Moving modules around so the runtime is under one master pom and can be built without building other modules that are in the repository
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29 * An object that maps keys to values. A map cannot contain duplicate keys;
30 * each key can map to at most one value.
32 * <p>This interface takes the place of the <tt>Dictionary</tt> class, which
33 * was a totally abstract class rather than an interface.
35 * <p>The <tt>Map</tt> interface provides three <i>collection views</i>, which
36 * allow a map's contents to be viewed as a set of keys, collection of values,
37 * or set of key-value mappings. The <i>order</i> of a map is defined as
38 * the order in which the iterators on the map's collection views return their
39 * elements. Some map implementations, like the <tt>TreeMap</tt> class, make
40 * specific guarantees as to their order; others, like the <tt>HashMap</tt>
43 * <p>Note: great care must be exercised if mutable objects are used as map
44 * keys. The behavior of a map is not specified if the value of an object is
45 * changed in a manner that affects <tt>equals</tt> comparisons while the
46 * object is a key in the map. A special case of this prohibition is that it
47 * is not permissible for a map to contain itself as a key. While it is
48 * permissible for a map to contain itself as a value, extreme caution is
49 * advised: the <tt>equals</tt> and <tt>hashCode</tt> methods are no longer
50 * well defined on such a map.
52 * <p>All general-purpose map implementation classes should provide two
53 * "standard" constructors: a void (no arguments) constructor which creates an
54 * empty map, and a constructor with a single argument of type <tt>Map</tt>,
55 * which creates a new map with the same key-value mappings as its argument.
56 * In effect, the latter constructor allows the user to copy any map,
57 * producing an equivalent map of the desired class. There is no way to
58 * enforce this recommendation (as interfaces cannot contain constructors) but
59 * all of the general-purpose map implementations in the JDK comply.
61 * <p>The "destructive" methods contained in this interface, that is, the
62 * methods that modify the map on which they operate, are specified to throw
63 * <tt>UnsupportedOperationException</tt> if this map does not support the
64 * operation. If this is the case, these methods may, but are not required
65 * to, throw an <tt>UnsupportedOperationException</tt> if the invocation would
66 * have no effect on the map. For example, invoking the {@link #putAll(Map)}
67 * method on an unmodifiable map may, but is not required to, throw the
68 * exception if the map whose mappings are to be "superimposed" is empty.
70 * <p>Some map implementations have restrictions on the keys and values they
71 * may contain. For example, some implementations prohibit null keys and
72 * values, and some have restrictions on the types of their keys. Attempting
73 * to insert an ineligible key or value throws an unchecked exception,
74 * typically <tt>NullPointerException</tt> or <tt>ClassCastException</tt>.
75 * Attempting to query the presence of an ineligible key or value may throw an
76 * exception, or it may simply return false; some implementations will exhibit
77 * the former behavior and some will exhibit the latter. More generally,
78 * attempting an operation on an ineligible key or value whose completion
79 * would not result in the insertion of an ineligible element into the map may
80 * throw an exception or it may succeed, at the option of the implementation.
81 * Such exceptions are marked as "optional" in the specification for this
84 * <p>This interface is a member of the
85 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
86 * Java Collections Framework</a>.
88 * <p>Many methods in Collections Framework interfaces are defined
89 * in terms of the {@link Object#equals(Object) equals} method. For
90 * example, the specification for the {@link #containsKey(Object)
91 * containsKey(Object key)} method says: "returns <tt>true</tt> if and
92 * only if this map contains a mapping for a key <tt>k</tt> such that
93 * <tt>(key==null ? k==null : key.equals(k))</tt>." This specification should
94 * <i>not</i> be construed to imply that invoking <tt>Map.containsKey</tt>
95 * with a non-null argument <tt>key</tt> will cause <tt>key.equals(k)</tt> to
96 * be invoked for any key <tt>k</tt>. Implementations are free to
97 * implement optimizations whereby the <tt>equals</tt> invocation is avoided,
98 * for example, by first comparing the hash codes of the two keys. (The
99 * {@link Object#hashCode()} specification guarantees that two objects with
100 * unequal hash codes cannot be equal.) More generally, implementations of
101 * the various Collections Framework interfaces are free to take advantage of
102 * the specified behavior of underlying {@link Object} methods wherever the
103 * implementor deems it appropriate.
105 * @param <K> the type of keys maintained by this map
106 * @param <V> the type of mapped values
117 public interface Map<K,V> {
121 * Returns the number of key-value mappings in this map. If the
122 * map contains more than <tt>Integer.MAX_VALUE</tt> elements, returns
123 * <tt>Integer.MAX_VALUE</tt>.
125 * @return the number of key-value mappings in this map
130 * Returns <tt>true</tt> if this map contains no key-value mappings.
132 * @return <tt>true</tt> if this map contains no key-value mappings
137 * Returns <tt>true</tt> if this map contains a mapping for the specified
138 * key. More formally, returns <tt>true</tt> if and only if
139 * this map contains a mapping for a key <tt>k</tt> such that
140 * <tt>(key==null ? k==null : key.equals(k))</tt>. (There can be
141 * at most one such mapping.)
143 * @param key key whose presence in this map is to be tested
144 * @return <tt>true</tt> if this map contains a mapping for the specified
146 * @throws ClassCastException if the key is of an inappropriate type for
148 * (<a href="Collection.html#optional-restrictions">optional</a>)
149 * @throws NullPointerException if the specified key is null and this map
150 * does not permit null keys
151 * (<a href="Collection.html#optional-restrictions">optional</a>)
153 boolean containsKey(Object key);
156 * Returns <tt>true</tt> if this map maps one or more keys to the
157 * specified value. More formally, returns <tt>true</tt> if and only if
158 * this map contains at least one mapping to a value <tt>v</tt> such that
159 * <tt>(value==null ? v==null : value.equals(v))</tt>. This operation
160 * will probably require time linear in the map size for most
161 * implementations of the <tt>Map</tt> interface.
163 * @param value value whose presence in this map is to be tested
164 * @return <tt>true</tt> if this map maps one or more keys to the
166 * @throws ClassCastException if the value is of an inappropriate type for
168 * (<a href="Collection.html#optional-restrictions">optional</a>)
169 * @throws NullPointerException if the specified value is null and this
170 * map does not permit null values
171 * (<a href="Collection.html#optional-restrictions">optional</a>)
173 boolean containsValue(Object value);
176 * Returns the value to which the specified key is mapped,
177 * or {@code null} if this map contains no mapping for the key.
179 * <p>More formally, if this map contains a mapping from a key
180 * {@code k} to a value {@code v} such that {@code (key==null ? k==null :
181 * key.equals(k))}, then this method returns {@code v}; otherwise
182 * it returns {@code null}. (There can be at most one such mapping.)
184 * <p>If this map permits null values, then a return value of
185 * {@code null} does not <i>necessarily</i> indicate that the map
186 * contains no mapping for the key; it's also possible that the map
187 * explicitly maps the key to {@code null}. The {@link #containsKey
188 * containsKey} operation may be used to distinguish these two cases.
190 * @param key the key whose associated value is to be returned
191 * @return the value to which the specified key is mapped, or
192 * {@code null} if this map contains no mapping for the key
193 * @throws ClassCastException if the key is of an inappropriate type for
195 * (<a href="Collection.html#optional-restrictions">optional</a>)
196 * @throws NullPointerException if the specified key is null and this map
197 * does not permit null keys
198 * (<a href="Collection.html#optional-restrictions">optional</a>)
202 // Modification Operations
205 * Associates the specified value with the specified key in this map
206 * (optional operation). If the map previously contained a mapping for
207 * the key, the old value is replaced by the specified value. (A map
208 * <tt>m</tt> is said to contain a mapping for a key <tt>k</tt> if and only
209 * if {@link #containsKey(Object) m.containsKey(k)} would return
212 * @param key key with which the specified value is to be associated
213 * @param value value to be associated with the specified key
214 * @return the previous value associated with <tt>key</tt>, or
215 * <tt>null</tt> if there was no mapping for <tt>key</tt>.
216 * (A <tt>null</tt> return can also indicate that the map
217 * previously associated <tt>null</tt> with <tt>key</tt>,
218 * if the implementation supports <tt>null</tt> values.)
219 * @throws UnsupportedOperationException if the <tt>put</tt> operation
220 * is not supported by this map
221 * @throws ClassCastException if the class of the specified key or value
222 * prevents it from being stored in this map
223 * @throws NullPointerException if the specified key or value is null
224 * and this map does not permit null keys or values
225 * @throws IllegalArgumentException if some property of the specified key
226 * or value prevents it from being stored in this map
228 V put(K key, V value);
231 * Removes the mapping for a key from this map if it is present
232 * (optional operation). More formally, if this map contains a mapping
233 * from key <tt>k</tt> to value <tt>v</tt> such that
234 * <code>(key==null ? k==null : key.equals(k))</code>, that mapping
235 * is removed. (The map can contain at most one such mapping.)
237 * <p>Returns the value to which this map previously associated the key,
238 * or <tt>null</tt> if the map contained no mapping for the key.
240 * <p>If this map permits null values, then a return value of
241 * <tt>null</tt> does not <i>necessarily</i> indicate that the map
242 * contained no mapping for the key; it's also possible that the map
243 * explicitly mapped the key to <tt>null</tt>.
245 * <p>The map will not contain a mapping for the specified key once the
248 * @param key key whose mapping is to be removed from the map
249 * @return the previous value associated with <tt>key</tt>, or
250 * <tt>null</tt> if there was no mapping for <tt>key</tt>.
251 * @throws UnsupportedOperationException if the <tt>remove</tt> operation
252 * is not supported by this map
253 * @throws ClassCastException if the key is of an inappropriate type for
255 * (<a href="Collection.html#optional-restrictions">optional</a>)
256 * @throws NullPointerException if the specified key is null and this
257 * map does not permit null keys
258 * (<a href="Collection.html#optional-restrictions">optional</a>)
260 V remove(Object key);
266 * Copies all of the mappings from the specified map to this map
267 * (optional operation). The effect of this call is equivalent to that
268 * of calling {@link #put(Object,Object) put(k, v)} on this map once
269 * for each mapping from key <tt>k</tt> to value <tt>v</tt> in the
270 * specified map. The behavior of this operation is undefined if the
271 * specified map is modified while the operation is in progress.
273 * @param m mappings to be stored in this map
274 * @throws UnsupportedOperationException if the <tt>putAll</tt> operation
275 * is not supported by this map
276 * @throws ClassCastException if the class of a key or value in the
277 * specified map prevents it from being stored in this map
278 * @throws NullPointerException if the specified map is null, or if
279 * this map does not permit null keys or values, and the
280 * specified map contains null keys or values
281 * @throws IllegalArgumentException if some property of a key or value in
282 * the specified map prevents it from being stored in this map
284 void putAll(Map<? extends K, ? extends V> m);
287 * Removes all of the mappings from this map (optional operation).
288 * The map will be empty after this call returns.
290 * @throws UnsupportedOperationException if the <tt>clear</tt> operation
291 * is not supported by this map
299 * Returns a {@link Set} view of the keys contained in this map.
300 * The set is backed by the map, so changes to the map are
301 * reflected in the set, and vice-versa. If the map is modified
302 * while an iteration over the set is in progress (except through
303 * the iterator's own <tt>remove</tt> operation), the results of
304 * the iteration are undefined. The set supports element removal,
305 * which removes the corresponding mapping from the map, via the
306 * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
307 * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
308 * operations. It does not support the <tt>add</tt> or <tt>addAll</tt>
311 * @return a set view of the keys contained in this map
316 * Returns a {@link Collection} view of the values contained in this map.
317 * The collection is backed by the map, so changes to the map are
318 * reflected in the collection, and vice-versa. If the map is
319 * modified while an iteration over the collection is in progress
320 * (except through the iterator's own <tt>remove</tt> operation),
321 * the results of the iteration are undefined. The collection
322 * supports element removal, which removes the corresponding
323 * mapping from the map, via the <tt>Iterator.remove</tt>,
324 * <tt>Collection.remove</tt>, <tt>removeAll</tt>,
325 * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not
326 * support the <tt>add</tt> or <tt>addAll</tt> operations.
328 * @return a collection view of the values contained in this map
330 Collection<V> values();
333 * Returns a {@link Set} view of the mappings contained in this map.
334 * The set is backed by the map, so changes to the map are
335 * reflected in the set, and vice-versa. If the map is modified
336 * while an iteration over the set is in progress (except through
337 * the iterator's own <tt>remove</tt> operation, or through the
338 * <tt>setValue</tt> operation on a map entry returned by the
339 * iterator) the results of the iteration are undefined. The set
340 * supports element removal, which removes the corresponding
341 * mapping from the map, via the <tt>Iterator.remove</tt>,
342 * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and
343 * <tt>clear</tt> operations. It does not support the
344 * <tt>add</tt> or <tt>addAll</tt> operations.
346 * @return a set view of the mappings contained in this map
348 Set<Map.Entry<K, V>> entrySet();
351 * A map entry (key-value pair). The <tt>Map.entrySet</tt> method returns
352 * a collection-view of the map, whose elements are of this class. The
353 * <i>only</i> way to obtain a reference to a map entry is from the
354 * iterator of this collection-view. These <tt>Map.Entry</tt> objects are
355 * valid <i>only</i> for the duration of the iteration; more formally,
356 * the behavior of a map entry is undefined if the backing map has been
357 * modified after the entry was returned by the iterator, except through
358 * the <tt>setValue</tt> operation on the map entry.
360 * @see Map#entrySet()
363 interface Entry<K,V> {
365 * Returns the key corresponding to this entry.
367 * @return the key corresponding to this entry
368 * @throws IllegalStateException implementations may, but are not
369 * required to, throw this exception if the entry has been
370 * removed from the backing map.
375 * Returns the value corresponding to this entry. If the mapping
376 * has been removed from the backing map (by the iterator's
377 * <tt>remove</tt> operation), the results of this call are undefined.
379 * @return the value corresponding to this entry
380 * @throws IllegalStateException implementations may, but are not
381 * required to, throw this exception if the entry has been
382 * removed from the backing map.
387 * Replaces the value corresponding to this entry with the specified
388 * value (optional operation). (Writes through to the map.) The
389 * behavior of this call is undefined if the mapping has already been
390 * removed from the map (by the iterator's <tt>remove</tt> operation).
392 * @param value new value to be stored in this entry
393 * @return old value corresponding to the entry
394 * @throws UnsupportedOperationException if the <tt>put</tt> operation
395 * is not supported by the backing map
396 * @throws ClassCastException if the class of the specified value
397 * prevents it from being stored in the backing map
398 * @throws NullPointerException if the backing map does not permit
399 * null values, and the specified value is null
400 * @throws IllegalArgumentException if some property of this value
401 * prevents it from being stored in the backing map
402 * @throws IllegalStateException implementations may, but are not
403 * required to, throw this exception if the entry has been
404 * removed from the backing map.
409 * Compares the specified object with this entry for equality.
410 * Returns <tt>true</tt> if the given object is also a map entry and
411 * the two entries represent the same mapping. More formally, two
412 * entries <tt>e1</tt> and <tt>e2</tt> represent the same mapping
414 * (e1.getKey()==null ?
415 * e2.getKey()==null : e1.getKey().equals(e2.getKey())) &&
416 * (e1.getValue()==null ?
417 * e2.getValue()==null : e1.getValue().equals(e2.getValue()))
419 * This ensures that the <tt>equals</tt> method works properly across
420 * different implementations of the <tt>Map.Entry</tt> interface.
422 * @param o object to be compared for equality with this map entry
423 * @return <tt>true</tt> if the specified object is equal to this map
426 boolean equals(Object o);
429 * Returns the hash code value for this map entry. The hash code
430 * of a map entry <tt>e</tt> is defined to be: <pre>
431 * (e.getKey()==null ? 0 : e.getKey().hashCode()) ^
432 * (e.getValue()==null ? 0 : e.getValue().hashCode())
434 * This ensures that <tt>e1.equals(e2)</tt> implies that
435 * <tt>e1.hashCode()==e2.hashCode()</tt> for any two Entries
436 * <tt>e1</tt> and <tt>e2</tt>, as required by the general
437 * contract of <tt>Object.hashCode</tt>.
439 * @return the hash code value for this map entry
440 * @see Object#hashCode()
441 * @see Object#equals(Object)
442 * @see #equals(Object)
447 // Comparison and hashing
450 * Compares the specified object with this map for equality. Returns
451 * <tt>true</tt> if the given object is also a map and the two maps
452 * represent the same mappings. More formally, two maps <tt>m1</tt> and
453 * <tt>m2</tt> represent the same mappings if
454 * <tt>m1.entrySet().equals(m2.entrySet())</tt>. This ensures that the
455 * <tt>equals</tt> method works properly across different implementations
456 * of the <tt>Map</tt> interface.
458 * @param o object to be compared for equality with this map
459 * @return <tt>true</tt> if the specified object is equal to this map
461 boolean equals(Object o);
464 * Returns the hash code value for this map. The hash code of a map is
465 * defined to be the sum of the hash codes of each entry in the map's
466 * <tt>entrySet()</tt> view. This ensures that <tt>m1.equals(m2)</tt>
467 * implies that <tt>m1.hashCode()==m2.hashCode()</tt> for any two maps
468 * <tt>m1</tt> and <tt>m2</tt>, as required by the general contract of
469 * {@link Object#hashCode}.
471 * @return the hash code value for this map
472 * @see Map.Entry#hashCode()
473 * @see Object#equals(Object)
474 * @see #equals(Object)