LinkedList类结构
LinkedList<E>
extends AbstractSequentialList<E>
implements List<E>, Deque<E>, Cloneable, java.io.Serializable
Node结构
双向链表结构(指向前一结点和后一节点的引用)
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;
}
}
声明变量
/**
* Pointer to first node.
* Invariant: (first == null && last == null) ||
* (first.prev == null && first.item != null)
*/
transient Node<E> first;
/**
* Pointer to last node.
* Invariant: (first == null && last == null) ||
* (last.next == null && last.item != null)
*/
transient Node<E> last;
链表添加首位
推导–>(链表添加末尾)
同理。可得到添加addBefore()上一元素,根据条件不同
/**private void addLast(E e){*/
private void andFirst(E e) {
/**final Node<E> l = last;*/
final Node<E> f = first;
//assert:last.next == null && first.item != null;
/**final Node<E> newNode = new Node<>(l,e,null);*/
//assert:first.prev == null && first.item != null
//init newNode
final Node<E> newNode = new Node<>(null, e, f);
/**last = newNode*/
first = newNode;
//如果首位结点为空,则直接添加。否则添加到结点元素的上一结点
/** if(l == null) first = newNode else l.next = newNode */
if (f == null)
last = newNode;
else
f.prev = newNode;
size++; // init size=0
modCount++;
}
添加上一元素
private void addBefore(E e,Node<E> target){
//assert: node.next = target && node.prev = target.prev != null
Node<E> newNode = (target.prev,e,target);
}
删除首元素,并且返回
推导–>删除末尾元素,并且返回下一个元素
如果需要删除任意一个未知结点Node X,需要判断两种极端情况(最末或者最前,然后往后(往前)推,当前位置清空回收
//private E removeLast(Node<E> f){
private E removeFirst(Node<E> f) {
//assert f == first && f != null;
final E element = f.item; //得到该元素
//final Node<E> prev = f.prev;
final Node<E> next = f.next; //得到它下一个引用
f.item = null; //清空
//f.prev = null;
f.next = null; // 回收内存(GC)
//last = prev;
first = next; //将下一个Node移到首位
//if(prev == null) first= null; else prev.next = null
//如果为空,则代表List只有一个元素,回收
//否则,移除该元素
if (next == null)
last = null;
else
next.prev = null;
size--;
modCount++;
return element;
}
E remove(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 { //填充在后一元素的位置
prev.next = next;
x.prev = null; //之前的位置清空回收
}
if (next == null) {
last = prev;
} else { //填充在前一元素的位置
next.prev = prev;
x.next = null; //之后的位置清空回收
}
x.item = null;
size--;
modCount++;
return element;
}