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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
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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 {@code Comparable}
38 * interface (or be accepted by the specified comparator). Furthermore, all
39 * such elements must be <i>mutually comparable</i>: {@code e1.compareTo(e2)}
40 * (or {@code comparator.compare(e1, e2)}) must not throw a
41 * {@code ClassCastException} for any elements {@code e1} and {@code e2} in
42 * the sorted set. Attempts to violate this restriction will cause the
43 * offending method or constructor invocation to throw a
44 * {@code ClassCastException}.
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 {@code Set} interface. (See
49 * the {@code Comparable} interface or {@code Comparator} interface for a
50 * precise definition of <i>consistent with equals</i>.) This is so because
51 * the {@code Set} interface is defined in terms of the {@code equals}
52 * operation, but a sorted set performs all element comparisons using its
53 * {@code compareTo} (or {@code compare}) 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 {@code Set} 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 {@code Comparator}, which creates an empty
64 * sorted set sorted according to the specified comparator. 3) A
65 * constructor with a single argument of type {@code Collection},
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 {@code SortedSet},
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 {@code lowEndpoint} to
79 * {@code successor(highEndpoint)}. For example, suppose that {@code s}
80 * is a sorted set of strings. The following idiom obtains a view
81 * containing all of the strings in {@code s} from {@code low} to
82 * {@code high}, 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 {@code s} from {@code low} to
88 * {@code high}, 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}/java/util/package-summary.html#CollectionsFramework">
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 {@code null} 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 {@code null} 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 {@code fromElement}, inclusive, to {@code toElement},
123 * exclusive. (If {@code fromElement} and {@code toElement} 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 {@code IllegalArgumentException}
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 * {@code fromElement}, inclusive, to {@code toElement}, exclusive
136 * @throws ClassCastException if {@code fromElement} and
137 * {@code toElement} 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 {@code fromElement} or
141 * {@code toElement} cannot be compared to elements currently in
142 * the set.
143 * @throws NullPointerException if {@code fromElement} or
144 * {@code toElement} is null and this set does not permit null
145 * elements
146 * @throws IllegalArgumentException if {@code fromElement} is
147 * greater than {@code toElement}; or if this set itself
148 * has a restricted range, and {@code fromElement} or
149 * {@code toElement} 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 {@code toElement}. 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 {@code IllegalArgumentException}
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 {@code toElement}
166 * @throws ClassCastException if {@code toElement} is not compatible
167 * with this set's comparator (or, if the set has no comparator,
168 * if {@code toElement} does not implement {@link Comparable}).
169 * Implementations may, but are not required to, throw this
170 * exception if {@code toElement} cannot be compared to elements
171 * currently in the set.
172 * @throws NullPointerException if {@code toElement} is null and
173 * this set does not permit null elements
174 * @throws IllegalArgumentException if this set itself has a
175 * restricted range, and {@code toElement} 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 {@code fromElement}. 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 {@code IllegalArgumentException}
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 {@code fromElement}
193 * @throws ClassCastException if {@code fromElement} is not compatible
194 * with this set's comparator (or, if the set has no comparator,
195 * if {@code fromElement} does not implement {@link Comparable}).
196 * Implementations may, but are not required to, throw this
197 * exception if {@code fromElement} cannot be compared to elements
198 * currently in the set.
199 * @throws NullPointerException if {@code fromElement} is null
200 * and this set does not permit null elements
201 * @throws IllegalArgumentException if this set itself has a
202 * restricted range, and {@code fromElement} 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
223 /**
224 * Creates a {@code Spliterator} over the elements in this sorted set.
225 *
226 * <p>The {@code Spliterator} reports {@link Spliterator#DISTINCT},
227 * {@link Spliterator#SORTED} and {@link Spliterator#ORDERED}.
228 * Implementations should document the reporting of additional
229 * characteristic values.
230 *
231 * <p>The spliterator's comparator (see
232 * {@link java.util.Spliterator#getComparator()}) must be {@code null} if
233 * the sorted set's comparator (see {@link #comparator()}) is {@code null}.
234 * Otherwise, the spliterator's comparator must be the same as or impose the
235 * same total ordering as the sorted set's comparator.
236 *
237 * @implSpec
238 * The default implementation creates a
239 * <em><a href="Spliterator.html#binding">late-binding</a></em> spliterator
240 * from the sorted set's {@code Iterator}. The spliterator inherits the
241 * <em>fail-fast</em> properties of the set's iterator. The
242 * spliterator's comparator is the same as the sorted set's comparator.
243 * <p>
244 * The created {@code Spliterator} additionally reports
245 * {@link Spliterator#SIZED}.
246 *
247 * @implNote
248 * The created {@code Spliterator} additionally reports
249 * {@link Spliterator#SUBSIZED}.
250 *
251 * @return a {@code Spliterator} over the elements in this sorted set
252 * @since 1.8
253 */
254 @Override
255 default Spliterator<E> spliterator() {
256 return new Spliterators.IteratorSpliterator<E>(
257 this, Spliterator.DISTINCT | Spliterator.SORTED | Spliterator.ORDERED) {
258 @Override
259 public Comparator<? super E> getComparator() {
260 return SortedSet.this.comparator();
261 }
262 };
263 }
264 }