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备战-Java 容器
玉阶生白露,夜久侵罗袜。
简介:备战-Java 容器
容器主要包括 Collection 和 Map 两种,Collection 存储着对象的集合,而 Map 存储着key-value 键值对(两个对象)的映射表。
TreeSet:基于红黑树实现,支持有序性操作,例如根据一个范围查找元素的操作。但是查找效率不如 HashSet,HashSet 查找的时间复杂度为 O(1),TreeSet 则为 O(logN)。
HashSet:基于哈希表实现,支持快速查找,但不支持有序性操作。并且失去了元素的插入顺序信息,也就是说使用 Iterator 遍历 HashSet 得到的结果是不确定的。
LinkedHashSet:具有 HashSet 的查找效率,并且内部使用双向链表维护元素的插入顺序。
ArrayList:基于动态数组实现,支持随机访问。
Vector:和 ArrayList 类似,但它是线程安全的。
LinkedList:基于双向链表实现,只能顺序访问,但是可以快速地在链表中间插入和删除元素。不仅如此,LinkedList 还可以用作栈、队列和双向队列。
LinkedList:可以用它来实现双向队列。
PriorityQueue:基于堆结构实现,可以用它来实现优先队列。
TreeMap:基于红黑树实现。
HashMap:基于哈希表实现。
HashTable:和 HashMap 类似,但它是线程安全的,这意味着同一时刻多个线程同时写入 HashTable 不会导致数据不一致。它是遗留类,不应该去使用它,而是使用 ConcurrentHashMap 来支持线程安全,ConcurrentHashMap 的效率会更高,因为 ConcurrentHashMap 引入了分段锁。
LinkedHashMap:使用双向链表来维护元素的顺序,顺序为插入顺序或者最近最少使用(LRU)顺序。(LRU算法是least Recently Used的缩写,即最近最少使用)
Collection 继承了 Iterable 接口,其中的 iterator() 方法能够产生一个 Iterator 对象,通过这个对象就可以迭代遍历 Collection 中的元素。
从 JDK 1.5 之后可以使用 foreach 方法来遍历实现了 Iterable 接口的聚合对象。
1 List<String> list = new ArrayList<>();
2 list.add("a");
3 list.add("b");
4 for (String item : list) {
5 System.out.println(item);
6 }
java.util.Arrays.asList() 可以把数组类型转换为 List 类型。
1 @SafeVarargs
2 public static <T> List<T> asList(T... a)
值得注意的是 asList() 的参数为泛型的变长参数,不能使用基本类型数组作为参数,只能使用相应的包装类型数组。
也可以使用以下方式调用 asList():
如果没有特别说明,以下源码分析基于 JDK 1.8。
在 IDEA 中 双击 shift 键调出 Search EveryWhere,查找源码文件,找到之后就可以阅读源码。
因为 ArrayList 是基于数组实现的,所以支持快速随机访问。RandomAccess 接口标识着该类支持快速随机访问,其默认数组大小为10
1 /*
2 * Copyright (C) 1997, 2017, Oracle and/or its affiliates. All rights reserved.
3 * OracLE PROPRIETARY/CONFIDENTIAl. Use is subject to license terms.
4 *
5 *
6 *
7 *
8 *
9 *
10 *
11 *
12 *
13 *
14 *
15 *
16 *
17 *
18 *
19 *
20 *
21 *
22 *
23 *
24 */
25
26 package java.util;
27
28 import java.util.function.Consumer;
29 import java.util.function.PreDicate;
30 import java.util.function.UnaryOperator;
31 import sun.misc.SharedSecrets;
32
33 /**
34 * Resizable-array implementation of the <tt>List</tt> interface. Implements
35 * all optional list operations, and permits all elements, including
36 * <tt>null</tt>. In addition to implemenTing the <tt>List</tt> interface,
37 * this class provides methods to manipulate the size of the array that is
38 * used internally to store the list. (This class is roughly equivalent to
39 * <tt>Vector</tt>, except that it is unsynchronized.)
40 *
41 * <p>The <tt>size</tt>, <tt>isEmpty</tt>, <tt>get</tt>, <tt>set</tt>,
42 * <tt>iterator</tt>, and <tt>listIterator</tt> operations run in constant
43 * time. The <tt>add</tt> operation runs in <i>amortized constant time</i>,
44 * that is, adding n elements requires O(n) time. All of the other operations
45 * run in linear time (roughly speaking). The constant factor is low compared
46 * to that for the <tt>LinkedList</tt> implementation.
47 *
48 * <p>Each <tt>ArrayList</tt> instance has a <i>capacity</i>. The capacity is
49 * the size of the array used to store the elements in the list. it is always
50 * at least as large as the list size. As elements are added to an ArrayList,
51 * its capacity grows automatically. The details of the growth policy are not
52 * specified beyond the fact that adding an element has constant amortized
53 * time cost.
54 *
55 * <p>An application can increase the capacity of an <tt>ArrayList</tt> instance
56 * before adding a large number of elements using the <tt>ensureCapacity</tt>
57 * operation. This may reduce the amount of incremental realLOCATIOn.
58 *
59 * <p><strong>Note that this implementation is not synchronized.</strong>
60 * If multiple threads access an <tt>ArrayList</tt> instance concurrently,
61 * and at least one of the threads modifies the list structurally, it
62 * <i>must</i> be synchronized externally. (A structural modification is
63 * any operation that adds or deletes one or more elements, or explicitly
64 * resizes the BACking array; merely setTing the value of an element is not
65 * a structural modification.) This is typically accomplished by
66 * synchronizing on some object that naturally encapsulates the list.
67 *
68 * If no such object exists, the list should be "wrapped" using the
69 * {@link Collections#synchronizedList Collections.synchronizedList}
70 * method. This is best done at creation time, to prevent accidental
71 * unsynchronized access to the list:<pre>
72 * List list = Collections.synchronizedList(new ArrayList(...));</pre>
73 *
74 * <p><a name="fail-fast">
75 * The iterators returned by this class's {@link #iterator() iterator} and
76 * {@link #listIterator(int) listIterator} methods are <em>fail-fast</em>:</a>
77 * if the list is structurally modified at any time after the iterator is
78 * created, in any way except through the iterator's own
79 * {@link ListIterator#remove() removE} or
80 * {@link ListIterator#add(Object) adD} methods, the iterator will throw a
81 * {@link ConcurrentModificationException}. Thus, in the face of
82 * concurrent modification, the iterator fails quickly and cleanly, rather
83 * than risking arbitrary, non-deterministic behavior at an undetermined
84 * time in the future.
85 *
86 * <p>Note that the fail-fast behavior of an iterator cAnnot be guaranteed
87 * as it is, generally speaking, impossible to make any hard guarantees in the
88 * presence of unsynchronized concurrent modification. Fail-fast iterators
89 * throw {@code ConcurrentModificationException} on a best-effort basis.
90 * Therefore, it would be wrong to write a program that depended on this
91 * exception for its correctness: <i>the fail-fast behavior of iterators
92 * should be used only to detect bugs.</i>
93 *
94 * <p>This class is a member of the
95 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
96 * Java Collections Framework</a>.
97 *
98 * @author Josh Bloch
99 * @author Neal Gafter
100 * @see Collection
101 * @see List
102 * @see LinkedList
103 * @see Vector
104 * @since 1.2
105 */
106
107 public class ArrayList<E> extends AbstractList<E>
108 implements List<E>, RandomAccess, Cloneable, java.io.serializable
109 {
110 private static final long serialVersionUID = 8683452581122892189L;
111
112 /**
113 * Default initial capacity.
114 */
115 private static final int DEFAULT_CAPACITY = 10;
116
117 /**
118 * Shared empty array instance used for empty instances.
119 */
120 private static final Object[] EMPTY_ELEMENTDATA = {};
121
122 /**
123 * Shared empty array instance used for default sized empty instances. We
124 * disTinguish this from EMPTY_ELEMENTDATA to know how much to inflate when
125 * first element is added.
126 */
127 private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};
128
129 /**
130 * The array buffer into which the elements of the ArrayList are stored.
131 * The capacity of the ArrayList is the length of this array buffer. Any
132 * empty ArrayList with elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA
133 * will be expanded to DEFAULT_CAPACITY when the first element is added.
134 */
135 transient Object[] elementData; // non-private to simplify nested class access
136
137 /**
138 * The size of the ArrayList (the number of elements it contains).
139 *
140 * @serial
141 */
142 private int size;
143
144 /**
145 * Constructs an empty list with the specified initial capacity.
146 *
147 * @param initialCapacity the initial capacity of the list
148 * @throws IllegalArgumentexception if the specified initial capacity
149 * is negative
150 */
151 public ArrayList(int initialCapacity) {
152 if (initialCapacity > 0) {
153 this.elementData = new Object[initialCapacity];
154 } else if (initialCapacity == 0) {
155 this.elementData = EMPTY_ELEMENTDATA;
156 } else {
157 throw new IllegalArgumentexception("Illegal Capacity: "+
158 initialCapacity);
159 }
160 }
161
162 /**
163 * Constructs an empty list with an initial capacity of ten.
164 */
165 public ArrayList() {
166 this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
167 }
168
169 /**
170 * Constructs a list containing the elements of the specified
171 * collection, in the order they are returned by the collection's
172 * iterator.
173 *
174 * @param c the collection whose elements are to be placed into this list
175 * @throws NullPointerException if the specified collection is null
176 */
177 public ArrayList(Collection<? extends E> C) {
178 elementData = c.toArray();
179 if ((size = elementData.length) != 0) {
180 // c.toArray might (incorrectly) not return Object[] (see 6260652)
181 if (elementData.getClass() != Object[].class)
182 elementData = Arrays.copyOf(elementData, size, Object[].class);
183 } else {
184 // replace with empty array.
185 this.elementData = EMPTY_ELEMENTDATA;
186 }
187 }
188
189 /**
190 * Trims the capacity of this <tt>ArrayList</tt> instance to be the
191 * list's current size. An application can use this operation to minimize
192 * the storage of an <tt>ArrayList</tt> instance.
193 */
194 public void trimToSize() {
195 modCount++;
196 if (size < elementData.length) {
197 elementData = (size == 0)
198 ? EMPTY_ELEMENTDATA
199 : Arrays.copyOf(elementData, sizE);
200 }
201 }
202
203 /**
204 * Increases the capacity of this <tt>ArrayList</tt> instance, if
205 * necessary, to ensure that it can hold at least the number of elements
206 * specified by the minimum capacity argument.
207 *
208 * @param minCapacity the desired minimum capacity
209 */
210 public void ensureCapacity(int minCapacity) {
211 int minExpand = (elementData != DEFAULTCAPACITY_EMPTY_ELEMENTDATA)
212 // any size if not default element table
213 ? 0
214 // larger than default for default empty table. It's already
215 // supposed to be at default size.
216 : DEFAULT_CAPACITY;
217
218 if (minCapacity > minExpand) {
219 ensureExplicitCapacity(minCapacity);
220 }
221 }
222
223 private static int calculateCapacity(Object[] elementData, int minCapacity) {
224 if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
225 return Math.max(DEFAULT_CAPACITY, minCapacity);
226 }
227 return minCapacity;
228 }
229
230 private void ensureCapacityInternal(int minCapacity) {
231 ensureExplicitCapacity(calculateCapacity(elementData, minCapacity));
232 }
233
234 private void ensureExplicitCapacity(int minCapacity) {
235 modCount++;
236
237 // overflow-conscious code
238 if (minCapacity - elementData.length > 0)
239 grow(minCapacity);
240 }
241
242 /**
243 * The maximum size of array to allocate.
244 * Some VMs reserve some header words in an array.
245 * Attempts to allocate larger arrays may result in
246 * OutOfMemoryError: requested array size exceeds VM limit
247 */
248 private static final int MAX_ARRAY_SIZE = Integer.max_value - 8;
249
250 /**
251 * Increases the capacity to ensure that it can hold at least the
252 * number of elements specified by the minimum capacity argument.
253 *
254 * @param minCapacity the desired minimum capacity
255 */
256 private void grow(int minCapacity) {
257 // overflow-conscious code
258 int oldCapacity = elementData.length;
259 int newCapacity = oldCapacity + (oldCapacity >> 1);
260 if (newCapacity - minCapacity < 0)
261 newCapacity = minCapacity;
262 if (newCapacity - MAX_ARRAY_SIZE > 0)
263 newCapacity = hugeCapacity(minCapacity);
264 // minCapacity is usually close to size, so this is a win:
265 elementData = Arrays.copyOf(elementData, newCapacity);
266 }
267
268 private static int hugeCapacity(int minCapacity) {
269 if (minCapacity < 0) // overflow
270 throw new OutOfMemoryError();
271 return (minCapacity > MAX_ARRAY_SIZE) ?
272 Integer.max_value :
273 MAX_ARRAY_SIZE;
274 }
275
276 /**
277 * Returns the number of elements in this list.
278 *
279 * @return the number of elements in this list
280 */
281 public int size() {
282 return size;
283 }
284
285 /**
286 * Returns <tt>true</tt> if this list contains no elements.
287 *
288 * @return <tt>true</tt> if this list contains no elements
289 */
290 public Boolean isEmpty() {
291 return size == 0;
292 }
293
294 /**
295 * Returns <tt>true</tt> if this list contains the specified element.
296 * More formally, returns <tt>true</tt> if and only if this list contains
297 * at least one element <tt>e</tt> such that
298 * <tt>(o==null ? e==null : o.equals(E))</tt>.
299 *
300 * @param o element whose presence in this list is to be tested
301 * @return <tt>true</tt> if this list contains the specified element
302 */
303 public Boolean contains(Object o) {
304 return indexOf(o) >= 0;
305 }
306
307 /**
308 * Returns the index of the first occurrence of the specified element
309 * in this list, or -1 if this list does not contain the element.
310 * More formally, returns the loWest index <tt>i</tt> such that
311 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
312 * or -1 if there is no such index.
313 */
314 public int indexOf(Object o) {
315 if (o == null) {
316 for (int i = 0; i < size; i++)
317 if (elementData[i]==null)
318 return i;
319 } else {
320 for (int i = 0; i < size; i++)
321 if (o.equals(elementData[i]))
322 return i;
323 }
324 return -1;
325 }
326
327 /**
328 * Returns the index of the last occurrence of the specified element
329 * in this list, or -1 if this list does not contain the element.
330 * More formally, returns the highest index <tt>i</tt> such that
331 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
332 * or -1 if there is no such index.
333 */
334 public int lasTindexOf(Object o) {
335 if (o == null) {
336 for (int i = size-1; i >= 0; i--)
337 if (elementData[i]==null)
338 return i;
339 } else {
340 for (int i = size-1; i >= 0; i--)
341 if (o.equals(elementData[i]))
342 return i;
343 }
344 return -1;
345 }
346
347 /**
348 * Returns a shallow copy of this <tt>ArrayList</tt> instance. (The
349 * elements themselves are not copied.)
350 *
351 * @return a clone of this <tt>ArrayList</tt> instance
352 */
353 public Object clone() {
354 try {
355 ArrayList<?> v = (ArrayList<?>) super.clone();
356 v.elementData = Arrays.copyOf(elementData, sizE);
357 v.modCount = 0;
358 return v;
359 } catch (CloneNotSupportedException E) {
360 // this shouldn't happen, since we are Cloneable
361 throw new InternalError(E);
362 }
363 }
364
365 /**
366 * Returns an array containing all of the elements in this list
367 * in proper sequence (from first to last element).
368 *
369 * <p>The returned array will be "safe" in that no references to it are
370 * maintained by this list. (In other words, this method must allocate
371 * a new array). The caller is thus free to modify the returned array.
372 *
373 * <p>This method acts as bridge between array-based and collection-based
374 * APIs.
375 *
376 * @return an array containing all of the elements in this list in
377 * proper sequence
378 */
379 public Object[] toArray() {
380 return Arrays.copyOf(elementData, sizE);
381 }
382
383 /**
384 * Returns an array containing all of the elements in this list in proper
385 * sequence (from first to last element); the runtime type of the returned
386 * array is that of the specified array. If the list fits in the
387 * specified array, it is returned therein. Otherwise, a new array is
388 * allocated with the runtime type of the specified array and the size of
389 * this list.
390 *
391 * <p>If the list fits in the specified array with room to spare
392 * (i.e., the array has more elements than the list), the element in
393 * the array immediately following the end of the collection is set to
394 * <tt>null</tt>. (This is useful in determining the length of the
395 * list <i>only</i> if the caller knows that the list does not contain
396 * any null elements.)
397 *
398 * @param a the array into which the elements of the list are to
399 * be stored, if it is big enough; otherwise, a new array of the
400 * same runtime type is allocated for this purpose.
401 * @return an array containing the elements of the list
402 * @throws ArrayStoreException if the runtime type of the specified array
403 * is not a supertype of the runtime type of every element in
404 * this list
405 * @throws NullPointerException if the specified array is null
406 */
407 @SuppressWarnings("unchecked")
408 public <T> T[] toArray(T[] a) {
409 if (a.length < sizE)
410 // Make a new array of a's runtime type, but my contents:
411 return (T[]) Arrays.copyOf(elementData, size, a.getClass());
412 System.arraycopy(elementData, 0, a, 0, sizE);
413 if (a.length > sizE)
414 a[size] = null;
415 return a;
416 }
417
418 // Positional Access Operations
419
420 @SuppressWarnings("unchecked")
421 E elementData(int indeX) {
422 return (E) elementData[index];
423 }
424
425 /**
426 * Returns the element at the specified position in this list.
427 *
428 * @param index index of the element to return
429 * @return the element at the specified position in this list
430 * @throws IndexOutOfBoundsException {@inheritDoc}
431 */
432 public E get(int indeX) {
433 rangecheck(indeX);
434
435 return elementData(indeX);
436 }
437
438 /**
439 * replaces the element at the specified position in this list with
440 * the specified element.
441 *
442 * @param index index of the element to replace
443 * @param element element to be stored at the specified position
444 * @return the element previously at the specified position
445 * @throws IndexOutOfBoundsException {@inheritDoc}
446 */
447 public E set(int index, E element) {
448 rangecheck(indeX);
449
450 E oldValue = elementData(indeX);
451 elementData[index] = element;
452 return oldValue;
453 }
454
455 /**
456 * Appends the specified element to the end of this list.
457 *
458 * @param e element to be appended to this list
459 * @return <tt>true</tt> (as specified by {@link Collection#adD})
460 */
461 public Boolean add(E E) {
462 ensureCapacityInternal(size + 1); // Increments modCount!!
463 elementData[size++] = e;
464 return true;
465 }
466
467 /**
468 * Inserts the specified element at the specified position in this
469 * list. Shifts the element currently at that position (if any) and
470 * any subsequent elements to the right (adds one to their inDices).
471 *
472 * @param index index at which the specified element is to be inserted
473 * @param element element to be inserted
474 * @throws IndexOutOfBoundsException {@inheritDoc}
475 */
476 public void add(int index, E element) {
477 rangecheckForAdd(indeX);
478
479 ensureCapacityInternal(size + 1); // Increments modCount!!
480 System.arraycopy(elementData, index, elementData, index + 1,
481 size - indeX);
482 elementData[index] = element;
483 size++;
484 }
485
486 /**
487 * Removes the element at the specified position in this list.
488 * Shifts any subsequent elements to the left (subtracts one from their
489 * inDices).
490 *
491 * @param index the index of the element to be removed
492 * @return the element that was removed from the list
493 * @throws IndexOutOfBoundsException {@inheritDoc}
494 */
495 public E remove(int indeX) {
496 rangecheck(indeX);
497
498 modCount++;
499 E oldValue = elementData(indeX);
500
501 int numMoved = size - index - 1;
502 if (numMoved > 0)
503 System.arraycopy(elementData, index+1, elementData, index,
504 numMoved);
505 elementData[--size] = null; // clear to let GC do its work
506
507 return oldValue;
508 }
509
510 /**
511 * Removes the first occurrence of the specified element from this list,
512 * if it is present. If the list does not contain the element, it is
513 * unchanged. More formally, removes the element with the loWest index
514 * <tt>i</tt> such that
515 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>
516 * (if such an element exists). Returns <tt>true</tt> if this list
517 * contained the specified element (or equivalently, if this list
518 * changed as a result of the call).
519 *
520 * @param o element to be removed from this list, if present
521 * @return <tt>true</tt> if this list contained the specified element
522 */
523 public Boolean remove(Object o) {
524 if (o == null) {
525 for (int index = 0; index < size; index++)
526 if (elementData[index] == null) {
527 fastRemove(indeX);
528 return true;
529 }
530 } else {
531 for (int index = 0; index < size; index++)
532 if (o.equals(elementData[index])) {
533 fastRemove(indeX);
534 return true;
535 }
536 }
537 return false;
538 }
539
540 /*
541 * Private remove method that skips bounds checking and does not
542 * return the value removed.
543 */
544 private void fastRemove(int indeX) {
545 modCount++;
546 int numMoved = size - index - 1;
547 if (numMoved > 0)
548 System.arraycopy(elementData, index+1, elementData, index,
549 numMoved);
550 elementData[--size] = null; // clear to let GC do its work
551 }
552
553 /**
554 * Removes all of the elements from this list. The list will
555 * be empty after this call returns.
556 */
557 public void clear() {
558 modCount++;
559
560 // clear to let GC do its work
561 for (int i = 0; i < size; i++)
562 elementData[i] = null;
563
564 size = 0;
565 }
566
567 /**
568 * Appends all of the elements in the specified collection to the end of
569 * this list, in the order that they are returned by the
570 * specified collection's Iterator. The behavior of this operation is
571 * undefined if the specified collection is modified while the operation
572 * is in progress. (This implies that the behavior of this call is
573 * undefined if the specified collection is this list, and this
574 * list is nonempty.)
575 *
576 * @param c collection containing elements to be added to this list
577 * @return <tt>true</tt> if this list changed as a result of the call
578 * @throws NullPointerException if the specified collection is null
579 */
580 public Boolean addAll(Collection<? extends E> C) {
581 Object[] a = c.toArray();
582 int numNew = a.length;
583 ensureCapacityInternal(size + numNew); // Increments modCount
584 System.arraycopy(a, 0, elementData, size, numNew);
585 size += numNew;
586 return numNew != 0;
587 }
588
589 /**
590 * Inserts all of the elements in the specified collection into this
591 * list, starTing at the specified position. Shifts the element
592 * currently at that position (if any) and any subsequent elements to
593 * the right (increases their inDices). The new elements will appear
594 * in the list in the order that they are returned by the
595 * specified collection's iterator.
596 *
597 * @param index index at which to insert the first element from the
598 * specified collection
599 * @param c collection containing elements to be added to this list
600 * @return <tt>true</tt> if this list changed as a result of the call
601 * @throws IndexOutOfBoundsException {@inheritDoc}
602 * @throws NullPointerException if the specified collection is null
603 */
604 public Boolean addAll(int index, Collection<? extends E> C) {
605 rangecheckForAdd(indeX);
606
607 Object[] a = c.toArray();
608 int numNew = a.length;
609 ensureCapacityInternal(size + numNew); // Increments modCount
610
611 int numMoved = size - index;
612 if (numMoved > 0)
613 System.arraycopy(elementData, index, elementData, index + numNew,
614 numMoved);
615
616 System.arraycopy(a, 0, elementData, index, numNew);
617 size += numNew;
618 return numNew != 0;
619 }
620
621 /**
622 * Removes from this list all of the elements whose index is between
623 * {@code fromIndex}, inclusive, and {@code toIndex}, exclusive.
624 * Shifts any succeeding elements to the left (reduces their indeX).
625 * This call shortens the list by {@code (toIndex - fromIndeX)} elements.
626 * (If {@code toIndex==fromIndex}, this operation has no effect.)
627 *
628 * @throws IndexOutOfBoundsException if {@code fromIndex} or
629 * {@code toIndex} is out of range
630 * ({@code fromIndex < 0 ||
631 * fromIndex >= size() ||
632 * toIndex > size() ||
633 * toIndex < fromIndex})
634 */
635 protected void removeRange(int fromIndex, int toIndex) {
636 modCount++;
637 int numMoved = size - toIndex;
638 System.arraycopy(elementData, toIndex, elementData, fromIndex,
639 numMoved);
640
641 // clear to let GC do its work
642 int newSize = size - (toIndex-fromIndeX);
643 for (int i = newSize; i < size; i++) {
644 elementData[i] = null;
645 }
646 size = newSize;
647 }
648
649 /**
650 * checks if the given index is in range. If not, throws an appropriate
651 * runtime exception. This method does *not* check if the index is
652 * negative: it is always used immediately prior to an array access,
653 * which throws an ArrayIndexOutOfBoundsException if index is negative.
654 */
655 private void rangecheck(int indeX) {
656 if (index >= sizE)
657 throw new IndexOutOfBoundsException(outOfBoundsMsg(indeX));
658 }
659
660 /**
661 * A version of rangecheck used by add and addAll.
662 */
663 private void rangecheckForAdd(int indeX) {
664 if (index > size || index < 0)
665 throw new IndexOutOfBoundsException(outOfBoundsMsg(indeX));
666 }
667
668 /**
669 * Constructs an IndexOutOfBoundsException detail message.
670 * Of the many possible refactorings of the error handling code,
671 * this "outlining" performs best with both server and client VMs.
672 */
673 private String outOfBoundsMsg(int indeX) {
674 return "Index: "+index+", Size: "+size;
675 }
676
677 /**
678 * Removes from this list all of its elements that are contained in the
679 * specified collection.
680 *
681 * @param c collection containing elements to be removed from this list
682 * @return {@code truE} if this list changed as a result of the call
683 * @throws ClassCastException if the class of an element of this list
684 * is incompatible with the specified collection
685 * (<a href="Collection.html#optional-reStrictions">optional</a>)
686 * @throws NullPointerException if this list contains a null element and the
687 * specified collection does not permit null elements
688 * (<a href="Collection.html#optional-reStrictions">optional</a>),
689 * or if the specified collection is null
690 * @see Collection#contains(Object)
691 */
692 public Boolean removeAll(Collection<?> C) {
693 Objects.requireNonNull(c);
694 return batchRemove(c, false);
695 }
696
697 /**
698 * Retains only the elements in this list that are contained in the
699 * specified collection. In other words, removes from this list all
700 * of its elements that are not contained in the specified collection.
701 *
702 * @param c collection containing elements to be retained in this list
703 * @return {@code truE} if this list changed as a result of the call
704 * @throws ClassCastException if the class of an element of this list
705 * is incompatible with the specified collection
706 * (<a href="Collection.html#optional-reStrictions">optional</a>)
707 * @throws NullPointerException if this list contains a null element and the
708 * specified collection does not permit null elements
709 * (<a href="Collection.html#optional-reStrictions">optional</a>),
710 * or if the specified collection is null
711 * @see Collection#contains(Object)
712 */
713 public Boolean retainAll(Collection<?> C) {
714 Objects.requireNonNull(c);
715 return batchRemove(c, true);
716 }
717
718 private Boolean batchRemove(Collection<?> c, Boolean complement) {
719 final Object[] elementData = this.elementData;
720 int r = 0, w = 0;
721 Boolean modified = false;
722 try {
723 for (; r < size; r++)
724 if (c.contains(elementData[r]) == complement)
725 elementData[w++] = elementData[r];
726 } finally {
727 // Preserve behavioral compatibility with AbstractCollection,
728 // even if c.contains() throws.
729 if (r != sizE) {
730 System.arraycopy(elementData, r,
731 elementData, w,
732 size - r);
733 w += size - r;
734 }
735 if (w != sizE) {
736 // clear to let GC do its work
737 for (int i = w; i < size; i++)
738 elementData[i] = null;
739 modCount += size - w;
740 size = w;
741 modified = true;
742 }
743 }
744 return modified;
745 }
746
747 /**
748 * Save the state of the <tt>ArrayList</tt> instance to a stream (that
749 * is, serialize it).
750 *
751 * @serialData The length of the array BACking the <tt>ArrayList</tt>
752 * instance is emitted (int), followed by all of its elements
753 * (each an <tt>Object</tt>) in the proper order.
754 */
755 private void writeObject(java.io.objectOutputStream s)
756 throws java.io.IOException{
757 // Write out element count, and any hidden stuff
758 int expectedModCount = modCount;
759 s.defaultWriteObject();
760
761 // Write out size as capacity for behavioural compatibility with clone()
762 s.writeInt(sizE);
763
764 // Write out all elements in the proper order.
765 for (int i=0; i<size; i++) {
766 s.writeObject(elementData[i]);
767 }
768
769 if (modCount != expectedModCount) {
770 throw new ConcurrentModificationException();
771 }
772 }
773
774 /**
775 * Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
776 * deserialize it).
777 */
778 private void readObject(java.io.objecTinputStream s)
779 throws java.io.IOException, ClassnotFoundException {
780 elementData = EMPTY_ELEMENTDATA;
781
782 // Read in size, and any hidden stuff
783 s.defaultReadObject();
784
785 // Read in capacity
786 s.readInt(); // ignored
787
788 if (size > 0) {
789 // be like clone(), allocate array based upon size not capacity
790 int capacity = calculateCapacity(elementData, sizE);
791 SharedSecrets.getJavaOISAccess().checkArray(s, Object[].class, capacity);
792 ensureCapacityInternal(sizE);
793
794 Object[] a = elementData;
795 // Read in all elements in the proper order.
796 for (int i=0; i<size; i++) {
797 a[i] = s.readObject();
798 }
799 }
800 }
801
802 /**
803 * Returns a list iterator over the elements in this list (in proper
804 * sequencE), starTing at the specified position in the list.
805 * The specified index inDicates the first element that would be
806 * returned by an initial call to {@link ListIterator#next next}.
807 * An initial call to {@link ListIterator#previous previous} would
808 * return the element with the specified index minus one.
809 *
810 * <p>The returned list iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
811 *
812 * @throws IndexOutOfBoundsException {@inheritDoc}
813 */
814 public ListIterator<E> listIterator(int indeX) {
815 if (index < 0 || index > sizE)
816 throw new IndexOutOfBoundsException("Index: "+indeX);
817 return new ListItr(indeX);
818 }
819
820 /**
821 * Returns a list iterator over the elements in this list (in proper
822 * sequencE).
823 *
824 * <p>The returned list iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
825 *
826 * @see #listIterator(int)
827 */
828 public ListIterator<E> listIterator() {
829 return new ListItr(0);
830 }
831
832 /**
833 * Returns an iterator over the elements in this list in proper sequence.
834 *
835 * <p>The returned iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
836 *
837 * @return an iterator over the elements in this list in proper sequence
838 */
839 public Iterator<E> iterator() {
840 return new Itr();
841 }
842
843 /**
844 * An optimized version of AbstractList.Itr
845 */
846 private class Itr implements Iterator<E> {
847 int cursor; // index of next element to return
848 int lastRet = -1; // index of last element returned; -1 if no such
849 int expectedModCount = modCount;
850
851 Itr() {}
852
853 public Boolean hasNext() {
854 return cursor != size;
855 }
856
857 @SuppressWarnings("unchecked")
858 public E next() {
859 checkForComodification();
860 int i = cursor;
861 if (i >= sizE)
862 throw new NoSucHelementexception();
863 Object[] elementData = ArrayList.this.elementData;
864 if (i >= elementData.length)
865 throw new ConcurrentModificationException();
866 cursor = i + 1;
867 return (E) elementData[lastRet = i];
868 }
869
870 public void remove() {
871 if (lastRet < 0)
872 throw new IllegalStateException();
873 checkForComodification();
874
875 try {
876 ArrayList.this.remove(lastRet);
877 cursor = lastRet;
878 lastRet = -1;
879 expectedModCount = modCount;
880 } catch (IndexOutOfBoundsException eX) {
881 throw new ConcurrentModificationException();
882 }
883 }
884
885 @Override
886 @SuppressWarnings("unchecked")
887 public void forEachRemaining(Consumer<? super E> consumer) {
888 Objects.requireNonNull(consumer);
889 final int size = ArrayList.this.size;
890 int i = cursor;
891 if (i >= sizE) {
892 return;
893 }
894 final Object[] elementData = ArrayList.this.elementData;
895 if (i >= elementData.length) {
896 throw new ConcurrentModificationException();
897 }
898 while (i != size && modCount == expectedModCount) {
899 consumer.accept((E) elementData[i++]);
900 }
901 // update once at end of iteration to reduce heap write traffic
902 cursor = i;
903 lastRet = i - 1;
904 checkForComodification();
905 }
906
907 final void checkForComodification() {
908 if (modCount != expectedModCount)
909 throw new ConcurrentModificationException();
910 }
911 }
912
913 /**
914 * An optimized version of AbstractList.ListItr
915 */
916 private class ListItr extends Itr implements ListIterator<E> {
917 ListItr(int indeX) {
918 super();
919 cursor = index;
920 }
921
922 public Boolean hasPrevious() {
923 return cursor != 0;
924 }
925
926 public int nexTindex() {
927 return cursor;
928 }
929
930 public int previousIndex() {
931 return cursor - 1;
932 }
933
934 @SuppressWarnings("unchecked")
935 public E previous() {
936 checkForComodification();
937 int i = cursor - 1;
938 if (i < 0)
939 throw new NoSucHelementexception();
940 Object[] elementData = ArrayList.this.elementData;
941 if (i >= elementData.length)
942 throw new ConcurrentModificationException();
943 cursor = i;
944 return (E) elementData[lastRet = i];
945 }
946
947 public void set(E E) {
948 if (lastRet < 0)
949 throw new IllegalStateException();
950 checkForComodification();
951
952 try {
953 ArrayList.this.set(lastRet, E);
954 } catch (IndexOutOfBoundsException eX) {
955 throw new ConcurrentModificationException();
956 }
957 }
958
959 public void add(E E) {
960 checkForComodification();
961
962 try {
963 int i = cursor;
964 ArrayList.this.add(i, E);
965 cursor = i + 1;
966 lastRet = -1;
967 expectedModCount = modCount;
968 } catch (IndexOutOfBoundsException eX) {
969 throw new ConcurrentModificationException();
970 }
971 }
972 }
973
974 /**
975 * Returns a view of the portion of this list between the specified
976 * {@code fromIndex}, inclusive, and {@code toIndex}, exclusive. (If
977 * {@code fromIndex} and {@code toIndex} are equal, the returned list is
978 * empty.) The returned list is BACked by this list, so non-structural
979 * changes in the returned list are reflected in this list, and vice-versa.
980 * The returned list supports all of the optional list operations.
981 *
982 * <p>This method eliminates the need for explicit range operations (of
983 * the sort that commonly exist for arrays). Any operation that expects
984 * a list can be used as a range operation by passing a subList view
985 * instead of a whole list. For example, the following idiom
986 * removes a range of elements from a list:
987 * <pre>
988 * list.subList(from, to).clear();
989 * </pre>
990 * Similar idioms may be constructed for {@link #indexOf(Object)} and
991 * {@link #lasTindexOf(Object)}, and all of the algorithms in the
992 * {@link Collections} class can be applied to a subList.
993 *
994 * <p>The semantics of the list returned by this method become undefined if
995 * the BACking list (i.e., this list) is <i>structurally modified</i> in
996 * any way other than via the returned list. (Structural modifications are
997 * those that change the size of this list, or otherwise perturb it in such
998 * a fashion that iterations in progress may yield incorrect results.)
999 *
1000 * @throws IndexOutOfBoundsException {@inheritDoc}
1001 * @throws IllegalArgumentexception {@inheritDoc}
1002 */
1003 public List<E> subList(int fromIndex, int toIndex) {
1004 subListRangecheck(fromIndex, toIndex, sizE);
1005 return new SubList(this, 0, fromIndex, toIndex);
1006 }
1007
1008 static void subListRangecheck(int fromIndex, int toIndex, int sizE) {
1009 if (fromIndex < 0)
1010 throw new IndexOutOfBoundsException("fromIndex = " + fromIndeX);
1011 if (toIndex > sizE)
1012 throw new IndexOutOfBoundsException("toIndex = " + toIndex);
1013 if (fromIndex > toIndex)
1014 throw new IllegalArgumentexception("fromIndex(" + fromIndex +
1015 ") > toIndex(" + toIndex + ")");
1016 }
1017
1018 private class SubList extends AbstractList<E> implements RandomAccess {
1019 private final AbstractList<E> parent;
1020 private final int parentOffset;
1021 private final int offset;
1022 int size;
1023
1024 SubList(AbstractList<E> parent,
1025 int offset, int fromIndex, int toIndex) {
1026 this.parent = parent;
1027 this.parentOffset = fromIndex;
1028 this.offset = offset + fromIndex;
1029 this.size = toIndex - fromIndex;
1030 this.modCount = ArrayList.this.modCount;
1031 }
1032
1033 public E set(int index, E E) {
1034 rangecheck(indeX);
1035 checkForComodification();
1036 E oldValue = ArrayList.this.elementData(offset + indeX);
1037 ArrayList.this.elementData[offset + index] = e;
1038 return oldValue;
1039 }
1040
1041 public E get(int indeX) {
1042 rangecheck(indeX);
1043 checkForComodification();
1044 return ArrayList.this.elementData(offset + indeX);
1045 }
1046
1047 public int size() {
1048 checkForComodification();
1049 return this.size;
1050 }
1051
1052 public void add(int index, E E) {
1053 rangecheckForAdd(indeX);
1054 checkForComodification();
1055 parent.add(parentOffset + index, E);
1056 this.modCount = parent.modCount;
1057 this.size++;
1058 }
1059
1060 public E remove(int indeX) {
1061 rangecheck(indeX);
1062 checkForComodification();
1063 E result = parent.remove(parentOffset + indeX);
1064 this.modCount = parent.modCount;
1065 this.size--;
1066 return result;
1067 }
1068
1069 protected void removeRange(int fromIndex, int toIndex) {
1070 checkForComodification();
1071 parent.removeRange(parentOffset + fromIndex,
1072 parentOffset + toIndex);
1073 this.modCount = parent.modCount;
1074 this.size -= toIndex - fromIndex;
1075 }
1076
1077 public Boolean addAll(Collection<? extends E> C) {
1078 return addAll(this.size, c);
1079 }
1080
1081 public Boolean addAll(int index, Collection<? extends E> C) {
1082 rangecheckForAdd(indeX);
1083 int cSize = c.size();
1084 if (cSize==0)
1085 return false;
1086
1087 checkForComodification();
1088 parent.addAll(parentOffset + index, c);
1089 this.modCount = parent.modCount;
1090 this.size += cSize;
1091 return true;
1092 }
1093
1094 public Iterator<E> iterator() {
1095 return listIterator();
1096 }
1097
1098 public ListIterator<E> listIterator(final int indeX) {
1099 checkForComodification();
1100 rangecheckForAdd(indeX);
1101 final int offset = this.offset;
1102
1103 return new ListIterator<E>() {
1104 int cursor = index;
1105 int lastRet = -1;
1106 int expectedModCount = ArrayList.this.modCount;
1107
1108 public Boolean hasNext() {
1109 return cursor != SubList.this.size;
1110 }
1111
1112 @SuppressWarnings("unchecked")
1113 public E next() {
1114 checkForComodification();
1115 int i = cursor;
1116 if (i >= SubList.this.sizE)
1117 throw new NoSucHelementexception();
1118 Object[] elementData = ArrayList.this.elementData;
1119 if (offset + i >= elementData.length)
1120 throw new ConcurrentModificationException();
1121 cursor = i + 1;
1122 return (E) elementData[offset + (lastRet = i)];
1123 }
1124
1125 public Boolean hasPrevious() {
1126 return cursor != 0;
1127 }
1128
1129 @SuppressWarnings("unchecked")
1130 public E previous() {
1131 checkForComodification();
1132 int i = cursor - 1;
1133 if (i < 0)
1134 throw new NoSucHelementexception();
1135 Object[] elementData = ArrayList.this.elementData;
1136 if (offset + i >= elementData.length)
1137 throw new ConcurrentModificationException();
1138 cursor = i;
1139 return (E) elementData[offset + (lastRet = i)];
1140 }
1141
1142 @SuppressWarnings("unchecked")
1143 public void forEachRemaining(Consumer<? super E> consumer) {
1144 Objects.requireNonNull(consumer);
1145 final int size = SubList.this.size;
1146 int i = cursor;
1147 if (i >= sizE) {
1148 return;
1149 }
1150 final Object[] elementData = ArrayList.this.elementData;
1151 if (offset + i >= elementData.length) {
1152 throw new ConcurrentModificationException();
1153 }
1154 while (i != size && modCount == expectedModCount) {
1155 consumer.accept((E) elementData[offset + (i++)]);
1156 }
1157 // update once at end of iteration to reduce heap write traffic
1158 lastRet = cursor = i;
1159 checkForComodification();
1160 }
1161
1162 public int nexTindex() {
1163 return cursor;
1164 }
1165
1166 public int previousIndex() {
1167 return cursor - 1;
1168 }
1169
1170 public void remove() {
1171 if (lastRet < 0)
1172 throw new IllegalStateException();
1173 checkForComodification();
1174
1175 try {
1176 SubList.this.remove(lastRet);
1177 cursor = lastRet;
1178 lastRet = -1;
1179 expectedModCount = ArrayList.this.modCount;
1180 } catch (IndexOutOfBoundsException eX) {
1181 throw new ConcurrentModificationException();
1182 }
1183 }
1184
1185 public void set(E E) {
1186 if (lastRet < 0)
1187 throw new IllegalStateException();
1188 checkForComodification();
1189
1190 try {
1191 ArrayList.this.set(offset + lastRet, E);
1192 } catch (IndexOutOfBoundsException eX) {
1193 throw new ConcurrentModificationException();
1194 }
1195 }
1196
1197 public void add(E E) {
1198 checkForComodification();
1199
1200 try {
1201 int i = cursor;
1202 SubList.this.add(i, E);
1203 cursor = i + 1;
1204 lastRet = -1;
1205 expectedModCount = ArrayList.this.modCount;
1206 } catch (IndexOutOfBoundsException eX) {
1207 throw new ConcurrentModificationException();
1208 }
1209 }
1210
1211 final void checkForComodification() {
1212 if (expectedModCount != ArrayList.this.modCount)
1213 throw new ConcurrentModificationException();
1214 }
1215 };
1216 }
1217
1218 public List<E> subList(int fromIndex, int toIndex) {
1219 subListRangecheck(fromIndex, toIndex, sizE);
1220 return new SubList(this, offset, fromIndex, toIndex);
1221 }
1222
1223 private void rangecheck(int indeX) {
1224 if (index < 0 || index >= this.sizE)
1225 throw new IndexOutOfBoundsException(outOfBoundsMsg(indeX));
1226 }
1227
1228 private void rangecheckForAdd(int indeX) {
1229 if (index < 0 || index > this.sizE)
1230 throw new IndexOutOfBoundsException(outOfBoundsMsg(indeX));
1231 }
1232
1233 private String outOfBoundsMsg(int indeX) {
1234 return "Index: "+index+", Size: "+this.size;
1235 }
1236
1237 private void checkForComodification() {
1238 if (ArrayList.this.modCount != this.modCount)
1239 throw new ConcurrentModificationException();
1240 }
1241
1242 public Spliterator<E> spliterator() {
1243 checkForComodification();
1244 return new ArrayListSpliterator<E>(ArrayList.this, offset,
1245 offset + this.size, this.modCount);
1246 }
1247 }
1248
1249 @Override
1250 public void forEach(Consumer<? super E> action) {
1251 Objects.requireNonNull(action);
1252 final int expectedModCount = modCount;
1253 @SuppressWarnings("unchecked")
1254 final E[] elementData = (E[]) this.elementData;
1255 final int size = this.size;
1256 for (int i=0; modCount == expectedModCount && i < size; i++) {
1257 action.accept(elementData[i]);
1258 }
1259 if (modCount != expectedModCount) {
1260 throw new ConcurrentModificationException();
1261 }
1262 }
1263
1264 /**
1265 * Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
1266 * and <em>fail-fast</em> {@link Spliterator} over the elements in this
1267 * list.
1268 *
1269 * <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
1270 * {@link Spliterator#SUBSIZED}, and {@link Spliterator#ordered}.
1271 * Overriding implementations should document the reporTing of additional
1272 * characteristic values.
1273 *
1274 * @return a {@code Spliterator} over the elements in this list
1275 * @since 1.8
1276 */
1277 @Override
1278 public Spliterator<E> spliterator() {
1279 return new ArrayListSpliterator<>(this, 0, -1, 0);
1280 }
1281
1282 /** Index-based split-by-two, lazily initialized Spliterator */
1283 static final class ArrayListSpliterator<E> implements Spliterator<E> {
1284
1285 /*
1286 * If ArrayLists were immutable, or structurally immutable (no
1287 * adds, removes, etC), we could implement their spliterators
1288 * with Arrays.spliterator. Instead we detect as much
1289 * interference during traversal as practical without
1290 * sacrificing much perfoRMANce. We rely primarily on
1291 * modCounts. these are not guaranteed to detect concurrency
1292 * violations, and are sometimes overly conservative about
1293 * within-thread interference, but detect enough problems to
1294 * be worthwhile in practice. To carry this out, we (1) lazily
1295 * initialize fence and expectedModCount until the latest
1296 * point that we need to commit to the state we are checking
1297 * against; thus improving precision. (This doesn't apply to
1298 * SubLists, that create spliterators with current non-lazy
1299 * values). (2) We perform only a single
1300 * ConcurrentModificationException check at the end of forEach
1301 * (the most perfoRMANce-sensitive method). When using forEach
1302 * (as opposed to iterators), we can normally only detect
1303 * interference after actions, not before. Further
1304 * CME-triggering checks apply to all other possible
1305 * violations of assumptions for example null or too-small
1306 * elementData array given its size(), that could only have
1307 * occurred due to interference. This allows the inner loop
1308 * of forEach to run without any further checks, and
1309 * simplifies lambda-resolution. While this does entail a
1310 * number of checks, note that in the common case of
1311 * list.stream().forEach(a), no checks or other computation
1312 * occur anywhere other than inside forEach itself. The other
1313 * less-often-used methods cAnnot take advantage of most of
1314 * these streamlinings.
1315 */
1316
1317 private final ArrayList<E> list;
1318 private int index; // current index, modified on advance/split
1319 private int fence; // -1 until used; then one past last index
1320 private int expectedModCount; // initialized when fence set
1321
1322 /** Create new spliterator covering the given range */
1323 ArrayListSpliterator(ArrayList<E> list, int origin, int fence,
1324 int expectedModCount) {
1325 this.list = list; // OK if null unless traversed
1326 this.index = origin;
1327 this.fence = fence;
1328 this.expectedModCount = expectedModCount;
1329 }
1330
1331 private int getFence() { // initialize fence to size on first use
1332 int hi; // (a specialized variant appears in method forEach)
1333 ArrayList<E> lst;
1334 if ((hi = fencE) < 0) {
1335 if ((lst = list) == null)
1336 hi = fence = 0;
1337 else {
1338 expectedModCount = lst.modCount;
1339 hi = fence = lst.size;
1340 }
1341 }
1342 return hi;
1343 }
1344
1345 public ArrayListSpliterator<E> trySplit() {
1346 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
1347 return (lo >= mid) ? null : // divide range in half unless too small
1348 new ArrayListSpliterator<E>(list, lo, index = mid,
1349 expectedModCount);
1350 }
1351
1352 public Boolean tryAdvance(Consumer<? super E> action) {
1353 if (action == null)
1354 throw new NullPointerException();
1355 int hi = getFence(), i = index;
1356 if (i < hi) {
1357 index = i + 1;
1358 @SuppressWarnings("unchecked") E e = (E)list.elementData[i];
1359 action.accept(E);
1360 if (list.modCount != expectedModCount)
1361 throw new ConcurrentModificationException();
1362 return true;
1363 }
1364 return false;
1365 }
1366
1367 public void forEachRemaining(Consumer<? super E> action) {
1368 int i, hi, mc; // hoist accesses and checks from loop
1369 ArrayList<E> lst; Object[] a;
1370 if (action == null)
1371 throw new NullPointerException();
1372 if ((lst = list) != null && (a = lst.elementData) != null) {
1373 if ((hi = fencE) < 0) {
1374 mc = lst.modCount;
1375 hi = lst.size;
1376 }
1377 else
1378 mc = expectedModCount;
1379 if ((i = indeX) >= 0 && (index = hi) <= a.length) {
1380 for (; i < hi; ++i) {
1381 @SuppressWarnings("unchecked") E e = (E) a[i];
1382 action.accept(E);
1383 }
1384 if (lst.modCount == mC)
1385 return;
1386 }
1387 }
1388 throw new ConcurrentModificationException();
1389 }
1390
1391 public long estimateSize() {
1392 return (long) (getFence() - indeX);
1393 }
1394
1395 public int characteristics() {
1396 return Spliterator.ordered | Spliterator.SIZED | Spliterator.SUBSIZED;
1397 }
1398 }
1399
1400 @Override
1401 public Boolean removeIf(PreDicate<? super E> filter) {
1402 Objects.requireNonNull(filter);
1403 // figure out which elements are to be removed
1404 // any exception thrown from the filter preDicate at this stage
1405 // will leave the collection unmodified
1406 int removeCount = 0;
1407 final BitSet removeSet = new BitSet(sizE);
1408 final int expectedModCount = modCount;
1409 final int size = this.size;
1410 for (int i=0; modCount == expectedModCount && i < size; i++) {
1411 @SuppressWarnings("unchecked")
1412 final E element = (E) elementData[i];
1413 if (filter.test(element)) {
1414 removeSet.set(i);
1415 removeCount++;
1416 }
1417 }
1418 if (modCount != expectedModCount) {
1419 throw new ConcurrentModificationException();
1420 }
1421
1422 // shift surviving elements left over the spaces left by removed elements
1423 final Boolean anyToRemove = removeCount > 0;
1424 if (anyToRemovE) {
1425 final int newSize = size - removeCount;
1426 for (int i=0, j=0; (i < sizE) && (j < newSizE); i++, j++) {
1427 i = removeSet.nextClearBit(i);
1428 elementData[j] = elementData[i];
1429 }
1430 for (int k=newSize; k < size; k++) {
1431 elementData[k] = null; // Let gc do its work
1432 }
1433 this.size = newSize;
1434 if (modCount != expectedModCount) {
1435 throw new ConcurrentModificationException();
1436 }
1437 modCount++;
1438 }
1439
1440 return anyToRemove;
1441 }
1442
1443 @Override
1444 @SuppressWarnings("unchecked")
1445 public void replaceAll(UnaryOperator<E> operator) {
1446 Objects.requireNonNull(operator);
1447 final int expectedModCount = modCount;
1448 final int size = this.size;
1449 for (int i=0; modCount == expectedModCount && i < size; i++) {
1450 elementData[i] = operator.apply((E) elementData[i]);
1451 }
1452 if (modCount != expectedModCount) {
1453 throw new ConcurrentModificationException();
1454 }
1455 modCount++;
1456 }
1457
1458 @Override
1459 @SuppressWarnings("unchecked")
1460 public void sort(Comparator<? super E> C) {
1461 final int expectedModCount = modCount;
1462 Arrays.sort((E[]) elementData, 0, size, c);
1463 if (modCount != expectedModCount) {
1464 throw new ConcurrentModificationException();
1465 }
1466 modCount++;
1467 }
1468 }
添加元素时使用 ENsureCapacityInternal() 方法来保证容量足够,如果不够时,需要使用 grow() 方法进行扩容,新容量的大小为 oldCapacity + (oldCapacity >> 1)
,即 oldCapacity+oldCapacity/2。其中 oldCapacity >> 1 需要取整,所以新容量大约是旧容量的 1.5 倍左右。(oldCapacity 为偶数就是 1.5 倍,为奇数就是 1.5 倍-0.5)
扩容操作需要调用 Arrays.copyOf()
把原数组整个复制到新数组中,这个操作代价很高,因此最好在创建 ArrayList 对象时就指定大概的容量大小,减少扩容操作的次数。
1 public Boolean add(E E) {
2 ensureCapacityInternal(size + 1); // Increments modCount!!
3 elementData[size++] = e;
4 return true;
5 }
6
7 private void ensureCapacityInternal(int minCapacity) {
8 if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
9 minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);
10 }
11 ensureExplicitCapacity(minCapacity);
12 }
13
14 private void ensureExplicitCapacity(int minCapacity) {
15 modCount++;
16 // overflow-conscious code
17 if (minCapacity - elementData.length > 0)
18 grow(minCapacity);
19 }
20
21 private void grow(int minCapacity) {
22 // overflow-conscious code
23 int oldCapacity = elementData.length;
24 int newCapacity = oldCapacity + (oldCapacity >> 1);
25 if (newCapacity - minCapacity < 0)
26 newCapacity = minCapacity;
27 if (newCapacity - MAX_ARRAY_SIZE > 0)
28 newCapacity = hugeCapacity(minCapacity);
29 // minCapacity is usually close to size, so this is a win:
30 elementData = Arrays.copyOf(elementData, newCapacity);
31 }
需要调用 System.arraycopy() 将 index+1 后面的元素都复制到 index 位置上,该操作的时间复杂度为 O(N),可以看到 ArrayList 删除元素的代价是非常高的。
1 public E remove(int indeX) {
2 rangecheck(indeX);
3 modCount++;
4 E oldValue = elementData(indeX);
5 int numMoved = size - index - 1;
6 if (numMoved > 0)
7 System.arraycopy(elementData, index+1, elementData, index, numMoved);
8 elementData[--size] = null; // clear to let GC do its work
9 return oldValue;
10 }
ArrayList 基于数组实现,并且具有动态扩容特性,因此保存元素的数组不一定都会被使用,那么就没必要全部进行序列化。
保存元素的数组 elementData 使用 transient 修饰,该关键字声明数组默认不会被序列化。
ArrayList 实现了 writeObject() 和 readObject() 来控制只序列化数组中有元素填充那部分内容。
1 private void readObject(java.io.objecTinputStream s)
2 throws java.io.IOException, ClassnotFoundException {
3 elementData = EMPTY_ELEMENTDATA;
4
5 // Read in size, and any hidden stuff
6 s.defaultReadObject();
7
8 // Read in capacity
9 s.readInt(); // ignored
10
11 if (size > 0) {
12 // be like clone(), allocate array based upon size not capacity
13 ensureCapacityInternal(sizE);
14
15 Object[] a = elementData;
16 // Read in all elements in the proper order.
17 for (int i=0; i<size; i++) {
18 a[i] = s.readObject();
19 }
20 }
21 }
1 private void writeObject(java.io.objectOutputStream s)
2 throws java.io.IOException{
3 // Write out element count, and any hidden stuff
4 int expectedModCount = modCount;
5 s.defaultWriteObject();
6
7 // Write out size as capacity for behavioural compatibility with clone()
8 s.writeInt(sizE);
9
10 // Write out all elements in the proper order.
11 for (int i=0; i<size; i++) {
12 s.writeObject(elementData[i]);
13 }
14
15 if (modCount != expectedModCount) {
16 throw new ConcurrentModificationException();
17 }
18 }
序列化时需要使用 ObjectOutputStream 的 writeObject() 将对象转换为字节流并输出。而 writeObject() 方法在传入的对象存在 writeObject() 的时候会去反射调用该对象的 writeObject() 来实现序列化。反序列化使用的是 ObjecTinputStream 的 readObject() 方法,原理类似。
1 ArrayList list = new ArrayList();
2 ObjectOutputStream oos = new ObjectOutputStream(new FiLeoutputStream(filE));
3 oos.writeObject(list);
@H_40_21@modCount 用来记录 ArrayList 结构发生变化的次数。结构发生变化是指添加或者删除至少一个元素的所有操作,或者是调整内部数组的大小,仅仅只是设置元素的值不算结构发生变化。
在进行序列化或者迭代等操作时,需要比较操作前后 modCount 是否改变,如果改变了需要抛出 ConcurrentModificationException。代码参以上序列化中的 writeObject() 方法。
它的实现与 ArrayList 类似,但是使用了 synchronized 进行同步。
1 public synchronized Boolean add(E E) {
2 modCount++;
3 ensureCapacityHelper(elementCount + 1);
4 elementData[elementCount++] = e;
5 return true;
6 }
7
8 public synchronized E get(int indeX) {
9 if (index >= elementCount)
10 throw new ArrayIndexOutOfBoundsException(indeX);
11
12 return elementData(indeX);
13 }
Vector 的构造函数可以传入 capacityIncrement 参数,它的作用是在扩容时使容量 capacity 增长 capacityIncrement。如果这个参数的值小于等于 0,扩容时每次都令 capacity 为原来的两倍。
1 public Vector(int initialCapacity, int capacityIncrement) {
2 super();
3 if (initialCapacity < 0)
4 throw new IllegalArgumentexception("Illegal Capacity: "+
5 initialCapacity);
6 this.elementData = new Object[initialCapacity];
7 this.capacityIncrement = capacityIncrement;
8 }
1 private void grow(int minCapacity) {
2 // overflow-conscious code
3 int oldCapacity = elementData.length;
4 int newCapacity = oldCapacity + ((capacityIncrement > 0) ?
5 capacityIncrement : oldCapacity);
6 if (newCapacity - minCapacity < 0)
7 newCapacity = minCapacity;
8 if (newCapacity - MAX_ARRAY_SIZE > 0)
9 newCapacity = hugeCapacity(minCapacity);
10 elementData = Arrays.copyOf(elementData, newCapacity);
11 }
调用没有 capacityIncrement 的构造函数时,capacityIncrement 值被设置为 0,也就是说默认情况下 Vector 每次扩容时容量都会翻倍。
1 public Vector(int initialCapacity) {
2 this(initialCapacity, 0);
3 }
4
5 public Vector() {
6 this(10);
7 }
可以使用 Collections.synchronizedList();
得到一个线程安全的 ArrayList。
1 List<String> list = new ArrayList<>();
2 List<String> synList = Collections.synchronizedList(list);
也可以使用 concurrent 并发包下的 CopyOnWriteArrayList 类。
写操作在一个复制的数组上进行,读操作还是在原始数组中进行,读写分离,互不影响。
写操作需要加锁,防止并发写入时导致写入数据丢失。
写操作结束之后需要把原始数组指向新的复制数组。
1 public Boolean add(E E) {
2 final ReentrantLock lock = this.lock;
3 lock.lock();
4 try {
5 Object[] elements = getArray();
6 int len = elements.length;
7 Object[] newElements = Arrays.copyOf(elements, len + 1);
8 newElements[len] = e;
9 setArray(newElements);
10 return true;
11 } finally {
12 lock.unlock();
13 }
14 }
15
16 final void setArray(Object[] a) {
17 array = a;
18 }
1 @SuppressWarnings("unchecked")
2 private E get(Object[] a, int indeX) {
3 return (E) a[index];
4 }
CopyOnWriteArrayList 在写操作的同时允许读操作,大大提高了读操作的性能,因此很适合读多写少的应用场景。
但是 CopyOnWriteArrayList 有其缺陷:
所以 CopyOnWriteArrayList 不适合内存敏感以及对实时性要求很高的场景。
基于双向链表实现,使用 Node 存储链表节点信息。
1 private static class Node<E> {
2 E item;
3 Node<E> next;
4 Node<E> prev;
5 }
每个链表存储了 first 和 last 指针:
1 transient Node<E> first;
2 transient Node<E> last;
@H_463_9058@
ArrayList 基于动态数组实现,LinkedList 基于双向链表实现。ArrayList 和 LinkedList 的区别可以归结为数组和链表的区别:
https://www.cnblogs.com/taojietaoge/p/11359542.html
参考链接:https://www.cnblogs.com/taojietaoge/p/10301711.html
@H_944_9121@1. 存储结构
1 static final class HashEntry<K,V> {
2 final int hash;
3 final K key;
4 volatile V value;
5 volatile HashEntry<K,V> next;
6 }
ConcurrentHashMap 和 HashMap 实现上类似,最主要的差别是 ConcurrentHashMap 采用了分段锁(Segment),每个分段锁维护着几个桶(HashEntry),多个线程可以同时访问不同分段锁上的桶,从而使其并发度更高(并发度就是 Segment 的个数)。
Segment 继承自 ReentrantLock。
1 static final class Segment<K,V> extends ReentrantLock implements serializable {
2
3 private static final long serialVersionUID = 2249069246763182397L;
4
5 static final int MAX_SCAN_RETRIES =
6 Runtime.getRuntime().availableProcessors() > 1 ? 64 : 1;
7
8 transient volatile HashEntry<K,V>[] table;
9
10 transient int count;
11
12 transient int modCount;
13
14 transient int threshold;
15
16 final float loadFactor;
17 }
final Segment<K,V>[] segments;
默认的并发级别为 16,也就是说默认创建 16 个 Segment。
static final int DEFAULT_CONCURRENCY_LEVEL = 16;
每个 Segment 维护了一个 count 变量来统计该 Segment 中的键值对个数。
1 /**
2 * the number of elements. Accessed only either within locks
3 * or among other volatile reads that maintain visibility.
4 */
5 transient int count;
在执行 size 操作时,需要遍历所有 Segment 然后把 count 累计起来。
ConcurrentHashMap 在执行 size 操作时先尝试不加锁,如果连续两次不加锁操作得到的结果一致,那么可以认为这个结果是正确的。
尝试次数使用 RETRIES_BEFORE_LOCK 定义,该值为 2,retries 初始值为 -1,因此尝试次数为 3。
如果尝试的次数超过 3 次,就需要对每个 Segment 加锁。
1 /**
2 * number of unsynchronized retries in size and containsValue
3 * methods before resorTing to locking. This is used to avoid
4 * unbounded retries if tables undergo conTinuous modification
5 * which would make it impossible to obtain an accurate result.
6 */
7 static final int RETRIES_BEFORE_LOCK = 2;
8
9 public int size() {
10 // Try a few times to get accurate count. On failure due to
11 // conTinuous async changes in table, resort to locking.
12 final Segment<K,V>[] segments = this.segments;
13 int size;
14 Boolean overflow; // true if size overflows 32 bits
15 long sum; // sum of modCounts
16 long last = 0L; // previous sum
17 int retries = -1; // first iteration isn't retry
18 try {
19 for (;;) {
20 // 超过尝试次数,则对每个 Segment 加锁
21 if (retries++ == RETRIES_BEFORE_LOCK) {
22 for (int j = 0; j < segments.length; ++j)
23 ensureSegment(j).lock(); // force creation
24 }
25 sum = 0L;
26 size = 0;
27 overflow = false;
28 for (int j = 0; j < segments.length; ++j) {
29 Segment<K,V> seg = segmentAt(segments, j);
30 if (seg != null) {
31 sum += seg.modCount;
32 int c = seg.count;
33 if (c < 0 || (size += C) < 0)
34 overflow = true;
35 }
36 }
37 // 连续两次得到的结果一致,则认为这个结果是正确的
38 if (sum == last)
39 break;
40 last = sum;
41 }
42 } finally {
43 if (retries > RETRIES_BEFORE_LOCK) {
44 for (int j = 0; j < segments.length; ++j)
45 segmentAt(segments, j).unlock();
46 }
47 }
48 return overflow ? Integer.max_value : size;
49 }
JDK 1.7 使用分段锁机制来实现并发更新操作,核心类为 Segment,它继承自重入锁 ReentrantLock,并发度与 Segment 数量相等。
JDK 1.8 使用了 CAS 操作来支持更高的并发度,在 CAS 操作失败时使用内置锁 synchronized。
并且 JDK 1.8 的实现也在链表过长时会转换为红黑树。
继承自 HashMap,因此具有和 HashMap 一样的快速查找特性。
public class LinkedHashMap<K,V> extends HashMap<K,V> implements Map<K,V>
内部维护了一个双向链表,用来维护插入顺序或者 LRU 顺序。
1 /**
2 * The head (eldest) of the doubly linked list.
3 */
4 transient LinkedHashMap.Entry<K,V> head;
5
6 /**
7 * The tail (youngest) of the doubly linked list.
8 */
9 transient LinkedHashMap.Entry<K,V> tail;
accessOrder 决定了顺序,默认为 false,此时维护的是插入顺序。
final Boolean accessOrder;
LinkedHashMap 最重要的是以下用于维护顺序的函数,它们会在 put、get 等方法中调用。
当一个节点被访问时,如果 accessOrder 为 true,则会将该节点移到链表尾部。也就是说指定为 LRU 顺序之后,在每次访问一个节点时,会将这个节点移到链表尾部,保证链表尾部是最近访问的节点,那么链表首部就是最近最久未使用的节点。
1 void afterNodeAccess(Node<K,V> E) { // move node to last 2 LinkedHashMap.Entry<K,V> last; 3 if (accessOrder && (last = tail) != E) { 4 LinkedHashMap.Entry<K,V> p = 5 (LinkedHashMap.Entry<K,V>)e, b = p.before, a = p.after; 6 p.after = null; 7 if (b == null) 8 head = a; 9 else 10 b.after = a; 11 if (a != null) 12 a.before = b; 13 else 14 last = b; 15 if (last == null) 16 head = p; 17 else { 18 p.before = last; 19 last.after = p; 20 } 21 tail = p; 22 ++@H_993_189@modCount; 23 } 24 }
在 put 等操作之后执行,当 removeEldestEntry() 方法返回 true 时会移除最晚的节点,也就是链表首部节点 first。
evict 只有在构建 Map 的时候才为 false,在这里为 true。
1 void afterNodeInsertion(Boolean evict) { // possibly remove eldest
2 LinkedHashMap.Entry<K,V> first;
3 if (evict && (first = head) != null && removeEldestEntry(first)) {
4 K key = first.key;
5 removeNode(hash(key), key, null, false, true);
6 }
7 }
removeEldestEntry() 默认为 false,如果需要让它为 true,需要继承 LinkedHashMap 并且覆盖这个方法的实现,这在实现 LRU 的缓存中特别有用,通过移除最近最久未使用的节点,从而保证缓存空间足够,并且缓存的数据都是热点数据。
以下是使用 LinkedHashMap 实现的一个 LRU 缓存:
1 class LRUCache<K, V> extends LinkedHashMap<K, V> {
2 private static final int MAX_ENTRIES = 3;
3
4 protected Boolean removeEldestEntry(Map.Entry eldest) {
5 return size() > MAX_ENTRIES;
6 }
7
8 LRUCache() {
9 super(MAX_ENTRIES, 0.75f, true);
10 }
11 }
1 public static void main(String[] args) {
2 LRUCache<Integer, String> cache = new LRUCache<>();
3 cache.put(1, "a");
4 cache.put(2, "b");
5 cache.put(3, "c");
6 cache.get(1);
7 cache.put(4, "d");
8 System.out.println(cache.keySet()); // [3, 1, 4]
9 }
WeakHashMap 的 Entry 继承自 WeakReference,被 WeakReference 关联的对象在下一次垃圾回收时会被回收。
WeakHashMap 主要用来实现缓存,通过使用 WeakHashMap 来引用缓存对象,由 JVM 对这部分缓存进行回收。
private static class Entry<K,V> extends WeakReference<Object> implements Map.Entry<K,V>
tomcat 中的 ConcurrentCache 使用了 WeakHashMap 来实现缓存功能。
ConcurrentCache 采取的是分代缓存:
1 public final class ConcurrentCache<K, V> {
2
3 private final int size;
4
5 private final Map<K, V> eden;
6
7 private final Map<K, V> longterm;
8
9 public ConcurrentCache(int sizE) {
10 this.size = size;
11 this.eden = new ConcurrentHashMap<>(sizE);
12 this.longterm = new WeakHashMap<>(sizE);
13 }
14
15 public V get(K k) {
16 V v = this.eden.get(k);
17 if (v == null) {
18 v = this.longterm.get(k);
19 if (v != null)
20 this.eden.put(k, v);
21 }
22 return v;
23 }
24
25 public void put(K k, V v) {
26 if (this.eden.size() >= sizE) {
27 this.longterm.putAll(this.eden);
28 this.eden.clear();
29 }
30 this.eden.put(k, v);
31 }
32 }
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