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
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7 * published by the Free Software Foundation. Oracle designates this
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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 *
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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 * 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 * @param <E> the type of elements in this list
93 *
94 * @author Josh Bloch
95 * @author Neal Gafter
96 * @see Collection
97 * @see Set
98 * @see ArrayList
99 * @see LinkedList
100 * @see Vector
101 * @see Arrays#asList(Object[])
102 * @see Collections#nCopies(int, Object)
103 * @see Collections#EMPTY_LIST
104 * @see AbstractList
105 * @see AbstractSequentialList
106 * @since 1.2
107 */
108
109 public interface List<E> extends Collection<E> {
110 // Query Operations
111
112 /**
113 * Returns the number of elements in this list. If this list contains
114 * more than <tt>Integer.MAX_VALUE</tt> elements, returns
115 * <tt>Integer.MAX_VALUE</tt>.
116 *
117 * @return the number of elements in this list
118 */
119 int size();
120
121 /**
122 * Returns <tt>true</tt> if this list contains no elements.
123 *
124 * @return <tt>true</tt> if this list contains no elements
125 */
126 boolean isEmpty();
127
128 /**
129 * Returns <tt>true</tt> if this list contains the specified element.
130 * More formally, returns <tt>true</tt> if and only if this list contains
131 * at least one element <tt>e</tt> such that
132 * <tt>(o==null ? e==null : o.equals(e))</tt>.
133 *
134 * @param o element whose presence in this list is to be tested
135 * @return <tt>true</tt> if this list contains the specified element
136 * @throws ClassCastException if the type of the specified element
137 * is incompatible with this list
138 * (<a href="Collection.html#optional-restrictions">optional</a>)
139 * @throws NullPointerException if the specified element is null and this
140 * list does not permit null elements
141 * (<a href="Collection.html#optional-restrictions">optional</a>)
142 */
143 boolean contains(Object o);
144
145 /**
146 * Returns an iterator over the elements in this list in proper sequence.
147 *
148 * @return an iterator over the elements in this list in proper sequence
149 */
150 Iterator<E> iterator();
151
152 /**
153 * Returns an array containing all of the elements in this list in proper
154 * sequence (from first to last element).
155 *
156 * <p>The returned array will be "safe" in that no references to it are
157 * maintained by this list. (In other words, this method must
158 * allocate a new array even if this list is backed by an array).
159 * The caller is thus free to modify the returned array.
160 *
161 * <p>This method acts as bridge between array-based and collection-based
162 * APIs.
163 *
164 * @return an array containing all of the elements in this list in proper
165 * sequence
166 * @see Arrays#asList(Object[])
167 */
168 Object[] toArray();
169
170 /**
171 * Returns an array containing all of the elements in this list in
172 * proper sequence (from first to last element); the runtime type of
173 * the returned array is that of the specified array. If the list fits
174 * in the specified array, it is returned therein. Otherwise, a new
175 * array is allocated with the runtime type of the specified array and
176 * the size of this list.
177 *
178 * <p>If the list fits in the specified array with room to spare (i.e.,
179 * the array has more elements than the list), the element in the array
180 * immediately following the end of the list is set to <tt>null</tt>.
181 * (This is useful in determining the length of the list <i>only</i> if
182 * the caller knows that the list does not contain any null elements.)
183 *
184 * <p>Like the {@link #toArray()} method, this method acts as bridge between
185 * array-based and collection-based APIs. Further, this method allows
186 * precise control over the runtime type of the output array, and may,
187 * under certain circumstances, be used to save allocation costs.
188 *
189 * <p>Suppose <tt>x</tt> is a list known to contain only strings.
190 * The following code can be used to dump the list into a newly
191 * allocated array of <tt>String</tt>:
192 *
193 * <pre>
194 * String[] y = x.toArray(new String[0]);</pre>
195 *
196 * Note that <tt>toArray(new Object[0])</tt> is identical in function to
197 * <tt>toArray()</tt>.
198 *
199 * @param a the array into which the elements of this list are to
200 * be stored, if it is big enough; otherwise, a new array of the
201 * same runtime type is allocated for this purpose.
202 * @return an array containing the elements of this list
203 * @throws ArrayStoreException if the runtime type of the specified array
204 * is not a supertype of the runtime type of every element in
205 * this list
206 * @throws NullPointerException if the specified array is null
207 */
208 <T> T[] toArray(T[] a);
209
210
211 // Modification Operations
212
213 /**
214 * Appends the specified element to the end of this list (optional
215 * operation).
216 *
217 * <p>Lists that support this operation may place limitations on what
218 * elements may be added to this list. In particular, some
219 * lists will refuse to add null elements, and others will impose
220 * restrictions on the type of elements that may be added. List
221 * classes should clearly specify in their documentation any restrictions
222 * on what elements may be added.
223 *
224 * @param e element to be appended to this list
225 * @return <tt>true</tt> (as specified by {@link Collection#add})
226 * @throws UnsupportedOperationException if the <tt>add</tt> operation
227 * is not supported by this list
228 * @throws ClassCastException if the class of the specified element
229 * prevents it from being added to this list
230 * @throws NullPointerException if the specified element is null and this
231 * list does not permit null elements
232 * @throws IllegalArgumentException if some property of this element
233 * prevents it from being added to this list
234 */
235 boolean add(E e);
236
237 /**
238 * Removes the first occurrence of the specified element from this list,
239 * if it is present (optional operation). If this list does not contain
240 * the element, it is unchanged. More formally, removes the element with
241 * the lowest index <tt>i</tt> such that
242 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>
243 * (if such an element exists). Returns <tt>true</tt> if this list
244 * contained the specified element (or equivalently, if this list changed
245 * as a result of the call).
246 *
247 * @param o element to be removed from this list, if present
248 * @return <tt>true</tt> if this list contained the specified element
249 * @throws ClassCastException if the type of the specified element
250 * is incompatible with this list
251 * (<a href="Collection.html#optional-restrictions">optional</a>)
252 * @throws NullPointerException if the specified element is null and this
253 * list does not permit null elements
254 * (<a href="Collection.html#optional-restrictions">optional</a>)
255 * @throws UnsupportedOperationException if the <tt>remove</tt> operation
256 * is not supported by this list
257 */
258 boolean remove(Object o);
259
260
261 // Bulk Modification Operations
262
263 /**
264 * Returns <tt>true</tt> if this list contains all of the elements of the
265 * specified collection.
266 *
267 * @param c collection to be checked for containment in this list
268 * @return <tt>true</tt> if this list contains all of the elements of the
269 * specified collection
270 * @throws ClassCastException if the types of one or more elements
271 * in the specified collection are incompatible with this
272 * list
273 * (<a href="Collection.html#optional-restrictions">optional</a>)
274 * @throws NullPointerException if the specified collection contains one
275 * or more null elements and this list does not permit null
276 * elements
277 * (<a href="Collection.html#optional-restrictions">optional</a>),
278 * or if the specified collection is null
279 * @see #contains(Object)
280 */
281 boolean containsAll(Collection<?> c);
282
283 /**
284 * Appends all of the elements in the specified collection to the end of
285 * this list, in the order that they are returned by the specified
286 * collection's iterator (optional operation). The behavior of this
287 * operation is undefined if the specified collection is modified while
288 * the operation is in progress. (Note that this will occur if the
289 * specified collection is this list, and it's nonempty.)
290 *
291 * @param c collection containing elements to be added to this list
292 * @return <tt>true</tt> if this list changed as a result of the call
293 * @throws UnsupportedOperationException if the <tt>addAll</tt> operation
294 * is not supported by this list
295 * @throws ClassCastException if the class of an element of the specified
296 * collection prevents it from being added to this list
297 * @throws NullPointerException if the specified collection contains one
298 * or more null elements and this list does not permit null
299 * elements, or if the specified collection is null
300 * @throws IllegalArgumentException if some property of an element of the
301 * specified collection prevents it from being added to this list
302 * @see #add(Object)
303 */
304 boolean addAll(Collection<? extends E> c);
305
306 /**
307 * Inserts all of the elements in the specified collection into this
308 * list at the specified position (optional operation). Shifts the
309 * element currently at that position (if any) and any subsequent
310 * elements to the right (increases their indices). The new elements
311 * will appear in this list in the order that they are returned by the
312 * specified collection's iterator. The behavior of this operation is
313 * undefined if the specified collection is modified while the
314 * operation is in progress. (Note that this will occur if the specified
315 * collection is this list, and it's nonempty.)
316 *
317 * @param index index at which to insert the first element from the
318 * specified collection
319 * @param c collection containing elements to be added to this list
320 * @return <tt>true</tt> if this list changed as a result of the call
321 * @throws UnsupportedOperationException if the <tt>addAll</tt> operation
322 * is not supported by this list
323 * @throws ClassCastException if the class of an element of the specified
324 * collection prevents it from being added to this list
325 * @throws NullPointerException if the specified collection contains one
326 * or more null elements and this list does not permit null
327 * elements, or if the specified collection is null
328 * @throws IllegalArgumentException if some property of an element of the
329 * specified collection prevents it from being added to this list
330 * @throws IndexOutOfBoundsException if the index is out of range
331 * (<tt>index < 0 || index > size()</tt>)
332 */
333 boolean addAll(int index, Collection<? extends E> c);
334
335 /**
336 * Removes from this list all of its elements that are contained in the
337 * specified collection (optional operation).
338 *
339 * @param c collection containing elements to be removed from this list
340 * @return <tt>true</tt> if this list changed as a result of the call
341 * @throws UnsupportedOperationException if the <tt>removeAll</tt> operation
342 * is not supported by this list
343 * @throws ClassCastException if the class of an element of this list
344 * is incompatible with the specified collection
345 * (<a href="Collection.html#optional-restrictions">optional</a>)
346 * @throws NullPointerException if this list contains a null element and the
347 * specified collection does not permit null elements
348 * (<a href="Collection.html#optional-restrictions">optional</a>),
349 * or if the specified collection is null
350 * @see #remove(Object)
351 * @see #contains(Object)
352 */
353 boolean removeAll(Collection<?> c);
354
355 /**
356 * Retains only the elements in this list that are contained in the
357 * specified collection (optional operation). In other words, removes
358 * from this list all of its elements that are not contained in the
359 * specified collection.
360 *
361 * @param c collection containing elements to be retained in this list
362 * @return <tt>true</tt> if this list changed as a result of the call
363 * @throws UnsupportedOperationException if the <tt>retainAll</tt> operation
364 * is not supported by this list
365 * @throws ClassCastException if the class of an element of this list
366 * is incompatible with the specified collection
367 * (<a href="Collection.html#optional-restrictions">optional</a>)
368 * @throws NullPointerException if this list contains a null element and the
369 * specified collection does not permit null elements
370 * (<a href="Collection.html#optional-restrictions">optional</a>),
371 * or if the specified collection is null
372 * @see #remove(Object)
373 * @see #contains(Object)
374 */
375 boolean retainAll(Collection<?> c);
376
377 /**
378 * Removes all of the elements from this list (optional operation).
379 * The list will be empty after this call returns.
380 *
381 * @throws UnsupportedOperationException if the <tt>clear</tt> operation
382 * is not supported by this list
383 */
384 void clear();
385
386
387 // Comparison and hashing
388
389 /**
390 * Compares the specified object with this list for equality. Returns
391 * <tt>true</tt> if and only if the specified object is also a list, both
392 * lists have the same size, and all corresponding pairs of elements in
393 * the two lists are <i>equal</i>. (Two elements <tt>e1</tt> and
394 * <tt>e2</tt> are <i>equal</i> if <tt>(e1==null ? e2==null :
395 * e1.equals(e2))</tt>.) In other words, two lists are defined to be
396 * equal if they contain the same elements in the same order. This
397 * definition ensures that the equals method works properly across
398 * different implementations of the <tt>List</tt> interface.
399 *
400 * @param o the object to be compared for equality with this list
401 * @return <tt>true</tt> if the specified object is equal to this list
402 */
403 boolean equals(Object o);
404
405 /**
406 * Returns the hash code value for this list. The hash code of a list
407 * is defined to be the result of the following calculation:
408 * <pre>
409 * int hashCode = 1;
410 * for (E e : list)
411 * hashCode = 31*hashCode + (e==null ? 0 : e.hashCode());
412 * </pre>
413 * This ensures that <tt>list1.equals(list2)</tt> implies that
414 * <tt>list1.hashCode()==list2.hashCode()</tt> for any two lists,
415 * <tt>list1</tt> and <tt>list2</tt>, as required by the general
416 * contract of {@link Object#hashCode}.
417 *
418 * @return the hash code value for this list
419 * @see Object#equals(Object)
420 * @see #equals(Object)
421 */
422 int hashCode();
423
424
425 // Positional Access Operations
426
427 /**
428 * Returns the element at the specified position in this list.
429 *
430 * @param index index of the element to return
431 * @return the element at the specified position in this list
432 * @throws IndexOutOfBoundsException if the index is out of range
433 * (<tt>index < 0 || index >= size()</tt>)
434 */
435 E get(int index);
436
437 /**
438 * Replaces the element at the specified position in this list with the
439 * specified element (optional operation).
440 *
441 * @param index index of the element to replace
442 * @param element element to be stored at the specified position
443 * @return the element previously at the specified position
444 * @throws UnsupportedOperationException if the <tt>set</tt> operation
445 * is not supported by this list
446 * @throws ClassCastException if the class of the specified element
447 * prevents it from being added to this list
448 * @throws NullPointerException if the specified element is null and
449 * this list does not permit null elements
450 * @throws IllegalArgumentException if some property of the specified
451 * element prevents it from being added to this list
452 * @throws IndexOutOfBoundsException if the index is out of range
453 * (<tt>index < 0 || index >= size()</tt>)
454 */
455 E set(int index, E element);
456
457 /**
458 * Inserts the specified element at the specified position in this list
459 * (optional operation). Shifts the element currently at that position
460 * (if any) and any subsequent elements to the right (adds one to their
461 * indices).
462 *
463 * @param index index at which the specified element is to be inserted
464 * @param element element to be inserted
465 * @throws UnsupportedOperationException if the <tt>add</tt> operation
466 * is not supported by this list
467 * @throws ClassCastException if the class of the specified element
468 * prevents it from being added to this list
469 * @throws NullPointerException if the specified element is null and
470 * this list does not permit null elements
471 * @throws IllegalArgumentException if some property of the specified
472 * element prevents it from being added to this list
473 * @throws IndexOutOfBoundsException if the index is out of range
474 * (<tt>index < 0 || index > size()</tt>)
475 */
476 void add(int index, E element);
477
478 /**
479 * Removes the element at the specified position in this list (optional
480 * operation). Shifts any subsequent elements to the left (subtracts one
481 * from their indices). Returns the element that was removed from the
482 * list.
483 *
484 * @param index the index of the element to be removed
485 * @return the element previously at the specified position
486 * @throws UnsupportedOperationException if the <tt>remove</tt> operation
487 * is not supported by this list
488 * @throws IndexOutOfBoundsException if the index is out of range
489 * (<tt>index < 0 || index >= size()</tt>)
490 */
491 E remove(int index);
492
493
494 // Search Operations
495
496 /**
497 * Returns the index of the first occurrence of the specified element
498 * in this list, or -1 if this list does not contain the element.
499 * More formally, returns the lowest index <tt>i</tt> such that
500 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
501 * or -1 if there is no such index.
502 *
503 * @param o element to search for
504 * @return the index of the first occurrence of the specified element in
505 * this list, or -1 if this list does not contain the element
506 * @throws ClassCastException if the type of the specified element
507 * is incompatible with this list
508 * (<a href="Collection.html#optional-restrictions">optional</a>)
509 * @throws NullPointerException if the specified element is null and this
510 * list does not permit null elements
511 * (<a href="Collection.html#optional-restrictions">optional</a>)
512 */
513 int indexOf(Object o);
514
515 /**
516 * Returns the index of the last occurrence of the specified element
517 * in this list, or -1 if this list does not contain the element.
518 * More formally, returns the highest index <tt>i</tt> such that
519 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
520 * or -1 if there is no such index.
521 *
522 * @param o element to search for
523 * @return the index of the last occurrence of the specified element in
524 * this list, or -1 if this list does not contain the element
525 * @throws ClassCastException if the type of the specified element
526 * is incompatible with this list
527 * (<a href="Collection.html#optional-restrictions">optional</a>)
528 * @throws NullPointerException if the specified element is null and this
529 * list does not permit null elements
530 * (<a href="Collection.html#optional-restrictions">optional</a>)
531 */
532 int lastIndexOf(Object o);
533
534
535 // List Iterators
536
537 /**
538 * Returns a list iterator over the elements in this list (in proper
539 * sequence).
540 *
541 * @return a list iterator over the elements in this list (in proper
542 * sequence)
543 */
544 ListIterator<E> listIterator();
545
546 /**
547 * Returns a list iterator over the elements in this list (in proper
548 * sequence), starting at the specified position in the list.
549 * The specified index indicates the first element that would be
550 * returned by an initial call to {@link ListIterator#next next}.
551 * An initial call to {@link ListIterator#previous previous} would
552 * return the element with the specified index minus one.
553 *
554 * @param index index of the first element to be returned from the
555 * list iterator (by a call to {@link ListIterator#next next})
556 * @return a list iterator over the elements in this list (in proper
557 * sequence), starting at the specified position in the list
558 * @throws IndexOutOfBoundsException if the index is out of range
559 * ({@code index < 0 || index > size()})
560 */
561 ListIterator<E> listIterator(int index);
562
563 // View
564
565 /**
566 * Returns a view of the portion of this list between the specified
567 * <tt>fromIndex</tt>, inclusive, and <tt>toIndex</tt>, exclusive. (If
568 * <tt>fromIndex</tt> and <tt>toIndex</tt> are equal, the returned list is
569 * empty.) The returned list is backed by this list, so non-structural
570 * changes in the returned list are reflected in this list, and vice-versa.
571 * The returned list supports all of the optional list operations supported
572 * by this list.<p>
573 *
574 * This method eliminates the need for explicit range operations (of
575 * the sort that commonly exist for arrays). Any operation that expects
576 * a list can be used as a range operation by passing a subList view
577 * instead of a whole list. For example, the following idiom
578 * removes a range of elements from a list:
579 * <pre>
580 * list.subList(from, to).clear();
581 * </pre>
582 * Similar idioms may be constructed for <tt>indexOf</tt> and
583 * <tt>lastIndexOf</tt>, and all of the algorithms in the
584 * <tt>Collections</tt> class can be applied to a subList.<p>
585 *
586 * The semantics of the list returned by this method become undefined if
587 * the backing list (i.e., this list) is <i>structurally modified</i> in
588 * any way other than via the returned list. (Structural modifications are
589 * those that change the size of this list, or otherwise perturb it in such
590 * a fashion that iterations in progress may yield incorrect results.)
591 *
592 * @param fromIndex low endpoint (inclusive) of the subList
593 * @param toIndex high endpoint (exclusive) of the subList
594 * @return a view of the specified range within this list
595 * @throws IndexOutOfBoundsException for an illegal endpoint index value
596 * (<tt>fromIndex < 0 || toIndex > size ||
597 * fromIndex > toIndex</tt>)
598 */
599 List<E> subList(int fromIndex, int toIndex);
600
601 /**
602 * Creates a {@link Spliterator} over the elements in this list.
603 *
604 * <p>The {@code Spliterator} reports {@link Spliterator#SIZED} and
605 * {@link Spliterator#ORDERED}. Implementations should document the
606 * reporting of additional characteristic values.
607 *
608 * @implSpec
609 * The default implementation creates a
610 * <em><a href="Spliterator.html#binding">late-binding</a></em> spliterator
611 * from the list's {@code Iterator}. The spliterator inherits the
612 * <em>fail-fast</em> properties of the collection's iterator.
613 *
614 * @implNote
615 * The created {@code Spliterator} additionally reports
616 * {@link Spliterator#SUBSIZED}.
617 *
618 * @return a {@code Spliterator} over the elements in this list
619 * @since 1.8
620 */
621 @Override
622 default Spliterator<E> spliterator() {
623 return Spliterators.spliterator(this, Spliterator.ORDERED);
624 }
625 }
626