LinkedList用法及源码解析

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转载请注明出处:http://blog.csdn.net/github_39430101/article/details/76861393

LinkedList简介

LinkedList是由双向链表实现的,对于随机访问get和set,ArrayList优于LinkedList,因为LinkedList要移动指针。对于新增和删除操作add和remove,LinedList比较占优势,因为ArrayList要移动数据。另外LinkedList实现了Deque接口,可以实现栈和队列的功能。

LinkedList结构

这里写图片描述

常见用法

package com.code.LinkedList;import java.util.LinkedList;public class TestLinkedList {    public static void main(String[] args) {        LinkedList<String> list = new LinkedList<String>();        /**         * 基本方法         */        list.add("关羽");        list.add("张飞");        list.add("刘备");        list.add("曹操");        //addFirst(E e)将指定元素添加到此列表的开头        list.addFirst("诸葛亮");        //addLast(E e)将指定元素添加到此列表的尾部        list.addLast("rank");        //contains()        if(list.contains("郭嘉")) {            System.out.println("若郭嘉在世");        }else System.out.println("岂有赤壁之败");        //get(int index)        System.out.println(list.get(4));        //getFirst()返回此列表中第一个元素        System.out.println("此列表的老大是:"+list.getFirst());        System.out.println("此列表中老末是:"+list.getLast());        System.out.println(list);//      peek()  peekFirst()  peekLast()获取但不移除//      poll()  pollFirst()  pollLast()获取且移除        //它们与remove的区别是遇到为空的链表会报异常        /**         * 实现栈和队列的功能         */        list.clear();        list.removeFirst();//会报异常 java.util.NoSuchElementException        //栈特点:先进后出,后进先出 push进栈 pop出栈        TestStack tl = new TestLinkedList().new TestStack();        for(int i=0;i<5;i++) {            tl.push(i);        }        System.out.println(tl.pop());        TestQueue tq = new TestLinkedList().new TestQueue();        for(int i=0;i<5;i++) {            tq.put(i);        }        System.out.println(tq.get());        //队列特点:先进先出,后进后出 put入列 get出列    }    class TestStack{        LinkedList<Object> list = new LinkedList<Object>();        public void push(Object o) {            list.addFirst(o);        }        public Object pop() {            return list.removeFirst();//removeFirst()和pollFirst()如果列表为空则removeFirst()报异常,而pollFirst()报null        }    }    class TestQueue{        LinkedList<Object> list = new LinkedList<Object>();        public void put(Object o) {            list.addFirst(o);        }        public Object get() {            return list.removeLast();        }    }}

源码

package java.util;import java.util.function.Consumer;//实现了Deque接口,可以实现栈和队列的功能 LinkedList是通过prev和next两个指针串联的public class LinkedList<E>    extends AbstractSequentialList<E>    implements List<E>, Deque<E>, Cloneable, java.io.Serializable{    //LinkedList中元素的个数    transient int size = 0;    //first指向链表的头结点    transient Node<E> first;    //last指向链表的尾节点    transient Node<E> last;    /**     * 空的构造函数     */    public LinkedList() {    }    //将c中元素添加到LinkedList中    public LinkedList(Collection<? extends E> c) {        this();        addAll(c);    }    /**     * 添加头结点     */    private void linkFirst(E e) {        final Node<E> f = first;//f向头节点        final Node<E> newNode = new Node<>(null, e, f); //新建一个节点        first = newNode;//first指向新的节点,f保存着之前first的节点        if (f == null)            last = newNode;//当节点为空时尾节点指向新的节点        else            f.prev = newNode;//赋给头节点        size++;        modCount++;    }    /**     * 添加尾节点     */    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;        else            l.next = newNode;        size++;        modCount++;    }    /**     * 在一个非空节点之前加入一个节点     */    void linkBefore(E e, Node<E> succ) {        // assert succ != null;        final Node<E> pred = succ.prev;         final Node<E> newNode = new Node<>(pred, e, succ);        succ.prev = newNode;        if (pred == null)            first = newNode;        else            pred.next = newNode;        size++;        modCount++;    }    /*     * 删除一个非空的头(first)节点,把指向该节点的指针都移除,同时把first指向它的next,如果next节点为空,说明这个节点是List中的最后一个节点,那么first和last都指向空     */    private E unlinkFirst(Node<E> f) {        // assert f == first && f != null;        final E element = f.item; //把节点中的值赋给element        final Node<E> next = f.next;         f.item = null;        f.next = null; // help GC        first = next; //把f元素的next值        if (next == null)            last = null;        else            next.prev = null;        size--;        modCount++;        return element;    }    /**     * 同理,删除一个非空的尾(last)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 GC        last = prev;        if (prev == null)            first = null;        else            prev.next = null;        size--;        modCount++;        return element;    }    /**     * Unlinks non-null node x.     */    E unlink(Node<E> x) {        // assert x != null;        final E element = x.item;        final Node<E> next = x.next;        final Node<E> prev = x.prev;        if (prev == null) {            first = next;        } else {            prev.next = next;            x.prev = null;        }        if (next == null) {            last = prev;        } else {            next.prev = prev;            x.next = null;        }        x.item = null;        size--;        modCount++;        return element;    }   //返回此列表的第一个元素    public E getFirst() {        final Node<E> f = first;        if (f == null)            throw new NoSuchElementException();        return f.item;    }   //返回此列表的最后一个元素    public E getLast() {        final Node<E> l = last;        if (l == null)            throw new NoSuchElementException();        return l.item;    }    //移除并且返回此列表的第一个元素    public E removeFirst() {        final Node<E> f = first;        if (f == null)            throw new NoSuchElementException();        return unlinkFirst(f);    }    /**     * Removes and returns the last element from this list.     *     * @return the last element from this list     * @throws NoSuchElementException if this list is empty     */    public E removeLast() {        final Node<E> l = last;        if (l == null)            throw new NoSuchElementException();        return unlinkLast(l);    }    /**     * Inserts the specified element at the beginning of this list.     *     * @param e the element to add     */    public void addFirst(E e) {        linkFirst(e);    }    /**     * Appends the specified element to the end of this list.     *     * <p>This method is equivalent to {@link #add}.     *     * @param e the element to add     */    public void addLast(E e) {        linkLast(e);    }    /**     * Returns {@code true} if this list contains the specified element.     * More formally, returns {@code true} if and only if this list contains     * at least one element {@code e} such that     * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>.     *     * @param o element whose presence in this list is to be tested     * @return {@code true} if this list contains the specified element     */    public boolean contains(Object o) {        return indexOf(o) != -1;    }    /**     * Returns the number of elements in this list.     *     * @return the number of elements in this list     */    public int size() {        return size;    }    /**     * Appends the specified element to the end of this list.     *     * <p>This method is equivalent to {@link #addLast}.     *     * @param e element to be appended to this list     * @return {@code true} (as specified by {@link Collection#add})     */    public boolean add(E e) {        linkLast(e);        return true;    }    /**     * Removes the first occurrence of the specified element from this list,     * if it is present.  If this list does not contain the element, it is     * unchanged.  More formally, removes the element with the lowest index     * {@code i} such that     * <tt>(o==null&nbsp;?&nbsp;get(i)==null&nbsp;:&nbsp;o.equals(get(i)))</tt>     * (if such an element exists).  Returns {@code true} if this list     * contained the specified element (or equivalently, if this list     * changed as a result of the call).     *     * @param o element to be removed from this list, if present     * @return {@code true} if this list contained the specified element     */    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;    }    /**     * Appends all of the elements in the specified collection to the end of     * this list, in the order that they are returned by the specified     * collection's iterator.  The behavior of this operation is undefined if     * the specified collection is modified while the operation is in     * progress.  (Note that this will occur if the specified collection is     * this list, and it's nonempty.)     *     * @param c collection containing elements to be added to this list     * @return {@code true} if this list changed as a result of the call     * @throws NullPointerException if the specified collection is null     */    public boolean addAll(Collection<? extends E> c) {        return addAll(size, c);    }    /**     * Inserts all of the elements in the specified collection into this     * list, starting at the specified position.  Shifts the element     * currently at that position (if any) and any subsequent elements to     * the right (increases their indices).  The new elements will appear     * in the list in the order that they are returned by the     * specified collection's iterator.     *     * @param index index at which to insert the first element     *              from the specified collection     * @param c collection containing elements to be added to this list     * @return {@code true} if this list changed as a result of the call     * @throws IndexOutOfBoundsException {@inheritDoc}     * @throws NullPointerException if the specified collection is null     */    public boolean addAll(int index, Collection<? extends E> c) {        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 {            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;            else                pred.next = newNode;            pred = newNode;        }        if (succ == null) {            last = pred;        } else {            pred.next = succ;            succ.prev = pred;        }        size += numNew;        modCount++;        return true;    }    /**     * Removes all of the elements from this list.     * The list will be empty after this call returns.     */    public void clear() {        // Clearing all of the links between nodes is "unnecessary", but:        // - helps a generational GC if the discarded nodes inhabit        //   more than one generation        // - is sure to free memory even if there is a reachable Iterator        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++;    }    // Positional Access Operations    /**     * Returns the element at the specified position in this list.     *     * @param index index of the element to return     * @return the element at the specified position in this list     * @throws IndexOutOfBoundsException {@inheritDoc}     */    public E get(int index) {        checkElementIndex(index);        return node(index).item;    }    /**     * Replaces the element at the specified position in this list with the     * specified element.     *     * @param index index of the element to replace     * @param element element to be stored at the specified position     * @return the element previously at the specified position     * @throws IndexOutOfBoundsException {@inheritDoc}     */    public E set(int index, E element) {        checkElementIndex(index);        Node<E> x = node(index);        E oldVal = x.item;        x.item = element;        return oldVal;    }    /**     * Inserts the specified element at the specified position in this list.     * Shifts the element currently at that position (if any) and any     * subsequent elements to the right (adds one to their indices).     *     * @param index index at which the specified element is to be inserted     * @param element element to be inserted     * @throws IndexOutOfBoundsException {@inheritDoc}     */    public void add(int index, E element) {        checkPositionIndex(index);        if (index == size)            linkLast(element);        else            linkBefore(element, node(index));    }    /**     * Removes the element at the specified position in this list.  Shifts any     * subsequent elements to the left (subtracts one from their indices).     * Returns the element that was removed from the list.     *     * @param index the index of the element to be removed     * @return the element previously at the specified position     * @throws IndexOutOfBoundsException {@inheritDoc}     */    public E remove(int index) {        checkElementIndex(index);        return unlink(node(index));    }    /**     * Tells if the argument is the index of an existing element.     */    private boolean isElementIndex(int index) {        return index >= 0 && index < size;    }    /**     * Tells if the argument is the index of a valid position for an     * iterator or an add operation.     */    private boolean isPositionIndex(int index) {        return index >= 0 && index <= size;    }    /**     * Constructs an IndexOutOfBoundsException detail message.     * Of the many possible refactorings of the error handling code,     * this "outlining" performs best with both server and client VMs.     */    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));    }    /**     * Returns the (non-null) Node at the specified element index.     */    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;        }    }    // Search Operations    /**     * Returns the index of the first occurrence of the specified element     * in this list, or -1 if this list does not contain the element.     * More formally, returns the lowest index {@code i} such that     * <tt>(o==null&nbsp;?&nbsp;get(i)==null&nbsp;:&nbsp;o.equals(get(i)))</tt>,     * or -1 if there is no such index.     *     * @param o element to search for     * @return the index of the first occurrence of the specified element in     *         this list, or -1 if this list does not contain the element     */    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;    }    //返回最后一次出现该对象的索引    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;    }    // Queue operations.    /**     * Retrieves, but does not remove, the head (first element) of this list.     *     * @return the head of this list, or {@code null} if this list is empty     * @since 1.5     */    public E peek() {        final Node<E> f = first;        return (f == null) ? null : f.item;    }    /**     * Retrieves, but does not remove, the head (first element) of this list.     *     * @return the head of this list     * @throws NoSuchElementException if this list is empty     * @since 1.5     */    public E element() {        return getFirst();    }    /**     * Retrieves and removes the head (first element) of this list.     *     * @return the head of this list, or {@code null} if this list is empty     * @since 1.5     */    public E poll() {        final Node<E> f = first;        return (f == null) ? null : unlinkFirst(f);    }    /**     * Retrieves and removes the head (first element) of this list.     *     * @return the head of this list     * @throws NoSuchElementException if this list is empty     * @since 1.5     */    public E remove() {        return removeFirst();    }    /**     * Adds the specified element as the tail (last element) of this list.     *     * @param e the element to add     * @return {@code true} (as specified by {@link Queue#offer})     * @since 1.5     */    public boolean offer(E e) {        return add(e);    }    // Deque operations    /**     * Inserts the specified element at the front of this list.     *     * @param e the element to insert     * @return {@code true} (as specified by {@link Deque#offerFirst})     * @since 1.6     */    public boolean offerFirst(E e) {        addFirst(e);        return true;    }    /**     * Inserts the specified element at the end of this list.     *     * @param e the element to insert     * @return {@code true} (as specified by {@link Deque#offerLast})     * @since 1.6     */    public boolean offerLast(E e) {        addLast(e);        return true;    }    /**     * Retrieves, but does not remove, the first element of this list,     * or returns {@code null} if this list is empty.     *     * @return the first element of this list, or {@code null}     *         if this list is empty     * @since 1.6     */    public E peekFirst() {        final Node<E> f = first;        return (f == null) ? null : f.item;     }    /**     * Retrieves, but does not remove, the last element of this list,     * or returns {@code null} if this list is empty.     *     * @return the last element of this list, or {@code null}     *         if this list is empty     * @since 1.6     */    public E peekLast() {        final Node<E> l = last;        return (l == null) ? null : l.item;    }    /**     * Retrieves and removes the first element of this list,     * or returns {@code null} if this list is empty.     *     * @return the first element of this list, or {@code null} if     *     this list is empty     * @since 1.6     */    public E pollFirst() {        final Node<E> f = first;        return (f == null) ? null : unlinkFirst(f);    }    /**     * Retrieves and removes the last element of this list,     * or returns {@code null} if this list is empty.     *     * @return the last element of this list, or {@code null} if     *     this list is empty     * @since 1.6     */    public E pollLast() {        final Node<E> l = last;        return (l == null) ? null : unlinkLast(l);    }    /**     * Pushes an element onto the stack represented by this list.  In other     * words, inserts the element at the front of this list.     *     * <p>This method is equivalent to {@link #addFirst}.     *     * @param e the element to push     * @since 1.6     */    public void push(E e) {        addFirst(e);    }    /**     * Pops an element from the stack represented by this list.  In other     * words, removes and returns the first element of this list.     *     * <p>This method is equivalent to {@link #removeFirst()}.     *     * @return the element at the front of this list (which is the top     *         of the stack represented by this list)     * @throws NoSuchElementException if this list is empty     * @since 1.6     */    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();        }    }    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();    }    /**     * Adapter to provide descending iterators via ListItr.previous     */    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;        }    }}
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