1 /*
2 * Copyright (c) 1997, 2011, 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
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
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 *
17 * You should have received a copy of the GNU General Public License version
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19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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 import java.util.function.UnaryOperator;
29
30 /**
31 * An ordered collection (also known as a <i>sequence</i>). The user of this
32 * interface has precise control over where in the list each element is
33 * inserted. The user can access elements by their integer index (position in
34 * the list), and search for elements in the list.<p>
35 *
36 * Unlike sets, lists typically allow duplicate elements. More formally,
37 * lists typically allow pairs of elements <tt>e1</tt> and <tt>e2</tt>
38 * such that <tt>e1.equals(e2)</tt>, and they typically allow multiple
39 * null elements if they allow null elements at all. It is not inconceivable
40 * that someone might wish to implement a list that prohibits duplicates, by
41 * throwing runtime exceptions when the user attempts to insert them, but we
42 * expect this usage to be rare.<p>
43 *
44 * The <tt>List</tt> interface places additional stipulations, beyond those
45 * specified in the <tt>Collection</tt> interface, on the contracts of the
46 * <tt>iterator</tt>, <tt>add</tt>, <tt>remove</tt>, <tt>equals</tt>, and
47 * <tt>hashCode</tt> methods. Declarations for other inherited methods are
48 * also included here for convenience.<p>
49 *
50 * The <tt>List</tt> interface provides four methods for positional (indexed)
51 * access to list elements. Lists (like Java arrays) are zero based. Note
52 * that these operations may execute in time proportional to the index value
53 * for some implementations (the <tt>LinkedList</tt> class, for
54 * example). Thus, iterating over the elements in a list is typically
55 * preferable to indexing through it if the caller does not know the
56 * implementation.<p>
57 *
58 * The <tt>List</tt> interface provides a special iterator, called a
59 * <tt>ListIterator</tt>, that allows element insertion and replacement, and
60 * bidirectional access in addition to the normal operations that the
61 * <tt>Iterator</tt> interface provides. A method is provided to obtain a
62 * list iterator that starts at a specified position in the list.<p>
63 *
64 * The <tt>List</tt> interface provides two methods to search for a specified
65 * object. From a performance standpoint, these methods should be used with
66 * caution. In many implementations they will perform costly linear
67 * searches.<p>
68 *
69 * The <tt>List</tt> interface provides two methods to efficiently insert and
70 * remove multiple elements at an arbitrary point in the list.<p>
71 *
72 * Note: While it is permissible for lists to contain themselves as elements,
73 * extreme caution is advised: the <tt>equals</tt> and <tt>hashCode</tt>
74 * methods are no longer well defined on such a list.
75 *
76 * <p>Some list implementations have restrictions on the elements that
77 * they may contain. For example, some implementations prohibit null elements,
78 * and some have restrictions on the types of their elements. Attempting to
79 * add an ineligible element throws an unchecked exception, typically
80 * <tt>NullPointerException</tt> or <tt>ClassCastException</tt>. Attempting
81 * to query the presence of an ineligible element may throw an exception,
82 * or it may simply return false; some implementations will exhibit the former
83 * behavior and some will exhibit the latter. More generally, attempting an
84 * operation on an ineligible element whose completion would not result in
85 * the insertion of an ineligible element into the list may throw an
86 * exception or it may succeed, at the option of the implementation.
87 * Such exceptions are marked as "optional" in the specification for this
88 * interface.
89 *
90 * <p>This interface is a member of the
91 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
92 * Java Collections Framework</a>.
93 *
94 * @param <E> the type of elements in this list
95 *
96 * @author Josh Bloch
97 * @author Neal Gafter
98 * @see Collection
99 * @see Set
100 * @see ArrayList
101 * @see LinkedList
102 * @see Vector
103 * @see Arrays#asList(Object[])
104 * @see Collections#nCopies(int, Object)
105 * @see Collections#EMPTY_LIST
106 * @see AbstractList
107 * @see AbstractSequentialList
108 * @since 1.2
109 */
110
111 public interface List<E> extends Collection<E> {
112 // Query Operations
113
114 /**
115 * Returns the number of elements in this list. If this list contains
116 * more than <tt>Integer.MAX_VALUE</tt> elements, returns
117 * <tt>Integer.MAX_VALUE</tt>.
118 *
119 * @return the number of elements in this list
120 */
121 int size();
122
123 /**
124 * Returns <tt>true</tt> if this list contains no elements.
125 *
126 * @return <tt>true</tt> if this list contains no elements
127 */
128 boolean isEmpty();
129
130 /**
131 * Returns <tt>true</tt> if this list contains the specified element.
132 * More formally, returns <tt>true</tt> if and only if this list contains
133 * at least one element <tt>e</tt> such that
134 * <tt>(o==null ? e==null : o.equals(e))</tt>.
135 *
136 * @param o element whose presence in this list is to be tested
137 * @return <tt>true</tt> if this list contains the specified element
138 * @throws ClassCastException if the type of the specified element
139 * is incompatible with this list
140 * (<a href="Collection.html#optional-restrictions">optional</a>)
141 * @throws NullPointerException if the specified element is null and this
142 * list does not permit null elements
143 * (<a href="Collection.html#optional-restrictions">optional</a>)
144 */
145 boolean contains(Object o);
146
147 /**
148 * Returns an iterator over the elements in this list in proper sequence.
149 *
150 * @return an iterator over the elements in this list in proper sequence
151 */
152 Iterator<E> iterator();
153
154 /**
155 * Returns an array containing all of the elements in this list in proper
156 * sequence (from first to last element).
157 *
158 * <p>The returned array will be "safe" in that no references to it are
159 * maintained by this list. (In other words, this method must
160 * allocate a new array even if this list is backed by an array).
161 * The caller is thus free to modify the returned array.
162 *
163 * <p>This method acts as bridge between array-based and collection-based
164 * APIs.
165 *
166 * @return an array containing all of the elements in this list in proper
167 * sequence
168 * @see Arrays#asList(Object[])
169 */
170 Object[] toArray();
171
172 /**
173 * Returns an array containing all of the elements in this list in
174 * proper sequence (from first to last element); the runtime type of
175 * the returned array is that of the specified array. If the list fits
176 * in the specified array, it is returned therein. Otherwise, a new
177 * array is allocated with the runtime type of the specified array and
178 * the size of this list.
179 *
180 * <p>If the list fits in the specified array with room to spare (i.e.,
181 * the array has more elements than the list), the element in the array
182 * immediately following the end of the list is set to <tt>null</tt>.
183 * (This is useful in determining the length of the list <i>only</i> if
184 * the caller knows that the list does not contain any null elements.)
185 *
186 * <p>Like the {@link #toArray()} method, this method acts as bridge between
187 * array-based and collection-based APIs. Further, this method allows
188 * precise control over the runtime type of the output array, and may,
189 * under certain circumstances, be used to save allocation costs.
190 *
191 * <p>Suppose <tt>x</tt> is a list known to contain only strings.
192 * The following code can be used to dump the list into a newly
193 * allocated array of <tt>String</tt>:
194 *
195 * <pre>
196 * String[] y = x.toArray(new String[0]);</pre>
197 *
198 * Note that <tt>toArray(new Object[0])</tt> is identical in function to
199 * <tt>toArray()</tt>.
200 *
201 * @param a the array into which the elements of this list are to
202 * be stored, if it is big enough; otherwise, a new array of the
203 * same runtime type is allocated for this purpose.
204 * @return an array containing the elements of this list
205 * @throws ArrayStoreException if the runtime type of the specified array
206 * is not a supertype of the runtime type of every element in
207 * this list
208 * @throws NullPointerException if the specified array is null
209 */
210 <T> T[] toArray(T[] a);
211
212
213 // Modification Operations
214
215 /**
216 * Appends the specified element to the end of this list (optional
217 * operation).
218 *
219 * <p>Lists that support this operation may place limitations on what
220 * elements may be added to this list. In particular, some
221 * lists will refuse to add null elements, and others will impose
222 * restrictions on the type of elements that may be added. List
223 * classes should clearly specify in their documentation any restrictions
224 * on what elements may be added.
225 *
226 * @param e element to be appended to this list
227 * @return <tt>true</tt> (as specified by {@link Collection#add})
228 * @throws UnsupportedOperationException if the <tt>add</tt> operation
229 * is not supported by this list
230 * @throws ClassCastException if the class of the specified element
231 * prevents it from being added to this list
232 * @throws NullPointerException if the specified element is null and this
233 * list does not permit null elements
234 * @throws IllegalArgumentException if some property of this element
235 * prevents it from being added to this list
236 */
237 boolean add(E e);
238
239 /**
240 * Removes the first occurrence of the specified element from this list,
241 * if it is present (optional operation). If this list does not contain
242 * the element, it is unchanged. More formally, removes the element with
243 * the lowest index <tt>i</tt> such that
244 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>
245 * (if such an element exists). Returns <tt>true</tt> if this list
246 * contained the specified element (or equivalently, if this list changed
247 * as a result of the call).
248 *
249 * @param o element to be removed from this list, if present
250 * @return <tt>true</tt> if this list contained the specified element
251 * @throws ClassCastException if the type of the specified element
252 * is incompatible with this list
253 * (<a href="Collection.html#optional-restrictions">optional</a>)
254 * @throws NullPointerException if the specified element is null and this
255 * list does not permit null elements
256 * (<a href="Collection.html#optional-restrictions">optional</a>)
257 * @throws UnsupportedOperationException if the <tt>remove</tt> operation
258 * is not supported by this list
259 */
260 boolean remove(Object o);
261
262
263 // Bulk Modification Operations
264
265 /**
266 * Returns <tt>true</tt> if this list contains all of the elements of the
267 * specified collection.
268 *
269 * @param c collection to be checked for containment in this list
270 * @return <tt>true</tt> if this list contains all of the elements of the
271 * specified collection
272 * @throws ClassCastException if the types of one or more elements
273 * in the specified collection are incompatible with this
274 * list
275 * (<a href="Collection.html#optional-restrictions">optional</a>)
276 * @throws NullPointerException if the specified collection contains one
277 * or more null elements and this list does not permit null
278 * elements
279 * (<a href="Collection.html#optional-restrictions">optional</a>),
280 * or if the specified collection is null
281 * @see #contains(Object)
282 */
283 boolean containsAll(Collection<?> c);
284
285 /**
286 * Appends all of the elements in the specified collection to the end of
287 * this list, in the order that they are returned by the specified
288 * collection's iterator (optional operation). The behavior of this
289 * operation is undefined if the specified collection is modified while
290 * the operation is in progress. (Note that this will occur if the
291 * specified collection is this list, and it's nonempty.)
292 *
293 * @param c collection containing elements to be added to this list
294 * @return <tt>true</tt> if this list changed as a result of the call
295 * @throws UnsupportedOperationException if the <tt>addAll</tt> operation
296 * is not supported by this list
297 * @throws ClassCastException if the class of an element of the specified
298 * collection prevents it from being added to this list
299 * @throws NullPointerException if the specified collection contains one
300 * or more null elements and this list does not permit null
301 * elements, or if the specified collection is null
302 * @throws IllegalArgumentException if some property of an element of the
303 * specified collection prevents it from being added to this list
304 * @see #add(Object)
305 */
306 boolean addAll(Collection<? extends E> c);
307
308 /**
309 * Inserts all of the elements in the specified collection into this
310 * list at the specified position (optional operation). Shifts the
311 * element currently at that position (if any) and any subsequent
312 * elements to the right (increases their indices). The new elements
313 * will appear in this list in the order that they are returned by the
314 * specified collection's iterator. The behavior of this operation is
315 * undefined if the specified collection is modified while the
316 * operation is in progress. (Note that this will occur if the specified
317 * collection is this list, and it's nonempty.)
318 *
319 * @param index index at which to insert the first element from the
320 * specified collection
321 * @param c collection containing elements to be added to this list
322 * @return <tt>true</tt> if this list changed as a result of the call
323 * @throws UnsupportedOperationException if the <tt>addAll</tt> operation
324 * is not supported by this list
325 * @throws ClassCastException if the class of an element of the specified
326 * collection prevents it from being added to this list
327 * @throws NullPointerException if the specified collection contains one
328 * or more null elements and this list does not permit null
329 * elements, or if the specified collection is null
330 * @throws IllegalArgumentException if some property of an element of the
331 * specified collection prevents it from being added to this list
332 * @throws IndexOutOfBoundsException if the index is out of range
333 * (<tt>index < 0 || index > size()</tt>)
334 */
335 boolean addAll(int index, Collection<? extends E> c);
336
337 /**
338 * Removes from this list all of its elements that are contained in the
339 * specified collection (optional operation).
340 *
341 * @param c collection containing elements to be removed from this list
342 * @return <tt>true</tt> if this list changed as a result of the call
343 * @throws UnsupportedOperationException if the <tt>removeAll</tt> operation
344 * is not supported by this list
345 * @throws ClassCastException if the class of an element of this list
346 * is incompatible with the specified collection
347 * (<a href="Collection.html#optional-restrictions">optional</a>)
348 * @throws NullPointerException if this list contains a null element and the
349 * specified collection does not permit null elements
350 * (<a href="Collection.html#optional-restrictions">optional</a>),
351 * or if the specified collection is null
352 * @see #remove(Object)
353 * @see #contains(Object)
354 */
355 boolean removeAll(Collection<?> c);
356
357 /**
358 * Retains only the elements in this list that are contained in the
359 * specified collection (optional operation). In other words, removes
360 * from this list all of its elements that are not contained in the
361 * specified collection.
362 *
363 * @param c collection containing elements to be retained in this list
364 * @return <tt>true</tt> if this list changed as a result of the call
365 * @throws UnsupportedOperationException if the <tt>retainAll</tt> operation
366 * is not supported by this list
367 * @throws ClassCastException if the class of an element of this list
368 * is incompatible with the specified collection
369 * (<a href="Collection.html#optional-restrictions">optional</a>)
370 * @throws NullPointerException if this list contains a null element and the
371 * specified collection does not permit null elements
372 * (<a href="Collection.html#optional-restrictions">optional</a>),
373 * or if the specified collection is null
374 * @see #remove(Object)
375 * @see #contains(Object)
376 */
377 boolean retainAll(Collection<?> c);
378
379 /**
380 * Removes all of the elements from this list (optional operation).
381 * The list will be empty after this call returns.
382 *
383 * @throws UnsupportedOperationException if the <tt>clear</tt> operation
384 * is not supported by this list
385 */
386 void clear();
387
388
389 // Comparison and hashing
390
391 /**
392 * Compares the specified object with this list for equality. Returns
393 * <tt>true</tt> if and only if the specified object is also a list, both
394 * lists have the same size, and all corresponding pairs of elements in
395 * the two lists are <i>equal</i>. (Two elements <tt>e1</tt> and
396 * <tt>e2</tt> are <i>equal</i> if <tt>(e1==null ? e2==null :
397 * e1.equals(e2))</tt>.) In other words, two lists are defined to be
398 * equal if they contain the same elements in the same order. This
399 * definition ensures that the equals method works properly across
400 * different implementations of the <tt>List</tt> interface.
401 *
402 * @param o the object to be compared for equality with this list
403 * @return <tt>true</tt> if the specified object is equal to this list
404 */
405 boolean equals(Object o);
406
407 /**
408 * Returns the hash code value for this list. The hash code of a list
409 * is defined to be the result of the following calculation:
410 * <pre>
411 * int hashCode = 1;
412 * for (E e : list)
413 * hashCode = 31*hashCode + (e==null ? 0 : e.hashCode());
414 * </pre>
415 * This ensures that <tt>list1.equals(list2)</tt> implies that
416 * <tt>list1.hashCode()==list2.hashCode()</tt> for any two lists,
417 * <tt>list1</tt> and <tt>list2</tt>, as required by the general
418 * contract of {@link Object#hashCode}.
419 *
420 * @return the hash code value for this list
421 * @see Object#equals(Object)
422 * @see #equals(Object)
423 */
424 int hashCode();
425
426
427 // Positional Access Operations
428
429 /**
430 * Returns the element at the specified position in this list.
431 *
432 * @param index index of the element to return
433 * @return the element at the specified position in this list
434 * @throws IndexOutOfBoundsException if the index is out of range
435 * (<tt>index < 0 || index >= size()</tt>)
436 */
437 E get(int index);
438
439 /**
440 * Replaces the element at the specified position in this list with the
441 * specified element (optional operation).
442 *
443 * @param index index of the element to replace
444 * @param element element to be stored at the specified position
445 * @return the element previously at the specified position
446 * @throws UnsupportedOperationException if the <tt>set</tt> operation
447 * is not supported by this list
448 * @throws ClassCastException if the class of the specified element
449 * prevents it from being added to this list
450 * @throws NullPointerException if the specified element is null and
451 * this list does not permit null elements
452 * @throws IllegalArgumentException if some property of the specified
453 * element prevents it from being added to this list
454 * @throws IndexOutOfBoundsException if the index is out of range
455 * (<tt>index < 0 || index >= size()</tt>)
456 */
457 E set(int index, E element);
458
459 /**
460 * Inserts the specified element at the specified position in this list
461 * (optional operation). Shifts the element currently at that position
462 * (if any) and any subsequent elements to the right (adds one to their
463 * indices).
464 *
465 * @param index index at which the specified element is to be inserted
466 * @param element element to be inserted
467 * @throws UnsupportedOperationException if the <tt>add</tt> operation
468 * is not supported by this list
469 * @throws ClassCastException if the class of the specified element
470 * prevents it from being added to this list
471 * @throws NullPointerException if the specified element is null and
472 * this list does not permit null elements
473 * @throws IllegalArgumentException if some property of the specified
474 * element prevents it from being added to this list
475 * @throws IndexOutOfBoundsException if the index is out of range
476 * (<tt>index < 0 || index > size()</tt>)
477 */
478 void add(int index, E element);
479
480 /**
481 * Removes the element at the specified position in this list (optional
482 * operation). Shifts any subsequent elements to the left (subtracts one
483 * from their indices). Returns the element that was removed from the
484 * list.
485 *
486 * @param index the index of the element to be removed
487 * @return the element previously at the specified position
488 * @throws UnsupportedOperationException if the <tt>remove</tt> operation
489 * is not supported by this list
490 * @throws IndexOutOfBoundsException if the index is out of range
491 * (<tt>index < 0 || index >= size()</tt>)
492 */
493 E remove(int index);
494
495
496 // Search Operations
497
498 /**
499 * Returns the index of the first occurrence of the specified element
500 * in this list, or -1 if this list does not contain the element.
501 * More formally, returns the lowest index <tt>i</tt> such that
502 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
503 * or -1 if there is no such index.
504 *
505 * @param o element to search for
506 * @return the index of the first occurrence of the specified element in
507 * this list, or -1 if this list does not contain the element
508 * @throws ClassCastException if the type of the specified element
509 * is incompatible with this list
510 * (<a href="Collection.html#optional-restrictions">optional</a>)
511 * @throws NullPointerException if the specified element is null and this
512 * list does not permit null elements
513 * (<a href="Collection.html#optional-restrictions">optional</a>)
514 */
515 int indexOf(Object o);
516
517 /**
518 * Returns the index of the last occurrence of the specified element
519 * in this list, or -1 if this list does not contain the element.
520 * More formally, returns the highest index <tt>i</tt> such that
521 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
522 * or -1 if there is no such index.
523 *
524 * @param o element to search for
525 * @return the index of the last occurrence of the specified element in
526 * this list, or -1 if this list does not contain the element
527 * @throws ClassCastException if the type of the specified element
528 * is incompatible with this list
529 * (<a href="Collection.html#optional-restrictions">optional</a>)
530 * @throws NullPointerException if the specified element is null and this
531 * list does not permit null elements
532 * (<a href="Collection.html#optional-restrictions">optional</a>)
533 */
534 int lastIndexOf(Object o);
535
536
537 // List Iterators
538
539 /**
540 * Returns a list iterator over the elements in this list (in proper
541 * sequence).
542 *
543 * @return a list iterator over the elements in this list (in proper
544 * sequence)
545 */
546 ListIterator<E> listIterator();
547
548 /**
549 * Returns a list iterator over the elements in this list (in proper
550 * sequence), starting at the specified position in the list.
551 * The specified index indicates the first element that would be
552 * returned by an initial call to {@link ListIterator#next next}.
553 * An initial call to {@link ListIterator#previous previous} would
554 * return the element with the specified index minus one.
555 *
556 * @param index index of the first element to be returned from the
557 * list iterator (by a call to {@link ListIterator#next next})
558 * @return a list iterator over the elements in this list (in proper
559 * sequence), starting at the specified position in the list
560 * @throws IndexOutOfBoundsException if the index is out of range
561 * ({@code index < 0 || index > size()})
562 */
563 ListIterator<E> listIterator(int index);
564
565 // View
566
567 /**
568 * Returns a view of the portion of this list between the specified
569 * <tt>fromIndex</tt>, inclusive, and <tt>toIndex</tt>, exclusive. (If
570 * <tt>fromIndex</tt> and <tt>toIndex</tt> are equal, the returned list is
571 * empty.) The returned list is backed by this list, so non-structural
572 * changes in the returned list are reflected in this list, and vice-versa.
573 * The returned list supports all of the optional list operations supported
574 * by this list.<p>
575 *
576 * This method eliminates the need for explicit range operations (of
577 * the sort that commonly exist for arrays). Any operation that expects
578 * a list can be used as a range operation by passing a subList view
579 * instead of a whole list. For example, the following idiom
580 * removes a range of elements from a list:
581 * <pre>
582 * list.subList(from, to).clear();
583 * </pre>
584 * Similar idioms may be constructed for <tt>indexOf</tt> and
585 * <tt>lastIndexOf</tt>, and all of the algorithms in the
586 * <tt>Collections</tt> class can be applied to a subList.<p>
587 *
588 * The semantics of the list returned by this method become undefined if
589 * the backing list (i.e., this list) is <i>structurally modified</i> in
590 * any way other than via the returned list. (Structural modifications are
591 * those that change the size of this list, or otherwise perturb it in such
592 * a fashion that iterations in progress may yield incorrect results.)
593 *
594 * @param fromIndex low endpoint (inclusive) of the subList
595 * @param toIndex high endpoint (exclusive) of the subList
596 * @return a view of the specified range within this list
597 * @throws IndexOutOfBoundsException for an illegal endpoint index value
598 * (<tt>fromIndex < 0 || toIndex > size ||
599 * fromIndex > toIndex</tt>)
600 */
601 List<E> subList(int fromIndex, int toIndex);
602
603 /**
604 * Apply the specified operator to each element of this list, replacing
605 * the element with the result of applying the operator to the current
606 * element.
607 *
608 * @param operator the operator to apply to each element
609 * @throws NullPointerException if the specified operator is null
610 * @since 1.8
611 */
612 public default void replaceAll(UnaryOperator<E> operator) {
613 Objects.requireNonNull(operator);
614 final ListIterator<E> li = this.listIterator();
615 while (li.hasNext()) {
616 li.set(operator.operate(li.next()));
617 }
618 }
619
620 /**
621 * Sort this list using the supplied {@code Comparator} to compare elements.
622 *
623 * @param c the {@code Comparator} used to compare list elements
624 * @throws NullPointerException if the specified comparator is null
625 * @since 1.8
626 */
627 public default void sort(Comparator<? super E> c) {
628 Objects.requireNonNull(c);
629 Collections.<E>sort(this, c);
630 }
631 }