从源码的定义中，我们可以看出linkedList是实现list接口和deque接口的双端链表
public class LinkedList<E>
extends AbstractSequentialList<E>
implements List<E>, Deque<E>, Cloneable, java.io.Serializable
LinkedList是一个双端链表结构，有两个变量 first指向头部，last指向链表尾部，size表示当前链表中的数据个数
transient int size = 0;
transient Node<E> first;
transient Node<E> last;
LinkedList 的带参构造函数
public LinkedList(Collection<? extends E> c) {
this();
addAll(c);
}
public boolean addAll(Collection<? extends E> c) {
return addAll(size, c);
}
addAll方法
public boolean addAll(int index, Collection<? extends E> c) {
checkPositionIndex(index);//检查下标是否正确
Object[] a = c.toArray();
int numNew = a.length;
if (numNew == 0)
return false;
Node<E> pred, succ;//定义前缀节点pred 和后续节点succ
if (index == size) {//在链表尾部插入
succ = null;
pred = last;
} else {
succ = node(index);
pred = succ.prev;
}
for (Object o : a) {//循环插入数据
@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) {//链表插入完毕，pred指向最后一个节点，若是后续节点为空，代表在尾部插入，那就更新last指向pred，
last = pred;
} else {//succ不为空，说明在中间插入，把链表链接到之前的链表上
pred.next = succ;
succ.prev = pred;
}
size += numNew;
modCount++;
return true;
}
private void linkFirst(E e) {
final Node<E> f = first;
final Node<E> newNode = new Node<>(null, e, f);//将f作为新节点的后继节点
first = newNode;//first指向newNode，因为newNode此刻为链表的头结点
if (f == null)//如果链表为空，那么first与last指向同一个元素newNode
last = newNode;
else
f.prev = newNode;
size++;
modCount++;
}
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;
}
}
void linkLast(E e)与linkFirst相同
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;
size++;
modCount++;
}
在指定节点前插入节点
void linkBefore(E e, Node<E> succ) {
// assert succ != null;
final Node<E> pred = succ.prev;//获取前缀
final Node<E> newNode = new Node<>(pred, e, succ);//生成新节点，指定前缀，后续节点
succ.prev = newNode;
if (pred == null)
first = newNode;
else
pred.next = newNode;
size++;
modCount++;
}
解链接非空的第一个节点F。
private E unlinkFirst(Node<E> f) {
// assert f == first && f != null;
final E element = f.item;//保留当前要删除的节点
final Node<E> next = f.next;
f.item = null;
f.next = null; // help GC
first = next;//直接让fist指向当前节点的下一个节点
if (next == null)
last = null;
else
next.prev = null;
size--;
modCount++;
return element;
}
解链接非空的最后一个节点l。
private E unlinkLast(Node<E> l) {
// assert l == last && l != null;
final E element = l.item;//保留当前要删除的最后一个节点
final Node<E> prev = l.prev;//得到要删除节点
l.item = null;
l.prev = null; // help GC
last = prev;//last前移
if (prev == null)//当前链表就一个节点
first = null;
else
prev.next = null;
size--;
modCount++;
return element;
}
删除不为空的节点node x
E unlink(Node<E> x) {
// assert x != null;
final E element = x.item;//保存当前jiedain
final Node<E> next = x.next;//要删除节点的后缀
final Node<E> prev = x.prev;//要删除节点的前缀
if (prev == null) {//若是前缀为空，表示删除的是第一个节点，first指向下一个节点，即next
first = next;
} else {//若不为空，直接让前缀的next指向next
prev.next = next;
x.prev = null;
}
if (next == null) {//同理
last = prev;
} else {
next.prev = prev;
x.next = null;
}
x.item = null;
size--;
modCount++;
return element;
}
得到第一个元素
public E getFirst() {
final Node<E> f = first;
if (f == null)//first不为空，直接返回first所指向的元素
throw new NoSuchElementException();
return f.item;
}
得到最后一个元素，同上
public E getLast() {
final Node<E> l = last;
if (l == null)
throw new NoSuchElementException();
return l.item;
}
移除第一个节点
public E removeFirst() {
final Node<E> f = first;
if (f == null)
throw new NoSuchElementException();
return unlinkFirst(f);//调用删除第一个元素的方法
}
移除最后一个节点与上面同理
public E removeLast() {
final Node<E> l = last;
if (l == null)
throw new NoSuchElementException();
return unlinkLast(l);
}
判断是否包含
public boolean contains(Object o) {
return indexOf(o) != -1;
}
public int indexOf(Object o) {//根据代码来看，链表判断是否包含，用的就是遍历，找到与之相匹配的，若是没有则不包含
int index = 0;
if (o == null) {
for (Node<E> x = first; x != null; x = x.next) {
if (x.item == null)
return index;
index++;
}
} else {
for (Node<E> x = first; x != null; x = x.next) {
if (o.equals(x.item))
return index;
index++;
}
}
return -1;
}
获取链表的大小
public int size() {
return size;
}
链表的add操作
public boolean add(E e) {//根据代码来看，链表的add操作就是在链表的尾部添加节点
linkLast(e);
return true;
}
链表的remove操作
public boolean remove(Object o) {//根据代码来看，remove操作就是遍历找到要移除的节点，然后调用unlink()方法
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;
}
链表的clear操作
public void clear() {
// Clearing all of the links between nodes is "unnecessary", but:
// - helps a generational GC if the discarded nodes inhabit
// more than one generation
// - is sure to free memory even if there is a reachable Iterator
for (Node<E> x = first; x != null; ) {//遍历把每个节点及其前缀后缀都置为空
Node<E> next = x.next;
x.item = null;
x.next = null;
x.prev = null;
x = next;//x向后移动一个节点
}
first = last = null;
size = 0;
modCount++;
}
得到指定下标的链表节点
public E get(int index) {
checkElementIndex(index);
return node(index).item;
}
Node<E> node(int index) {
// assert isElementIndex(index);
if (index < (size >> 1)) {//若是index小于size的一半，就从first开始查找
Node<E> x = first;
for (int i = 0; i < index; i++)//遍历找到下标对应的节点，并且返回该节点
x = x.next;
return x;
} else {//若是index大于size的一半就从last开始查找
Node<E> x = last;
for (int i = size - 1; i > index; i--)
x = x.prev;
return x;
}
}
替换指定位置的节点
public E set(int index, E element) {
checkElementIndex(index);
Node<E> x = node(index);
E oldVal = x.item;
x.item = element;
return oldVal;
}
添加节点到指定位置
public void add(int index, E element) {
checkPositionIndex(index);
if (index == size)
linkLast(element);
else
linkBefore(element, node(index));//调用linkBefore方法
}
移除指定下标节点
public E remove(int index) {
checkElementIndex(index);
return unlink(node(index));
}
list的基本操作的源码如上述所示