#来自ゾフィー(佐菲)
1 简介
LinkedList 的底层数据结构是双向链表。可以当作链表、栈、队列、双端队列来使用。有以下特点:
- 在插入或删除数据时,性能好;
- 允许有 null 值;
- 查询效率不高;
- 线程不安全;
public class LinkedList<E>
extends AbstractSequentialList<E>
implements List<E>, Deque<E>, Cloneable, java.io.Serializable
{}
2 源码
LinkedList 数据结构:
private static class Node<E> {
E item; //结点值
Node<E> next; //后驱节点
Node<E> prev; //前驱节点
Node(Node<E> prev, E element, Node<E> next) {
this.item = element;
this.next = next;
this.prev = prev;
}
}
LinkedList 两个构造函数:
public LinkedList() {}
public LinkedList(Collection<? extends E> c) {
this();
addAll(c);
}
addAll()
public boolean addAll(int index, Collection<? extends E> c) {
//校验 index 是否合理
checkPositionIndex(index);
Object[] a = c.toArray();
int numNew = a.length;
if (numNew == 0)
return false;
//succ:待添加节点的位置。
//pred:待添加节点的前驱节点。
Node<E> pred, succ;
if (index == size) {//在末尾插入
succ = null;
pred = last;
} else { //不在末尾插入
succ = node(index); //这个方法 会折半
pred = succ.prev;
}
for (Object o : a) {
//创建新节点
@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;
}
//把集合的大小设置为新的大小
size += numNew;
modCount++;
return true;
}
get() -> 会有折半
public E get(int index) {
//校验 index 是否越界
checkElementIndex(index);
return node(index).item;
}
Node<E> node(int index) {
// assert isElementIndex(index);
//分一半查找
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;
}
}
add()
public boolean add(E e) {
//在末尾追加元素的方法。
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) //为空链表
first = newNode;
else
l.next = newNode;
size++;//size 自增
modCount++;
}
remove()
public boolean remove(Object o) {
if (o == null) {
for (Node<E> x = first; x != null; x = x.next) {
if (x.item == null) {
//移除节点
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;
}
//删除节点
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;
//1 -> 2 -> 3 1 -> 3
if (prev == null) { //移除的是头节点
first = next;
} else {
prev.next = next;
x.prev = null;
}
if (next == null) { //移除的是尾节点
last = prev;
} else {
next.prev = prev;
x.next = null;
}
x.item = null;
size--;
modCount++;
return element;
}
toArray()
public Object[] toArray() {
//创建一个新数组 然后遍历链表,将每个元素存在数组里,返回
Object[] result = new Object[size];
int i = 0;
for (Node<E> x = first; x != null; x = x.next)
result[i++] = x.item;
return result;
}