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package java.util;

/**

 * A {@link Set} that further provides a <i>total ordering</i> on its elements.

 * The elements are ordered using their {@linkplain Comparable natural

 * ordering}, or by a {@link Comparator} typically provided at sorted

 * set creation time.  The set's iterator will traverse the set in

 * ascending element order. Several additional operations are provided

 * to take advantage of the ordering.  (This interface is the set

 * analogue of {@link SortedMap}.)

 *

 * <p>All elements inserted into a sorted set must implement the <tt>Comparable</tt>

 * interface (or be accepted by the specified comparator).  Furthermore, all

 * such elements must be <i>mutually comparable</i>: <tt>e1.compareTo(e2)</tt>

 * (or <tt>comparator.compare(e1, e2)</tt>) must not throw a

 * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and <tt>e2</tt> in

 * the sorted set.  Attempts to violate this restriction will cause the

 * offending method or constructor invocation to throw a

 * <tt>ClassCastException</tt>.

 *

 * <p>Note that the ordering maintained by a sorted set (whether or not an

 * explicit comparator is provided) must be <i>consistent with equals</i> if

 * the sorted set is to correctly implement the <tt>Set</tt> interface.  (See

 * the <tt>Comparable</tt> interface or <tt>Comparator</tt> interface for a

 * precise definition of <i>consistent with equals</i>.)  This is so because

 * the <tt>Set</tt> interface is defined in terms of the <tt>equals</tt>

 * operation, but a sorted set performs all element comparisons using its

 * <tt>compareTo</tt> (or <tt>compare</tt>) method, so two elements that are

 * deemed equal by this method are, from the standpoint of the sorted set,

 * equal.  The behavior of a sorted set <i>is</i> well-defined even if its

 * ordering is inconsistent with equals; it just fails to obey the general

 * contract of the <tt>Set</tt> interface.

 *

 * <p>All general-purpose sorted set implementation classes should

 * provide four "standard" constructors: 1) A void (no arguments)

 * constructor, which creates an empty sorted set sorted according to

 * the natural ordering of its elements.  2) A constructor with a

 * single argument of type <tt>Comparator</tt>, which creates an empty

 * sorted set sorted according to the specified comparator.  3) A

 * constructor with a single argument of type <tt>Collection</tt>,

 * which creates a new sorted set with the same elements as its

 * argument, sorted according to the natural ordering of the elements.

 * 4) A constructor with a single argument of type <tt>SortedSet</tt>,

 * which creates a new sorted set with the same elements and the same

 * ordering as the input sorted set.  There is no way to enforce this

 * recommendation, as interfaces cannot contain constructors.

 *

 * <p>Note: several methods return subsets with restricted ranges.

 * Such ranges are <i>half-open</i>, that is, they include their low

 * endpoint but not their high endpoint (where applicable).

 * If you need a <i>closed range</i> (which includes both endpoints), and

 * the element type allows for calculation of the successor of a given

 * value, merely request the subrange from <tt>lowEndpoint</tt> to

 * <tt>successor(highEndpoint)</tt>.  For example, suppose that <tt>s</tt>

 * is a sorted set of strings.  The following idiom obtains a view

 * containing all of the strings in <tt>s</tt> from <tt>low</tt> to

 * <tt>high</tt>, inclusive:<pre>

 *   SortedSet&lt;String&gt; sub = s.subSet(low, high+"\0");</pre>

 *

 * A similar technique can be used to generate an <i>open range</i> (which

 * contains neither endpoint).  The following idiom obtains a view

 * containing all of the Strings in <tt>s</tt> from <tt>low</tt> to

 * <tt>high</tt>, exclusive:<pre>

 *   SortedSet&lt;String&gt; sub = s.subSet(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 <E> the type of elements maintained by this set

 *

 * @author  Josh Bloch

 * @see Set

 * @see TreeSet

 * @see SortedMap

 * @see Collection

 * @see Comparable

 * @see Comparator

 * @see ClassCastException

 * @since 1.2

 */

public interface SortedSet<E> extends Set<E> {

    /**

     * Returns the comparator used to order the elements in this set,

     * or <tt>null</tt> if this set uses the {@linkplain Comparable

     * natural ordering} of its elements.

     *

     * @return the comparator used to order the elements in this set,

     *         or <tt>null</tt> if this set uses the natural ordering

     *         of its elements

     */

    Comparator<? super E> comparator();

    /**

     * Returns a view of the portion of this set whose elements range

     * from <tt>fromElement</tt>, inclusive, to <tt>toElement</tt>,

     * exclusive.  (If <tt>fromElement</tt> and <tt>toElement</tt> are

     * equal, the returned set is empty.)  The returned set is backed

     * by this set, so changes in the returned set are reflected in

     * this set, and vice-versa.  The returned set supports all

     * optional set operations that this set supports.

     *

     * <p>The returned set will throw an <tt>IllegalArgumentException</tt>

     * on an attempt to insert an element outside its range.

     *

     * @param fromElement low endpoint (inclusive) of the returned set

     * @param toElement high endpoint (exclusive) of the returned set

     * @return a view of the portion of this set whose elements range from

     *         <tt>fromElement</tt>, inclusive, to <tt>toElement</tt>, exclusive

     * @throws ClassCastException if <tt>fromElement</tt> and

     *         <tt>toElement</tt> cannot be compared to one another using this

     *         set's comparator (or, if the set has no comparator, using

     *         natural ordering).  Implementations may, but are not required

     *         to, throw this exception if <tt>fromElement</tt> or

     *         <tt>toElement</tt> cannot be compared to elements currently in

     *         the set.

     * @throws NullPointerException if <tt>fromElement</tt> or

     *         <tt>toElement</tt> is null and this set does not permit null

     *         elements

     * @throws IllegalArgumentException if <tt>fromElement</tt> is

     *         greater than <tt>toElement</tt>; or if this set itself

     *         has a restricted range, and <tt>fromElement</tt> or

     *         <tt>toElement</tt> lies outside the bounds of the range

     */

    SortedSet<E> subSet(E fromElement, E toElement);

    /**

     * Returns a view of the portion of this set whose elements are

     * strictly less than <tt>toElement</tt>.  The returned set is

     * backed by this set, so changes in the returned set are

     * reflected in this set, and vice-versa.  The returned set

     * supports all optional set operations that this set supports.

     *

     * <p>The returned set will throw an <tt>IllegalArgumentException</tt>

     * on an attempt to insert an element outside its range.

     *

     * @param toElement high endpoint (exclusive) of the returned set

     * @return a view of the portion of this set whose elements are strictly

     *         less than <tt>toElement</tt>

     * @throws ClassCastException if <tt>toElement</tt> is not compatible

     *         with this set's comparator (or, if the set has no comparator,

     *         if <tt>toElement</tt> does not implement {@link Comparable}).

     *         Implementations may, but are not required to, throw this

     *         exception if <tt>toElement</tt> cannot be compared to elements

     *         currently in the set.

     * @throws NullPointerException if <tt>toElement</tt> is null and

     *         this set does not permit null elements

     * @throws IllegalArgumentException if this set itself has a

     *         restricted range, and <tt>toElement</tt> lies outside the

     *         bounds of the range

     */

    SortedSet<E> headSet(E toElement);

    /**

     * Returns a view of the portion of this set whose elements are

     * greater than or equal to <tt>fromElement</tt>.  The returned

     * set is backed by this set, so changes in the returned set are

     * reflected in this set, and vice-versa.  The returned set

     * supports all optional set operations that this set supports.

     *

     * <p>The returned set will throw an <tt>IllegalArgumentException</tt>

     * on an attempt to insert an element outside its range.

     *

     * @param fromElement low endpoint (inclusive) of the returned set

     * @return a view of the portion of this set whose elements are greater

     *         than or equal to <tt>fromElement</tt>

     * @throws ClassCastException if <tt>fromElement</tt> is not compatible

     *         with this set's comparator (or, if the set has no comparator,

     *         if <tt>fromElement</tt> does not implement {@link Comparable}).

     *         Implementations may, but are not required to, throw this

     *         exception if <tt>fromElement</tt> cannot be compared to elements

     *         currently in the set.

     * @throws NullPointerException if <tt>fromElement</tt> is null

     *         and this set does not permit null elements

     * @throws IllegalArgumentException if this set itself has a

     *         restricted range, and <tt>fromElement</tt> lies outside the

     *         bounds of the range

     */

    SortedSet<E> tailSet(E fromElement);

    /**

     * Returns the first (lowest) element currently in this set.

     *

     * @return the first (lowest) element currently in this set

     * @throws NoSuchElementException if this set is empty

     */

    E first();

    /**

     * Returns the last (highest) element currently in this set.

     *

     * @return the last (highest) element currently in this set

     * @throws NoSuchElementException if this set is empty

     */

    E last();

}