map are
       * reflected in the set, and vice-versa.  If the map is modified
       * while an iteration over the set is in progress (except through
       * the iterator's own {@code remove} operation, or through the
       * {@code setValue} operation on a map entry returned by the
       * iterator) the results of the iteration are undefined.  The set
       * supports element removal, which removes the corresponding
       * mapping from the map, via the {@code Iterator.remove},
       * {@code Set.remove}, {@code removeAll}, {@code retainAll} and
       * {@code clear} operations.  It does not support the
       * {@code add} or {@code addAll} operations.
       *
       * @return a set view of the mappings contained in this map,
       *         sorted in ascending key order
       */
      Set<Entry<K, V>> entrySet();
  }
  