1. /*

  2.  * @(#)SortedSet.java	1.18 03/01/23

  3.  *

  4.  * Copyright 2003 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 SDK implementation (the

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

  53.  *

  54.  * This interface is a member of the 

  55.  * <a href="{@docRoot}/../guide/collections/index.html">

  56.  * Java Collections Framework</a>.

  57.  *

  58.  * @author  Josh Bloch

  59.  * @version 1.18, 01/23/03

  60.  * @see Set

  61.  * @see TreeSet

  62.  * @see SortedMap

  63.  * @see Collection

  64.  * @see Comparable

  65.  * @see Comparator

  66.  * @see java.lang.ClassCastException

  67.  * @since 1.2

  68.  */

  69. 

  70. public interface SortedSet extends Set {

  71.     /**

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

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

  74.      *

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

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

  77.      */

  78.     Comparator comparator();

  79. 

  80.     /**

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

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

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

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

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

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

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

  88.      *

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

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

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

  92.      * 

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

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

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

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

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

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

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

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

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

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

  103.      * </pre>

  104.      * 

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

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

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

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

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

  110.      * </pre>

  111.      *

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

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

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

  115.      * 

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

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

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

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

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

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

  122.      *         the set.

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

  124.      *         <tt>toElement</tt> or if this set is itself a subSet, headSet,

  125.      *         or tailSet, and <tt>fromElement</tt> or <tt>toElement</tt> are

  126.      *         not within the specified range of the subSet, headSet, or

  127.      *         tailSet.

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

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

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

  131.      */

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

  133. 

  134.     /**

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

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

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

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

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

  140.      *

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

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

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

  144.      *

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

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

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

  148.      * value, merely request a headSet bounded by

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

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

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

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

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

  154.      *

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

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

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

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

  159.      *         if <tt>toElement</tt> does not implement <tt>Comparable</tt>).

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

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

  162.      *         currently in the set.

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

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

  165.      * @throws IllegalArgumentException if this set is itself a subSet,

  166.      *         headSet, or tailSet, and <tt>toElement</tt> is not within the

  167.      *         specified range of the subSet, headSet, or tailSet.

  168.      */

  169.     SortedSet headSet(Object toElement);

  170. 

  171.     /**

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

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

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

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

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

  177.      *

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

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

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

  181.      *

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

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

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

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

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

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

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

  189.      * 

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

  191.      *

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

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

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

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

  196.      *         if <tt>fromElement</tt> does not implement <tt>Comparable</tt>).

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

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

  199.      *         currently in the set.

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

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

  202.      * @throws IllegalArgumentException if this set is itself a subSet,

  203.      *         headSet, or tailSet, and <tt>fromElement</tt> is not within the

  204.      *         specified range of the subSet, headSet, or tailSet.

  205.      */

  206.     SortedSet tailSet(Object fromElement);

  207. 

  208.     /**

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

  210.      *

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

  212.      * @throws    NoSuchElementException sorted set is empty.

  213.      */

  214.     Object first();

  215. 

  216.     /**

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

  218.      *

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

  220.      * @throws    NoSuchElementException sorted set is empty.

  221.      */

  222.     Object last();

  223. }