package Queue;
import java.util.*;
import java.util.function.Consumer;
/**
* 双端队列主要实现list接口和Deque接口，实现了所有list操作，元素允许为null
* 该实现是不同步的,not synchronized.
* 可以使用 Collections.synchronizedList封装防止不同不的情况出现
* 即：List list = Collections.synchronizedList(new LinkedList(...))
* 该类中的迭代器使用快速失败模式：fail-fast，如果list在迭代器被创建之后的任意时间内被其他方法修改了结构，
* （除了迭代器自己的remove()或add()方法），都是立刻报错
*/
public class LinkedList<E>
extends AbstractSequentialList<E>
implements List<E>, Deque<E>, Cloneable, java.io.Serializable
{
//定义了三个成员变量，链表元素个数的size，指向第一个元素的first，指向最后一个元素的last
//队列中元素的个数
transient int size = 0;
//永远指向链表中的第一个节点
transient Node<E> first;
//永远指向链表中的最后一个节点
transient Node<E> last;
//构造方法有两个，一个是构造一个空的链表，一个是根据已有的集合构造新的链表
//初始化空队列
public LinkedList() {
}
//根据已有的集合对象构造一个队列
public LinkedList(Collection<? extends E> c) {
this();//调用空的初始化队列
addAll(c);//向空队列中添加所有初始化的元素
}
//内部类，定义链表上的一个节点对象
//每个节点有三部分组成，中间的是节点自身的值，和指向链表前一个节点的指针prev,以及指向链表后一个节点的指针next
private static class Node<E> {
E item;
Node<E> next;
Node<E> prev;
//初始化一个节点对象时，接收三个参数。指向前一个节点的指针，自己本身，和指向后一个节点的指针
Node(Node<E> prev, E element, Node<E> next) {
this.item = element;
this.next = next;
this.prev = prev;
}
}
//移除指定元素，遍历链表，碰到第一个相等的就移除这个元素
public boolean remove(Object o) {
//要移除元素为null的情况
if (o == null) {
//遍历链表
for (Node<E> x = first; x != null; x = x.next) {
if (x.item == null) {
unlink(x);//移除某个元素的具体实现
return true;
}
}
//要移除元素不为null的情况
} else {
for (Node<E> x = first; x != null; x = x.next) {
if (o.equals(x.item)) {
unlink(x);
return true;
}
}
}
return false;
}
//移除一个节点的具体实现方法
E unlink(Node<E> x) {
// assert x != null;
//拿到本节点上的三个元素
final E element = x.item;
final Node<E> next = x.next;
final Node<E> prev = x.prev;
//处理前一个节点对下一个节点的指向
if (prev == null) {
first = next;
} else {
prev.next = next;
x.prev = null;
}
//处理后一个节点对前一个节点的指向
if (next == null) {
last = prev;
} else {
next.prev = prev;
x.next = null;
}
x.item = null;
size--;
modCount++;
return element;
}
//向链表头部第一个位置添加一个元素
private void linkFirst(E e) {
//保存first的引用
final Node<E> f = first;
//根据传进来的元素e，构建一个新的节点，因为节点是放在头部第一个位置，所有prev=null
//构建一个新的节点时，就直接指定了前一个，自己，后一个。
final Node<E> newNode = new Node<>(null, e, f);
//把first指向新加入的一个元素
first = newNode;
//处理原先第一个节点（现在已经时第二个了）对新节点的引用
if (f == null)
last = newNode;
else
f.prev = newNode;
size++;
modCount++;
}
//向链表尾部最后一个位置添加一个元素
void linkLast(E e) {
final Node<E> l = last;
//构建一个新的节点
final Node<E> newNode = new Node<>(l, e, null);
last = newNode;
if (l == null)
first = newNode;
else
l.next = newNode;
size++;
modCount++;
}
//在某个节点之前添加一个元素
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++;
}
//移除链表的第一个元素
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;
}
//移除链表的最后一个元素
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;
}
//仅仅查看链表中第一个节点的值，链表为null时，抛出异常
public E getFirst() {
final Node<E> f = first;
if (f == null)
throw new NoSuchElementException();
return f.item;
}
////返回链表中最后一个节点的值，链表为null时，抛出异常
public E getLast() {
final Node<E> l = last;
if (l == null)
throw new NoSuchElementException();
return l.item;
}
//从链表中删除并返回头部的第一个元素，如果链表为null，则抛出异常
public E removeFirst() {
final Node<E> f = first;
if (f == null)
throw new NoSuchElementException();
return unlinkFirst(f);
}
//从链表中删除并返回头部的第一个元素，如果链表为null，则抛出异常
public E removeLast() {
final Node<E> l = last;
if (l == null)
throw new NoSuchElementException();
return unlinkLast(l);
}
//在链表头部第一个位置上插入元素，没有返回值
public void addFirst(E e) {
linkFirst(e);
}
//在链表尾部最后一个位置上插入元素，没有返回值
public void addLast(E e) {
linkLast(e);
}
//检查链表是否包含某个值，返回布尔值
public boolean contains(Object o) {
return indexOf(o) != -1;
}
//返回链表元素的个数
public int size() {
return size;
}
//在链表尾部最后一个位置上插入元素，返回布尔值
public boolean add(E e) {
linkLast(e);
return true;
}
//向链表中追加指定集合中的所有元素
public boolean addAll(Collection<? extends E> c) {
return addAll(size, c);
}
//在指定位置开始追加指定集合内的所有元素
public boolean addAll(int index, Collection<? extends E> c) {
//先检查指定位置的是否合法
checkPositionIndex(index);
//把集合内的元素换成数组结构
Object[] a = c.toArray();
//检查数组的大小是否合法
int numNew = a.length;
if (numNew == 0)
return false;
//定义两个节点变量
Node<E> pred, succ;
//如果是从链表的最后开始添加
if (index == size) {
succ = null;
pred = last;
//如果是从链表的中间开始添加
} else {
//要是index开始添加，所有，index对应的节点需要后移
succ = node(index);//拿到处于index位置的节点
pred = succ.prev;//拿到index前一个节点
}
//遍历数组的元素
for (Object o : a) {
@SuppressWarnings("unchecked") E e = (E) o;
//根据数组的元素拿到构建新的节点，并指定前一个节点，因为后一个节点还不知道
Node<E> newNode = new Node<>(pred, e, null);
if (pred == null)
first = newNode;
else
//更新新加节点的下一个节点的指向
pred.next = newNode;
//更改前一个节点，方便下一个循环的添加
pred = newNode;
}
//添加完数组内的元素，把其和原来的部分进行拼接
if (succ == null) {
last = pred;
} else {
pred.next = succ;
succ.prev = pred;
}
size += numNew;
modCount++;
return true;
}
//移除链表的所有元素
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
//遍历，使所有的引用都指向null
for (Node<E> x = first; x != null; ) {
Node<E> next = x.next;
x.item = null;
x.next = null;
x.prev = null;
x = next;
}
first = last = null;
size = 0;
modCount++;
}
// Positional Access Operations
//返回指定索引号上的元素值
public E get(int index) {
checkElementIndex(index);
return node(index).item;
}
//对索引号上对应的节点的值进行修改
public E set(int index, E element) {
checkElementIndex(index);
Node<E> x = node(index);
E oldVal = x.item;
x.item = element;
return oldVal;
}
//在指定位置添加一个节点
public void add(int index, E element) {
checkPositionIndex(index);
if (index == size)
linkLast(element);
else
linkBefore(element, node(index));
}
//删除并返回指定位置上的元素
public E remove(int index) {
checkElementIndex(index);
return unlink(node(index));
}
/**
* Tells if the argument is the index of an existing element.
*/
private boolean isElementIndex(int index) {
return index >= 0 && index < size;
}
/**
* Tells if the argument is the index of a valid position for an
* iterator or an add operation.
*/
private boolean isPositionIndex(int index) {
return index >= 0 && index <= size;
}
/**
* Constructs an IndexOutOfBoundsException detail message.
* Of the many possible refactorings of the error handling code,
* this "outlining" performs best with both server and client VMs.
*/
private String outOfBoundsMsg(int index) {
return "Index: "+index+", Size: "+size;
}
private void checkElementIndex(int index) {
if (!isElementIndex(index))
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
private void checkPositionIndex(int index) {
if (!isPositionIndex(index))
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
//按索引号返回节点
Node<E> node(int index) {
// assert isElementIndex(index);
//如果索引值小于总数量的1/2，从头部开始遍历
if (index < (size >> 1)) {
Node<E> x = first;
for (int i = 0; i < index; i++)
x = x.next;
return x;
//如果索引值大于或等于总数量的1/2，从尾部开始遍历
} else {
Node<E> x = last;
for (int i = size - 1; i > index; i--)
x = x.prev;
return x;
}
}
// Search Operations
//返回指定元素在链表中第一次出现的索引号，若无则返回-1
public int indexOf(Object o) {
int index = 0;
//处理o为null和不为null的情况
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;
}
//返回指定元素在链表中最后一次出现的索引号，若无则返回-1
public int lastIndexOf(Object o) {
int index = size;
if (o == null) {
//遍历查找的时候只需要倒序就可以，问题不大
for (Node<E> x = last; x != null; x = x.prev) {
index--;
if (x.item == null)
return index;
}
} else {
for (Node<E> x = last; x != null; x = x.prev) {
index--;
if (o.equals(x.item))
return index;
}
}
return -1;
}
// Queue operations.
//仅仅查看队列的第一个元素
public E peek() {
final Node<E> f = first;
return (f == null) ? null : f.item;
}
//仅仅查看链表中第一个节点的值，链表为null时，抛出异常
public E element() {
return getFirst();
}
//移除并返回链表头部的第一个元素
public E poll() {
final Node<E> f = first;
return (f == null) ? null : unlinkFirst(f);
}
//从链表中删除并返回头部的第一个元素，如果链表为null，则抛出异常
public E remove() {
return removeFirst();
}
//在链表尾部最后一个位置上插入元素，返回布尔值
public boolean offer(E e) {
return add(e);
}
// Deque operations
//在链表头部第一个位置上插入元素，返回布尔值
public boolean offerFirst(E e) {
addFirst(e);
return true;
}
//在链表尾部最后一个位置上插入元素，返回布尔值
public boolean offerLast(E e) {
addLast(e);
return true;
}
//仅仅查看链表中第一个节点的值。不删除
public E peekFirst() {
final Node<E> f = first;
return (f == null) ? null : f.item;
}
//仅仅查看链表中最后一个节点的值。不删除
public E peekLast() {
final Node<E> l = last;
return (l == null) ? null : l.item;
}
//移除链表的第一个元素
public E pollFirst() {
final Node<E> f = first;
return (f == null) ? null : unlinkFirst(f);
}
//移除链表的最后一个元素
public E pollLast() {
final Node<E> l = last;
return (l == null) ? null : unlinkLast(l);
}
//栈操作，压入元素
public void push(E e) {
addFirst(e);
}
//栈操作，弹出元素
public E pop() {
return removeFirst();
}
//移除指定元素，遍历链表，碰到第一个相等的就移除这个元素
public boolean removeFirstOccurrence(Object o) {
return remove(o);
}
//移除链表中最后一个跟指定元素相同的元素
public boolean removeLastOccurrence(Object o) {
if (o == null) {
for (Node<E> x = last; x != null; x = x.prev) {
if (x.item == null) {
unlink(x);
return true;
}
}
} else {
for (Node<E> x = last; x != null; x = x.prev) {
if (o.equals(x.item)) {
unlink(x);
return true;
}
}
}
return false;
}
//返回一个从index开始到最后的ListIterator迭代器
public ListIterator<E> listIterator(int index) {
checkPositionIndex(index);
return new ListItr(index);
}
//内部类，迭代器的实现
private class ListItr implements ListIterator<E> {
private Node<E> lastReturned;
private Node<E> next;
private int nextIndex;
private int expectedModCount = modCount;
ListItr(int index) {
// assert isPositionIndex(index);
next = (index == size) ? null : node(index);
nextIndex = index;
}
public boolean hasNext() {
return nextIndex < size;
}
public E next() {
checkForComodification();
if (!hasNext())
throw new NoSuchElementException();
lastReturned = next;
next = next.next;
nextIndex++;
return lastReturned.item;
}
public boolean hasPrevious() {
return nextIndex > 0;
}
public E previous() {
checkForComodification();
if (!hasPrevious())
throw new NoSuchElementException();
lastReturned = next = (next == null) ? last : next.prev;
nextIndex--;
return lastReturned.item;
}
public int nextIndex() {
return nextIndex;
}
public int previousIndex() {
return nextIndex - 1;
}
public void remove() {
checkForComodification();
if (lastReturned == null)
throw new IllegalStateException();
Node<E> lastNext = lastReturned.next;
unlink(lastReturned);
if (next == lastReturned)
next = lastNext;
else
nextIndex--;
lastReturned = null;
expectedModCount++;
}
public void set(E e) {
if (lastReturned == null)
throw new IllegalStateException();
checkForComodification();
lastReturned.item = e;
}
public void add(E e) {
checkForComodification();
lastReturned = null;
if (next == null)
linkLast(e);
else
linkBefore(e, next);
nextIndex++;
expectedModCount++;
}
public void forEachRemaining(Consumer<? super E> action) {
Objects.requireNonNull(action);
while (modCount == expectedModCount && nextIndex < size) {
action.accept(next.item);
lastReturned = next;
next = next.next;
nextIndex++;
}
checkForComodification();
}
final void checkForComodification() {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
}
}
public Iterator<E> descendingIterator() {
return new DescendingIterator();
}
//内部类，反序的迭代器
private class DescendingIterator implements Iterator<E> {
private final ListItr itr = new ListItr(size());
public boolean hasNext() {
return itr.hasPrevious();
}
public E next() {
return itr.previous();
}
public void remove() {
itr.remove();
}
}
@SuppressWarnings("unchecked")
private LinkedList<E> superClone() {
try {
return (LinkedList<E>) super.clone();
} catch (CloneNotSupportedException e) {
throw new InternalError(e);
}
}
//返回一个浅克隆对象
public Object clone() {
LinkedList<E> clone = superClone();
// Put clone into "virgin" state
clone.first = clone.last = null;
clone.size = 0;
clone.modCount = 0;
// Initialize clone with our elements
for (Node<E> x = first; x != null; x = x.next)
clone.add(x.item);
return clone;
}
//返回一个包含此列表中所有元素的数组
//返回的数组是Object[]数组
public Object[] toArray() {
Object[] result = new Object[size];
int i = 0;
for (Node<E> x = first; x != null; x = x.next)
result[i++] = x.item;
return result;
}
//以正确的顺序返回一个包含此列表中所有元素的数组（从第一个到最后一个元素）;
// 返回的数组的运行时类型是指定数组的运行时类型
public <T> 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<E> x = first; x != null; x = x.next)
result[i++] = x.item;
if (a.length > size)
a[size] = null;
return a;
}
private static final long serialVersionUID = 876323262645176354L;
/**
* Saves the state of this {@code LinkedList} instance to a stream
* (that is, serializes it).
*
* @serialData The size of the list (the number of elements it
* contains) is emitted (int), followed by all of its
* elements (each an Object) in the proper order.
*/
private void writeObject(java.io.ObjectOutputStream s)
throws java.io.IOException {
// Write out any hidden serialization magic
s.defaultWriteObject();
// Write out size
s.writeInt(size);
// Write out all elements in the proper order.
for (Node<E> x = first; x != null; x = x.next)
s.writeObject(x.item);
}
/**
* Reconstitutes this {@code LinkedList} instance from a stream
* (that is, deserializes it).
*/
@SuppressWarnings("unchecked")
private void readObject(java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException {
// Read in any hidden serialization magic
s.defaultReadObject();
// Read in size
int size = s.readInt();
// Read in all elements in the proper order.
for (int i = 0; i < size; i++)
linkLast((E)s.readObject());
}
//并行迭代器
@Override
public Spliterator<E> spliterator() {
return new LLSpliterator<E>(this, -1, 0);
}
/** A customized variant of Spliterators.IteratorSpliterator */
static final class LLSpliterator<E> implements Spliterator<E> {
static final int BATCH_UNIT = 1 << 10; // batch array size increment
static final int MAX_BATCH = 1 << 25; // max batch array size;
final LinkedList<E> list; // null OK unless traversed
Node<E> current; // current node; null until initialized
int est; // size estimate; -1 until first needed
int expectedModCount; // initialized when est set
int batch; // batch size for splits
LLSpliterator(LinkedList<E> list, int est, int expectedModCount) {
this.list = list;
this.est = est;
this.expectedModCount = expectedModCount;
}
final int getEst() {
int s; // force initialization
final LinkedList<E> lst;
if ((s = est) < 0) {
if ((lst = list) == null)
s = est = 0;
else {
expectedModCount = lst.modCount;
current = lst.first;
s = est = lst.size;
}
}
return s;
}
public long estimateSize() { return (long) getEst(); }
public Spliterator<E> trySplit() {
Node<E> p;
int s = getEst();
if (s > 1 && (p = current) != null) {
int n = batch + BATCH_UNIT;
if (n > s)
n = s;
if (n > MAX_BATCH)
n = MAX_BATCH;
Object[] a = new Object[n];
int j = 0;
do { a[j++] = p.item; } while ((p = p.next) != null && j < n);
current = p;
batch = j;
est = s - j;
return Spliterators.spliterator(a, 0, j, Spliterator.ORDERED);
}
return null;
}
public void forEachRemaining(Consumer<? super E> action) {
Node<E> p; int n;
if (action == null) throw new NullPointerException();
if ((n = getEst()) > 0 && (p = current) != null) {
current = null;
est = 0;
do {
E e = p.item;
p = p.next;
action.accept(e);
} while (p != null && --n > 0);
}
if (list.modCount != expectedModCount)
throw new ConcurrentModificationException();
}
public boolean tryAdvance(Consumer<? super E> action) {
Node<E> p;
if (action == null) throw new NullPointerException();
if (getEst() > 0 && (p = current) != null) {
--est;
E e = p.item;
current = p.next;
action.accept(e);
if (list.modCount != expectedModCount)
throw new ConcurrentModificationException();
return true;
}
return false;
}
public int characteristics() {
return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED;
}
}
}
