1. /*

  2.  * @(#)SortedSet.java	1.11 01/11/29

  3.  *

  4.  * Copyright 2002 Sun Microsystems, Inc. All rights reserved.

  5.  * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.

  6.  */

  7. 

  8. package java.util;

  9. 

  10. /**

  11.  * A set that further guarantees that its iterator will traverse the set in

  12.  * ascending element order, sorted according to the <i>natural ordering</i> of

  13.  * its elements (see Comparable), or by a Comparator provided at sorted set

  14.  * creation time.  Several additional operations are provided to take

  15.  * advantage of the ordering.  (This interface is the set analogue of

  16.  * SortedMap.)<p>

  17.  *

  18.  * All elements inserted into an sorted set must implement the Comparable

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

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

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

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

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

  24.  * offending method or constructor invocation to throw a

  25.  * <tt>ClassCastException</tt>.<p>

  26.  *

  27.  * Note that the ordering maintained by a sorted set (whether or not an

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

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

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

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

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

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

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

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

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

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

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

  39.  *

  40.  * All general-purpose sorted set implementation classes should provide four

  41.  * "standard" constructors: 1) A void (no arguments) constructor, which

  42.  * creates an empty sorted set sorted according to the <i>natural order</i> of

  43.  * its elements.  2) A constructor with a single argument of type

  44.  * <tt>Comparator</tt>, which creates an empty sorted set sorted according to

  45.  * the specified comparator.  3) A constructor with a single argument of type

  46.  * <tt>Collection</tt>, which creates a new sorted set with the same elements

  47.  * as its argument, sorted according to the elements' natural ordering.  4) A

  48.  * constructor with a single argument of type <tt>SortedSet</tt>, which

  49.  * creates a new sorted set with the same elements and the same ordering as

  50.  * the input sorted set.  There is no way to enforce this recommendation (as

  51.  * interfaces cannot contain constructors) but the JDK implementation (the

  52.  * <tt>TreeSet</tt> class) complies.

  53.  *

  54.  * @author  Josh Bloch

  55.  * @version 1.11 11/29/01

  56.  * @see Set

  57.  * @see TreeSet

  58.  * @see SortedMap

  59.  * @see Collection

  60.  * @see Comparable

  61.  * @see Comparator

  62.  * @see java.lang.ClassCastException

  63.  * @since JDK1.2

  64.  */

  65. 

  66. public interface SortedSet extends Set {

  67.     /**

  68.      * Returns the comparator associated with this sorted set, or

  69.      * <tt>null</tt> if it uses its elements' natural ordering.

  70.      *

  71.      * @return the comparator associated with this sorted set, or

  72.      * 	       <tt>null</tt> if it uses its elements' natural ordering.

  73.      */

  74.     Comparator comparator();

  75. 

  76.     /**

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

  78.      * from <tt>fromElement</tt>, inclusive, to <tt>toElement</tt>, exclusive.

  79.      * (If <tt>fromElement</tt> and <tt>toElement</tt> are equal, the returned

  80.      * sorted set is empty.)  The returned sorted set is backed by this sorted

  81.      * set, so changes in the returned sorted set are reflected in this sorted

  82.      * set, and vice-versa.  The returned sorted set supports all optional set

  83.      * operations that this sorted set supports.<p>

  84.      *

  85.      * The sorted set returned by this method will throw an

  86.      * <tt>IllegalArgumentException</tt> if the user attempts to insert a

  87.      * element outside the specified range.<p>

  88.      * 

  89.      * Note: this method always returns a <i>half-open range</i> (which

  90.      * includes its low endpoint but not its high endpoint).  If you need a

  91.      * <i>closed range</i> (which includes both endpoints), and the element

  92.      * type allows for calculation of the successor a given value, merely

  93.      * request the subrange from <tt>lowEndpoint</tt> to

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

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

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

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

  98.      * SortedSet sub = s.subSet(low, high+"\0");

  99.      * </pre>

  100.      * 

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

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

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

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

  105.      * SortedSet sub = s.subSet(low+"\0", high);

  106.      * </pre>

  107.      *

  108.      * @param fromElement low endpoint (inclusive) of the subSet.

  109.      * @param toElement high endpoint (exclusive) of the subSet.

  110.      * @return a view of the specified range within this sorted set.

  111.      * 

  112.      * @throws ClassCastException if <tt>fromElement</tt> or <tt>toElement</tt>

  113.      *		  cannot be compared with the elements currently in the sorted

  114.      *		  set.  (Implementations may, but are not required to, throw

  115.      *		  this exception under these circumstances.)

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

  117.      *		  <tt>toElement</tt> is <tt>null</tt> and this sorted set does

  118.      *		  not tolerate <tt>null</tt> elements.

  119.      * @throws IllegalArgumentException if <tt>fromElement</tt> is greater

  120.      *         than <tt>toElement</tt>.

  121.      */

  122.     SortedSet subSet(Object fromElement, Object toElement);

  123. 

  124.     /**

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

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

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

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

  129.      * supports all optional set operations.<p>

  130.      *

  131.      * The sorted set returned by this method will throw an

  132.      * <tt>IllegalArgumentException</tt> if the user attempts to insert a

  133.      * element outside the specified range.<p>

  134.      *

  135.      * Note: this method always returns a view that does not contain its

  136.      * (high) endpoint.  If you need a view that does contain this endpoint,

  137.      * and the element type allows for calculation of the successor a given

  138.      * value, merely request a headSet bounded by

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

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

  141.      * containing all of the strings in <tt>s</tt> that are less than or equal

  142.      * to <tt>high</tt>:

  143.      * 	    <pre>    SortedSet head = s.headSet(high+"\0");</pre>

  144.      *

  145.      * @param toElement high endpoint (exclusive) of the headSet.

  146.      * @return a view of the specified initial range of this sorted set.

  147.      * 

  148.      * @throws ClassCastException if <tt>toElement</tt> cannot be compared

  149.      *		  with the elements currently in the sorted set.

  150.      *		  (Implementations may, but are not required to, throw this

  151.      *		  exception under these circumstances.)

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

  153.      *         this sorted set does not tolerate <tt>null</tt> elements.

  154.      */

  155.     SortedSet headSet(Object toElement);

  156. 

  157.     /**

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

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

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

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

  162.      * supports all optional set operations.<p>

  163.      *

  164.      * The sorted set returned by this method will throw an

  165.      * <tt>IllegalArgumentException</tt> if the user attempts to insert a

  166.      * element outside the specified range.<p>

  167.      *

  168.      * Note: this method always returns a view that contains its (low)

  169.      * endpoint.  If you need a view that does not contain this endpoint, and

  170.      * the element type allows for calculation of the successor a given value,

  171.      * merely request a tailSet bounded by <tt>successor(lowEndpoint)</tt>.

  172.      * For example, suppose that <tt>s</tt> is a sorted set of strings.  The

  173.      * following idiom obtains a view containing all of the strings in

  174.      * <tt>s</tt> that are strictly greater than <tt>low</tt>:

  175.      * 

  176.      * 	    <pre>    SortedSet tail = s.tailSet(low+"\0");</pre>

  177.      *

  178.      * @param fromElement low endpoint (inclusive) of the tailSet.

  179.      * @return a view of the specified final range of this sorted set.

  180.      * 

  181.      * @throws ClassCastException if <tt>fromElement</tt> cannot be compared

  182.      *		  with the elements currently in the sorted set.

  183.      *		  (Implementations may, but are not required to, throw this

  184.      *		  exception under these circumstances.)

  185.      * 

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

  187.      *            and this sorted set does not tolerate <tt>null</tt>

  188.      *            elements.

  189.      */

  190.     SortedSet tailSet(Object fromElement);

  191. 

  192.     /**

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

  194.      *

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

  196.      * @throws    NoSuchElementException sorted set is empty.

  197.      */

  198.     Object first();

  199. 

  200.     /**

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

  202.      *

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

  204.      * @throws    NoSuchElementException sorted set is empty.

  205.      */

  206.     Object last();

  207. }