ArrayList是實(shí)現(xiàn)了基于動(dòng)態(tài)數(shù)組的數(shù)據(jù)結(jié)構(gòu)，LinkedList基于鏈表的數(shù)據(jù)結(jié)構(gòu)。
LinkedList不支持高效的隨機(jī)元素訪問慧耍。
ArrayList的空間浪費(fèi)主要體現(xiàn)在在list列表的結(jié)尾預(yù)留一定的容量空間，而LinkedList的空間花費(fèi)則體現(xiàn)在它的每一個(gè)元素都需要消耗相當(dāng)?shù)目臻g，就存儲(chǔ)密度來說昌腰，ArrayList是優(yōu)于LinkedList的。

public class LinkedList<E> extends AbstractSequentialList<E> implements List<E>, Deque<E>, Cloneable, java.io.Serializable
{
   //實(shí)現(xiàn)Serilizable接口時(shí)膀跌，將不需要序列化的屬性前添加關(guān)鍵字transient遭商，序列化對(duì)象的時(shí)候，這個(gè)屬性就不會(huì)序列化到指定的目的地中捅伤。
    transient int size = 0;
    //指向首節(jié)點(diǎn)
    transient Node<E> first;
    //指向最后一個(gè)節(jié)點(diǎn)
    transient Node<E> last;
    //構(gòu)建一個(gè)空列表
    public LinkedList() {
    }
    //構(gòu)建一個(gè)包含集合c的列表
    public LinkedList(Collection<? extends E> c) {
        this();
        addAll(c);
    }
   //將節(jié)點(diǎn)值為e的節(jié)點(diǎn)作為首節(jié)點(diǎn)
    private void linkFirst(E e) {
        final Node<E> f = first;
        //構(gòu)建一個(gè)prev值為null,next為f,節(jié)點(diǎn)值為e的節(jié)點(diǎn)
        final Node<E> newNode = new Node<>(null, e, f);
        //將newNode作為首節(jié)點(diǎn)
        first = newNode;
        //如果newNode后面沒有節(jié)點(diǎn)就將newNode作為最后一個(gè)節(jié)點(diǎn)
        if (f == null)
            last = newNode;
        //否則就將newNode賦給其prev
        else
            f.prev = newNode;
        //列表長度加一
        size++;
        modCount++;
    }
    //將節(jié)點(diǎn)值為e的節(jié)點(diǎn)作為最后一個(gè)節(jié)點(diǎn)
    void linkLast(E e) {
        final Node<E> l = last;
      //構(gòu)建一個(gè)prev值為l,next為null,節(jié)點(diǎn)值為e的節(jié)點(diǎn)
        final Node<E> newNode = new Node<>(l, e, null);
        last = newNode;
        if (l == null)
            first = newNode;
        else
            l.next = newNode;
        size++;
        modCount++;
    }
    //在非空節(jié)點(diǎn)succ之前插入節(jié)點(diǎn)e
    void linkBefore(E e, Node<E> succ) {
        final Node<E> pred = succ.prev;
        //將succ前面的節(jié)點(diǎn)和succ作為其prev和next
        final Node<E> newNode = new Node<>(pred, e, succ);
        //然后將newNode作為succ的prev
        succ.prev = newNode; 
        //如果原來succ是首節(jié)點(diǎn)劫流，則將newNode設(shè)置為首節(jié)點(diǎn)
        if (pred == null)
            first = newNode;
        else
            pred.next = newNode;
        size++;
        modCount++;
    }
     //釋放非空的首節(jié)點(diǎn)f
    private E unlinkFirst(Node<E> f) {
        final E element = f.item;
        final Node<E> next = f.next;
        f.item = null;
        f.next = null; // help GC
        //將first節(jié)點(diǎn)后面的節(jié)點(diǎn)設(shè)為首節(jié)點(diǎn)
        first = next;
        if (next == null)
            last = null;
        else
            next.prev = null;
        size--;
        modCount++;
        return element;
    }
     //釋放非空的尾節(jié)點(diǎn)l
       private E unlinkLast(Node<E> l) {
        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;
    }
    //刪除非空節(jié)點(diǎn)x
    E unlink(Node<E> x) 
    {
        final E element = x.item;
        final Node<E> next = x.next;    //x后面的節(jié)點(diǎn)
        final Node<E> prev = x.prev;    //x前面的節(jié)點(diǎn)

        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;
    }
    //返回列表首節(jié)點(diǎn)元素值
    public E getFirst() {
        final Node<E> f = first;
        if (f == null)
            throw new NoSuchElementException();
        return f.item;
    }
    //返列表尾節(jié)點(diǎn)元素值
    public E getLast() {
        final Node<E> l = last;
        if (l == null)
            throw new NoSuchElementException();
        return l.item;
    }
    //移除首節(jié)點(diǎn)
    public E removeFirst() {
        final Node<E> f = first;
        if (f == null)
            throw new NoSuchElementException();
        return unlinkFirst(f);
    }
   //刪除尾節(jié)點(diǎn)
    public E removeLast() {
        final Node<E> l = last;
        if (l == null)
            throw new NoSuchElementException();
        return unlinkLast(l);
    }
  //在列表首部插入節(jié)點(diǎn)e
    public void addFirst(E e) {
        linkFirst(e);
    }
    //在列表尾部插入節(jié)點(diǎn)e
    public void addLast(E e) {
        linkLast(e);
    }
   //判斷列表中是否包含有元素o
    public boolean contains(Object o) {
        return indexOf(o) != -1;
    }
    //返回列表長度大小
    public int size() {
        return size;
    }
    //在列表尾部插入元素
    public boolean add(E e) {
        linkLast(e);
        return true;
    }
    //刪除元素為o的節(jié)點(diǎn)
    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;
    }
   //將集合c中所有元素添加到列表的尾部
    public boolean addAll(Collection<? extends E> c) {
        return addAll(size, c);
    }
   //從指定的位置index開始，將集合c中的元素插入到列表中
    public boolean addAll(int index, Collection<? extends E> c) {
        //首先判斷插入位置的合法性
        checkPositionIndex(index);
        Object[] a = c.toArray();
        int numNew = a.length;
        if (numNew == 0)
            return false;
        Node<E> pred, succ;
        if (index == size) {//說明在列表尾部插入集合元素
            succ = null;
            pred = last;
        } 
        else {  //否則丛忆，找到index所在的節(jié)點(diǎn)
            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;
    }
    //刪除列表中所有節(jié)點(diǎn)
    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++;
    }
    //獲取指定索引位置節(jié)點(diǎn)的元素值
    public E get(int index) {
        checkElementIndex(index);
        return node(index).item;
    }
    //替換指定索引位置節(jié)點(diǎn)的元素值
    public E set(int index, E element) {
        checkElementIndex(index);
        Node<E> x = node(index);
        E oldVal = x.item;
        x.item = element;
        return oldVal;
    }
    //在指定索引位置之前插入元素e
    public void add(int index, E element) {
        checkPositionIndex(index);   
        if (index == size)
            linkLast(element);
        else
            linkBefore(element, node(index));
    }
    //刪除指定位置的元素
    public E remove(int index) {
        checkElementIndex(index);
        return unlink(node(index));
    }
    //判斷指定索引位置的元素是否存在
    private boolean isElementIndex(int index) {
        return index >= 0 && index < size;
    }
    private boolean isPositionIndex(int index) {
        return index >= 0 && index <= size;
    }
    //構(gòu)建 IndexOutOfBoundsException詳細(xì)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));
    }
    //返回指定索引位置的節(jié)點(diǎn)
    Node<E> node(int index) {
        //此處是一個(gè)小技巧祠汇，當(dāng)index<size/2時(shí)，從列表前半部分開始熄诡，否則從后半部分開始
        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;
        }
    }//返回列表中第一次出現(xiàn)o的位置座哩，若不存在則返回-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;
    }
    //逆向搜索，返回第一出現(xiàn)o的位置粮彤，不存在則返回-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;
    }
   //獲取列表首節(jié)點(diǎn)元素值
    public E peek() {
        final Node<E> f = first;
        return (f == null) ? null : f.item;
    }

    //獲取列表首節(jié)點(diǎn)元素值根穷，若為空則拋異常
    public E element() {
        return getFirst();
    }
   //檢索首節(jié)點(diǎn)，若空則返回null,不為空則返回其元素值并刪除首節(jié)點(diǎn)
    public E poll() {
        final Node<E> f = first;
        return (f == null) ? null : unlinkFirst(f);
    }
    //檢索首節(jié)點(diǎn)导坟，若空則拋異常,不為空則返回其元素值并刪除首節(jié)點(diǎn)
    public E remove() {
        return removeFirst();
    }
   //在列表尾部增加節(jié)點(diǎn)e
    public boolean offer(E e) {
        return add(e);
    }
   //在列表首部插入節(jié)點(diǎn)e
    public boolean offerFirst(E e) {
        addFirst(e);
        return true;
    }
  //在列表尾部插入節(jié)點(diǎn)e
    public boolean offerLast(E e) {
        addLast(e);
        return true;
    }
    public E peekFirst() {
        final Node<E> f = first;
        return (f == null) ? null : f.item;
     }
  //獲取列表尾節(jié)點(diǎn)元素值
    public E peekLast() {
        final Node<E> l = last;
        return (l == null) ? null : l.item;
    }
    public E pollFirst() {
        final Node<E> f = first;
        return (f == null) ? null : unlinkFirst(f);
    }
    public E pollLast() {
        final Node<E> l = last;
        return (l == null) ? null : unlinkLast(l);
    }
   //入棧
    public void push(E e)
    {
        addFirst(e);
    }
    //出棧
    public E pop() {
        return removeFirst();
    }
    //刪除列表中第一出現(xiàn)o的節(jié)點(diǎn)
    public boolean removeFirstOccurrence(Object o) {
        return remove(o);
    }
    //逆向搜索屿良，刪除第一次出現(xiàn)o的節(jié)點(diǎn)
    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;
    }