- 001
/* - 002
* @(#)Set.java 1.39 06/04/21 - 003 *
- 004 * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
- 005 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
- 006
*/ - 007
- 008package java.util;
- 009
- 010/**
- 011 * A collection that contains no duplicate elements. More formally, sets
- 012 * contain no pair of elements <code>e1</code> and <code>e2</code> such that
- 013 * <code>e1.equals(e2)</code>, and at most one null element. As implied by
- 014 * its name, this interface models the mathematical <i>set</i> abstraction.
- 015 *
- 016 * <p>The <tt>Set</tt> interface places additional stipulations, beyond those
- 017 * inherited from the <tt>Collection</tt> interface, on the contracts of all
- 018 * constructors and on the contracts of the <tt>add</tt>, <tt>equals</tt> and
- 019 * <tt>hashCode</tt> methods. Declarations for other inherited methods are
- 020 * also included here for convenience. (The specifications accompanying these
- 021 * declarations have been tailored to the <tt>Set</tt> interface, but they do
- 022 * not contain any additional stipulations.)
- 023 *
- 024 * <p>The additional stipulation on constructors is, not surprisingly,
- 025 * that all constructors must create a set that contains no duplicate elements
- 026 * (as defined above).
- 027 *
- 028 * <p>Note: Great care must be exercised if mutable objects are used as set
- 029 * elements. The behavior of a set is not specified if the value of an object
- 030 * is changed in a manner that affects <tt>equals</tt> comparisons while the
- 031 * object is an element in the set. A special case of this prohibition is
- 032 * that it is not permissible for a set to contain itself as an element.
- 033 *
- 034 * <p>Some set implementations have restrictions on the elements that
- 035 * they may contain. For example, some implementations prohibit null elements,
- 036 * and some have restrictions on the types of their elements. Attempting to
- 037 * add an ineligible element throws an unchecked exception, typically
- 038 * <tt>NullPointerException</tt> or <tt>ClassCastException</tt>. Attempting
- 039 * to query the presence of an ineligible element may throw an exception,
- 040 * or it may simply return false; some implementations will exhibit the former
- 041 * behavior and some will exhibit the latter. More generally, attempting an
- 042 * operation on an ineligible element whose completion would not result in
- 043 * the insertion of an ineligible element into the set may throw an
- 044 * exception or it may succeed, at the option of the implementation.
- 045 * Such exceptions are marked as "optional" in the specification for this
- 046 * interface.
- 047 *
- 048 * <p>This interface is a member of the
- 049 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
- 050 * Java Collections Framework</a>.
- 051 *
- 052 * @param <E> the type of elements maintained by this set
- 053 *
- 054 * @author Josh Bloch
- 055 * @author Neal Gafter
- 056 * @version 1.39, 04/21/06
- 057 * @see Collection
- 058 * @see List
- 059 * @see SortedSet
- 060 * @see HashSet
- 061 * @see TreeSet
- 062 * @see AbstractSet
- 063 * @see Collections#singleton(java.lang.Object)
- 064 * @see Collections#EMPTY_SET
- 065 * @since 1.2
- 066 */
- 067
- 068public interface Set<E> extends Collection<E> {
- 069 // Query Operations
- 070
- 071 /**
- 072 * Returns the number of elements in this set (its cardinality). If this
- 073 * set contains more than <tt>Integer.MAX_VALUE</tt> elements, returns
- 074 * <tt>Integer.MAX_VALUE</tt>.
- 075 *
- 076 * @return the number of elements in this set (its cardinality)
- 077 */
- 078 int size();
- 079
- 080 /**
- 081 * Returns <tt>true</tt> if this set contains no elements.
- 082 *
- 083 * @return <tt>true</tt> if this set contains no elements
- 084 */
- 085 boolean isEmpty();
- 086
- 087 /**
- 088 * Returns <tt>true</tt> if this set contains the specified element.
- 089 * More formally, returns <tt>true</tt> if and only if this set
- 090 * contains an element <tt>e</tt> such that
- 091 * <tt>(o==null ? e==null : o.equals(e))</tt>.
- 092 *
- 093 * @param o element whose presence in this set is to be tested
- 094 * @return <tt>true</tt> if this set contains the specified element
- 095 * @throws ClassCastException if the type of the specified element
- 096 * is incompatible with this set (optional)
- 097 * @throws NullPointerException if the specified element is null and this
- 098 * set does not permit null elements (optional)
- 099 */
- 100 boolean contains(Object o);
- 101
- 102 /**
- 103 * Returns an iterator over the elements in this set. The elements are
- 104 * returned in no particular order (unless this set is an instance of some
- 105 * class that provides a guarantee).
- 106 *
- 107 * @return an iterator over the elements in this set
- 108 */
- 109 Iterator<E> iterator();
- 110
- 111 /**
- 112 * Returns an array containing all of the elements in this set.
- 113 * If this set makes any guarantees as to what order its elements
- 114 * are returned by its iterator, this method must return the
- 115 * elements in the same order.
- 116 *
- 117 * <p>The returned array will be "safe" in that no references to it
- 118 * are maintained by this set. (In other words, this method must
- 119 * allocate a new array even if this set is backed by an array).
- 120 * The caller is thus free to modify the returned array.
- 121 *
- 122 * <p>This method acts as bridge between array-based and collection-based
- 123 * APIs.
- 124 *
- 125 * @return an array containing all the elements in this set
- 126 */
- 127 Object[] toArray();
- 128
- 129 /**
- 130 * Returns an array containing all of the elements in this set; the
- 131 * runtime type of the returned array is that of the specified array.
- 132 * If the set fits in the specified array, it is returned therein.
- 133 * Otherwise, a new array is allocated with the runtime type of the
- 134 * specified array and the size of this set.
- 135 *
- 136 * <p>If this set fits in the specified array with room to spare
- 137 * (i.e., the array has more elements than this set), the element in
- 138 * the array immediately following the end of the set is set to
- 139 * <tt>null</tt>. (This is useful in determining the length of this
- 140 * set <i>only</i> if the caller knows that this set does not contain
- 141 * any null elements.)
- 142 *
- 143 * <p>If this set makes any guarantees as to what order its elements
- 144 * are returned by its iterator, this method must return the elements
- 145 * in the same order.
- 146 *
- 147 * <p>Like the {@link #toArray()} method, this method acts as bridge between
- 148 * array-based and collection-based APIs. Further, this method allows
- 149 * precise control over the runtime type of the output array, and may,
- 150 * under certain circumstances, be used to save allocation costs.
- 151 *
- 152 * <p>Suppose <tt>x</tt> is a set known to contain only strings.
- 153 * The following code can be used to dump the set into a newly allocated
- 154 * array of <tt>String</tt>:
- 155 *
- 156 * <pre>
- 157 * String[] y = x.toArray(new String[0]);</pre>
- 158 *
- 159 * Note that <tt>toArray(new Object[0])</tt> is identical in function to
- 160 * <tt>toArray()</tt>.
- 161 *
- 162 * @param a the array into which the elements of this set are to be
- 163 * stored, if it is big enough; otherwise, a new array of the same
- 164 * runtime type is allocated for this purpose.
- 165 * @return an array containing all the elements in this set
- 166 * @throws ArrayStoreException if the runtime type of the specified array
- 167 * is not a supertype of the runtime type of every element in this
- 168 * set
- 169 * @throws NullPointerException if the specified array is null
- 170 */
- 171 <T> T[] toArray(T[] a);
- 172
- 173
- 174 // Modification Operations
- 175
- 176 /**
- 177 * Adds the specified element to this set if it is not already present
- 178 * (optional operation). More formally, adds the specified element
- 179 * <tt>e</tt> to this set if the set contains no element <tt>e2</tt>
- 180 * such that
- 181 * <tt>(e==null ? e2==null : e.equals(e2))</tt>.
- 182 * If this set already contains the element, the call leaves the set
- 183 * unchanged and returns <tt>false</tt>. In combination with the
- 184 * restriction on constructors, this ensures that sets never contain
- 185 * duplicate elements.
- 186 *
- 187 * <p>The stipulation above does not imply that sets must accept all
- 188 * elements; sets may refuse to add any particular element, including
- 189 * <tt>null</tt>, and throw an exception, as described in the
- 190 * specification for {@link Collection#add Collection.add}.
- 191 * Individual set implementations should clearly document any
- 192 * restrictions on the elements that they may contain.
- 193 *
- 194 * @param e element to be added to this set
- 195 * @return <tt>true</tt> if this set did not already contain the specified
- 196 * element
- 197 * @throws UnsupportedOperationException if the <tt>add</tt> operation
- 198 * is not supported by this set
- 199 * @throws ClassCastException if the class of the specified element
- 200 * prevents it from being added to this set
- 201 * @throws NullPointerException if the specified element is null and this
- 202 * set does not permit null elements
- 203 * @throws IllegalArgumentException if some property of the specified element
- 204 * prevents it from being added to this set
- 205 */
- 206 boolean add(E e);
- 207
- 208
- 209 /**
- 210 * Removes the specified element from this set if it is present
- 211 * (optional operation). More formally, removes an element <tt>e</tt>
- 212 * such that
- 213 * <tt>(o==null ? e==null : o.equals(e))</tt>, if
- 214 * this set contains such an element. Returns <tt>true</tt> if this set
- 215 * contained the element (or equivalently, if this set changed as a
- 216 * result of the call). (This set will not contain the element once the
- 217 * call returns.)
- 218 *
- 219 * @param o object to be removed from this set, if present
- 220 * @return <tt>true</tt> if this set contained the specified element
- 221 * @throws ClassCastException if the type of the specified element
- 222 * is incompatible with this set (optional)
- 223 * @throws NullPointerException if the specified element is null and this
- 224 * set does not permit null elements (optional)
- 225 * @throws UnsupportedOperationException if the <tt>remove</tt> operation
- 226 * is not supported by this set
- 227 */
- 228 boolean remove(Object o);
- 229
- 230
- 231 // Bulk Operations
- 232
- 233 /**
- 234 * Returns <tt>true</tt> if this set contains all of the elements of the
- 235 * specified collection. If the specified collection is also a set, this
- 236 * method returns <tt>true</tt> if it is a <i>subset</i> of this set.
- 237 *
- 238 * @param c collection to be checked for containment in this set
- 239 * @return <tt>true</tt> if this set contains all of the elements of the
- 240 * specified collection
- 241 * @throws ClassCastException if the types of one or more elements
- 242 * in the specified collection are incompatible with this
- 243 * set (optional)
- 244 * @throws NullPointerException if the specified collection contains one
- 245 * or more null elements and this set does not permit null
- 246 * elements (optional), or if the specified collection is null
- 247 * @see #contains(Object)
- 248 */
- 249 boolean containsAll(Collection<?> c);
- 250
- 251 /**
- 252 * Adds all of the elements in the specified collection to this set if
- 253 * they're not already present (optional operation). If the specified
- 254 * collection is also a set, the <tt>addAll</tt> operation effectively
- 255 * modifies this set so that its value is the <i>union</i> of the two
- 256 * sets. The behavior of this operation is undefined if the specified
- 257 * collection is modified while the operation is in progress.
- 258 *
- 259 * @param c collection containing elements to be added to this set
- 260 * @return <tt>true</tt> if this set changed as a result of the call
- 261 *
- 262 * @throws UnsupportedOperationException if the <tt>addAll</tt> operation
- 263 * is not supported by this set
- 264 * @throws ClassCastException if the class of an element of the
- 265 * specified collection prevents it from being added to this set
- 266 * @throws NullPointerException if the specified collection contains one
- 267 * or more null elements and this set does not permit null
- 268 * elements, or if the specified collection is null
- 269 * @throws IllegalArgumentException if some property of an element of the
- 270 * specified collection prevents it from being added to this set
- 271 * @see #add(Object)
- 272 */
- 273 boolean addAll(Collection<? extends E> c);
- 274
- 275 /**
- 276 * Retains only the elements in this set that are contained in the
- 277 * specified collection (optional operation). In other words, removes
- 278 * from this set all of its elements that are not contained in the
- 279 * specified collection. If the specified collection is also a set, this
- 280 * operation effectively modifies this set so that its value is the
- 281 * <i>intersection</i> of the two sets.
- 282 *
- 283 * @param c collection containing elements to be retained in this set
- 284 * @return <tt>true</tt> if this set changed as a result of the call
- 285 * @throws UnsupportedOperationException if the <tt>retainAll</tt> operation
- 286 * is not supported by this set
- 287 * @throws ClassCastException if the class of an element of this set
- 288 * is incompatible with the specified collection (optional)
- 289 * @throws NullPointerException if this set contains a null element and the
- 290 * specified collection does not permit null elements (optional),
- 291 * or if the specified collection is null
- 292 * @see #remove(Object)
- 293 */
- 294 boolean retainAll(Collection<?> c);
- 295
- 296 /**
- 297 * Removes from this set all of its elements that are contained in the
- 298 * specified collection (optional operation). If the specified
- 299 * collection is also a set, this operation effectively modifies this
- 300 * set so that its value is the <i>asymmetric set difference</i> of
- 301 * the two sets.
- 302 *
- 303 * @param c collection containing elements to be removed from this set
- 304 * @return <tt>true</tt> if this set changed as a result of the call
- 305 * @throws UnsupportedOperationException if the <tt>removeAll</tt> operation
- 306 * is not supported by this set
- 307 * @throws ClassCastException if the class of an element of this set
- 308 * is incompatible with the specified collection (optional)
- 309 * @throws NullPointerException if this set contains a null element and the
- 310 * specified collection does not permit null elements (optional),
- 311 * or if the specified collection is null
- 312 * @see #remove(Object)
- 313 * @see #contains(Object)
- 314 */
- 315 boolean removeAll(Collection<?> c);
- 316
- 317 /**
- 318 * Removes all of the elements from this set (optional operation).
- 319 * The set will be empty after this call returns.
- 320 *
- 321 * @throws UnsupportedOperationException if the <tt>clear</tt> method
- 322 * is not supported by this set
- 323 */
- 324 void clear();
- 325
- 326
- 327 // Comparison and hashing
- 328
- 329 /**
- 330 * Compares the specified object with this set for equality. Returns
- 331 * <tt>true</tt> if the specified object is also a set, the two sets
- 332 * have the same size, and every member of the specified set is
- 333 * contained in this set (or equivalently, every member of this set is
- 334 * contained in the specified set). This definition ensures that the
- 335 * equals method works properly across different implementations of the
- 336 * set interface.
- 337 *
- 338 * @param o object to be compared for equality with this set
- 339 * @return <tt>true</tt> if the specified object is equal to this set
- 340 */
- 341 boolean equals(Object o);
- 342
- 343 /**
- 344 * Returns the hash code value for this set. The hash code of a set is
- 345 * defined to be the sum of the hash codes of the elements in the set,
- 346 * where the hash code of a <tt>null</tt> element is defined to be zero.
- 347 * This ensures that <tt>s1.equals(s2)</tt> implies that
- 348 * <tt>s1.hashCode()==s2.hashCode()</tt> for any two sets <tt>s1</tt>
- 349 * and <tt>s2</tt>, as required by the general contract of
- 350 * {@link Object#hashCode}.
- 351 *
- 352 * @return the hash code value for this set
- 353 * @see Object#equals(Object)
- 354 * @see Set#equals(Object)
- 355 */
- 356 int hashCode();
- 357}
