4 LinkedList

1 LinkedList

public class LinkedList<E> extends AbstractSequentialList<E> implements List<E>, Deque<E>, Cloneable, java.io.Serializable

实现原理，通过双向链表实现的。适合插入、删除操作。

2 节点

LinkedList使用双向链表实现，而双向链表通过节点来实现，我们来看看节点的定义。

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;
        }
}

3 元素操作

LinkedList默认大小为0，没有扩容机制，每增加一个元素，容量加1。

(1) add

    public boolean add(E e) {
        linkLast(e);
        return true;
    }

    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++;
    }

(2) remove

    public E remove(int index) {
        checkElementIndex(index);
        return unlink(node(index));
    }

    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;
    }

(3) get

    public E get(int index) {
        checkElementIndex(index);
        return node(index).item;
    }

    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;
        }
    }

4、其他方法

getFirst()

getLast()

addFirst()

addLast()

removeFirst()

removeLast()