java8集合--LinkedList纯源码

package Queue;

import java.util.*;
import java.util.function.Consumer;

/**
 * 双端队列主要实现list接口和Deque接口，实现了所有list操作，元素允许为null
 * 该实现是不同步的,not synchronized.
 * 可以使用 Collections.synchronizedList封装防止不同不的情况出现
 * 即：List list = Collections.synchronizedList(new LinkedList(...))
 * 该类中的迭代器使用快速失败模式：fail-fast，如果list在迭代器被创建之后的任意时间内被其他方法修改了结构，
 * （除了迭代器自己的remove()或add()方法），都是立刻报错
 */

public class LinkedList<E>
    extends AbstractSequentialList<E>
    implements List<E>, Deque<E>, Cloneable, java.io.Serializable
{
    //定义了三个成员变量，链表元素个数的size，指向第一个元素的first，指向最后一个元素的last
    //队列中元素的个数
    transient int size = 0;

    //永远指向链表中的第一个节点
    transient Node<E> first;

    //永远指向链表中的最后一个节点
    transient Node<E> last;

    //构造方法有两个，一个是构造一个空的链表，一个是根据已有的集合构造新的链表
    //初始化空队列
    public LinkedList() {
    }

    //根据已有的集合对象构造一个队列
    public LinkedList(Collection<? extends E> c) {
        this();//调用空的初始化队列
        addAll(c);//向空队列中添加所有初始化的元素
    }

    //内部类，定义链表上的一个节点对象
    //每个节点有三部分组成，中间的是节点自身的值，和指向链表前一个节点的指针prev,以及指向链表后一个节点的指针next
    private static class Node<E> {
        E item;
        Node<E> next;
        Node<E> prev;
        //初始化一个节点对象时，接收三个参数。指向前一个节点的指针，自己本身，和指向后一个节点的指针
        Node(Node<E> prev, E element, Node<E> next) {
            this.item = element;
            this.next = next;
            this.prev = prev;
        }
    }

    //移除指定元素，遍历链表，碰到第一个相等的就移除这个元素
    public boolean remove(Object o) {
        //要移除元素为null的情况
        if (o == null) {
            //遍历链表
            for (Node<E> x = first; x != null; x = x.next) {
                if (x.item == null) {
                    unlink(x);//移除某个元素的具体实现
                    return true;
                }
            }
            //要移除元素不为null的情况
        } else {
            for (Node<E> x = first; x != null; x = x.next) {
                if (o.equals(x.item)) {
                    unlink(x);
                    return true;
                }
            }
        }
        return false;
    }

    //移除一个节点的具体实现方法
    E unlink(Node<E> x) {
        // assert x != null;
        //拿到本节点上的三个元素
        final E element = x.item;
        final Node<E> next = x.next;
        final Node<E> prev = x.prev;
        //处理前一个节点对下一个节点的指向
        if (prev == null) {
            first = next;
        } else {
            prev.next = next;
            x.prev = null;
        }
        //处理后一个节点对前一个节点的指向
        if (next == null) {
            last = prev;
        } else {
            next.prev = prev;
            x.next = null;
        }

        x.item = null;
        size--;
        modCount++;
        return element;
    }

    //向链表头部第一个位置添加一个元素
    private void linkFirst(E e) {
        //保存first的引用
        final Node<E> f = first;
        //根据传进来的元素e，构建一个新的节点，因为节点是放在头部第一个位置，所有prev=null
        //构建一个新的节点时，就直接指定了前一个，自己，后一个。
        final Node<E> newNode = new Node<>(null, e, f);
        //把first指向新加入的一个元素
        first = newNode;
        //处理原先第一个节点（现在已经时第二个了）对新节点的引用
        if (f == null)
            last = newNode;
        else
            f.prev = newNode;
        size++;
        modCount++;
    }

    //向链表尾部最后一个位置添加一个元素
    void linkLast(E e) {
        final Node<E> l = last;
        //构建一个新的节点
        final Node<E> newNode = new Node<>(l, e, null);
        last = newNode;
        if (l == null)
            first = newNode;
        else
            l.next = newNode;
        size++;
        modCount++;
    }

    //在某个节点之前添加一个元素
    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++;
    }

    //移除链表的第一个元素
    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 GC
        first = next;
        if (next == null)
            last = null;
        else
            next.prev = null;
        size--;
        modCount++;
        return element;
    }

    //移除链表的最后一个元素
    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;
    }

    //仅仅查看链表中第一个节点的值，链表为null时，抛出异常
    public E getFirst() {
        final Node<E> f = first;
        if (f == null)
            throw new NoSuchElementException();
        return f.item;
    }

    ////返回链表中最后一个节点的值，链表为null时，抛出异常
    public E getLast() {
        final Node<E> l = last;
        if (l == null)
            throw new NoSuchElementException();
        return l.item;
    }

    //从链表中删除并返回头部的第一个元素，如果链表为null，则抛出异常
    public E removeFirst() {
        final Node<E> f = first;
        if (f == null)
            throw new NoSuchElementException();
        return unlinkFirst(f);
    }

    //从链表中删除并返回头部的第一个元素，如果链表为null，则抛出异常
    public E removeLast() {
        final Node<E> l = last;
        if (l == null)
            throw new NoSuchElementException();
        return unlinkLast(l);
    }

    //在链表头部第一个位置上插入元素，没有返回值
    public void addFirst(E e) {
        linkFirst(e);
    }

    //在链表尾部最后一个位置上插入元素，没有返回值
    public void addLast(E e) {
        linkLast(e);
    }

    //检查链表是否包含某个值，返回布尔值
    public boolean contains(Object o) {
        return indexOf(o) != -1;
    }

    //返回链表元素的个数
    public int size() {
        return size;
    }

    //在链表尾部最后一个位置上插入元素，返回布尔值
    public boolean add(E e) {
        linkLast(e);
        return true;
    }

    //向链表中追加指定集合中的所有元素
    public boolean addAll(Collection<? extends E> c) {
        return addAll(size, c);
    }

    //在指定位置开始追加指定集合内的所有元素
    public boolean addAll(int index, Collection<? extends E> c) {
        //先检查指定位置的是否合法
        checkPositionIndex(index);
        //把集合内的元素换成数组结构
        Object[] a = c.toArray();
        //检查数组的大小是否合法
        int numNew = a.length;
        if (numNew == 0)
            return false;
        //定义两个节点变量
        Node<E> pred, succ;
        //如果是从链表的最后开始添加
        if (index == size) {
            succ = null;
            pred = last;
        //如果是从链表的中间开始添加
        } else {
            //要是index开始添加，所有，index对应的节点需要后移
            succ = node(index);//拿到处于index位置的节点
            pred = succ.prev;//拿到index前一个节点
        }
        //遍历数组的元素
        for (Object o : a) {
            @SuppressWarnings("unchecked") E e = (E) o;
            //根据数组的元素拿到构建新的节点，并指定前一个节点，因为后一个节点还不知道
            Node<E> newNode = new Node<>(pred, e, null);
            if (pred == null)
                first = newNode;
            else
                //更新新加节点的下一个节点的指向
                pred.next = newNode;
            //更改前一个节点，方便下一个循环的添加
            pred = newNode;
        }

        //添加完数组内的元素，把其和原来的部分进行拼接
        if (succ == null) {
            last = pred;
        } else {
            pred.next = succ;
            succ.prev = pred;
        }

        size += numNew;
        modCount++;
        return true;
    }

    //移除链表的所有元素
    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
        //遍历，使所有的引用都指向null
        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

    //返回指定索引号上的元素值
    public E get(int index) {
        checkElementIndex(index);
        return node(index).item;
    }

    //对索引号上对应的节点的值进行修改
    public E set(int index, E element) {
        checkElementIndex(index);
        Node<E> x = node(index);
        E oldVal = x.item;
        x.item = element;
        return oldVal;
    }

    //在指定位置添加一个节点
    public void add(int index, E element) {
        checkPositionIndex(index);

        if (index == size)
            linkLast(element);
        else
            linkBefore(element, node(index));
    }

    //删除并返回指定位置上的元素
    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));
    }

    //按索引号返回节点
    Node<E> node(int index) {
        // assert isElementIndex(index);
        //如果索引值小于总数量的1/2，从头部开始遍历
        if (index < (size >> 1)) {
            Node<E> x = first;
            for (int i = 0; i < index; i++)
                x = x.next;
            return x;
        //如果索引值大于或等于总数量的1/2，从尾部开始遍历
        } else {
            Node<E> x = last;
            for (int i = size - 1; i > index; i--)
                x = x.prev;
            return x;
        }
    }

    // Search Operations

    //返回指定元素在链表中第一次出现的索引号，若无则返回-1
    public int indexOf(Object o) {
        int index = 0;
        //处理o为null和不为null的情况
        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;
    }

    //返回指定元素在链表中最后一次出现的索引号，若无则返回-1
    public int lastIndexOf(Object o) {
        int index = size;
        if (o == null) {
            //遍历查找的时候只需要倒序就可以，问题不大
            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.

    //仅仅查看队列的第一个元素
    public E peek() {
        final Node<E> f = first;
        return (f == null) ? null : f.item;
    }

    //仅仅查看链表中第一个节点的值，链表为null时，抛出异常
    public E element() {
        return getFirst();
    }

    //移除并返回链表头部的第一个元素
    public E poll() {
        final Node<E> f = first;
        return (f == null) ? null : unlinkFirst(f);
    }

    //从链表中删除并返回头部的第一个元素，如果链表为null，则抛出异常
    public E remove() {
        return removeFirst();
    }

    //在链表尾部最后一个位置上插入元素，返回布尔值
    public boolean offer(E e) {
        return add(e);
    }

    // Deque operations
    //在链表头部第一个位置上插入元素，返回布尔值
    public boolean offerFirst(E e) {
        addFirst(e);
        return true;
    }

    //在链表尾部最后一个位置上插入元素，返回布尔值
    public boolean offerLast(E e) {
        addLast(e);
        return true;
    }

    //仅仅查看链表中第一个节点的值。不删除
    public E peekFirst() {
        final Node<E> f = first;
        return (f == null) ? null : f.item;
     }

    //仅仅查看链表中最后一个节点的值。不删除
    public E peekLast() {
        final Node<E> l = last;
        return (l == null) ? null : l.item;
    }

    //移除链表的第一个元素
    public E pollFirst() {
        final Node<E> f = first;
        return (f == null) ? null : unlinkFirst(f);
    }

    //移除链表的最后一个元素
    public E pollLast() {
        final Node<E> l = last;
        return (l == null) ? null : unlinkLast(l);
    }

    //栈操作，压入元素
    public void push(E e) {
        addFirst(e);
    }

    //栈操作，弹出元素
    public E pop() {
        return removeFirst();
    }

    //移除指定元素，遍历链表，碰到第一个相等的就移除这个元素
    public boolean removeFirstOccurrence(Object o) {
        return remove(o);
    }

    //移除链表中最后一个跟指定元素相同的元素
    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;
    }

    //返回一个从index开始到最后的ListIterator迭代器
    public ListIterator<E> listIterator(int index) {
        checkPositionIndex(index);
        return new ListItr(index);
    }

    //内部类，迭代器的实现
    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();
        }
    }

    public Iterator<E> descendingIterator() {
        return new DescendingIterator();
    }

    //内部类，反序的迭代器
    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);
        }
    }

    //返回一个浅克隆对象
    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;
    }

    //返回一个包含此列表中所有元素的数组
    //返回的数组是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;
    }

    //以正确的顺序返回一个包含此列表中所有元素的数组（从第一个到最后一个元素）;
    // 返回的数组的运行时类型是指定数组的运行时类型
    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());
    }

    //并行迭代器
    @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;
        }
    }

}