//LinkedList只有头节点和尾节点，每个节点有一个元素值，和两个节点引用
public class LinkedList
extends AbstractSequentialList
implements List, Deque, Cloneable, java.io.Serializable
{
transient int size = 0;
/**
* Pointer to first node.
* Invariant: (first == null && last == null) ||
* (first.prev == null && first.item != null)
*/
transient Node first;
/**
* Pointer to last node.
* Invariant: (first == null && last == null) ||
* (last.next == null && last.item != null)
*/
transient Node last;
//获取头节点的元素值
public E getFirst() {
final Node f = first;
if (f == null)
throw new NoSuchElementException();
return f.item;
}
//获取尾节点的元素值
public E getLast() {
final Node l = last;
if (l == null)
throw new NoSuchElementException();
return l.item;
}
//移除头节点
public E removeFirst() {
final Node f = first;
if (f == null)
throw new NoSuchElementException();
return unlinkFirst(f);
}
//链表断开头节点：将头节点的元素值和下一个节点取出，
//然后置空，让GC回收【不置空会浪费内存】，
//将取出的元素值返回，将取出的节点【如果不为空，将尾节点也置空】作为新的头节点
//更新链表大小，和链表被修改的次数
private E unlinkFirst(Node f) {
// assert f == first && f != null;
final E element = f.item;
final Node 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;
}
//移除尾节点
public E removeLast() {
final Node l = last;
if (l == null)
throw new NoSuchElementException();
return unlinkLast(l);
}
//链表断开尾节点
private E unlinkLast(Node l) {
// assert l == last && l != null;
final E element = l.item;
final Node 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;
}
//添加头节点
public void addFirst(E e) {
linkFirst(e);
}
//链表头连接节点
private void linkFirst(E e) {
final Node f = first;
final Node newNode = new Node<>(null, e, f);
first = newNode;
if (f == null)//原来的头指针为空【整个链表为空】
last = newNode;//首尾指针指向新添加的节点，该节点没有prev,next
else
f.prev = newNode;
size++;
modCount++;
}
//添加尾节点
public void addLast(E e) {
linkLast(e);
}
//链表尾连接节点
void linkLast(E e) {
final Node l = last;
final Node newNode = new Node<>(l, e, null);
last = newNode;
if (l == null)//原来的尾指针为空【整个链表为空】
first = newNode;//首尾指针指向新添加的节点，该节点没有prev,next
else
l.next = newNode;
size++;
modCount++;
}
//在某个节点前面添加节点
void linkBefore(E e, Node succ) {
// assert succ != null;
final Node pred = succ.prev;
final Node newNode = new Node<>(pred, e, succ);
succ.prev = newNode;//将插入节点的后一个节点的prev，指向插入的节点
if (pred == null)
first = newNode;//如果插入节点的前一个节点为空，即插入的节点将作为头指针
else
pred.next = newNode;//不为空，则插入节点的前一个节点的next，指向插入的节点
size++;
modCount++;
}
//删除某个节点
E unlink(Node x) {
// assert x != null;
final E element = x.item;
final Node next = x.next;
final Node 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;
}
//常规添加接口：调用的是尾添加
public boolean add(E e) {
linkLast(e);
return true;
}
//常规删除接口：非元素为空和不为空
public boolean remove(Object o) {
if (o == null) {
for (Node x = first; x != null; x = x.next) {
if (x.item == null) {
unlink(x);
return true;
}
}
} else {
for (Node x = first; x != null; x = x.next) {
if (o.equals(x.item)) {
unlink(x);
return true;
}
}
}
return false;
}
//添加集合
public boolean addAll(Collection c) {
return addAll(size, c);
}
//添加集合具体实现
public boolean addAll(int index, Collection c) {
checkPositionIndex(index);
Object[] a = c.toArray();
int numNew = a.length;
if (numNew == 0)
return false;
Node pred, succ;
if (index == size) {
succ = null;
pred = last;
} else {
succ = node(index);
pred = succ.prev;
}
for (Object o : a) {
@SuppressWarnings("unchecked") E e = (E) o;
Node 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;
}
//取得某个位置的节点
Node node(int index) {
// assert isElementIndex(index);
if (index < (size >> 1)) {
Node x = first;
for (int i = 0; i < index; i++)
x = x.next;
return x;
} else {
Node x = last;
for (int i = size - 1; i > index; i--)
x = x.prev;
return x;
}
}
//清空链表
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 x = first; x != null; ) {
Node next = x.next;
x.item = null;
x.next = null;
x.prev = null;
x = next;
}
first = last = null;
size = 0;
modCount++;
}
//获取指定位置元素
public E get(int index) {
checkElementIndex(index);
return node(index).item;
}
//修改指定位置的元素
public E set(int index, E element) {
checkElementIndex(index);
Node x = node(index);
E oldVal = x.item;
x.item = element;
return oldVal;
}
//指定位置添加元素
public void add(int index, E element) {
checkPositionIndex(index);
if (index == size)
linkLast(element);
else
linkBefore(element, node(index));//先获取到指定位置的节点，再使用linkBefore添加新节点
}
//删除指定位置节点
public E remove(int index) {
checkElementIndex(index);
return unlink(node(index));//想获取到指定位置的节点，在使用unlink删除节点
}
//获取某个元素的位置
public int indexOf(Object o) {
int index = 0;
if (o == null) {
for (Node x = first; x != null; x = x.next) {
if (x.item == null)
return index;
index++;
}
} else {
for (Node x = first; x != null; x = x.next) {
if (o.equals(x.item))
return index;
index++;
}
}
return -1;
}
//获取头指针元素
public E peek() {
final Node f = first;
return (f == null) ? null : f.item;
}
//删除头节点
public E poll() {
final Node f = first;
return (f == null) ? null : unlinkFirst(f);
}
//转为数组【无参】
public Object[] toArray() {
Object[] result = new Object[size];
int i = 0;
for (Node x = first; x != null; x = x.next)
result[i++] = x.item;
return result;
}
//转为数组【传数组】
public T[] toArray(T[] a) {
if (a.length < size)
a = (T[])java.lang.reflect.Array.newInstance(
a.getClass().getComponentType(), size);
int i = 0;
Object[] result = a;
for (Node x = first; x != null; x = x.next)
result[i++] = x.item;
if (a.length > size)
a[size] = null;
return a;
}
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