JDK1.8 LinkedList 源码解析

package com.tanoak.jdk.linkedlist;

import java.io.Serializable;
import java.util.NoSuchElementException;

/**
 * @author tanoak@qq.com
 * @date 2018/8/23 0:29
 * @Desc
 */
public class TkSingleLinkedList<E>  implements Serializable {
    /**
     * transient 反序列化
     *
     */
     
    /**
     * 修改次数
     */
    
    protected transient int modCount = 0;
    /**
     * 集合大小
     */
    transient int size = 0;
    
    /**
     * Pointer to first node.
     * 首节点
     */
    transient Node<E> first;
    
    /**
     * 尾节点
     */
    transient Node<E> last;
    
    /**
    * 私有静态内部类
    *
    */
    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;
        }
    }
    /**
     * Constructs an empty list.
     */
    public TkSingleLinkedList() {
    }
    
    /**
     * 将一个元素添加至list尾部
     * @param e 泛型
     * @return
     */
    public boolean add(E e) {
        linkLast(e);
        return true;
    }
 
    /**
     * Links e as last element.
     * @param e  泛型
     */
    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;
        }
        /*
        *计数
        */
        size++;
        modCount++;
    }
    
    /**
     * Returns the (non-null) Node at the specified element index.
     */
    private 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;
        }
    }
    
    /**
     * 根据下标获值
     *  @param index
     * @return
     */
    public E get(int index) {
        checkElementIndex(index);
        return node(index).item;
    }
    
    /**
     * 检查下标是否越界
     * @param index
     */
    private void checkElementIndex(int index) {
        if (!isElementIndex(index)){
            throw new IndexOutOfBoundsException("下标越界");
        }
    }
    /**
     * 判断参数是否有对应索引.
     */
    private boolean isElementIndex(int index) {
        return index >= 0 && index < size;
    }
    
    /**
     *根据下标删除
     * @param index
     * @return
     */
    public E remove(int index) {
        checkElementIndex(index);
        return unlink(node(index));
    }
    
    /**
     *  删除第一个匹配的指定元素
     * @param o
     * @return
     */
    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;
    }
    /**
     * Unlinks non-null node x.
     */
    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;
    }
    /**
     * 集合大小
     * @return 集合当前容量
     */
    public int size() {
        return size;
    }
    
    /**
     * 无参 删除节点
     * @return
     */
    public E remove() {
        //调用删除第一个节点的方法
        return removeFirst();
    }
    
    /**
     * 删除第一个节点
     * @return
     */
    public E removeFirst() {
        final Node<E> f = first;
        if (f == null)
            throw new NoSuchElementException();
        return unlinkFirst(f);
    }
    
    /**
     * 删除第一个节点
     * 实际执行的方法
     */
    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; 
        first = next;
        if (next == null)
            last = null;
        else
            next.prev = null;
        size--;
        modCount++;
        return element;
    }
}