三、LinkedList
底层是由双向链表实现的
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;
}
}
相当于一个结构体
struct node{
e item;
node *next;
node *prev;
}node;
有了头结点,其他的数据我们都可以获取得到了
3.1 构造方法
/**
* Constructs an empty list.
*/
public LinkedList() {
}
/**
* Constructs a list containing the elements of the specified
* collection, in the order they are returned by the collection's
* iterator.
*
* @param c the collection whose elements are to be placed into this list
* @throws NullPointerException if the specified collection is null
*/
public LinkedList(Collection<? extends E> c) {
this();
addAll(c);
}
一共两个构造方法,一个空构造方法
public boolean addAll(int index, Collection<? extends E> c) {
checkPositionIndex(index);
Object[] a = c.toArray(); //将c转换为数组
int numNew = a.length;//存储a的长度
if (numNew == 0)//如果没有元素返回false
return false;
Node<E> pred, succ; //创建节点
if (index == size) {//如果index刚好等于链表大小,存入最后一个
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;
}
3.2 add(int index, E element)
- add实际上就是往链表的最后添加元素
public void add(int index, E element) {
checkPositionIndex(index);
if (index == size)
linkLast(element);
else
linkBefore(element, node(index));
}
3.3 remove方法
public boolean remove(Object o) {
if (o == null) {
for (Node<E> x = first; x != null; x = x.next) {
if (x.item == null) {
unlink(x);//删除元素
return true;
}
}
} else {
for (Node<E> x = first; x != null; x = x.next) {
if (o.equals(x.item)) {//删除元素,看看元素是否在里面
unlink(x);
return true;
}
}
}
return false;
}
//*********************unlike******************
/**
* 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;
}
相当于这张图
3.4 get方法
public E get(int index) {
checkElementIndex(index);
return node(index).item;
}
/**
* Returns the (non-null) Node at the specified element index.
*/
Node<E> node(int index) {
// assert isElementIndex(index);
if (index < (size >> 1)) {//下标小于长度的一般就从头遍历
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--)//否则从尾部开始遍历
x = x.prev;
return x;
}
}
3.5 set方法
set方法和get方法其实差不多,根据下标来判断是从头遍历还是从尾遍历
public E set(int index, E element) {
checkElementIndex(index);
Node<E> x = node(index);
E oldVal = x.item;
x.item = element;
return oldVal;
}
3.6 总结
- LInkedLIst的实质是一个双向链表
- LikedList是非线程安全的
- 查询多用ArrayList,增删多用LinkedList。