- 001
/* - 002
* @(#)Map.java 1.56 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 * An object that maps keys to values. A map cannot contain duplicate keys;
- 012 * each key can map to at most one value.
- 013 *
- 014 * <p>This interface takes the place of the <tt>Dictionary</tt> class, which
- 015 * was a totally abstract class rather than an interface.
- 016 *
- 017 * <p>The <tt>Map</tt> interface provides three <i>collection views</i>, which
- 018 * allow a map's contents to be viewed as a set of keys, collection of values,
- 019 * or set of key-value mappings. The <i>order</i> of a map is defined as
- 020 * the order in which the iterators on the map's collection views return their
- 021 * elements. Some map implementations, like the <tt>TreeMap</tt> class, make
- 022 * specific guarantees as to their order; others, like the <tt>HashMap</tt>
- 023 * class, do not.
- 024 *
- 025 * <p>Note: great care must be exercised if mutable objects are used as map
- 026 * keys. The behavior of a map is not specified if the value of an object is
- 027 * changed in a manner that affects <tt>equals</tt> comparisons while the
- 028 * object is a key in the map. A special case of this prohibition is that it
- 029 * is not permissible for a map to contain itself as a key. While it is
- 030 * permissible for a map to contain itself as a value, extreme caution is
- 031 * advised: the <tt>equals</tt> and <tt>hashCode</tt> methods are no longer
- 032 * well defined on such a map.
- 033 *
- 034 * <p>All general-purpose map implementation classes should provide two
- 035 * "standard" constructors: a void (no arguments) constructor which creates an
- 036 * empty map, and a constructor with a single argument of type <tt>Map</tt>,
- 037 * which creates a new map with the same key-value mappings as its argument.
- 038 * In effect, the latter constructor allows the user to copy any map,
- 039 * producing an equivalent map of the desired class. There is no way to
- 040 * enforce this recommendation (as interfaces cannot contain constructors) but
- 041 * all of the general-purpose map implementations in the JDK comply.
- 042 *
- 043 * <p>The "destructive" methods contained in this interface, that is, the
- 044 * methods that modify the map on which they operate, are specified to throw
- 045 * <tt>UnsupportedOperationException</tt> if this map does not support the
- 046 * operation. If this is the case, these methods may, but are not required
- 047 * to, throw an <tt>UnsupportedOperationException</tt> if the invocation would
- 048 * have no effect on the map. For example, invoking the {@link #putAll(Map)}
- 049 * method on an unmodifiable map may, but is not required to, throw the
- 050 * exception if the map whose mappings are to be "superimposed" is empty.
- 051 *
- 052 * <p>Some map implementations have restrictions on the keys and values they
- 053 * may contain. For example, some implementations prohibit null keys and
- 054 * values, and some have restrictions on the types of their keys. Attempting
- 055 * to insert an ineligible key or value throws an unchecked exception,
- 056 * typically <tt>NullPointerException</tt> or <tt>ClassCastException</tt>.
- 057 * Attempting to query the presence of an ineligible key or value may throw an
- 058 * exception, or it may simply return false; some implementations will exhibit
- 059 * the former behavior and some will exhibit the latter. More generally,
- 060 * attempting an operation on an ineligible key or value whose completion
- 061 * would not result in the insertion of an ineligible element into the map may
- 062 * throw an exception or it may succeed, at the option of the implementation.
- 063 * Such exceptions are marked as "optional" in the specification for this
- 064 * interface.
- 065 *
- 066 * <p>This interface is a member of the
- 067 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
- 068 * Java Collections Framework</a>.
- 069 *
- 070 * <p>Many methods in Collections Framework interfaces are defined
- 071 * in terms of the {@link Object#equals(Object) equals} method. For
- 072 * example, the specification for the {@link #containsKey(Object)
- 073 * containsKey(Object key)} method says: "returns <tt>true</tt> if and
- 074 * only if this map contains a mapping for a key <tt>k</tt> such that
- 075 * <tt>(key==null ? k==null : key.equals(k))</tt>." This specification should
- 076 * <i>not</i> be construed to imply that invoking <tt>Map.containsKey</tt>
- 077 * with a non-null argument <tt>key</tt> will cause <tt>key.equals(k)</tt> to
- 078 * be invoked for any key <tt>k</tt>. Implementations are free to
- 079 * implement optimizations whereby the <tt>equals</tt> invocation is avoided,
- 080 * for example, by first comparing the hash codes of the two keys. (The
- 081 * {@link Object#hashCode()} specification guarantees that two objects with
- 082 * unequal hash codes cannot be equal.) More generally, implementations of
- 083 * the various Collections Framework interfaces are free to take advantage of
- 084 * the specified behavior of underlying {@link Object} methods wherever the
- 085 * implementor deems it appropriate.
- 086 *
- 087 * @param <K> the type of keys maintained by this map
- 088 * @param <V> the type of mapped values
- 089 *
- 090 * @author Josh Bloch
- 091 * @version 1.56, 04/21/06
- 092 * @see HashMap
- 093 * @see TreeMap
- 094 * @see Hashtable
- 095 * @see SortedMap
- 096 * @see Collection
- 097 * @see Set
- 098 * @since 1.2
- 099 */
- 100public interface Map<K,V> {
- 101 // Query Operations
- 102
- 103 /**
- 104 * Returns the number of key-value mappings in this map. If the
- 105 * map contains more than <tt>Integer.MAX_VALUE</tt> elements, returns
- 106 * <tt>Integer.MAX_VALUE</tt>.
- 107 *
- 108 * @return the number of key-value mappings in this map
- 109 */
- 110 int size();
- 111
- 112 /**
- 113 * Returns <tt>true</tt> if this map contains no key-value mappings.
- 114 *
- 115 * @return <tt>true</tt> if this map contains no key-value mappings
- 116 */
- 117 boolean isEmpty();
- 118
- 119 /**
- 120 * Returns <tt>true</tt> if this map contains a mapping for the specified
- 121 * key. More formally, returns <tt>true</tt> if and only if
- 122 * this map contains a mapping for a key <tt>k</tt> such that
- 123 * <tt>(key==null ? k==null : key.equals(k))</tt>. (There can be
- 124 * at most one such mapping.)
- 125 *
- 126 * @param key key whose presence in this map is to be tested
- 127 * @return <tt>true</tt> if this map contains a mapping for the specified
- 128 * key
- 129 * @throws ClassCastException if the key is of an inappropriate type for
- 130 * this map (optional)
- 131 * @throws NullPointerException if the specified key is null and this map
- 132 * does not permit null keys (optional)
- 133 */
- 134 boolean containsKey(Object key);
- 135
- 136 /**
- 137 * Returns <tt>true</tt> if this map maps one or more keys to the
- 138 * specified value. More formally, returns <tt>true</tt> if and only if
- 139 * this map contains at least one mapping to a value <tt>v</tt> such that
- 140 * <tt>(value==null ? v==null : value.equals(v))</tt>. This operation
- 141 * will probably require time linear in the map size for most
- 142 * implementations of the <tt>Map</tt> interface.
- 143 *
- 144 * @param value value whose presence in this map is to be tested
- 145 * @return <tt>true</tt> if this map maps one or more keys to the
- 146 * specified value
- 147 * @throws ClassCastException if the value is of an inappropriate type for
- 148 * this map (optional)
- 149 * @throws NullPointerException if the specified value is null and this
- 150 * map does not permit null values (optional)
- 151 */
- 152 boolean containsValue(Object value);
- 153
- 154 /**
- 155 * Returns the value to which the specified key is mapped,
- 156 * or {@code null} if this map contains no mapping for the key.
- 157 *
- 158 * <p>More formally, if this map contains a mapping from a key
- 159 * {@code k} to a value {@code v} such that {@code (key==null ? k==null :
- 160 * key.equals(k))}, then this method returns {@code v}; otherwise
- 161 * it returns {@code null}. (There can be at most one such mapping.)
- 162 *
- 163 * <p>If this map permits null values, then a return value of
- 164 * {@code null} does not <i>necessarily</i> indicate that the map
- 165 * contains no mapping for the key; it's also possible that the map
- 166 * explicitly maps the key to {@code null}. The {@link #containsKey
- 167 * containsKey} operation may be used to distinguish these two cases.
- 168 *
- 169 * @param key the key whose associated value is to be returned
- 170 * @return the value to which the specified key is mapped, or
- 171 * {@code null} if this map contains no mapping for the key
- 172 * @throws ClassCastException if the key is of an inappropriate type for
- 173 * this map (optional)
- 174 * @throws NullPointerException if the specified key is null and this map
- 175 * does not permit null keys (optional)
- 176 */
- 177 V get(Object key);
- 178
- 179 // Modification Operations
- 180
- 181 /**
- 182 * Associates the specified value with the specified key in this map
- 183 * (optional operation). If the map previously contained a mapping for
- 184 * the key, the old value is replaced by the specified value. (A map
- 185 * <tt>m</tt> is said to contain a mapping for a key <tt>k</tt> if and only
- 186 * if {@link #containsKey(Object) m.containsKey(k)} would return
- 187 * <tt>true</tt>.)
- 188 *
- 189 * @param key key with which the specified value is to be associated
- 190 * @param value value to be associated with the specified key
- 191 * @return the previous value associated with <tt>key</tt>, or
- 192 * <tt>null</tt> if there was no mapping for <tt>key</tt>.
- 193 * (A <tt>null</tt> return can also indicate that the map
- 194 * previously associated <tt>null</tt> with <tt>key</tt>,
- 195 * if the implementation supports <tt>null</tt> values.)
- 196 * @throws UnsupportedOperationException if the <tt>put</tt> operation
- 197 * is not supported by this map
- 198 * @throws ClassCastException if the class of the specified key or value
- 199 * prevents it from being stored in this map
- 200 * @throws NullPointerException if the specified key or value is null
- 201 * and this map does not permit null keys or values
- 202 * @throws IllegalArgumentException if some property of the specified key
- 203 * or value prevents it from being stored in this map
- 204 */
- 205 V put(K key, V value);
- 206
- 207 /**
- 208 * Removes the mapping for a key from this map if it is present
- 209 * (optional operation). More formally, if this map contains a mapping
- 210 * from key <tt>k</tt> to value <tt>v</tt> such that
- 211 * <code>(key==null ? k==null : key.equals(k))</code>, that mapping
- 212 * is removed. (The map can contain at most one such mapping.)
- 213 *
- 214 * <p>Returns the value to which this map previously associated the key,
- 215 * or <tt>null</tt> if the map contained no mapping for the key.
- 216 *
- 217 * <p>If this map permits null values, then a return value of
- 218 * <tt>null</tt> does not <i>necessarily</i> indicate that the map
- 219 * contained no mapping for the key; it's also possible that the map
- 220 * explicitly mapped the key to <tt>null</tt>.
- 221 *
- 222 * <p>The map will not contain a mapping for the specified key once the
- 223 * call returns.
- 224 *
- 225 * @param key key whose mapping is to be removed from the map
- 226 * @return the previous value associated with <tt>key</tt>, or
- 227 * <tt>null</tt> if there was no mapping for <tt>key</tt>.
- 228 * @throws UnsupportedOperationException if the <tt>remove</tt> operation
- 229 * is not supported by this map
- 230 * @throws ClassCastException if the key is of an inappropriate type for
- 231 * this map (optional)
- 232 * @throws NullPointerException if the specified key is null and this
- 233 * map does not permit null keys (optional)
- 234 */
- 235 V remove(Object key);
- 236
- 237
- 238 // Bulk Operations
- 239
- 240 /**
- 241 * Copies all of the mappings from the specified map to this map
- 242 * (optional operation). The effect of this call is equivalent to that
- 243 * of calling {@link #put(Object,Object) put(k, v)} on this map once
- 244 * for each mapping from key <tt>k</tt> to value <tt>v</tt> in the
- 245 * specified map. The behavior of this operation is undefined if the
- 246 * specified map is modified while the operation is in progress.
- 247 *
- 248 * @param m mappings to be stored in this map
- 249 * @throws UnsupportedOperationException if the <tt>putAll</tt> operation
- 250 * is not supported by this map
- 251 * @throws ClassCastException if the class of a key or value in the
- 252 * specified map prevents it from being stored in this map
- 253 * @throws NullPointerException if the specified map is null, or if
- 254 * this map does not permit null keys or values, and the
- 255 * specified map contains null keys or values
- 256 * @throws IllegalArgumentException if some property of a key or value in
- 257 * the specified map prevents it from being stored in this map
- 258 */
- 259 void putAll(Map<? extends K, ? extends V> m);
- 260
- 261 /**
- 262 * Removes all of the mappings from this map (optional operation).
- 263 * The map will be empty after this call returns.
- 264 *
- 265 * @throws UnsupportedOperationException if the <tt>clear</tt> operation
- 266 * is not supported by this map
- 267 */
- 268 void clear();
- 269
- 270
- 271 // Views
- 272
- 273 /**
- 274 * Returns a {@link Set} view of the keys contained in this map.
- 275 * The set is backed by the map, so changes to the map are
- 276 * reflected in the set, and vice-versa. If the map is modified
- 277 * while an iteration over the set is in progress (except through
- 278 * the iterator's own <tt>remove</tt> operation), the results of
- 279 * the iteration are undefined. The set supports element removal,
- 280 * which removes the corresponding mapping from the map, via the
- 281 * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
- 282 * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
- 283 * operations. It does not support the <tt>add</tt> or <tt>addAll</tt>
- 284 * operations.
- 285 *
- 286 * @return a set view of the keys contained in this map
- 287 */
- 288 Set<K> keySet();
- 289
- 290 /**
- 291 * Returns a {@link Collection} view of the values contained in this map.
- 292 * The collection is backed by the map, so changes to the map are
- 293 * reflected in the collection, and vice-versa. If the map is
- 294 * modified while an iteration over the collection is in progress
- 295 * (except through the iterator's own <tt>remove</tt> operation),
- 296 * the results of the iteration are undefined. The collection
- 297 * supports element removal, which removes the corresponding
- 298 * mapping from the map, via the <tt>Iterator.remove</tt>,
- 299 * <tt>Collection.remove</tt>, <tt>removeAll</tt>,
- 300 * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not
- 301 * support the <tt>add</tt> or <tt>addAll</tt> operations.
- 302 *
- 303 * @return a collection view of the values contained in this map
- 304 */
- 305 Collection<V> values();
- 306
- 307 /**
- 308 * Returns a {@link Set} view of the mappings contained in this map.
- 309 * The set is backed by the map, so changes to the map are
- 310 * reflected in the set, and vice-versa. If the map is modified
- 311 * while an iteration over the set is in progress (except through
- 312 * the iterator's own <tt>remove</tt> operation, or through the
- 313 * <tt>setValue</tt> operation on a map entry returned by the
- 314 * iterator) the results of the iteration are undefined. The set
- 315 * supports element removal, which removes the corresponding
- 316 * mapping from the map, via the <tt>Iterator.remove</tt>,
- 317 * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and
- 318 * <tt>clear</tt> operations. It does not support the
- 319 * <tt>add</tt> or <tt>addAll</tt> operations.
- 320 *
- 321 * @return a set view of the mappings contained in this map
- 322 */
- 323 Set<Map.Entry<K, V>> entrySet();
- 324
- 325 /**
- 326 * A map entry (key-value pair). The <tt>Map.entrySet</tt> method returns
- 327 * a collection-view of the map, whose elements are of this class. The
- 328 * <i>only</i> way to obtain a reference to a map entry is from the
- 329 * iterator of this collection-view. These <tt>Map.Entry</tt> objects are
- 330 * valid <i>only</i> for the duration of the iteration; more formally,
- 331 * the behavior of a map entry is undefined if the backing map has been
- 332 * modified after the entry was returned by the iterator, except through
- 333 * the <tt>setValue</tt> operation on the map entry.
- 334 *
- 335 * @see Map#entrySet()
- 336 * @since 1.2
- 337 */
- 338 interface Entry<K,V> {
- 339 /**
- 340 * Returns the key corresponding to this entry.
- 341 *
- 342 * @return the key corresponding to this entry
- 343 * @throws IllegalStateException implementations may, but are not
- 344 * required to, throw this exception if the entry has been
- 345 * removed from the backing map.
- 346 */
- 347 K getKey();
- 348
- 349 /**
- 350 * Returns the value corresponding to this entry. If the mapping
- 351 * has been removed from the backing map (by the iterator's
- 352 * <tt>remove</tt> operation), the results of this call are undefined.
- 353 *
- 354 * @return the value corresponding to this entry
- 355 * @throws IllegalStateException implementations may, but are not
- 356 * required to, throw this exception if the entry has been
- 357 * removed from the backing map.
- 358 */
- 359 V getValue();
- 360
- 361 /**
- 362 * Replaces the value corresponding to this entry with the specified
- 363 * value (optional operation). (Writes through to the map.) The
- 364 * behavior of this call is undefined if the mapping has already been
- 365 * removed from the map (by the iterator's <tt>remove</tt> operation).
- 366 *
- 367 * @param value new value to be stored in this entry
- 368 * @return old value corresponding to the entry
- 369 * @throws UnsupportedOperationException if the <tt>put</tt> operation
- 370 * is not supported by the backing map
- 371 * @throws ClassCastException if the class of the specified value
- 372 * prevents it from being stored in the backing map
- 373 * @throws NullPointerException if the backing map does not permit
- 374 * null values, and the specified value is null
- 375 * @throws IllegalArgumentException if some property of this value
- 376 * prevents it from being stored in the backing map
- 377 * @throws IllegalStateException implementations may, but are not
- 378 * required to, throw this exception if the entry has been
- 379 * removed from the backing map.
- 380 */
- 381 V setValue(V value);
- 382
- 383 /**
- 384 * Compares the specified object with this entry for equality.
- 385 * Returns <tt>true</tt> if the given object is also a map entry and
- 386 * the two entries represent the same mapping. More formally, two
- 387 * entries <tt>e1</tt> and <tt>e2</tt> represent the same mapping
- 388 * if<pre>
- 389 * (e1.getKey()==null ?
- 390 * e2.getKey()==null : e1.getKey().equals(e2.getKey())) &&
- 391 * (e1.getValue()==null ?
- 392 * e2.getValue()==null : e1.getValue().equals(e2.getValue()))
- 393 * </pre>
- 394 * This ensures that the <tt>equals</tt> method works properly across
- 395 * different implementations of the <tt>Map.Entry</tt> interface.
- 396 *
- 397 * @param o object to be compared for equality with this map entry
- 398 * @return <tt>true</tt> if the specified object is equal to this map
- 399 * entry
- 400 */
- 401 boolean equals(Object o);
- 402
- 403 /**
- 404 * Returns the hash code value for this map entry. The hash code
- 405 * of a map entry <tt>e</tt> is defined to be: <pre>
- 406 * (e.getKey()==null ? 0 : e.getKey().hashCode()) ^
- 407 * (e.getValue()==null ? 0 : e.getValue().hashCode())
- 408 * </pre>
- 409 * This ensures that <tt>e1.equals(e2)</tt> implies that
- 410 * <tt>e1.hashCode()==e2.hashCode()</tt> for any two Entries
- 411 * <tt>e1</tt> and <tt>e2</tt>, as required by the general
- 412 * contract of <tt>Object.hashCode</tt>.
- 413 *
- 414 * @return the hash code value for this map entry
- 415 * @see Object#hashCode()
- 416 * @see Object#equals(Object)
- 417 * @see #equals(Object)
- 418 */
- 419 int hashCode();
- 420 }
- 421
- 422 // Comparison and hashing
- 423
- 424 /**
- 425 * Compares the specified object with this map for equality. Returns
- 426 * <tt>true</tt> if the given object is also a map and the two maps
- 427 * represent the same mappings. More formally, two maps <tt>m1</tt> and
- 428 * <tt>m2</tt> represent the same mappings if
- 429 * <tt>m1.entrySet().equals(m2.entrySet())</tt>. This ensures that the
- 430 * <tt>equals</tt> method works properly across different implementations
- 431 * of the <tt>Map</tt> interface.
- 432 *
- 433 * @param o object to be compared for equality with this map
- 434 * @return <tt>true</tt> if the specified object is equal to this map
- 435 */
- 436 boolean equals(Object o);
- 437
- 438 /**
- 439 * Returns the hash code value for this map. The hash code of a map is
- 440 * defined to be the sum of the hash codes of each entry in the map's
- 441 * <tt>entrySet()</tt> view. This ensures that <tt>m1.equals(m2)</tt>
- 442 * implies that <tt>m1.hashCode()==m2.hashCode()</tt> for any two maps
- 443 * <tt>m1</tt> and <tt>m2</tt>, as required by the general contract of
- 444 * {@link Object#hashCode}.
- 445 *
- 446 * @return the hash code value for this map
- 447 * @see Map.Entry#hashCode()
- 448 * @see Object#equals(Object)
- 449 * @see #equals(Object)
- 450 */
- 451 int hashCode();
- 452}
