1 /*
2 * Copyright (c) 1997, 2010, 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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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 *
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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 (optional)
138 * @throws NullPointerException if the specified element is null and this
139 * list does not permit null elements (optional)
140 */
141 boolean contains(Object o);
142
143 /**
144 * Returns an iterator over the elements in this list in proper sequence.
145 *
146 * @return an iterator over the elements in this list in proper sequence
147 */
148 Iterator<E> iterator();
149
150 /**
151 * Returns an array containing all of the elements in this list in proper
152 * sequence (from first to last element).
153 *
154 * <p>The returned array will be "safe" in that no references to it are
155 * maintained by this list. (In other words, this method must
156 * allocate a new array even if this list is backed by an array).
157 * The caller is thus free to modify the returned array.
158 *
159 * <p>This method acts as bridge between array-based and collection-based
160 * APIs.
161 *
162 * @return an array containing all of the elements in this list in proper
163 * sequence
164 * @see Arrays#asList(Object[])
165 */
166 Object[] toArray();
167
168 /**
169 * Returns an array containing all of the elements in this list in
170 * proper sequence (from first to last element); the runtime type of
171 * the returned array is that of the specified array. If the list fits
172 * in the specified array, it is returned therein. Otherwise, a new
173 * array is allocated with the runtime type of the specified array and
174 * the size of this list.
175 *
176 * <p>If the list fits in the specified array with room to spare (i.e.,
177 * the array has more elements than the list), the element in the array
178 * immediately following the end of the list is set to <tt>null</tt>.
179 * (This is useful in determining the length of the list <i>only</i> if
180 * the caller knows that the list does not contain any null elements.)
181 *
182 * <p>Like the {@link #toArray()} method, this method acts as bridge between
183 * array-based and collection-based APIs. Further, this method allows
184 * precise control over the runtime type of the output array, and may,
185 * under certain circumstances, be used to save allocation costs.
186 *
187 * <p>Suppose <tt>x</tt> is a list known to contain only strings.
188 * The following code can be used to dump the list into a newly
189 * allocated array of <tt>String</tt>:
190 *
191 * <pre>
192 * String[] y = x.toArray(new String[0]);</pre>
193 *
194 * Note that <tt>toArray(new Object[0])</tt> is identical in function to
195 * <tt>toArray()</tt>.
196 *
197 * @param a the array into which the elements of this list are to
198 * be stored, if it is big enough; otherwise, a new array of the
199 * same runtime type is allocated for this purpose.
200 * @return an array containing the elements of this list
201 * @throws ArrayStoreException if the runtime type of the specified array
202 * is not a supertype of the runtime type of every element in
203 * this list
204 * @throws NullPointerException if the specified array is null
205 */
206 <T> T[] toArray(T[] a);
207
208
209 // Modification Operations
210
211 /**
212 * Appends the specified element to the end of this list (optional
213 * operation).
214 *
215 * <p>Lists that support this operation may place limitations on what
216 * elements may be added to this list. In particular, some
217 * lists will refuse to add null elements, and others will impose
218 * restrictions on the type of elements that may be added. List
219 * classes should clearly specify in their documentation any restrictions
220 * on what elements may be added.
221 *
222 * @param e element to be appended to this list
223 * @return <tt>true</tt> (as specified by {@link Collection#add})
224 * @throws UnsupportedOperationException if the <tt>add</tt> operation
225 * is not supported by this list
226 * @throws ClassCastException if the class of the specified element
227 * prevents it from being added to this list
228 * @throws NullPointerException if the specified element is null and this
229 * list does not permit null elements
230 * @throws IllegalArgumentException if some property of this element
231 * prevents it from being added to this list
232 */
233 boolean add(E e);
234
235 /**
236 * Removes the first occurrence of the specified element from this list,
237 * if it is present (optional operation). If this list does not contain
238 * the element, it is unchanged. More formally, removes the element with
239 * the lowest index <tt>i</tt> such that
240 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>
241 * (if such an element exists). Returns <tt>true</tt> if this list
242 * contained the specified element (or equivalently, if this list changed
243 * as a result of the call).
244 *
245 * @param o element to be removed from this list, if present
246 * @return <tt>true</tt> if this list contained the specified element
247 * @throws ClassCastException if the type of the specified element
248 * is incompatible with this list (optional)
249 * @throws NullPointerException if the specified element is null and this
250 * list does not permit null elements (optional)
251 * @throws UnsupportedOperationException if the <tt>remove</tt> operation
252 * is not supported by this list
253 */
254 boolean remove(Object o);
255
256
257 // Bulk Modification Operations
258
259 /**
260 * Returns <tt>true</tt> if this list contains all of the elements of the
261 * specified collection.
262 *
263 * @param c collection to be checked for containment in this list
264 * @return <tt>true</tt> if this list contains all of the elements of the
265 * specified collection
266 * @throws ClassCastException if the types of one or more elements
267 * in the specified collection are incompatible with this
268 * list (optional)
269 * @throws NullPointerException if the specified collection contains one
270 * or more null elements and this list does not permit null
271 * elements (optional), or if the specified collection is null
272 * @see #contains(Object)
273 */
274 boolean containsAll(Collection<?> c);
275
276 /**
277 * Appends all of the elements in the specified collection to the end of
278 * this list, in the order that they are returned by the specified
279 * collection's iterator (optional operation). The behavior of this
280 * operation is undefined if the specified collection is modified while
281 * the operation is in progress. (Note that this will occur if the
282 * specified collection is this list, and it's nonempty.)
283 *
284 * @param c collection containing elements to be added to this list
285 * @return <tt>true</tt> if this list changed as a result of the call
286 * @throws UnsupportedOperationException if the <tt>addAll</tt> operation
287 * is not supported by this list
288 * @throws ClassCastException if the class of an element of the specified
289 * collection prevents it from being added to this list
290 * @throws NullPointerException if the specified collection contains one
291 * or more null elements and this list does not permit null
292 * elements, or if the specified collection is null
293 * @throws IllegalArgumentException if some property of an element of the
294 * specified collection prevents it from being added to this list
295 * @see #add(Object)
296 */
297 boolean addAll(Collection<? extends E> c);
298
299 /**
300 * Inserts all of the elements in the specified collection into this
301 * list at the specified position (optional operation). Shifts the
302 * element currently at that position (if any) and any subsequent
303 * elements to the right (increases their indices). The new elements
304 * will appear in this list in the order that they are returned by the
305 * specified collection's iterator. The behavior of this operation is
306 * undefined if the specified collection is modified while the
307 * operation is in progress. (Note that this will occur if the specified
308 * collection is this list, and it's nonempty.)
309 *
310 * @param index index at which to insert the first element from the
311 * specified collection
312 * @param c collection containing elements to be added to this list
313 * @return <tt>true</tt> if this list changed as a result of the call
314 * @throws UnsupportedOperationException if the <tt>addAll</tt> operation
315 * is not supported by this list
316 * @throws ClassCastException if the class of an element of the specified
317 * collection prevents it from being added to this list
318 * @throws NullPointerException if the specified collection contains one
319 * or more null elements and this list does not permit null
320 * elements, or if the specified collection is null
321 * @throws IllegalArgumentException if some property of an element of the
322 * specified collection prevents it from being added to this list
323 * @throws IndexOutOfBoundsException if the index is out of range
324 * (<tt>index < 0 || index > size()</tt>)
325 */
326 boolean addAll(int index, Collection<? extends E> c);
327
328 /**
329 * Removes from this list all of its elements that are contained in the
330 * specified collection (optional operation).
331 *
332 * @param c collection containing elements to be removed from this list
333 * @return <tt>true</tt> if this list changed as a result of the call
334 * @throws UnsupportedOperationException if the <tt>removeAll</tt> operation
335 * is not supported by this list
336 * @throws ClassCastException if the class of an element of this list
337 * is incompatible with the specified collection (optional)
338 * @throws NullPointerException if this list contains a null element and the
339 * specified collection does not permit null elements (optional),
340 * or if the specified collection is null
341 * @see #remove(Object)
342 * @see #contains(Object)
343 */
344 boolean removeAll(Collection<?> c);
345
346 /**
347 * Retains only the elements in this list that are contained in the
348 * specified collection (optional operation). In other words, removes
349 * from this list all of its elements that are not contained in the
350 * specified collection.
351 *
352 * @param c collection containing elements to be retained in this list
353 * @return <tt>true</tt> if this list changed as a result of the call
354 * @throws UnsupportedOperationException if the <tt>retainAll</tt> operation
355 * is not supported by this list
356 * @throws ClassCastException if the class of an element of this list
357 * is incompatible with the specified collection (optional)
358 * @throws NullPointerException if this list contains a null element and the
359 * specified collection does not permit null elements (optional),
360 * or if the specified collection is null
361 * @see #remove(Object)
362 * @see #contains(Object)
363 */
364 boolean retainAll(Collection<?> c);
365
366 /**
367 * Removes all of the elements from this list (optional operation).
368 * The list will be empty after this call returns.
369 *
370 * @throws UnsupportedOperationException if the <tt>clear</tt> operation
371 * is not supported by this list
372 */
373 void clear();
374
375
376 // Comparison and hashing
377
378 /**
379 * Compares the specified object with this list for equality. Returns
380 * <tt>true</tt> if and only if the specified object is also a list, both
381 * lists have the same size, and all corresponding pairs of elements in
382 * the two lists are <i>equal</i>. (Two elements <tt>e1</tt> and
383 * <tt>e2</tt> are <i>equal</i> if <tt>(e1==null ? e2==null :
384 * e1.equals(e2))</tt>.) In other words, two lists are defined to be
385 * equal if they contain the same elements in the same order. This
386 * definition ensures that the equals method works properly across
387 * different implementations of the <tt>List</tt> interface.
388 *
389 * @param o the object to be compared for equality with this list
390 * @return <tt>true</tt> if the specified object is equal to this list
391 */
392 boolean equals(Object o);
393
394 /**
395 * Returns the hash code value for this list. The hash code of a list
396 * is defined to be the result of the following calculation:
397 * <pre>
398 * int hashCode = 1;
399 * for (E e : list)
400 * hashCode = 31*hashCode + (e==null ? 0 : e.hashCode());
401 * </pre>
402 * This ensures that <tt>list1.equals(list2)</tt> implies that
403 * <tt>list1.hashCode()==list2.hashCode()</tt> for any two lists,
404 * <tt>list1</tt> and <tt>list2</tt>, as required by the general
405 * contract of {@link Object#hashCode}.
406 *
407 * @return the hash code value for this list
408 * @see Object#equals(Object)
409 * @see #equals(Object)
410 */
411 int hashCode();
412
413
414 // Positional Access Operations
415
416 /**
417 * Returns the element at the specified position in this list.
418 *
419 * @param index index of the element to return
420 * @return the element at the specified position in this list
421 * @throws IndexOutOfBoundsException if the index is out of range
422 * (<tt>index < 0 || index >= size()</tt>)
423 */
424 E get(int index);
425
426 /**
427 * Replaces the element at the specified position in this list with the
428 * specified element (optional operation).
429 *
430 * @param index index of the element to replace
431 * @param element element to be stored at the specified position
432 * @return the element previously at the specified position
433 * @throws UnsupportedOperationException if the <tt>set</tt> operation
434 * is not supported by this list
435 * @throws ClassCastException if the class of the specified element
436 * prevents it from being added to this list
437 * @throws NullPointerException if the specified element is null and
438 * this list does not permit null elements
439 * @throws IllegalArgumentException if some property of the specified
440 * element prevents it from being added to this list
441 * @throws IndexOutOfBoundsException if the index is out of range
442 * (<tt>index < 0 || index >= size()</tt>)
443 */
444 E set(int index, E element);
445
446 /**
447 * Inserts the specified element at the specified position in this list
448 * (optional operation). Shifts the element currently at that position
449 * (if any) and any subsequent elements to the right (adds one to their
450 * indices).
451 *
452 * @param index index at which the specified element is to be inserted
453 * @param element element to be inserted
454 * @throws UnsupportedOperationException if the <tt>add</tt> operation
455 * is not supported by this list
456 * @throws ClassCastException if the class of the specified element
457 * prevents it from being added to this list
458 * @throws NullPointerException if the specified element is null and
459 * this list does not permit null elements
460 * @throws IllegalArgumentException if some property of the specified
461 * element prevents it from being added to this list
462 * @throws IndexOutOfBoundsException if the index is out of range
463 * (<tt>index < 0 || index > size()</tt>)
464 */
465 void add(int index, E element);
466
467 /**
468 * Removes the element at the specified position in this list (optional
469 * operation). Shifts any subsequent elements to the left (subtracts one
470 * from their indices). Returns the element that was removed from the
471 * list.
472 *
473 * @param index the index of the element to be removed
474 * @return the element previously at the specified position
475 * @throws UnsupportedOperationException if the <tt>remove</tt> operation
476 * is not supported by this list
477 * @throws IndexOutOfBoundsException if the index is out of range
478 * (<tt>index < 0 || index >= size()</tt>)
479 */
480 E remove(int index);
481
482
483 // Search Operations
484
485 /**
486 * Returns the index of the first occurrence of the specified element
487 * in this list, or -1 if this list does not contain the element.
488 * More formally, returns the lowest index <tt>i</tt> such that
489 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
490 * or -1 if there is no such index.
491 *
492 * @param o element to search for
493 * @return the index of the first occurrence of the specified element in
494 * this list, or -1 if this list does not contain the element
495 * @throws ClassCastException if the type of the specified element
496 * is incompatible with this list (optional)
497 * @throws NullPointerException if the specified element is null and this
498 * list does not permit null elements (optional)
499 */
500 int indexOf(Object o);
501
502 /**
503 * Returns the index of the last occurrence of the specified element
504 * in this list, or -1 if this list does not contain the element.
505 * More formally, returns the highest index <tt>i</tt> such that
506 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
507 * or -1 if there is no such index.
508 *
509 * @param o element to search for
510 * @return the index of the last occurrence of the specified element in
511 * this list, or -1 if this list does not contain the element
512 * @throws ClassCastException if the type of the specified element
513 * is incompatible with this list (optional)
514 * @throws NullPointerException if the specified element is null and this
515 * list does not permit null elements (optional)
516 */
517 int lastIndexOf(Object o);
518
519
520 // List Iterators
521
522 /**
523 * Returns a list iterator over the elements in this list (in proper
524 * sequence).
525 *
526 * @return a list iterator over the elements in this list (in proper
527 * sequence)
528 */
529 ListIterator<E> listIterator();
530
531 /**
532 * Returns a list iterator over the elements in this list (in proper
533 * sequence), starting at the specified position in the list.
534 * The specified index indicates the first element that would be
535 * returned by an initial call to {@link ListIterator#next next}.
536 * An initial call to {@link ListIterator#previous previous} would
537 * return the element with the specified index minus one.
538 *
539 * @param index index of the first element to be returned from the
540 * list iterator (by a call to {@link ListIterator#next next})
541 * @return a list iterator over the elements in this list (in proper
542 * sequence), starting at the specified position in the list
543 * @throws IndexOutOfBoundsException if the index is out of range
544 * ({@code index < 0 || index > size()})
545 */
546 ListIterator<E> listIterator(int index);
547
548 // View
549
550 /**
551 * Returns a view of the portion of this list between the specified
552 * <tt>fromIndex</tt>, inclusive, and <tt>toIndex</tt>, exclusive. (If
553 * <tt>fromIndex</tt> and <tt>toIndex</tt> are equal, the returned list is
554 * empty.) The returned list is backed by this list, so non-structural
555 * changes in the returned list are reflected in this list, and vice-versa.
556 * The returned list supports all of the optional list operations supported
557 * by this list.<p>
558 *
559 * This method eliminates the need for explicit range operations (of
560 * the sort that commonly exist for arrays). Any operation that expects
561 * a list can be used as a range operation by passing a subList view
562 * instead of a whole list. For example, the following idiom
563 * removes a range of elements from a list:
564 * <pre>
565 * list.subList(from, to).clear();
566 * </pre>
567 * Similar idioms may be constructed for <tt>indexOf</tt> and
568 * <tt>lastIndexOf</tt>, and all of the algorithms in the
569 * <tt>Collections</tt> class can be applied to a subList.<p>
570 *
571 * The semantics of the list returned by this method become undefined if
572 * the backing list (i.e., this list) is <i>structurally modified</i> in
573 * any way other than via the returned list. (Structural modifications are
574 * those that change the size of this list, or otherwise perturb it in such
575 * a fashion that iterations in progress may yield incorrect results.)
576 *
577 * @param fromIndex low endpoint (inclusive) of the subList
578 * @param toIndex high endpoint (exclusive) of the subList
579 * @return a view of the specified range within this list
580 * @throws IndexOutOfBoundsException for an illegal endpoint index value
581 * (<tt>fromIndex < 0 || toIndex > size ||
582 * fromIndex > toIndex</tt>)
583 */
584 List<E> subList(int fromIndex, int toIndex);
585 }