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1 /*
2 * Copyright (c) 1998, 2006, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.util;
27
28 /**
29 * A {@link Set} that further provides a <i>total ordering</i> on its elements.
30 * The elements are ordered using their {@linkplain Comparable natural
31 * ordering}, or by a {@link Comparator} typically provided at sorted
32 * set creation time. The set's iterator will traverse the set in
33 * ascending element order. Several additional operations are provided
34 * to take advantage of the ordering. (This interface is the set
35 * analogue of {@link SortedMap}.)
36 *
37 * <p>All elements inserted into a sorted set must implement the <tt>Comparable</tt>
38 * interface (or be accepted by the specified comparator). Furthermore, all
39 * such elements must be <i>mutually comparable</i>: <tt>e1.compareTo(e2)</tt>
40 * (or <tt>comparator.compare(e1, e2)</tt>) must not throw a
41 * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and <tt>e2</tt> in
42 * the sorted set. Attempts to violate this restriction will cause the
43 * offending method or constructor invocation to throw a
44 * <tt>ClassCastException</tt>.
45 *
46 * <p>Note that the ordering maintained by a sorted set (whether or not an
47 * explicit comparator is provided) must be <i>consistent with equals</i> if
48 * the sorted set is to correctly implement the <tt>Set</tt> interface. (See
49 * the <tt>Comparable</tt> interface or <tt>Comparator</tt> interface for a
50 * precise definition of <i>consistent with equals</i>.) This is so because
51 * the <tt>Set</tt> interface is defined in terms of the <tt>equals</tt>
52 * operation, but a sorted set performs all element comparisons using its
53 * <tt>compareTo</tt> (or <tt>compare</tt>) method, so two elements that are
54 * deemed equal by this method are, from the standpoint of the sorted set,
55 * equal. The behavior of a sorted set <i>is</i> well-defined even if its
56 * ordering is inconsistent with equals; it just fails to obey the general
57 * contract of the <tt>Set</tt> interface.
58 *
59 * <p>All general-purpose sorted set implementation classes should
60 * provide four "standard" constructors: 1) A void (no arguments)
61 * constructor, which creates an empty sorted set sorted according to
62 * the natural ordering of its elements. 2) A constructor with a
63 * single argument of type <tt>Comparator</tt>, which creates an empty
64 * sorted set sorted according to the specified comparator. 3) A
65 * constructor with a single argument of type <tt>Collection</tt>,
66 * which creates a new sorted set with the same elements as its
67 * argument, sorted according to the natural ordering of the elements.
68 * 4) A constructor with a single argument of type <tt>SortedSet</tt>,
69 * which creates a new sorted set with the same elements and the same
70 * ordering as the input sorted set. There is no way to enforce this
71 * recommendation, as interfaces cannot contain constructors.
72 *
73 * <p>Note: several methods return subsets with restricted ranges.
74 * Such ranges are <i>half-open</i>, that is, they include their low
75 * endpoint but not their high endpoint (where applicable).
76 * If you need a <i>closed range</i> (which includes both endpoints), and
77 * the element type allows for calculation of the successor of a given
78 * value, merely request the subrange from <tt>lowEndpoint</tt> to
79 * <tt>successor(highEndpoint)</tt>. For example, suppose that <tt>s</tt>
80 * is a sorted set of strings. The following idiom obtains a view
81 * containing all of the strings in <tt>s</tt> from <tt>low</tt> to
82 * <tt>high</tt>, inclusive:<pre>
83 * SortedSet<String> sub = s.subSet(low, high+"\0");</pre>
84 *
85 * A similar technique can be used to generate an <i>open range</i> (which
86 * contains neither endpoint). The following idiom obtains a view
87 * containing all of the Strings in <tt>s</tt> from <tt>low</tt> to
88 * <tt>high</tt>, exclusive:<pre>
89 * SortedSet<String> sub = s.subSet(low+"\0", high);</pre>
90 *
91 * <p>This interface is a member of the
92 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
93 * Java Collections Framework</a>.
94 *
95 * @param <E> the type of elements maintained by this set
96 *
97 * @author Josh Bloch
98 * @see Set
99 * @see TreeSet
100 * @see SortedMap
101 * @see Collection
102 * @see Comparable
103 * @see Comparator
104 * @see ClassCastException
105 * @since 1.2
106 */
107
108 public interface SortedSet<E> extends Set<E> {
109 /**
110 * Returns the comparator used to order the elements in this set,
111 * or <tt>null</tt> if this set uses the {@linkplain Comparable
112 * natural ordering} of its elements.
113 *
114 * @return the comparator used to order the elements in this set,
115 * or <tt>null</tt> if this set uses the natural ordering
116 * of its elements
117 */
118 Comparator<? super E> comparator();
119
120 /**
121 * Returns a view of the portion of this set whose elements range
122 * from <tt>fromElement</tt>, inclusive, to <tt>toElement</tt>,
123 * exclusive. (If <tt>fromElement</tt> and <tt>toElement</tt> are
124 * equal, the returned set is empty.) The returned set is backed
125 * by this set, so changes in the returned set are reflected in
126 * this set, and vice-versa. The returned set supports all
127 * optional set operations that this set supports.
128 *
129 * <p>The returned set will throw an <tt>IllegalArgumentException</tt>
130 * on an attempt to insert an element outside its range.
131 *
132 * @param fromElement low endpoint (inclusive) of the returned set
133 * @param toElement high endpoint (exclusive) of the returned set
134 * @return a view of the portion of this set whose elements range from
135 * <tt>fromElement</tt>, inclusive, to <tt>toElement</tt>, exclusive
136 * @throws ClassCastException if <tt>fromElement</tt> and
137 * <tt>toElement</tt> cannot be compared to one another using this
138 * set's comparator (or, if the set has no comparator, using
139 * natural ordering). Implementations may, but are not required
140 * to, throw this exception if <tt>fromElement</tt> or
141 * <tt>toElement</tt> cannot be compared to elements currently in
142 * the set.
143 * @throws NullPointerException if <tt>fromElement</tt> or
144 * <tt>toElement</tt> is null and this set does not permit null
145 * elements
146 * @throws IllegalArgumentException if <tt>fromElement</tt> is
147 * greater than <tt>toElement</tt>; or if this set itself
148 * has a restricted range, and <tt>fromElement</tt> or
149 * <tt>toElement</tt> lies outside the bounds of the range
150 */
151 SortedSet<E> subSet(E fromElement, E toElement);
152
153 /**
154 * Returns a view of the portion of this set whose elements are
155 * strictly less than <tt>toElement</tt>. The returned set is
156 * backed by this set, so changes in the returned set are
157 * reflected in this set, and vice-versa. The returned set
158 * supports all optional set operations that this set supports.
159 *
160 * <p>The returned set will throw an <tt>IllegalArgumentException</tt>
161 * on an attempt to insert an element outside its range.
162 *
163 * @param toElement high endpoint (exclusive) of the returned set
164 * @return a view of the portion of this set whose elements are strictly
165 * less than <tt>toElement</tt>
166 * @throws ClassCastException if <tt>toElement</tt> is not compatible
167 * with this set's comparator (or, if the set has no comparator,
168 * if <tt>toElement</tt> does not implement {@link Comparable}).
169 * Implementations may, but are not required to, throw this
170 * exception if <tt>toElement</tt> cannot be compared to elements
171 * currently in the set.
172 * @throws NullPointerException if <tt>toElement</tt> is null and
173 * this set does not permit null elements
174 * @throws IllegalArgumentException if this set itself has a
175 * restricted range, and <tt>toElement</tt> lies outside the
176 * bounds of the range
177 */
178 SortedSet<E> headSet(E toElement);
179
180 /**
181 * Returns a view of the portion of this set whose elements are
182 * greater than or equal to <tt>fromElement</tt>. The returned
183 * set is backed by this set, so changes in the returned set are
184 * reflected in this set, and vice-versa. The returned set
185 * supports all optional set operations that this set supports.
186 *
187 * <p>The returned set will throw an <tt>IllegalArgumentException</tt>
188 * on an attempt to insert an element outside its range.
189 *
190 * @param fromElement low endpoint (inclusive) of the returned set
191 * @return a view of the portion of this set whose elements are greater
192 * than or equal to <tt>fromElement</tt>
193 * @throws ClassCastException if <tt>fromElement</tt> is not compatible
194 * with this set's comparator (or, if the set has no comparator,
195 * if <tt>fromElement</tt> does not implement {@link Comparable}).
196 * Implementations may, but are not required to, throw this
197 * exception if <tt>fromElement</tt> cannot be compared to elements
198 * currently in the set.
199 * @throws NullPointerException if <tt>fromElement</tt> is null
200 * and this set does not permit null elements
201 * @throws IllegalArgumentException if this set itself has a
202 * restricted range, and <tt>fromElement</tt> lies outside the
203 * bounds of the range
204 */
205 SortedSet<E> tailSet(E fromElement);
206
207 /**
208 * Returns the first (lowest) element currently in this set.
209 *
210 * @return the first (lowest) element currently in this set
211 * @throws NoSuchElementException if this set is empty
212 */
213 E first();
214
215 /**
216 * Returns the last (highest) element currently in this set.
217 *
218 * @return the last (highest) element currently in this set
219 * @throws NoSuchElementException if this set is empty
220 */
221 E last();
222 }
```