1 /*
2 * Copyright 1997-2007 Sun Microsystems, Inc. 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. Sun designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
22 * CA 95054 USA or visit www.sun.com if you need additional information or
23 * have any questions.
24 */
25
26 package java.util;
27
28 /**
29 * An ordered collection (also known as a <i>sequence</i>). The user of this
30 * interface has precise control over where in the list each element is
31 * inserted. The user can access elements by their integer index (position in
32 * the list), and search for elements in the list.<p>
33 *
34 * Unlike sets, lists typically allow duplicate elements. More formally,
35 * lists typically allow pairs of elements <tt>e1</tt> and <tt>e2</tt>
36 * such that <tt>e1.equals(e2)</tt>, and they typically allow multiple
37 * null elements if they allow null elements at all. It is not inconceivable
38 * that someone might wish to implement a list that prohibits duplicates, by
39 * throwing runtime exceptions when the user attempts to insert them, but we
40 * expect this usage to be rare.<p>
41 *
42 * The <tt>List</tt> interface places additional stipulations, beyond those
43 * specified in the <tt>Collection</tt> interface, on the contracts of the
44 * <tt>iterator</tt>, <tt>add</tt>, <tt>remove</tt>, <tt>equals</tt>, and
45 * <tt>hashCode</tt> methods. Declarations for other inherited methods are
46 * also included here for convenience.<p>
47 *
48 * The <tt>List</tt> interface provides four methods for positional (indexed)
49 * access to list elements. Lists (like Java arrays) are zero based. Note
50 * that these operations may execute in time proportional to the index value
51 * for some implementations (the <tt>LinkedList</tt> class, for
52 * example). Thus, iterating over the elements in a list is typically
53 * preferable to indexing through it if the caller does not know the
54 * implementation.<p>
55 *
56 * The <tt>List</tt> interface provides a special iterator, called a
57 * <tt>ListIterator</tt>, that allows element insertion and replacement, and
58 * bidirectional access in addition to the normal operations that the
59 * <tt>Iterator</tt> interface provides. A method is provided to obtain a
60 * list iterator that starts at a specified position in the list.<p>
61 *
62 * The <tt>List</tt> interface provides two methods to search for a specified
63 * object. From a performance standpoint, these methods should be used with
64 * caution. In many implementations they will perform costly linear
65 * searches.<p>
66 *
67 * The <tt>List</tt> interface provides two methods to efficiently insert and
68 * remove multiple elements at an arbitrary point in the list.<p>
69 *
70 * Note: While it is permissible for lists to contain themselves as elements,
71 * extreme caution is advised: the <tt>equals</tt> and <tt>hashCode</tt>
72 * methods are no longer well defined on such a list.
73 *
74 * <p>Some list implementations have restrictions on the elements that
75 * they may contain. For example, some implementations prohibit null elements,
76 * and some have restrictions on the types of their elements. Attempting to
77 * add an ineligible element throws an unchecked exception, typically
78 * <tt>NullPointerException</tt> or <tt>ClassCastException</tt>. Attempting
79 * to query the presence of an ineligible element may throw an exception,
80 * or it may simply return false; some implementations will exhibit the former
81 * behavior and some will exhibit the latter. More generally, attempting an
82 * operation on an ineligible element whose completion would not result in
83 * the insertion of an ineligible element into the list may throw an
84 * exception or it may succeed, at the option of the implementation.
85 * Such exceptions are marked as "optional" in the specification for this
86 * interface.
87 *
88 * <p>This interface is a member of the
89 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
90 * Java Collections Framework</a>.
91 *
92 * @author Josh Bloch
93 * @author Neal Gafter
94 * @see Collection
95 * @see Set
96 * @see ArrayList
97 * @see LinkedList
98 * @see Vector
99 * @see Arrays#asList(Object[])
100 * @see Collections#nCopies(int, Object)
101 * @see Collections#EMPTY_LIST
102 * @see AbstractList
103 * @see AbstractSequentialList
104 * @since 1.2
105 */
106
107 public interface List<E> extends Collection<E> {
108 // Query Operations
109
110 /**
111 * Returns the number of elements in this list. If this list contains
112 * more than <tt>Integer.MAX_VALUE</tt> elements, returns
113 * <tt>Integer.MAX_VALUE</tt>.
114 *
115 * @return the number of elements in this list
116 */
117 int size();
118
119 /**
120 * Returns <tt>true</tt> if this list contains no elements.
121 *
122 * @return <tt>true</tt> if this list contains no elements
123 */
124 boolean isEmpty();
125
126 /**
127 * Returns <tt>true</tt> if this list contains the specified element.
128 * More formally, returns <tt>true</tt> if and only if this list contains
129 * at least one element <tt>e</tt> such that
130 * <tt>(o==null ? e==null : o.equals(e))</tt>.
131 *
132 * @param o element whose presence in this list is to be tested
133 * @return <tt>true</tt> if this list contains the specified element
134 * @throws ClassCastException if the type of the specified element
135 * is incompatible with this list (optional)
136 * @throws NullPointerException if the specified element is null and this
137 * list does not permit null elements (optional)
138 */
139 boolean contains(Object o);
140
141 /**
142 * Returns an iterator over the elements in this list in proper sequence.
143 *
144 * @return an iterator over the elements in this list in proper sequence
145 */
146 Iterator<E> iterator();
147
148 /**
149 * Returns an array containing all of the elements in this list in proper
150 * sequence (from first to last element).
151 *
152 * <p>The returned array will be "safe" in that no references to it are
153 * maintained by this list. (In other words, this method must
154 * allocate a new array even if this list is backed by an array).
155 * The caller is thus free to modify the returned array.
156 *
157 * <p>This method acts as bridge between array-based and collection-based
158 * APIs.
159 *
160 * @return an array containing all of the elements in this list in proper
161 * sequence
162 * @see Arrays#asList(Object[])
163 */
164 Object[] toArray();
165
166 /**
167 * Returns an array containing all of the elements in this list in
168 * proper sequence (from first to last element); the runtime type of
169 * the returned array is that of the specified array. If the list fits
170 * in the specified array, it is returned therein. Otherwise, a new
171 * array is allocated with the runtime type of the specified array and
172 * the size of this list.
173 *
174 * <p>If the list fits in the specified array with room to spare (i.e.,
175 * the array has more elements than the list), the element in the array
176 * immediately following the end of the list is set to <tt>null</tt>.
177 * (This is useful in determining the length of the list <i>only</i> if
178 * the caller knows that the list does not contain any null elements.)
179 *
180 * <p>Like the {@link #toArray()} method, this method acts as bridge between
181 * array-based and collection-based APIs. Further, this method allows
182 * precise control over the runtime type of the output array, and may,
183 * under certain circumstances, be used to save allocation costs.
184 *
185 * <p>Suppose <tt>x</tt> is a list known to contain only strings.
186 * The following code can be used to dump the list into a newly
187 * allocated array of <tt>String</tt>:
188 *
189 * <pre>
190 * String[] y = x.toArray(new String[0]);</pre>
191 *
192 * Note that <tt>toArray(new Object[0])</tt> is identical in function to
193 * <tt>toArray()</tt>.
194 *
195 * @param a the array into which the elements of this list are to
196 * be stored, if it is big enough; otherwise, a new array of the
197 * same runtime type is allocated for this purpose.
198 * @return an array containing the elements of this list
199 * @throws ArrayStoreException if the runtime type of the specified array
200 * is not a supertype of the runtime type of every element in
201 * this list
202 * @throws NullPointerException if the specified array is null
203 */
204 <T> T[] toArray(T[] a);
205
206
207 // Modification Operations
208
209 /**
210 * Appends the specified element to the end of this list (optional
211 * operation).
212 *
213 * <p>Lists that support this operation may place limitations on what
214 * elements may be added to this list. In particular, some
215 * lists will refuse to add null elements, and others will impose
216 * restrictions on the type of elements that may be added. List
217 * classes should clearly specify in their documentation any restrictions
218 * on what elements may be added.
219 *
220 * @param e element to be appended to this list
221 * @return <tt>true</tt> (as specified by {@link Collection#add})
222 * @throws UnsupportedOperationException if the <tt>add</tt> operation
223 * is not supported by this list
224 * @throws ClassCastException if the class of the specified element
225 * prevents it from being added to this list
226 * @throws NullPointerException if the specified element is null and this
227 * list does not permit null elements
228 * @throws IllegalArgumentException if some property of this element
229 * prevents it from being added to this list
230 */
231 boolean add(E e);
232
233 /**
234 * Removes the first occurrence of the specified element from this list,
235 * if it is present (optional operation). If this list does not contain
236 * the element, it is unchanged. More formally, removes the element with
237 * the lowest index <tt>i</tt> such that
238 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>
239 * (if such an element exists). Returns <tt>true</tt> if this list
240 * contained the specified element (or equivalently, if this list changed
241 * as a result of the call).
242 *
243 * @param o element to be removed from this list, if present
244 * @return <tt>true</tt> if this list contained the specified element
245 * @throws ClassCastException if the type of the specified element
246 * is incompatible with this list (optional)
247 * @throws NullPointerException if the specified element is null and this
248 * list does not permit null elements (optional)
249 * @throws UnsupportedOperationException if the <tt>remove</tt> operation
250 * is not supported by this list
251 */
252 boolean remove(Object o);
253
254
255 // Bulk Modification Operations
256
257 /**
258 * Returns <tt>true</tt> if this list contains all of the elements of the
259 * specified collection.
260 *
261 * @param c collection to be checked for containment in this list
262 * @return <tt>true</tt> if this list contains all of the elements of the
263 * specified collection
264 * @throws ClassCastException if the types of one or more elements
265 * in the specified collection are incompatible with this
266 * list (optional)
267 * @throws NullPointerException if the specified collection contains one
268 * or more null elements and this list does not permit null
269 * elements (optional), or if the specified collection is null
270 * @see #contains(Object)
271 */
272 boolean containsAll(Collection<?> c);
273
274 /**
275 * Appends all of the elements in the specified collection to the end of
276 * this list, in the order that they are returned by the specified
277 * collection's iterator (optional operation). The behavior of this
278 * operation is undefined if the specified collection is modified while
279 * the operation is in progress. (Note that this will occur if the
280 * specified collection is this list, and it's nonempty.)
281 *
282 * @param c collection containing elements to be added to this list
283 * @return <tt>true</tt> if this list changed as a result of the call
284 * @throws UnsupportedOperationException if the <tt>addAll</tt> operation
285 * is not supported by this list
286 * @throws ClassCastException if the class of an element of the specified
287 * collection prevents it from being added to this list
288 * @throws NullPointerException if the specified collection contains one
289 * or more null elements and this list does not permit null
290 * elements, or if the specified collection is null
291 * @throws IllegalArgumentException if some property of an element of the
292 * specified collection prevents it from being added to this list
293 * @see #add(Object)
294 */
295 boolean addAll(Collection<? extends E> c);
296
297 /**
298 * Inserts all of the elements in the specified collection into this
299 * list at the specified position (optional operation). Shifts the
300 * element currently at that position (if any) and any subsequent
301 * elements to the right (increases their indices). The new elements
302 * will appear in this list in the order that they are returned by the
303 * specified collection's iterator. The behavior of this operation is
304 * undefined if the specified collection is modified while the
305 * operation is in progress. (Note that this will occur if the specified
306 * collection is this list, and it's nonempty.)
307 *
308 * @param index index at which to insert the first element from the
309 * specified collection
310 * @param c collection containing elements to be added to this list
311 * @return <tt>true</tt> if this list changed as a result of the call
312 * @throws UnsupportedOperationException if the <tt>addAll</tt> operation
313 * is not supported by this list
314 * @throws ClassCastException if the class of an element of the specified
315 * collection prevents it from being added to this list
316 * @throws NullPointerException if the specified collection contains one
317 * or more null elements and this list does not permit null
318 * elements, or if the specified collection is null
319 * @throws IllegalArgumentException if some property of an element of the
320 * specified collection prevents it from being added to this list
321 * @throws IndexOutOfBoundsException if the index is out of range
322 * (<tt>index < 0 || index > size()</tt>)
323 */
324 boolean addAll(int index, Collection<? extends E> c);
325
326 /**
327 * Removes from this list all of its elements that are contained in the
328 * specified collection (optional operation).
329 *
330 * @param c collection containing elements to be removed from this list
331 * @return <tt>true</tt> if this list changed as a result of the call
332 * @throws UnsupportedOperationException if the <tt>removeAll</tt> operation
333 * is not supported by this list
334 * @throws ClassCastException if the class of an element of this list
335 * is incompatible with the specified collection (optional)
336 * @throws NullPointerException if this list contains a null element and the
337 * specified collection does not permit null elements (optional),
338 * or if the specified collection is null
339 * @see #remove(Object)
340 * @see #contains(Object)
341 */
342 boolean removeAll(Collection<?> c);
343
344 /**
345 * Retains only the elements in this list that are contained in the
346 * specified collection (optional operation). In other words, removes
347 * from this list all of its elements that are not contained in the
348 * specified collection.
349 *
350 * @param c collection containing elements to be retained in this list
351 * @return <tt>true</tt> if this list changed as a result of the call
352 * @throws UnsupportedOperationException if the <tt>retainAll</tt> operation
353 * is not supported by this list
354 * @throws ClassCastException if the class of an element of this list
355 * is incompatible with the specified collection (optional)
356 * @throws NullPointerException if this list contains a null element and the
357 * specified collection does not permit null elements (optional),
358 * or if the specified collection is null
359 * @see #remove(Object)
360 * @see #contains(Object)
361 */
362 boolean retainAll(Collection<?> c);
363
364 /**
365 * Removes all of the elements from this list (optional operation).
366 * The list will be empty after this call returns.
367 *
368 * @throws UnsupportedOperationException if the <tt>clear</tt> operation
369 * is not supported by this list
370 */
371 void clear();
372
373
374 // Comparison and hashing
375
376 /**
377 * Compares the specified object with this list for equality. Returns
378 * <tt>true</tt> if and only if the specified object is also a list, both
379 * lists have the same size, and all corresponding pairs of elements in
380 * the two lists are <i>equal</i>. (Two elements <tt>e1</tt> and
381 * <tt>e2</tt> are <i>equal</i> if <tt>(e1==null ? e2==null :
382 * e1.equals(e2))</tt>.) In other words, two lists are defined to be
383 * equal if they contain the same elements in the same order. This
384 * definition ensures that the equals method works properly across
385 * different implementations of the <tt>List</tt> interface.
386 *
387 * @param o the object to be compared for equality with this list
388 * @return <tt>true</tt> if the specified object is equal to this list
389 */
390 boolean equals(Object o);
391
392 /**
393 * Returns the hash code value for this list. The hash code of a list
394 * is defined to be the result of the following calculation:
395 * <pre>
396 * int hashCode = 1;
397 * for (E e : list)
398 * hashCode = 31*hashCode + (e==null ? 0 : e.hashCode());
399 * </pre>
400 * This ensures that <tt>list1.equals(list2)</tt> implies that
401 * <tt>list1.hashCode()==list2.hashCode()</tt> for any two lists,
402 * <tt>list1</tt> and <tt>list2</tt>, as required by the general
403 * contract of {@link Object#hashCode}.
404 *
405 * @return the hash code value for this list
406 * @see Object#equals(Object)
407 * @see #equals(Object)
408 */
409 int hashCode();
410
411
412 // Positional Access Operations
413
414 /**
415 * Returns the element at the specified position in this list.
416 *
417 * @param index index of the element to return
418 * @return the element at the specified position in this list
419 * @throws IndexOutOfBoundsException if the index is out of range
420 * (<tt>index < 0 || index >= size()</tt>)
421 */
422 E get(int index);
423
424 /**
425 * Replaces the element at the specified position in this list with the
426 * specified element (optional operation).
427 *
428 * @param index index of the element to replace
429 * @param element element to be stored at the specified position
430 * @return the element previously at the specified position
431 * @throws UnsupportedOperationException if the <tt>set</tt> operation
432 * is not supported by this list
433 * @throws ClassCastException if the class of the specified element
434 * prevents it from being added to this list
435 * @throws NullPointerException if the specified element is null and
436 * this list does not permit null elements
437 * @throws IllegalArgumentException if some property of the specified
438 * element prevents it from being added to this list
439 * @throws IndexOutOfBoundsException if the index is out of range
440 * (<tt>index < 0 || index >= size()</tt>)
441 */
442 E set(int index, E element);
443
444 /**
445 * Inserts the specified element at the specified position in this list
446 * (optional operation). Shifts the element currently at that position
447 * (if any) and any subsequent elements to the right (adds one to their
448 * indices).
449 *
450 * @param index index at which the specified element is to be inserted
451 * @param element element to be inserted
452 * @throws UnsupportedOperationException if the <tt>add</tt> operation
453 * is not supported by this list
454 * @throws ClassCastException if the class of the specified element
455 * prevents it from being added to this list
456 * @throws NullPointerException if the specified element is null and
457 * this list does not permit null elements
458 * @throws IllegalArgumentException if some property of the specified
459 * element prevents it from being added to this list
460 * @throws IndexOutOfBoundsException if the index is out of range
461 * (<tt>index < 0 || index > size()</tt>)
462 */
463 void add(int index, E element);
464
465 /**
466 * Removes the element at the specified position in this list (optional
467 * operation). Shifts any subsequent elements to the left (subtracts one
468 * from their indices). Returns the element that was removed from the
469 * list.
470 *
471 * @param index the index of the element to be removed
472 * @return the element previously at the specified position
473 * @throws UnsupportedOperationException if the <tt>remove</tt> operation
474 * is not supported by this list
475 * @throws IndexOutOfBoundsException if the index is out of range
476 * (<tt>index < 0 || index >= size()</tt>)
477 */
478 E remove(int index);
479
480
481 // Search Operations
482
483 /**
484 * Returns the index of the first occurrence of the specified element
485 * in this list, or -1 if this list does not contain the element.
486 * More formally, returns the lowest index <tt>i</tt> such that
487 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
488 * or -1 if there is no such index.
489 *
490 * @param o element to search for
491 * @return the index of the first occurrence of the specified element in
492 * this list, or -1 if this list does not contain the element
493 * @throws ClassCastException if the type of the specified element
494 * is incompatible with this list (optional)
495 * @throws NullPointerException if the specified element is null and this
496 * list does not permit null elements (optional)
497 */
498 int indexOf(Object o);
499
500 /**
501 * Returns the index of the last occurrence of the specified element
502 * in this list, or -1 if this list does not contain the element.
503 * More formally, returns the highest index <tt>i</tt> such that
504 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
505 * or -1 if there is no such index.
506 *
507 * @param o element to search for
508 * @return the index of the last occurrence of the specified element in
509 * this list, or -1 if this list does not contain the element
510 * @throws ClassCastException if the type of the specified element
511 * is incompatible with this list (optional)
512 * @throws NullPointerException if the specified element is null and this
513 * list does not permit null elements (optional)
514 */
515 int lastIndexOf(Object o);
516
517
518 // List Iterators
519
520 /**
521 * Returns a list iterator over the elements in this list (in proper
522 * sequence).
523 *
524 * @return a list iterator over the elements in this list (in proper
525 * sequence)
526 */
527 ListIterator<E> listIterator();
528
529 /**
530 * Returns a list iterator over the elements in this list (in proper
531 * sequence), starting at the specified position in the list.
532 * The specified index indicates the first element that would be
533 * returned by an initial call to {@link ListIterator#next next}.
534 * An initial call to {@link ListIterator#previous previous} would
535 * return the element with the specified index minus one.
536 *
537 * @param index index of the first element to be returned from the
538 * list iterator (by a call to {@link ListIterator#next next})
539 * @return a list iterator over the elements in this list (in proper
540 * sequence), starting at the specified position in the list
541 * @throws IndexOutOfBoundsException if the index is out of range
542 * ({@code index < 0 || index > size()})
543 */
544 ListIterator<E> listIterator(int index);
545
546 // View
547
548 /**
549 * Returns a view of the portion of this list between the specified
550 * <tt>fromIndex</tt>, inclusive, and <tt>toIndex</tt>, exclusive. (If
551 * <tt>fromIndex</tt> and <tt>toIndex</tt> are equal, the returned list is
552 * empty.) The returned list is backed by this list, so non-structural
553 * changes in the returned list are reflected in this list, and vice-versa.
554 * The returned list supports all of the optional list operations supported
555 * by this list.<p>
556 *
557 * This method eliminates the need for explicit range operations (of
558 * the sort that commonly exist for arrays). Any operation that expects
559 * a list can be used as a range operation by passing a subList view
560 * instead of a whole list. For example, the following idiom
561 * removes a range of elements from a list:
562 * <pre>
563 * list.subList(from, to).clear();
564 * </pre>
565 * Similar idioms may be constructed for <tt>indexOf</tt> and
566 * <tt>lastIndexOf</tt>, and all of the algorithms in the
567 * <tt>Collections</tt> class can be applied to a subList.<p>
568 *
569 * The semantics of the list returned by this method become undefined if
570 * the backing list (i.e., this list) is <i>structurally modified</i> in
571 * any way other than via the returned list. (Structural modifications are
572 * those that change the size of this list, or otherwise perturb it in such
573 * a fashion that iterations in progress may yield incorrect results.)
574 *
575 * @param fromIndex low endpoint (inclusive) of the subList
576 * @param toIndex high endpoint (exclusive) of the subList
577 * @return a view of the specified range within this list
578 * @throws IndexOutOfBoundsException for an illegal endpoint index value
579 * (<tt>fromIndex < 0 || toIndex > size ||
580 * fromIndex > toIndex</tt>)
581 */
582 List<E> subList(int fromIndex, int toIndex);
583 }
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