1 /* 2 * Copyright (c) 1997, 2013, 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 collection that contains no duplicate elements. More formally, sets 30 * contain no pair of elements <code>e1</code> and <code>e2</code> such that 31 * <code>e1.equals(e2)</code>, and at most one null element. As implied by 32 * its name, this interface models the mathematical <i>set</i> abstraction. 33 * 34 * <p>The <tt>Set</tt> interface places additional stipulations, beyond those 35 * inherited from the <tt>Collection</tt> interface, on the contracts of all 36 * constructors and on the contracts of the <tt>add</tt>, <tt>equals</tt> and 37 * <tt>hashCode</tt> methods. Declarations for other inherited methods are 38 * also included here for convenience. (The specifications accompanying these 39 * declarations have been tailored to the <tt>Set</tt> interface, but they do 40 * not contain any additional stipulations.) 41 * 42 * <p>The additional stipulation on constructors is, not surprisingly, 43 * that all constructors must create a set that contains no duplicate elements 44 * (as defined above). 45 * 46 * <p>Note: Great care must be exercised if mutable objects are used as set 47 * elements. The behavior of a set is not specified if the value of an object 48 * is changed in a manner that affects <tt>equals</tt> comparisons while the 49 * object is an element in the set. A special case of this prohibition is 50 * that it is not permissible for a set to contain itself as an element. 51 * 52 * <p>Some set implementations have restrictions on the elements that 53 * they may contain. For example, some implementations prohibit null elements, 54 * and some have restrictions on the types of their elements. Attempting to 55 * add an ineligible element throws an unchecked exception, typically 56 * <tt>NullPointerException</tt> or <tt>ClassCastException</tt>. Attempting 57 * to query the presence of an ineligible element may throw an exception, 58 * or it may simply return false; some implementations will exhibit the former 59 * behavior and some will exhibit the latter. More generally, attempting an 60 * operation on an ineligible element whose completion would not result in 61 * the insertion of an ineligible element into the set may throw an 62 * exception or it may succeed, at the option of the implementation. 63 * Such exceptions are marked as "optional" in the specification for this 64 * interface. 65 * 66 * <p>This interface is a member of the 67 * <a href="{@docRoot}/../technotes/guides/collections/index.html"> 68 * Java Collections Framework</a>. 69 * 70 * @param <E> the type of elements maintained by this set 71 * 72 * @author Josh Bloch 73 * @author Neal Gafter 74 * @see Collection 75 * @see List 76 * @see SortedSet 77 * @see HashSet 78 * @see TreeSet 79 * @see AbstractSet 80 * @see Collections#singleton(java.lang.Object) 81 * @see Collections#EMPTY_SET 82 * @since 1.2 83 */ 84 85 public interface Set<E> extends Collection<E> { 86 // Query Operations 87 88 /** 89 * Returns the number of elements in this set (its cardinality). If this 90 * set contains more than <tt>Integer.MAX_VALUE</tt> elements, returns 91 * <tt>Integer.MAX_VALUE</tt>. 92 * 93 * @return the number of elements in this set (its cardinality) 94 */ size()95 int size(); 96 97 /** 98 * Returns <tt>true</tt> if this set contains no elements. 99 * 100 * @return <tt>true</tt> if this set contains no elements 101 */ isEmpty()102 boolean isEmpty(); 103 104 /** 105 * Returns <tt>true</tt> if this set contains the specified element. 106 * More formally, returns <tt>true</tt> if and only if this set 107 * contains an element <tt>e</tt> such that 108 * <tt>(o==null ? e==null : o.equals(e))</tt>. 109 * 110 * @param o element whose presence in this set is to be tested 111 * @return <tt>true</tt> if this set contains the specified element 112 * @throws ClassCastException if the type of the specified element 113 * is incompatible with this set 114 * (<a href="Collection.html#optional-restrictions">optional</a>) 115 * @throws NullPointerException if the specified element is null and this 116 * set does not permit null elements 117 * (<a href="Collection.html#optional-restrictions">optional</a>) 118 */ contains(Object o)119 boolean contains(Object o); 120 121 /** 122 * Returns an iterator over the elements in this set. The elements are 123 * returned in no particular order (unless this set is an instance of some 124 * class that provides a guarantee). 125 * 126 * @return an iterator over the elements in this set 127 */ iterator()128 Iterator<E> iterator(); 129 130 /** 131 * Returns an array containing all of the elements in this set. 132 * If this set makes any guarantees as to what order its elements 133 * are returned by its iterator, this method must return the 134 * elements in the same order. 135 * 136 * <p>The returned array will be "safe" in that no references to it 137 * are maintained by this set. (In other words, this method must 138 * allocate a new array even if this set is backed by an array). 139 * The caller is thus free to modify the returned array. 140 * 141 * <p>This method acts as bridge between array-based and collection-based 142 * APIs. 143 * 144 * @return an array containing all the elements in this set 145 */ toArray()146 Object[] toArray(); 147 148 /** 149 * Returns an array containing all of the elements in this set; the 150 * runtime type of the returned array is that of the specified array. 151 * If the set fits in the specified array, it is returned therein. 152 * Otherwise, a new array is allocated with the runtime type of the 153 * specified array and the size of this set. 154 * 155 * <p>If this set fits in the specified array with room to spare 156 * (i.e., the array has more elements than this set), the element in 157 * the array immediately following the end of the set is set to 158 * <tt>null</tt>. (This is useful in determining the length of this 159 * set <i>only</i> if the caller knows that this set does not contain 160 * any null elements.) 161 * 162 * <p>If this set makes any guarantees as to what order its elements 163 * are returned by its iterator, this method must return the elements 164 * in the same order. 165 * 166 * <p>Like the {@link #toArray()} method, this method acts as bridge between 167 * array-based and collection-based APIs. Further, this method allows 168 * precise control over the runtime type of the output array, and may, 169 * under certain circumstances, be used to save allocation costs. 170 * 171 * <p>Suppose <tt>x</tt> is a set known to contain only strings. 172 * The following code can be used to dump the set into a newly allocated 173 * array of <tt>String</tt>: 174 * 175 * <pre> 176 * String[] y = x.toArray(new String[0]);</pre> 177 * 178 * Note that <tt>toArray(new Object[0])</tt> is identical in function to 179 * <tt>toArray()</tt>. 180 * 181 * @param a the array into which the elements of this set are to be 182 * stored, if it is big enough; otherwise, a new array of the same 183 * runtime type is allocated for this purpose. 184 * @return an array containing all the elements in this set 185 * @throws ArrayStoreException if the runtime type of the specified array 186 * is not a supertype of the runtime type of every element in this 187 * set 188 * @throws NullPointerException if the specified array is null 189 */ toArray(T[] a)190 <T> T[] toArray(T[] a); 191 192 193 // Modification Operations 194 195 /** 196 * Adds the specified element to this set if it is not already present 197 * (optional operation). More formally, adds the specified element 198 * <tt>e</tt> to this set if the set contains no element <tt>e2</tt> 199 * such that 200 * <tt>(e==null ? e2==null : e.equals(e2))</tt>. 201 * If this set already contains the element, the call leaves the set 202 * unchanged and returns <tt>false</tt>. In combination with the 203 * restriction on constructors, this ensures that sets never contain 204 * duplicate elements. 205 * 206 * <p>The stipulation above does not imply that sets must accept all 207 * elements; sets may refuse to add any particular element, including 208 * <tt>null</tt>, and throw an exception, as described in the 209 * specification for {@link Collection#add Collection.add}. 210 * Individual set implementations should clearly document any 211 * restrictions on the elements that they may contain. 212 * 213 * @param e element to be added to this set 214 * @return <tt>true</tt> if this set did not already contain the specified 215 * element 216 * @throws UnsupportedOperationException if the <tt>add</tt> operation 217 * is not supported by this set 218 * @throws ClassCastException if the class of the specified element 219 * prevents it from being added to this set 220 * @throws NullPointerException if the specified element is null and this 221 * set does not permit null elements 222 * @throws IllegalArgumentException if some property of the specified element 223 * prevents it from being added to this set 224 */ add(E e)225 boolean add(E e); 226 227 228 /** 229 * Removes the specified element from this set if it is present 230 * (optional operation). More formally, removes an element <tt>e</tt> 231 * such that 232 * <tt>(o==null ? e==null : o.equals(e))</tt>, if 233 * this set contains such an element. Returns <tt>true</tt> if this set 234 * contained the element (or equivalently, if this set changed as a 235 * result of the call). (This set will not contain the element once the 236 * call returns.) 237 * 238 * @param o object to be removed from this set, if present 239 * @return <tt>true</tt> if this set contained the specified element 240 * @throws ClassCastException if the type of the specified element 241 * is incompatible with this set 242 * (<a href="Collection.html#optional-restrictions">optional</a>) 243 * @throws NullPointerException if the specified element is null and this 244 * set does not permit null elements 245 * (<a href="Collection.html#optional-restrictions">optional</a>) 246 * @throws UnsupportedOperationException if the <tt>remove</tt> operation 247 * is not supported by this set 248 */ remove(Object o)249 boolean remove(Object o); 250 251 252 // Bulk Operations 253 254 /** 255 * Returns <tt>true</tt> if this set contains all of the elements of the 256 * specified collection. If the specified collection is also a set, this 257 * method returns <tt>true</tt> if it is a <i>subset</i> of this set. 258 * 259 * @param c collection to be checked for containment in this set 260 * @return <tt>true</tt> if this set contains all of the elements of the 261 * specified collection 262 * @throws ClassCastException if the types of one or more elements 263 * in the specified collection are incompatible with this 264 * set 265 * (<a href="Collection.html#optional-restrictions">optional</a>) 266 * @throws NullPointerException if the specified collection contains one 267 * or more null elements and this set does not permit null 268 * elements 269 * (<a href="Collection.html#optional-restrictions">optional</a>), 270 * or if the specified collection is null 271 * @see #contains(Object) 272 */ containsAll(Collection<?> c)273 boolean containsAll(Collection<?> c); 274 275 /** 276 * Adds all of the elements in the specified collection to this set if 277 * they're not already present (optional operation). If the specified 278 * collection is also a set, the <tt>addAll</tt> operation effectively 279 * modifies this set so that its value is the <i>union</i> of the two 280 * sets. The behavior of this operation is undefined if the specified 281 * collection is modified while the operation is in progress. 282 * 283 * @param c collection containing elements to be added to this set 284 * @return <tt>true</tt> if this set changed as a result of the call 285 * 286 * @throws UnsupportedOperationException if the <tt>addAll</tt> operation 287 * is not supported by this set 288 * @throws ClassCastException if the class of an element of the 289 * specified collection prevents it from being added to this set 290 * @throws NullPointerException if the specified collection contains one 291 * or more null elements and this set does not permit null 292 * elements, or if the specified collection is null 293 * @throws IllegalArgumentException if some property of an element of the 294 * specified collection prevents it from being added to this set 295 * @see #add(Object) 296 */ addAll(Collection<? extends E> c)297 boolean addAll(Collection<? extends E> c); 298 299 /** 300 * Retains only the elements in this set that are contained in the 301 * specified collection (optional operation). In other words, removes 302 * from this set all of its elements that are not contained in the 303 * specified collection. If the specified collection is also a set, this 304 * operation effectively modifies this set so that its value is the 305 * <i>intersection</i> of the two sets. 306 * 307 * @param c collection containing elements to be retained in this set 308 * @return <tt>true</tt> if this set changed as a result of the call 309 * @throws UnsupportedOperationException if the <tt>retainAll</tt> operation 310 * is not supported by this set 311 * @throws ClassCastException if the class of an element of this set 312 * is incompatible with the specified collection 313 * (<a href="Collection.html#optional-restrictions">optional</a>) 314 * @throws NullPointerException if this set contains a null element and the 315 * specified collection does not permit null elements 316 * (<a href="Collection.html#optional-restrictions">optional</a>), 317 * or if the specified collection is null 318 * @see #remove(Object) 319 */ retainAll(Collection<?> c)320 boolean retainAll(Collection<?> c); 321 322 /** 323 * Removes from this set all of its elements that are contained in the 324 * specified collection (optional operation). If the specified 325 * collection is also a set, this operation effectively modifies this 326 * set so that its value is the <i>asymmetric set difference</i> of 327 * the two sets. 328 * 329 * @param c collection containing elements to be removed from this set 330 * @return <tt>true</tt> if this set changed as a result of the call 331 * @throws UnsupportedOperationException if the <tt>removeAll</tt> operation 332 * is not supported by this set 333 * @throws ClassCastException if the class of an element of this set 334 * is incompatible with the specified collection 335 * (<a href="Collection.html#optional-restrictions">optional</a>) 336 * @throws NullPointerException if this set contains a null element and the 337 * specified collection does not permit null elements 338 * (<a href="Collection.html#optional-restrictions">optional</a>), 339 * or if the specified collection is null 340 * @see #remove(Object) 341 * @see #contains(Object) 342 */ removeAll(Collection<?> c)343 boolean removeAll(Collection<?> c); 344 345 /** 346 * Removes all of the elements from this set (optional operation). 347 * The set will be empty after this call returns. 348 * 349 * @throws UnsupportedOperationException if the <tt>clear</tt> method 350 * is not supported by this set 351 */ clear()352 void clear(); 353 354 355 // Comparison and hashing 356 357 /** 358 * Compares the specified object with this set for equality. Returns 359 * <tt>true</tt> if the specified object is also a set, the two sets 360 * have the same size, and every member of the specified set is 361 * contained in this set (or equivalently, every member of this set is 362 * contained in the specified set). This definition ensures that the 363 * equals method works properly across different implementations of the 364 * set interface. 365 * 366 * @param o object to be compared for equality with this set 367 * @return <tt>true</tt> if the specified object is equal to this set 368 */ equals(Object o)369 boolean equals(Object o); 370 371 /** 372 * Returns the hash code value for this set. The hash code of a set is 373 * defined to be the sum of the hash codes of the elements in the set, 374 * where the hash code of a <tt>null</tt> element is defined to be zero. 375 * This ensures that <tt>s1.equals(s2)</tt> implies that 376 * <tt>s1.hashCode()==s2.hashCode()</tt> for any two sets <tt>s1</tt> 377 * and <tt>s2</tt>, as required by the general contract of 378 * {@link Object#hashCode}. 379 * 380 * @return the hash code value for this set 381 * @see Object#equals(Object) 382 * @see Set#equals(Object) 383 */ hashCode()384 int hashCode(); 385 386 /** 387 * Creates a {@code Spliterator} over the elements in this set. 388 * 389 * <p>The {@code Spliterator} reports {@link Spliterator#DISTINCT}. 390 * Implementations should document the reporting of additional 391 * characteristic values. 392 * 393 * @implSpec 394 * The default implementation creates a 395 * <em><a href="Spliterator.html#binding">late-binding</a></em> spliterator 396 * from the set's {@code Iterator}. The spliterator inherits the 397 * <em>fail-fast</em> properties of the set's iterator. 398 * <p> 399 * The created {@code Spliterator} additionally reports 400 * {@link Spliterator#SIZED}. 401 * 402 * @implNote 403 * The created {@code Spliterator} additionally reports 404 * {@link Spliterator#SUBSIZED}. 405 * 406 * @return a {@code Spliterator} over the elements in this set 407 * @since 1.8 408 */ 409 @Override spliterator()410 default Spliterator<E> spliterator() { 411 return Spliterators.spliterator(this, Spliterator.DISTINCT); 412 } 413 } 414