LinkedList原始碼分析(JDk6)

public class LinkedList<E>
extends AbstractSequentialList<E>
implements List<E>, Deque<E>, Cloneable, java.io.Serializable
{
    //連結串列的表頭，表頭不含有任何資料
    private transient Entry<E> header = new Entry<E>(null, null, null);
    //linkedList的元素個數
    private transient int size = 0;

    //建立一個空的Linkedlist
    public LinkedList() {
        header.next = header.previous = header;
    }

    //建立一個包含集合的LinkedList
    public LinkedList(Collection<? extends E> c) {
    this();
    addAll(c);
    }

   //返回連結串列的第一個元素，為空丟擲異常
    public E getFirst() {
    if (size==0)
        throw new NoSuchElementException();

    return header.next.element;
    }

   //返回連結串列的最後一個元素，為空丟擲異常
    public E getLast()  {
    if (size==0)
        throw new NoSuchElementException();

    return header.previous.element;
    }

    //刪除連結串列第一個元素，並且返回刪除元素
    public E removeFirst() {
    return remove(header.next);
    }

   //刪除連結串列的最後一個元素，並返回刪除元素
    public E removeLast() {
    return remove(header.previous);
    }

   //將元素新增的連結串列的起始位置
    public void addFirst(E e) {
    addBefore(e, header.next);
    }

   //將元素新增到連結串列的最後
    public void addLast(E e) {
    addBefore(e, header);
    }

   //是否包含某個元素
    public boolean contains(Object o) {
        return indexOf(o) != -1;
    }

   //返回LinkedList的大小
    public int size() {
    return size;
    }

   //將元素新增到LinkedList中，新增到雙向連結串列的末端
    public boolean add(E e) {
    addBefore(e, header);
        return true;
    }

    //從LinkedList中刪除某個元素，先判斷元素是否為null,都是從連結串列頭開始查詢，並刪除元素，返回true
    public boolean remove(Object o) {
        if (o==null) {
            for (Entry<E> e = header.next; e != header; e = e.next) {
                if (e.element==null) {
                    remove(e);
                    return true;
                }
            }
        } else {
            for (Entry<E> e = header.next; e != header; e = e.next) {
                if (o.equals(e.element)) {
                    remove(e);
                    return true;
                }
            }
        }
        return false;
    }

    //將集合新增到雙向連結串列的末端
    public boolean addAll(Collection<? extends E> c) {
        return addAll(size, c);
    }

    //從雙向連結串列的index開始，將集合新增的連結串列中（1.邊界判定 2.新增元素）
    public boolean addAll(int index, Collection<? extends E> c) {
        if (index < 0 || index > size)
            throw new IndexOutOfBoundsException("Index: "+index+
                                                ", Size: "+size);
        Object[] a = c.toArray();
        int numNew = a.length;
        if (numNew==0)
            return false;
        modCount++;
        //設定當前要插入節點的後一節點    
        Entry<E> successor = (index==size ? header : entry(index));
        //設定當前要插入節點的前一節點
        Entry<E> predecessor = successor.previous;
        //將集合新增到雙向連結串列中
        for (int i=0; i<numNew; i++) {
            Entry<E> e = new Entry<E>((E)a[i], successor, predecessor);
            predecessor.next = e;
            predecessor = e;
        }
        successor.previous = predecessor;

        size += numNew;
        return true;
    }

    //清除雙向連結串列，從連結串列頭開始。
    public void clear() {
        Entry<E> e = header.next;
        while (e != header) {
            Entry<E> next = e.next;
            e.next = e.previous = null;
            e.element = null;
            e = next;
        }
        header.next = header.previous = header;
        size = 0;
        modCount++;
    }

    //返回index位置對應的節點元素
    public E get(int index) {
        return entry(index).element;
    }

   //設定index位置的元素值為element,並返回原值
    public E set(int index, E element) {
        Entry<E> e = entry(index);
        E oldVal = e.element;
        e.element = element;
        return oldVal;
    }

    //在index前新增節點，並且節點的值為element
    public void add(int index, E element) {
        addBefore(element, (index==size ? header : entry(index)));
    }

   //刪除Index位置是元素，並返回
    public E remove(int index) {
        return remove(entry(index));
    }

   //獲取雙向連結串列中index位置的節點（1.邊界判定 2.二分查詢）
    private Entry<E> entry(int index) {
        if (index < 0 || index >= size)
            throw new IndexOutOfBoundsException("Index: "+index+
                                                ", Size: "+size);
        Entry<E> e = header;
        if (index < (size >> 1)) {
            for (int i = 0; i <= index; i++)
                e = e.next;
        } else {
            for (int i = size; i > index; i--)
                e = e.previous;
        }
        return e;
    }

    //從前往後查詢返回值物件o對應的位置索引
    public int indexOf(Object o) {
        int index = 0;
        if (o==null) {
            for (Entry e = header.next; e != header; e = e.next) {
                if (e.element==null)
                    return index;
                index++;
            }
        } else {
            for (Entry e = header.next; e != header; e = e.next) {
                if (o.equals(e.element))
                    return index;
                index++;
            }
        }
        return -1;
    }

    //從後往前查詢值物件o對應的位置索引
    public int lastIndexOf(Object o) {
        int index = size;
        if (o==null) {
            for (Entry e = header.previous; e != header; e = e.previous) {
                index--;
                if (e.element==null)
                    return index;
            }
        } else {
            for (Entry e = header.previous; e != header; e = e.previous) {
                index--;
                if (o.equals(e.element))
                    return index;
            }
        }
        return -1;
    }
    //返回第一個節點，如果LinkedList的大小為0，則返回Null   
    public E peek() {
        if (size==0)
            return null;
        return getFirst();
    }

   //返回第一個節點，如果LinkedList的大小為0，則丟擲異常
    public E element() {
        return getFirst();
    }

    //刪除並返回第一個節點，如果大小為0，則返回Null
    public E poll() {
        if (size==0)
            return null;
        return removeFirst();
    }
    //刪除並返回第一個節點，如果大小為0，丟擲異常
    public E remove() {
        return removeFirst();
    }

   //將e新增到雙向連結串列尾部
    public boolean offer(E e) {
        return add(e);
    }

  //將e新增到雙向連結串列頭部
    public boolean offerFirst(E e) {
        addFirst(e);
        return true;
    }
    //將E新增到雙向連結串列頭部
    public boolean offerLast(E e) {
        addLast(e);
        return true;
    }

  //返回第一個節點，大小為0，返回Null
    public E peekFirst() {
        if (size==0)
            return null;
        return getFirst();
    }
 //返回最後一個節點，大小為0，返回Null
    public E peekLast() {
        if (size==0)
            return null;
        return getLast();
    }
    //刪除並返回第一個節點，大小為0,返回Null
    public E pollFirst() {
        if (size==0)
            return null;
        return removeFirst();
    }

  //刪除並返回最後一個節點，大小為0，返回Null
    public E pollLast() {
        if (size==0)
            return null;
        return removeLast();
    }
    //將e新增到第一個節點
    public void push(E e) {
        addFirst(e);
    }

   //刪除並返回第一個節點
    public E pop() {
        return removeFirst();
    }

   //從linkedList頭往後查詢，刪除第一個值為o的元素的節點
    public boolean removeFirstOccurrence(Object o) {
        return remove(o);
    }
    public boolean removeLastOccurrence(Object o) {
        if (o==null) {
            for (Entry<E> e = header.previous; e != header; e = e.previous) {
                if (e.element==null) {
                    remove(e);
                    return true;
                }
            }
        } else {
            for (Entry<E> e = header.previous; e != header; e = e.previous) {
                if (o.equals(e.element)) {
                    remove(e);
                    return true;
                }
            }
        }
        return false;
    }

  //返回index到尾部的全部節點對應的ListIterator物件
    public ListIterator<E> listIterator(int index) {
        return new ListItr(index);
    }

    //list迭代器
    private class ListItr implements ListIterator<E> {
        private Entry<E> lastReturned = header; //上一次返回的節點
        private Entry<E> next;//下一個節點
        private int nextIndex;//下一個節點對應的索引值
        private int expectedModCount = modCount;//期望的改變計數

        //建構函式，從in
        ListItr(int index) {
            if (index < 0 || index > size)
            throw new IndexOutOfBoundsException("Index: "+index+
                                ", Size: "+size);
            if (index < (size >> 1)) {
                next = header.next;
                for (nextIndex=0; nextIndex<index; nextIndex++)
                next = next.next;
            } else {
                next = header;
                for (nextIndex=size; nextIndex>index; nextIndex--)
                    next = next.previous;
            }
        }
        //是否存在下一個元素
        public boolean hasNext() {
            return nextIndex != size;
        }
        //獲取下一個元素
        public E next() {
            checkForComodification();
            if (nextIndex == size)
            throw new NoSuchElementException();

            lastReturned = next;
            next = next.next;
            nextIndex++;
            return lastReturned.element;
        }
        //是否存在上一個元素
        public boolean hasPrevious() {
            return nextIndex != 0;
        }
        //獲取上一個元素
        public E previous() {
            if (nextIndex == 0)
            throw new NoSuchElementException();

            lastReturned = next = next.previous;
            nextIndex--;
            checkForComodification();
            return lastReturned.element;
        }
        //獲取下一位置索引
        public int nextIndex() {
            return nextIndex;
        }
        //獲取上一位置索引
        public int previousIndex() {
            return nextIndex-1;
        }
        //刪除雙向連結串列的當前節點
        public void remove() {
                checkForComodification();
                Entry<E> lastNext = lastReturned.next;
                try {
                    LinkedList.this.remove(lastReturned);
                } catch (NoSuchElementException e) {
                    throw new IllegalStateException();
                }
            if (next==lastReturned)
                    next = lastNext;
                else
            nextIndex--;
            lastReturned = header;
            expectedModCount++;
        }
        //設定當前節點為E
        public void set(E e) {
            if (lastReturned == header)
            throw new IllegalStateException();
            checkForComodification();
            lastReturned.element = e;
        }
        //將e新增到當前節點前面
        public void add(E e) {
            checkForComodification();
            lastReturned = header;
            addBefore(e, next);
            nextIndex++;
            expectedModCount++;
        }
         // 判斷 “modCount和expectedModCount是否相等”，依次來實現fail-fast機制。
        final void checkForComodification() {
            if (modCount != expectedModCount)
            throw new ConcurrentModificationException();
        }
    }
     // 雙向連結串列的節點所對應的資料結構。  
    // 包含3部分：上一節點，下一節點，當前節點值。
    private static class Entry<E> {
    E element;
    Entry<E> next;
    Entry<E> previous;

    Entry(E element, Entry<E> next, Entry<E> previous) {
        this.element = element;
        this.next = next;
        this.previous = previous;
    }
    }

    private Entry<E> addBefore(E e, Entry<E> entry) {
    Entry<E> newEntry = new Entry<E>(e, entry, entry.previous);
    newEntry.previous.next = newEntry;
    newEntry.next.previous = newEntry;
    size++;
    modCount++;
    return newEntry;
    }

    private E remove(Entry<E> e) {
        if (e == header)
            throw new NoSuchElementException();

        E result = e.element;
        e.previous.next = e.next;
        e.next.previous = e.previous;
        e.next = e.previous = null;
        e.element = null;
        size--;
        modCount++;
        return result;
    }

   // 反向迭代器
    public Iterator<E> descendingIterator() {
        return new DescendingIterator();
    }

   // 反向迭代器實現類。
    private class DescendingIterator implements Iterator {
        final ListItr itr = new ListItr(size());
        public boolean hasNext() {
            return itr.hasPrevious();
        }
        public E next() {
                return itr.previous();
            }
        public void remove() {
                itr.remove();
            }
    }

   //克隆函式，返回LinkedList的克隆物件
    public Object clone() {
        LinkedList<E> clone = null;
        try {
            clone = (LinkedList<E>) super.clone();
        } catch (CloneNotSupportedException e) {
            throw new InternalError();
        }

        // Put clone into "virgin" state
        clone.header = new Entry<E>(null, null, null);
        clone.header.next = clone.header.previous = clone.header;
        clone.size = 0;
        clone.modCount = 0;

        // Initialize clone with our elements
        for (Entry<E> e = header.next; e != header; e = e.next)
            clone.add(e.element);

        return clone;
    }

    // 返回LinkedList的Object[]陣列
    public Object[] toArray() {
        Object[] result = new Object[size];
        int i = 0;
        for (Entry<E> e = header.next; e != header; e = e.next)
            result[i++] = e.element;
        return result;
    }


    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 (Entry<E> e = header.next; e != header; e = e.next)
            result[i++] = e.element;

        if (a.length > size)
            a[size] = null;

        return a;
    }

    private static final long serialVersionUID = 876323262645176354L;


    private void writeObject(java.io.ObjectOutputStream s)
        throws java.io.IOException {

        s.defaultWriteObject();

        // Write out size
        s.writeInt(size);

        // Write out all elements in the proper order.
        for (Entry e = header.next; e != header; e = e.next)
            s.writeObject(e.element);
    }


    private void readObject(java.io.ObjectInputStream s)
        throws java.io.IOException, ClassNotFoundException {

        s.defaultReadObject();

        // Read in size
        int size = s.readInt();

        // Initialize header
        header = new Entry<E>(null, null, null);
        header.next = header.previous = header;

    // Read in all elements in the proper order.
        for (int i=0; i<size; i++)
            addBefore((E)s.readObject(), header);
    }
}
 

注意：對比過jdk6和jdk8的原始碼，對於linkedList的改變不是很多，重要的方法基本一致，屬性有改動，jdk6只是在Entryheader操作，而jdk8我認為為了便於操作和區分，引入node(first和last)這個node的本質和Entry是一樣的，都包括前一節點，後一節點，節點值。

LinkedList不存在容量不足的問題，同時它實現了serializable介面，當寫入到輸出流時，先寫入容量，在寫入每一個節點的值；當讀出輸出流先讀取容量，在讀取每一個元素

（3）LinkedList遍歷方式

1)通過迭代器（Iterator）遍歷

for(Iterator iter = list.iterator(); iter.hasNext();)
iter.next();  
 

2)通過快速隨機訪問這個其實我感覺就是for迴圈，那麼就不解釋增強for了

int size = list.size();
for (int i=0; i<size; i++) {
    list.get(i);        
}  

3）通過pollFirst/pollLast遍歷：

while(list.pollFirst() != null);   
while(list.pollLast() != null); 

4）通過removeFirst/removeLast遍歷：

try {
    while(list.removeFirst() != null)
        ;
} catch (NoSuchElementException e) {
}
try {
    while(list.removeLast() != null)
        ;
} catch (NoSuchElementException e) {
}  
 

通過removeFirst/removeLast效率最高，但是會刪除元素資料，如果只是單獨的讀取不刪除資料，可以使用for遍歷，通過隨機訪問太慢慢