目录
- 继承体系
- 数据结构
- 源码解析
- 1.属性
- 2.构造方法
- LinkedList()
- LinkedList(Collection<? extends E> c)
- 3.添加元素
- add(E e)
- addFirst(E e)
- addLast(E e)
- add(int index, E element)
- offer(E e)
- offerFirst(E e)
- offerLast(E e)
- 总结
- 4.获取元素
- get(int index)
- getFirst()
- getLast()
- peek()
- 5.删除元素
- remove()
- removeLast()
- removeLast()
- pollFirst()
- pollLast()
- 总结
LinkedList是一种以带头尾指针的双向链表实现的 List,与 ArrayList 相比,其插入元素快,不需要将元素向后移动,但是其获取元素却没有 ArrayList 方便。
继承体系
数据结构
在linkedList中维护了一个双向链表
源码解析
1.属性
//长度,默认为0
transient int size = 0;
//首节点
transient Node<E> first;
//尾节点
transient Node<E> last;
2.构造方法
LinkedList()
public LinkedList() {
}
LinkedList(Collection<? extends E> c)
public LinkedList(Collection<? extends E> c) {
this();
addAll(c);
}
public boolean addAll(Collection<? extends E> c) {
return addAll(size, c);
}
public boolean addAll(int index, Collection<? extends E> c) {
//边界判断
checkPositionIndex(index);
//先把集合变成数组
Object[] a = c.toArray();
int numNew = a.length;
//集合为空,不用进行添加
if (numNew == 0)
return false;
Node<E> pred, succ;
//在链表的index处添加元素
if (index == size) {
succ = null;
pred = last;
} else {
succ = node(index);
pred = succ.prev;
}
//把c中元素添加到链表中
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;
}
//确定链表中元素个数
size += numNew;
//修改次数加一
modCount++;
return true;
}
3.添加元素
add(E e)
public boolean add(E e) {
linkLast(e);
return true;
}
//通过尾插法,添加链表元素
void linkLast(E e) {
final Node<E> l = last;
final Node<E> newNode = new Node<>(l, e, null);
last = newNode;
//判断链表中是否存在节点
if (l == null)
first = newNode;
else
l.next = newNode;
size++;
modCount++;
}
addFirst(E e)
public void addFirst(E e) {
linkFirst(e);
}
//通过头插法存入元素
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++;
}
addLast(E e)
public void addLast(E e) {
//同add方法通过尾插法,插入元素
linkLast(e);
}
add(int index, E element)
public void add(int index, E element) {
//边界值检测
checkPositionIndex(index);
if (index == size)
//插入位置等于元素个数,直接插在链表尾部
linkLast(element);
else
//获取对应index位置的元素
linkBefore(element, node(index));
}
//把e元素生成的节点添加到succ前面
void linkBefore(E e, Node<E> succ) {
// assert succ != null;
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++;
}
offer(E e)
public boolean offer(E e) {
return add(e);
}
将指定元素添加到链表尾部。
offerFirst(E e)
public boolean offerFirst(E e) {
addFirst(e);
return true;
}
将指定元素添加到链表头
offerLast(E e)
public boolean offerLast(E e) {
addLast(e);
return true;
}
链表尾部添加节点
总结
向链表中间添加元素效率较慢,为O(n)。其他方式添加元素快,时间复杂度为O(1)
4.获取元素
get(int index)
public E get(int index) {
checkElementIndex(index);
return node(index).item;
}
//获取指定索引位置的元素
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;
}
}
getFirst()
public E getFirst() {
final Node<E> f = first;
if (f == null)
throw new NoSuchElementException();
return f.item;
}
getLast()
public E getLast() {
final Node<E> l = last;
if (l == null)
throw new NoSuchElementException();
return l.item;
}
peek()
public E peek() {
final Node<E> f = first;
return (f == null) ? null : f.item;
}
5.删除元素
remove()
public E remove() {
return removeFirst();
}
public E removeFirst() {
final Node<E> f = first;
if (f == null)
throw new NoSuchElementException();
return unlinkFirst(f);
}
//判断是否为头节点,然后进行删除
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; // help GC
first = next;
if (next == null)
last = null;
else
next.prev = null;
size--;
modCount++;
return element;
}
removeLast()
public E removeLast() {
final Node<E> l = last;
if (l == null)
throw new NoSuchElementException();
return unlinkLast(l);
}
//对尾节点进行删除
private E unlinkLast(Node<E> l) {
// assert l == last && l != null;
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;
}
removeLast()
public E removeLast() {
final Node<E> l = last;
if (l == null)
throw new NoSuchElementException();
return unlinkLast(l);
}
pollFirst()
public E pollFirst() {
final Node<E> f = first;
return (f == null) ? null : unlinkFirst(f);
}
pollLast()
public E pollLast() {
final Node<E> l = last;
return (l == null) ? null : unlinkLast(l);
}
总结
- LinkedList是一个以双向链表实现的List;
- LinkedList还是一个双端队列,具有队列、双端队列、栈的特性;
- LinkedList在队列首尾添加、删除元素非常高效,时间复杂度为O(1);
- LinkedList在中间添加、删除元素比较低效,时间复杂度为O(n);
- LinkedList不支持随机访问,所以访问非队列首尾的元素比较低效;
- LinkedList在功能上等于ArrayList + ArrayDeque;
ArrayList代表了List的典型实现,LInkedList代表了Deque的典型实现,同时LinkedList也实现了List,通过这两个类一首一尾正好可以把整个集合贯穿起来。
原文地址:https://www.cnblogs.com/wf614/p/12399049.html
时间: 2024-10-24 09:07:00