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# LinkedList -- 增删快。# 1.继承关系：public class LinkedList<E>extends AbstractSequentialList<E>implements List<E>, Deque<E>, Cloneable, java.io.Serializable# 2. 属性：// 默认容量transient int size = 0;// 首字节transient Node<E> first;// 尾字节transient Node<E> last;# 3.方法：// 无参构造函数public LinkedList() {}// 返回包含指定集合元素的构造public LinkedList(Collection<? extends E> c) {this();addAll(c);}// 添加第一个元素private void linkFirst(E e) {// 定义 f ，赋值为首节点。final Node<E> f = first;// 定义新节点 newNode ，设置其后一节点为原首节点：f。final Node<E> newNode = new Node<>(null, e, f);// 把原首节点赋值为新节点：newNode。first = newNode;if (f == null)//　集合中无元素则，则新节点也是最后一节点。last = newNode;else// 设置 f 的前一节点为新节点。（final 修饰的变量其引用指针不可改，但其属性可改。）f.prev = newNode;size++;modCount++;}// 添加最后一个元素void linkLast(E e) {final Node<E> l = last;final Node<E> newNode = new Node<>(l, e, null);last = newNode;if (l == null)first = newNode;elsel.next = newNode;// 集合元素加1。size++;// 集合修改次数加1。modCount++;}// 在指定的非空节点前添加元素void linkBefore(E e, Node<E> succ) {// succ 不为空。定义 pred ，赋值为 succ 的前一节点。final Node<E> pred = succ.prev;// 定义新节点 newNode，前一节点为：pred，后一节点为 succ。final Node<E> newNode = new Node<>(pred, e, succ);// 设置 succ 前一节点为 newNode 。succ.prev = newNode;if (pred == null)first = newNode;else// 设置 pred 的后一节点为新节点：newNode。pred.next = newNode;size++;modCount++;}// 删除第一个节点private E unlinkFirst(Node<E> f) {// assert f == first && f != null;final E element = f.item;final Node<E> next = f.next;f.item = null;f.next = null; // help GCfirst = next;if (next == null)last = null;elsenext.prev = null;size--;modCount++;return element;}// 删除最后一个节点private E unlinkLast(Node<E> l) {// assert l == last && l != null;final E element = l.item;final Node<E> prev = l.prev;l.item = null;l.prev = null; // help GClast = prev;if (prev == null)first = null;elseprev.next = null;size--;modCount++;return element;}// 删除非空节点E unlink(Node<E> x) {// assert x != null;// 把要删除的元素 x 赋值给 element，用于返回。final E element = x.item;// 定义 next，赋值为ｘ的后一节点。final Node<E> next = x.next;// 定义 prev，赋值为 x 的前一节点。final Node<E> prev = x.prev;// 无前节点，则 x 的后一节点为首节点。if (prev == null) {first = next;} else {// 设置（ｘ的前一节点）prev 的后一节点为ｘ的后一节点： next。（跳过 x 节点）prev.next = next;// x 的前节点置空。x.prev = null;}//　不存在ｘ的后一节点，则最后节点为ｘ的前节点。if (next == null) {last = prev;} else {// 设置（ｘ的后一节点）next 的前一节点为ｘ的前一节点。（跳过 x 节点）next.prev = prev;// x 的后节点置空。x.next = null;}// x 本身的值置空。x.item = null;// 集合元数个数减1。size--;modCount++;return element;}// 查第一个节点。public E getFirst() {final Node<E> f = first;if (f == null)throw new NoSuchElementException();return f.item;}// 查最后一节点。public E getLast() {final Node<E> l = last;if (l == null)throw new NoSuchElementException();return l.item;}// 删除并返回第一个节点public E removeFirst() {final Node<E> f = first;if (f == null)throw new NoSuchElementException();return unlinkFirst(f);}// 删除并返回最后一个节点public E removeLast() {final Node<E> l = last;if (l == null)throw new NoSuchElementException();return unlinkLast(l);}// 新增第一个节点。public void addFirst(E e) {linkFirst(e);}// 新增最后一节点public void addLast(E e) {linkLast(e);}// 查是否存在指定节点public boolean contains(Object o) {return indexOf(o) != -1;}// 查集合中元素个数public int size() {return size;}// 新增最后一节点，并返回该节点。public boolean add(E e) {linkLast(e);return true;}// 删除第一个和指定节点匹配的节点，指定节点不存在则不变。public boolean remove(Object o) {if (o == null) {for (Node<E> x = first; x != null; x = x.next) {if (x.item == null) {unlink(x);return true;}}} else {for (Node<E> x = first; x != null; x = x.next) {if (o.equals(x.item)) {unlink(x);return true;}}}return false;}// 在原集合尾部追加指定的集合。public boolean addAll(Collection<? extends E> c) {return addAll(size, c);}// 在指定位置插入指定的集合。index：元素在集合中的位置public boolean addAll(int index, Collection<? extends E> c) {// 查 index 对应节点是否在元素中，不在则抛异常checkPositionIndex(index);Object[] a = c.toArray();int numNew = a.length;if (numNew == 0)return false;Node<E> pred, succ;if (index == size) {succ = null;pred = last;} else {// 不断2分查找，至找到 index 对应节点。succ = node(index);pred = succ.prev;}for (Object o : a) {@SuppressWarnings("unchecked") E e = (E) o;Node<E> newNode = new Node<>(pred, e, null);if (pred == null)first = newNode;elsepred.next = newNode;pred = newNode;}if (succ == null) {last = pred;} else {pred.next = succ;succ.prev = pred;}size += numNew;modCount++;return true;}// 删除全部节点。有节点被引用也会释放内存。public void clear() {for (Node<E> x = first; x != null; ) {Node<E> next = x.next;x.item = null;x.next = null;x.prev = null;x = next;}first = last = null;size = 0;modCount++;}// 查指定位置节点public E get(int index) {// 检查 index （ 即：>0，< size）checkElementIndex(index);return node(index).item;}// 替换指定位置节点。返回旧节点。public E set(int index, E element) {checkElementIndex(index);Node<E> x = node(index);E oldVal = x.item;x.item = element;return oldVal;}// 指定位置插入指定节点public void add(int index, E element) {checkPositionIndex(index);if (index == size)linkLast(element);elselinkBefore(element, node(index));}// 删除指定位置节点。public E remove(int index) {checkElementIndex(index);return unlink(node(index));}// 检查索引是否有效。private boolean isElementIndex(int index) {return index >= 0 && index < size;}// 检查索引是否有效。private boolean isPositionIndex(int index) {return index >= 0 && index <= size;}// 构造提示信息。private String outOfBoundsMsg(int index) {return "Index: "+index+", Size: "+size;}private void checkElementIndex(int index) {if (!isElementIndex(index))throw new IndexOutOfBoundsException(outOfBoundsMsg(index));}private void checkPositionIndex(int index) {if (!isPositionIndex(index))throw new IndexOutOfBoundsException(outOfBoundsMsg(index));}// 查指定非空节点。（不断2分查找）Node<E> node(int index) {// assert isElementIndex(index);if (index < (size >> 1)) {Node<E> x = first;for (int i = 0; i < index; i++)x = x.next;return x;} else {Node<E> x = last;for (int i = size - 1; i > index; i--)x = x.prev;return x;}}// 正向检查指定节点是否存在。不存在返回-1。public int indexOf(Object o) {int index = 0;if (o == null) {for (Node<E> x = first; x != null; x = x.next) {if (x.item == null)return index;index++;}} else {for (Node<E> x = first; x != null; x = x.next) {if (o.equals(x.item))return index;index++;}}return -1;}// 反向检查指定节点是否存在。不存在返回-1。public int lastIndexOf(Object o) {int index = size;if (o == null) {for (Node<E> x = last; x != null; x = x.prev) {index--;if (x.item == null)return index;}} else {for (Node<E> x = last; x != null; x = x.prev) {index--;if (o.equals(x.item))return index;}}return -1;}// 查首节点public E peek() {final Node<E> f = first;return (f == null) ? null : f.item;}// 查首节点，集合为空则抛异常。public E element() {return getFirst();}// 查并删除首节点。public E poll() {final Node<E> f = first;return (f == null) ? null : unlinkFirst(f);}// 查并删除首节点，集合为空则抛异常。public E remove() {return removeFirst();}// 追加尾节点。public boolean offer(E e) {return add(e);}// 新增首节点。public boolean offerFirst(E e) {addFirst(e);return true;}// 追加尾节点。public boolean offerLast(E e) {addLast(e);return true;}// 查首节点。public E peekFirst() {final Node<E> f = first;return (f == null) ? null : f.item;}// 查尾节点public E peekLast() {final Node<E> l = last;return (l == null) ? null : l.item;}// 查并删除首节点。public E pollFirst() {final Node<E> f = first;return (f == null) ? null : unlinkFirst(f);}// 查并删除尾节点。public E pollLast() {final Node<E> l = last;return (l == null) ? null : unlinkLast(l);}// 新增首节点public void push(E e) {addFirst(e);}// 删除并返回首节点。public E pop() {return removeFirst();}// 正向删除指定节点。节点不存在则集合不变，返回 false 。public boolean removeFirstOccurrence(Object o) {return remove(o);}// 反向删除指定节点。节点不存在则集合不变，返回 false 。public boolean removeLastOccurrence(Object o) {if (o == null) {for (Node<E> x = last; x != null; x = x.prev) {if (x.item == null) {unlink(x);return true;}}} else {for (Node<E> x = last; x != null; x = x.prev) {if (o.equals(x.item)) {unlink(x);return true;}}}return false;}// 返回迭代器public ListIterator<E> listIterator(int index) {checkPositionIndex(index);return new ListItr(index);}private class ListItr implements ListIterator<E> {private Node<E> lastReturned;private Node<E> next;private int nextIndex;private int expectedModCount = modCount;ListItr(int index) {// assert isPositionIndex(index);next = (index == size) ? null : node(index);nextIndex = index;}public boolean hasNext() {return nextIndex < size;}public E next() {checkForComodification();if (!hasNext())throw new NoSuchElementException();lastReturned = next;next = next.next;nextIndex++;return lastReturned.item;}public boolean hasPrevious() {return nextIndex > 0;}public E previous() {checkForComodification();if (!hasPrevious())throw new NoSuchElementException();lastReturned = next = (next == null) ? last : next.prev;nextIndex--;return lastReturned.item;}public int nextIndex() {return nextIndex;}public int previousIndex() {return nextIndex - 1;}public void remove() {checkForComodification();if (lastReturned == null)throw new IllegalStateException();Node<E> lastNext = lastReturned.next;unlink(lastReturned);if (next == lastReturned)next = lastNext;elsenextIndex--;lastReturned = null;expectedModCount++;}public void set(E e) {if (lastReturned == null)throw new IllegalStateException();checkForComodification();lastReturned.item = e;}public void add(E e) {checkForComodification();lastReturned = null;if (next == null)linkLast(e);elselinkBefore(e, next);nextIndex++;expectedModCount++;}public void forEachRemaining(Consumer<? super E> action) {Objects.requireNonNull(action);while (modCount == expectedModCount && nextIndex < size) {action.accept(next.item);lastReturned = next;next = next.next;nextIndex++;}checkForComodification();}final void checkForComodification() {if (modCount != expectedModCount)throw new ConcurrentModificationException();}}private static class Node<E> {E item;Node<E> next;Node<E> prev;Node(Node<E> prev, E element, Node<E> next) {this.item = element;this.next = next;this.prev = prev;}}/*** @since 1.6*/public Iterator<E> descendingIterator() {return new DescendingIterator();}// 返回降序迭代器。private class DescendingIterator implements Iterator<E> {private final ListItr itr = new ListItr(size());public boolean hasNext() {return itr.hasPrevious();}public E next() {return itr.previous();}public void remove() {itr.remove();}}@SuppressWarnings("unchecked")private LinkedList<E> superClone() {try {return (LinkedList<E>) super.clone();} catch (CloneNotSupportedException e) {throw new InternalError(e);}}// 浅clone 。public Object clone() {LinkedList<E> clone = superClone();// Put clone into "virgin" stateclone.first = clone.last = null;clone.size = 0;clone.modCount = 0;// Initialize clone with our elementsfor (Node<E> x = first; x != null; x = x.next)clone.add(x.item);return clone;}// 转为 Object 数组public Object[] toArray() {Object[] result = new Object[size];int i = 0;for (Node<E> x = first; x != null; x = x.next)result[i++] = x.item;return result;}// 拷贝原集合元素到指定数组。@SuppressWarnings("unchecked")public <T> T[] toArray(T[] a) {if (a.length < size)a = (T[])java.lang.reflect.Array.newInstance(a.getClass().getComponentType(), size);int i = 0;Object[] result = a;for (Node<E> x = first; x != null; x = x.next)result[i++] = x.item;if (a.length > size)a[size] = null;return a;}private static final long serialVersionUID = 876323262645176354L;// 写出到流，序列化。private void writeObject(java.io.ObjectOutputStream s)throws java.io.IOException {// Write out any hidden serialization magics.defaultWriteObject();// Write out sizes.writeInt(size);// Write out all elements in the proper order.for (Node<E> x = first; x != null; x = x.next)s.writeObject(x.item);}// 从流读入，反序列化。@SuppressWarnings("unchecked")private void readObject(java.io.ObjectInputStream s)throws java.io.IOException, ClassNotFoundException {// Read in any hidden serialization magics.defaultReadObject();// Read in sizeint size = s.readInt();// Read in all elements in the proper order.for (int i = 0; i < size; i++)linkLast((E)s.readObject());}// 创建拆分器@Overridepublic Spliterator<E> spliterator() {return new LLSpliterator<E>(this, -1, 0);}static final class LLSpliterator<E> implements Spliterator<E> {static final int BATCH_UNIT = 1 << 10;  // batch array size incrementstatic final int MAX_BATCH = 1 << 25;  // max batch array size;final LinkedList<E> list; // null OK unless traversedNode<E> current;      // current node; null until initializedint est;              // size estimate; -1 until first neededint expectedModCount; // initialized when est setint batch;            // batch size for splitsLLSpliterator(LinkedList<E> list, int est, int expectedModCount) {this.list = list;this.est = est;this.expectedModCount = expectedModCount;}final int getEst() {int s; // force initializationfinal LinkedList<E> lst;if ((s = est) < 0) {if ((lst = list) == null)s = est = 0;else {expectedModCount = lst.modCount;current = lst.first;s = est = lst.size;}}return s;}public long estimateSize() { return (long) getEst(); }public Spliterator<E> trySplit() {Node<E> p;int s = getEst();if (s > 1 && (p = current) != null) {int n = batch + BATCH_UNIT;if (n > s)n = s;if (n > MAX_BATCH)n = MAX_BATCH;Object[] a = new Object[n];int j = 0;do { a[j++] = p.item; } while ((p = p.next) != null && j < n);current = p;batch = j;est = s - j;return Spliterators.spliterator(a, 0, j, Spliterator.ORDERED);}return null;}public void forEachRemaining(Consumer<? super E> action) {Node<E> p; int n;if (action == null) throw new NullPointerException();if ((n = getEst()) > 0 && (p = current) != null) {current = null;est = 0;do {E e = p.item;p = p.next;action.accept(e);} while (p != null && --n > 0);}if (list.modCount != expectedModCount)throw new ConcurrentModificationException();}public boolean tryAdvance(Consumer<? super E> action) {Node<E> p;if (action == null) throw new NullPointerException();if (getEst() > 0 && (p = current) != null) {--est;E e = p.item;current = p.next;action.accept(e);if (list.modCount != expectedModCount)throw new ConcurrentModificationException();return true;}return false;}public int characteristics() {return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED;}}