Java之LinkedList源码解读（JDK 1.8）

java.util.LinkedList

•     双向链表实现的List。
•     基于JDK 1.8。
•     没有使用标准的注释，并适当调整了代码的缩进以方便介绍。
•     里面很多方法的实现是一样的，不过可以让外界感觉其提供了更多的行为。
•     需要花比ArrayList更多一点的时间理解

package com.anxpp.thinkinjava.chapter11.sourse;import java.util.AbstractSequentialList;import java.util.Collection;import java.util.ConcurrentModificationException;import java.util.Deque;import java.util.Iterator;import java.util.List;import java.util.ListIterator;import java.util.NoSuchElementException;import java.util.Objects;import java.util.Spliterator;import java.util.Spliterators;import java.util.function.Consumer;/** * LinkedList底层使用双向链表，实现了List和deque。实现所有的可选List操作，并可以只有所有元素（包括空值） * 其大小理论上仅受内存大小的限制 * * 所有的操作都可以作为一个双联列表来执行（及对双向链表操作）。 * 把对链表的操作封装起来，并对外提供看起来是对普通列表操作的方法。 * 遍历从起点、终点、或指定位置开始 * 内部方法，注释会描述为节点的操作(如删除第一个节点)，公开的方法会描述为元素的操作(如删除第一个元素) * * LinkedList不是线程安全的，如果在多线程中使用（修改），需要在外部作同步处理。 *  * 需要弄清元素（节点）的索引和位置的区别，不然有几个地方不好理解，具体在碰到的地方会解释。 *  * 迭代器可以快速报错 */public class LinkedList<E> extends AbstractSequentialList<E> implements List<E>, Deque<E>, Cloneable, java.io.Serializable{    //容量    transient int size = 0;    //首节点    transient Node<E> first;    //尾节点    transient Node<E> last;    //默认构造函数    public LinkedList() {    }    //通过一个集合初始化LinkedList，元素顺序有这个集合的迭代器返回顺序决定    public LinkedList(Collection<? extends E> c) {        this();        addAll(c);    }    //使用对应参数作为第一个节点，内部使用    private void linkFirst(E e) {        final Node<E> f = first;//得到首节点        final Node<E> newNode = new Node<>(null, e, f);//创建一个节点        first = newNode;        //设置首节点        if (f == null)            last = newNode;     //如果之前首节点为空(size==0)，那么尾节点就是首节点        else            f.prev = newNode;   //如果之前首节点不为空，之前的首节点的前一个节点为当前首节点        size++;                 //长度+1        modCount++;             //修改次数+1    }    //使用对应参数作为尾节点    void linkLast(E e) {        final Node<E> l = last; //得到尾节点        final Node<E> newNode = new Node<>(l, e, null);//使用参数创建一个节点        last = newNode;         //设置尾节点        if (l == null)            first = newNode;    //如果之前尾节点为空(size==0)，首节点即尾节点        else            l.next = newNode;   //如果之前尾节点不为空，之前的尾节点的后一个就是当前的尾节点        size++;        modCount++;    }    //在指定节点前插入节点，节点succ不能为空    void linkBefore(E e, Node<E> succ) {        final Node<E> pred = succ.prev;//获取前一个节点        final Node<E> newNode = new Node<>(pred, e, succ);//使用参数创建新的节点，向前指向前一个节点，向后指向当前节点        succ.prev = newNode;//当前节点指向新的节点        if (pred == null)            first = newNode;//如果前一个节点为null，新的节点就是首节点        else            pred.next = newNode;//如果存在前节点，那么前节点的向后指向新节点        size++;        modCount++;    }    //删除首节点并返回删除前首节点的值，内部使用    private E unlinkFirst(Node<E> f) {        final E element = f.item;//获取首节点的值        final Node<E> next = f.next;//得到下一个节点        f.item = null;        f.next = null;      //便于垃圾回收期清理        first = next;       //首节点的下一个节点成为新的首节点        if (next == null)            last = null;    //如果不存在下一个节点，则首尾都为null(空表)        else            next.prev = null;//如果存在下一个节点，那它向前指向null        size--;        modCount++;        return element;    }    //删除尾节点并返回删除前尾节点的值，内部使用    private E unlinkLast(Node<E> l) {        final E element = l.item;//获取值        final Node<E> prev = l.prev;//获取尾节点前一个节点        l.item = null;        l.prev = null;      //便于垃圾回收期清理        last = prev;        //前一个节点成为新的尾节点        if (prev == null)            first = null;   //如果前一个节点不存在，则首尾都为null(空表)        else            prev.next = null;//如果前一个节点存在，先后指向null        size--;        modCount++;        return element;    }    //删除指定节点并返回被删除的元素值    E unlink(Node<E> x) {        //获取当前值和前后节点        final E element = x.item;        final Node<E> next = x.next;        final Node<E> prev = x.prev;        if (prev == null) {            first = next;   //如果前一个节点为空(如当前节点为首节点)，后一个节点成为新的首节点        } else {            prev.next = next;//如果前一个节点不为空，那么他先后指向当前的下一个节点            x.prev = null;  //方便gc回收        }        if (next == null) {            last = prev;    //如果后一个节点为空(如当前节点为尾节点)，当前节点前一个成为新的尾节点        } else {            next.prev = prev;//如果后一个节点不为空，后一个节点向前指向当前的前一个节点            x.next = null;  //方便gc回收        }        x.item = null;      //方便gc回收        size--;        modCount++;        return element;    }    //获取第一个元素    public E getFirst() {        final Node<E> f = first;//得到首节点        if (f == null)          //如果为空，抛出异常            throw new NoSuchElementException();        return f.item;    }    //获取最后一个元素    public E getLast() {        final Node<E> l = last;//得到尾节点        if (l == null)          //如果为空，抛出异常            throw new NoSuchElementException();        return l.item;    }    //删除第一个元素并返回删除的元素    public E removeFirst() {        final Node<E> f = first;//得到第一个节点        if (f == null)          //如果为空，抛出异常            throw new NoSuchElementException();        return unlinkFirst(f);    }    //删除最后一个元素并返回删除的值    public E removeLast() {        final Node<E> l = last;//得到最后一个节点        if (l == null)          //如果为空，抛出异常            throw new NoSuchElementException();        return unlinkLast(l);    }    //添加元素作为第一个元素    public void addFirst(E e) {        linkFirst(e);    }    //店家元素作为最后一个元素    public void addLast(E e) {        linkLast(e);    }    //检查是否包含某个元素，返回bool    public boolean contains(Object o) {        return indexOf(o) != -1;//返回指定元素的索引位置，不存在就返回-1，然后比较返回bool值    }    //返回列表长度    public int size() {        return size;    }    //添加一个元素，默认添加到末尾作为最后一个元素    public boolean add(E e) {        linkLast(e);        return true;    }    //删除指定元素，默认从first节点开始，删除第一次出现的那个元素    public boolean remove(Object o) {        //会根据是否为null分开处理。若值不是null，会用到对象的equals()方法        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;    }    //添加指定集合的元素到列表，默认从最后开始添加    public boolean addAll(Collection<? extends E> c) {        return addAll(size, c);//size表示最后一个位置，可以理解为元素的位置分别为1~size    }    //从指定位置（而不是下标！下标即索引从0开始，位置可以看做从1开始，其实也是0）后面添加指定集合的元素到列表中，只要有至少一次添加就会返回true    //index换成position应该会更好理解，所以也就是从索引为index(position)的元素的前面索引为index-1的后面添加！    //当然位置可以为0啊，为0的时候就是从位置0(虽然它不存在)后面开始添加嘛，所以理所当前就是添加到第一个位置（位置1的前面）的前面了啊！    //比如列表：0 1 2 3，如果此处index=4(实际索引为3)，就是在元素3后面添加；如果index=3(实际索引为2)，就在元素2后面添加。    //原谅我的表达水平，我已经尽力解释了...    public boolean addAll(int index, Collection<? extends E> c) {        checkPositionIndex(index);  //检查索引是否正确（0<=index<=size）        Object[] a = c.toArray();   //得到元素数组        int numNew = a.length;      //得到元素个数        if (numNew == 0)            //若没有元素要添加，直接返回false            return false;        Node<E> pred, succ;        if (index == size) {    //如果是在末尾开始添加，当前节点后一个节点初始化为null，前一个节点为尾节点            succ = null;        //这里可以看做node(index)，不过index=size了（index最大只能是size-1），所以这里的succ只能=null，也方便后面判断            pred = last;        //这里看做noede(index-1)，当然实现是不能这么写的，看做这样只是为了好理解，所以就是在node(index-1的后面开始添加元素)        } else {                //如果不是从末尾开始添加，当前位置的节点为指定位置的节点，前一个节点为要添加的节点的前一个节点            succ = node(index); //添加好元素后(整个新加的)的后一个节点            pred = succ.prev;   //这里依然是node(index-1)        }        //遍历数组并添加到列表中        for (Object o : a) {            @SuppressWarnings("unchecked")            E e = (E) o;            Node<E> newNode = new Node<>(pred, e, null);//创建一个节点，向前指向上面得到的前节点            if (pred == null)                first = newNode;    //若果前节点为null，则新加的节点为首节点            else                pred.next = newNode;//如果存在前节点，前节点会向后指向新加的节点            pred = newNode;         //新加的节点成为前一个节点        }        if (succ == null) {            //pred.next = null  //加上这句也可以更好的理解            last = pred;        //如果是从最后开始添加的，则最后添加的节点成为尾节点        } else {            pred.next = succ;   //如果不是从最后开始添加的，则最后添加的节点向后指向之前得到的后续第一个节点            succ.prev = pred;   //当前，后续的第一个节点也应改为向前指向最后一个添加的节点        }        size += numNew;        modCount++;        return true;    }    //清空表    public void clear() {        //方便gc回收垃圾        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++;    }    //获取指定索引的节点的值    public E get(int index) {        checkElementIndex(index);        return node(index).item;    }    //修改指定索引的值并返回之前的值    public E set(int index, E element) {        checkElementIndex(index);        Node<E> x = node(index);        E oldVal = x.item;        x.item = element;        return oldVal;    }    //指定位置后面（即索引为这个值的元素的前面）添加元素    public void add(int index, E element) {        checkPositionIndex(index);        if (index == size)            linkLast(element);  //如果指定位置为最后，则添加到链表最后        else                    //如果指定位置不是最后，则添加到指定位置前            linkBefore(element, node(index));    }    //删除指定位置的元素，    public E remove(int index) {        checkElementIndex(index);        return unlink(node(index));    }    //检查索引是否超出范围，因为元素索引是0~size-1的，所以index必须满足0<=index<size    private boolean isElementIndex(int index) {        return index >= 0 && index < size;    }    //检查位置是否超出范围，index必须在index~size之间（含），如果超出，返回false    private boolean isPositionIndex(int index) {        return index >= 0 && index <= size;    }    //异常详情    private String outOfBoundsMsg(int index) {        return "Index: "+index+", Size: "+size;    }    //检查元素索引是否超出范围，若已超出，就抛出异常    private void checkElementIndex(int index) {        if (!isElementIndex(index))            throw new IndexOutOfBoundsException(outOfBoundsMsg(index));    }    //检查位置是否超出范围，若已超出，就抛出异常    private void checkPositionIndex(int index) {        if (!isPositionIndex(index))            throw new IndexOutOfBoundsException(outOfBoundsMsg(index));    }    //获取指定位置的节点    Node<E> node(int index) {        //如果位置索引小于列表长度的一半(或一半减一)，从前面开始遍历；否则，从后面开始遍历        if (index < (size >> 1)) {            Node<E> x = first;//index==0时不会循环，直接返回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;        }    }    //获取指定元素从first开始的索引位置，不存在就返回-1    //不能按条件双向找了，所以通常根据索引获得元素的速度比通过元素获得索引的速度快    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;    }    //获取指定元素从first开始最后出现的索引，不存在就返回-1    //但实际查找是从last开始的    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;    }    //提供普通队列和双向队列的功能，当然，也可以实现栈，FIFO，FILO    //出队（从前端），获得第一个元素，不存在会返回null，不会删除元素（节点）    public E peek() {        final Node<E> f = first;        return (f == null) ? null : f.item;    }    //出队（从前端），不删除元素，若为null会抛出异常而不是返回null    public E element() {        return getFirst();    }    //出队（从前端），如果不存在会返回null，存在的话会返回值并移除这个元素（节点）    public E poll() {        final Node<E> f = first;        return (f == null) ? null : unlinkFirst(f);    }    //出队（从前端），如果不存在会抛出异常而不是返回null，存在的话会返回值并移除这个元素（节点）    public E remove() {        return removeFirst();    }    //入队（从后端），始终返回true    public boolean offer(E e) {        return add(e);    }    //入队（从前端），始终返回true    public boolean offerFirst(E e) {        addFirst(e);        return true;    }    //入队（从后端），始终返回true    public boolean offerLast(E e) {        addLast(e);//linkLast(e)        return true;    }    //出队（从前端），获得第一个元素，不存在会返回null，不会删除元素（节点）    public E peekFirst() {        final Node<E> f = first;        return (f == null) ? null : f.item;     }    //出队（从后端），获得最后一个元素，不存在会返回null，不会删除元素（节点）    public E peekLast() {        final Node<E> l = last;        return (l == null) ? null : l.item;    }    //出队（从前端），获得第一个元素，不存在会返回null，会删除元素（节点）    public E pollFirst() {        final Node<E> f = first;        return (f == null) ? null : unlinkFirst(f);    }    //出队（从后端），获得最后一个元素，不存在会返回null，会删除元素（节点）    public E pollLast() {        final Node<E> l = last;        return (l == null) ? null : unlinkLast(l);    }    //入栈，从前面添加    public void push(E e) {        addFirst(e);    }    //出栈，返回栈顶元素，从前面移除（会删除）    public E pop() {        return removeFirst();    }    /**     * Removes the first occurrence of the specified element in this     * list (when traversing the list from head to tail).  If the list     * does not contain the element, it is unchanged.     *     * @param o element to be removed from this list, if present     * @return {@code true} if the list contained the specified element     * @since 1.6     */    public boolean removeFirstOccurrence(Object o) {        return remove(o);    }    /**     * Removes the last occurrence of the specified element in this     * list (when traversing the list from head to tail).  If the list     * does not contain the element, it is unchanged.     *     * @param o element to be removed from this list, if present     * @return {@code true} if the list contained the specified element     * @since 1.6     */    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;    }    /**     * Returns a list-iterator of the elements in this list (in proper     * sequence), starting at the specified position in the list.     * Obeys the general contract of {@code List.listIterator(int)}.<p>     *     * The list-iterator is <i>fail-fast</i>: if the list is structurally     * modified at any time after the Iterator is created, in any way except     * through the list-iterator's own {@code remove} or {@code add}     * methods, the list-iterator will throw a     * {@code ConcurrentModificationException}.  Thus, in the face of     * concurrent modification, the iterator fails quickly and cleanly, rather     * than risking arbitrary, non-deterministic behavior at an undetermined     * time in the future.     *     * @param index index of the first element to be returned from the     *              list-iterator (by a call to {@code next})     * @return a ListIterator of the elements in this list (in proper     *         sequence), starting at the specified position in the list     * @throws IndexOutOfBoundsException {@inheritDoc}     * @see List#listIterator(int)     */    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;            else                nextIndex--;            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);            else                linkBefore(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();        }    }    //节点的数据结构，包含前后节点的引用和当前节点    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;        }    }    //返回迭代器    public Iterator<E> descendingIterator() {        return new DescendingIterator();    }    //因为采用链表实现，所以迭代器很简单    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);        }    }    /**     * Returns a shallow copy of this {@code LinkedList}. (The elements     * themselves are not cloned.)     *     * @return a shallow copy of this {@code LinkedList} instance     */    public Object clone() {        LinkedList<E> clone = superClone();        // Put clone into "virgin" state        clone.first = clone.last = null;        clone.size = 0;        clone.modCount = 0;        // Initialize clone with our elements        for (Node<E> x = first; x != null; x = x.next)            clone.add(x.item);        return clone;    }    /**     * Returns an array containing all of the elements in this list     * in proper sequence (from first to last element).     *     * <p>The returned array will be "safe" in that no references to it are     * maintained by this list.  (In other words, this method must allocate     * a new array).  The caller is thus free to modify the returned array.     *     * <p>This method acts as bridge between array-based and collection-based     * APIs.     *     * @return an array containing all of the elements in this list     *         in proper sequence     */    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;    }    /**     * Returns an array containing all of the elements in this list in     * proper sequence (from first to last element); the runtime type of     * the returned array is that of the specified array.  If the list fits     * in the specified array, it is returned therein.  Otherwise, a new     * array is allocated with the runtime type of the specified array and     * the size of this list.     *     * <p>If the list fits in the specified array with room to spare (i.e.,     * the array has more elements than the list), the element in the array     * immediately following the end of the list is set to {@code null}.     * (This is useful in determining the length of the list <i>only</i> if     * the caller knows that the list does not contain any null elements.)     *     * <p>Like the {@link #toArray()} method, this method acts as bridge between     * array-based and collection-based APIs.  Further, this method allows     * precise control over the runtime type of the output array, and may,     * under certain circumstances, be used to save allocation costs.     *     * <p>Suppose {@code x} is a list known to contain only strings.     * The following code can be used to dump the list into a newly     * allocated array of {@code String}:     *     * <pre>     *     String[] y = x.toArray(new String[0]);</pre>     *     * Note that {@code toArray(new Object[0])} is identical in function to     * {@code toArray()}.     *     * @param a the array into which the elements of the list are to     *          be stored, if it is big enough; otherwise, a new array of the     *          same runtime type is allocated for this purpose.     * @return an array containing the elements of the list     * @throws ArrayStoreException if the runtime type of the specified array     *         is not a supertype of the runtime type of every element in     *         this list     * @throws NullPointerException if the specified array is null     */    @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;    /**     * Saves the state of this {@code LinkedList} instance to a stream     * (that is, serializes it).     *     * @serialData The size of the list (the number of elements it     *             contains) is emitted (int), followed by all of its     *             elements (each an Object) in the proper order.     */    private void writeObject(java.io.ObjectOutputStream s)        throws java.io.IOException {        // Write out any hidden serialization magic        s.defaultWriteObject();        // Write out size        s.writeInt(size);        // Write out all elements in the proper order.        for (Node<E> x = first; x != null; x = x.next)            s.writeObject(x.item);    }    /**     * Reconstitutes this {@code LinkedList} instance from a stream     * (that is, deserializes it).     */    @SuppressWarnings("unchecked")    private void readObject(java.io.ObjectInputStream s)        throws java.io.IOException, ClassNotFoundException {        // Read in any hidden serialization magic        s.defaultReadObject();        // Read in size        int size = s.readInt();        // Read in all elements in the proper order.        for (int i = 0; i < size; i++)            linkLast((E)s.readObject());    }    /**     * Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>     * and <em>fail-fast</em> {@link Spliterator} over the elements in this     * list.     *     * <p>The {@code Spliterator} reports {@link Spliterator#SIZED} and     * {@link Spliterator#ORDERED}.  Overriding implementations should document     * the reporting of additional characteristic values.     *     * @implNote     * The {@code Spliterator} additionally reports {@link Spliterator#SUBSIZED}     * and implements {@code trySplit} to permit limited parallelism..     *     * @return a {@code Spliterator} over the elements in this list     * @since 1.8     */    @Override    public Spliterator<E> spliterator() {        return new LLSpliterator<E>(this, -1, 0);    }    /** A customized variant of Spliterators.IteratorSpliterator */    static final class LLSpliterator<E> implements Spliterator<E> {        static final int BATCH_UNIT = 1 << 10;  // batch array size increment        static final int MAX_BATCH = 1 << 25;  // max batch array size;        final LinkedList<E> list; // null OK unless traversed        Node<E> current;      // current node; null until initialized        int est;              // size estimate; -1 until first needed        int expectedModCount; // initialized when est set        int batch;            // batch size for splits        LLSpliterator(LinkedList<E> list, int est, int expectedModCount) {            this.list = list;            this.est = est;            this.expectedModCount = expectedModCount;        }        final int getEst() {            int s; // force initialization            final 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;        }    }}