【Java8源码分析】集合框架-LinkedList

一、总结

（1）LinkedList有两个构造参数，一个为无參构造，只是新建一个空对象，第二个为有参构造，新建一个空对象，然后把所有元素添加进去。

（2）LinkedList的存储单元为一个名为Node的内部类，包含pre指针，next指针，和item元素，实现为双向链表

（3）LinkedList的删除、添加操作时间复杂度为O(1)，查找时间复杂度为O(n)，查找函数有一定优化，容器会先判断查找的元素是离头部较近，还是尾部较近，来决定从头部开始遍历还是尾部开始遍历

（4）LinkedList实现了Deque接口，因此也可以作为栈、队列和双端队列来使用。

二、源码分析

package java.util;import java.util.function.Consumer;public class LinkedList<E>    extends AbstractSequentialList<E>    implements List<E>, Deque<E>, Cloneable, java.io.Serializable{    transient int size = 0;    // 记录了链表的第一个元素和第二个元素，为双向链表    transient Node<E> first;    transient Node<E> last;    public LinkedList() {    }    // 该构造函数，先创建一个空的LinkedList，然后把所有元素加进去    public LinkedList(Collection<? extends E> c) {        this();        addAll(c);    }    // 把一个元素添加都第一个位置    // 注意：以下link、unlink开头的函数都为私有函数    private void linkFirst(E e) {        final Node<E> f = first;        final Node<E> newNode = new Node<>(null, e, f);        first = newNode;        if (f == null)            last = newNode;        else            f.prev = newNode;        size++;        modCount++;    }    // 把一个元素添加到最后一个位置    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++;    }    // 在某个元素前添加元素    void linkBefore(E e, Node<E> succ) {        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++;    }    // 删除第一个元素，注意传入的需为第一个元素，不然链表会出现违背本意情况    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        first = next;        if (next == null)            last = null;        else            next.prev = null;        size--;        modCount++;        return element;    }    // 删除某个元素    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;    }    // 删除某个元素    E unlink(Node<E> x) {        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;    }    // 获取第一个元素    public E getFirst() {        final Node<E> f = first;        if (f == null)            throw new NoSuchElementException();        return f.item;    }    // 获取最后一个元素    public E getLast() {        final Node<E> l = last;        if (l == null)            throw new NoSuchElementException();        return l.item;    }    public E removeFirst() {        final Node<E> f = first;        if (f == null)            throw new NoSuchElementException();        return unlinkFirst(f);    }    public E removeLast() {        final Node<E> l = last;        if (l == null)            throw new NoSuchElementException();        return unlinkLast(l);    }    public void addFirst(E e) {        linkFirst(e);    }    public void addLast(E e) {        linkLast(e);    }    public boolean contains(Object o) {        return indexOf(o) != -1;    }    public int size() {        return size;    }    public boolean add(E e) {        linkLast(e);        return true;    }    // 只删除第一个出现的元素    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;    }    public boolean addAll(Collection<? extends E> c) {        return addAll(size, c);    }    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;    }    public void clear() {        // 确保GC能回收        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++;    }    // 以下为位置相关操作    public E get(int index) {        checkElementIndex(index);        return node(index).item;    }    public E set(int index, E element) {        checkElementIndex(index);        Node<E> x = node(index);        E oldVal = x.item;        x.item = element;        return oldVal;    }    public void add(int index, E element) {        checkPositionIndex(index);        if (index == size)            linkLast(element);        else            linkBefore(element, node(index));    }    public E remove(int index) {        checkElementIndex(index);        return unlink(node(index));    }    // 判断现有的链表范围，即 <= 0 < n    private boolean isElementIndex(int index) {        return index >= 0 && index < size;    }    // 判断是否为正确位置，如对于迭代器，或者添加操作，即 <= 0 <＝ n    private boolean isPositionIndex(int index) {        return index >= 0 && index <= size;    }    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));    }    // 该方法会判断元素离头部比较近，还是尾巴比较近，然后开始遍历    Node<E> node(int 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;        }    }    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;    }    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;    }    // 以下为队列操作    public E peek() {        final Node<E> f = first;        return (f == null) ? null : f.item;    }    public E element() {        return getFirst();    }    public E poll() {        final Node<E> f = first;        return (f == null) ? null : unlinkFirst(f);    }    public E remove() {        return removeFirst();    }    public boolean offer(E e) {        return add(e);    }    // 以下为双向队列操作    public boolean offerFirst(E e) {        addFirst(e);        return true;    }    public boolean offerLast(E e) {        addLast(e);        return true;    }    public E peekFirst() {        final Node<E> f = first;        return (f == null) ? null : f.item;     }    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);    }    public void push(E e) {        addFirst(e);    }    public E pop() {        return removeFirst();    }    public boolean removeFirstOccurrence(Object o) {        return remove(o);    }    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;    }    // 浅拷贝    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;    }    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;    }    @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;    // java.io.Serializable的写入函数        // 将LinkedList的“容量，所有的元素值”都写入到输出流中     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);    }    // java.io.Serializable的读取函数：根据写入方式反向读出        // 先将LinkedList的“容量”读出，然后将“所有的元素值”读出     @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());    }}

三、参考

http://blog.csdn.net/ns_code/article/details/35787253