import java.util.AbstractList;
import java.util.Arrays;
import java.util.BitSet;
import java.util.Collection;
import java.util.Comparator;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;
import java.util.NoSuchElementException;
import java.util.Objects;
import java.util.RandomAccess;
import java.util.Spliterator;
import java.util.function.Consumer;
import java.util.function.Predicate;
import java.util.function.UnaryOperator;
/**
 * 概述：
 * List接口可調整大小的數(shù)組實現(xiàn)。實現(xiàn)所有可選的List操作，并允許所有元素，包括null，元素可重復。
 * 除了列表接口外，該類提供了一種方法來操作該數(shù)組的大小來存儲該列表中的數(shù)組的大小。
 * 
 * 時間復雜度：
 * 方法size、isEmpty、get、set、iterator和listIterator的調用是常數(shù)時間的。
 * 添加刪除的時間復雜度為O(N)。其他所有操作也都是線性時間復雜度。
 *
 * 容量：
 * 每個ArrayList都有容量，容量大小至少為List元素的長度，默認初始化為10。
 * 容量可以自動增長。
 * 如果提前知道數(shù)組元素較多，可以在添加元素前通過調用ensureCapacity()方法提前增加容量以減小后期容量自動增長的開銷。
 * 也可以通過帶初始容量的構造器初始化這個容量。
 *
 * 線程不安全：
 * ArrayList不是線程安全的。
 * 如果需要應用到多線程中，需要在外部做同步
 *
 * modCount：
 * 定義在AbstractList中：protected transient int modCount = 0;
 * 已從結構上修改此列表的次數(shù)。從結構上修改是指更改列表的大小，或者打亂列表，從而使正在進行的迭代產生錯誤的結果。
 * 此字段由iterator和listiterator方法返回的迭代器和列表迭代器實現(xiàn)使用。
 * 如果意外更改了此字段中的值，則迭代器（或列表迭代器）將拋出concurrentmodificationexception來響應next、remove、previous、set或add操作。
 * 在迭代期間面臨并發(fā)修改時，它提供了快速失敗 行為，而不是非確定性行為。
 * 子類是否使用此字段是可選的。
 * 如果子類希望提供快速失敗迭代器（和列表迭代器），則它只需在其 add(int,e)和remove(int)方法（以及它所重寫的、導致列表結構上修改的任何其他方法）中增加此字段。
 * 對add(int, e)或remove(int)的單個調用向此字段添加的數(shù)量不得超過 1，否則迭代器（和列表迭代器）將拋出虛假的 concurrentmodificationexceptions。
 * 如果某個實現(xiàn)不希望提供快速失敗迭代器，則可以忽略此字段。
 *
 * transient：
 * 默認情況下,對象的所有成員變量都將被持久化.在某些情況下,如果你想避免持久化對象的一些成員變量,你可以使用transient關鍵字來標記他們,transient也是java中的保留字(JDK 1.8)
 */
public class ArrayList<E> extends AbstractList<E> implements List<E>, RandomAccess, Cloneable, java.io.Serializable
{
  private static final long serialVersionUID = 8683452581122892189L;
  //默認初始容量
  private static final int DEFAULT_CAPACITY = 10;
  //用于空實例共享空數(shù)組實例。
  private static final Object[] EMPTY_ELEMENTDATA = {};
  //默認的空數(shù)組
  private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};
  //對的，存放元素的數(shù)組，包訪問權限
  transient Object[] elementData;
  //大小，創(chuàng)建對象時Java會將int初始化為0
  private int size;
  //用指定的數(shù)設置初始化容量的構造函數(shù)，負數(shù)會拋出異常
  public ArrayList(int initialCapacity) {
    if (initialCapacity > 0) {
      this.elementData = new Object[initialCapacity];
    } else if (initialCapacity == 0) {
      this.elementData = EMPTY_ELEMENTDATA;
    } else {
      throw new IllegalArgumentException("Illegal Capacity: "+initialCapacity);
    }
  }
  //默認構造函數(shù)，使用控數(shù)組初始化
  public ArrayList() {
    this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
  }
  //以集合的迭代器返回順序，構造一個含有集合中元素的列表
  public ArrayList(Collection<? extends E> c) {
    elementData = c.toArray();
    if ((size = elementData.length) != 0) {
      // c.toarray可能（錯誤地）不返回對象[]（見JAVA BUG編號6260652）
      if (elementData.getClass() != Object[].class)
        elementData = Arrays.copyOf(elementData, size, Object[].class);
    } else {
      // 使用空數(shù)組
      this.elementData = EMPTY_ELEMENTDATA;
    }
  }
  //因為容量常常會大于實際元素的數(shù)量。內存緊張時，可以調用該方法刪除預留的位置，調整容量為元素實際數(shù)量。
  //如果確定不會再有元素添加進來時也可以調用該方法來節(jié)約空間
  public void trimToSize() {
    modCount++;
    if (size < elementData.length) {
      elementData = (size == 0) ? EMPTY_ELEMENTDATA : Arrays.copyOf(elementData, size);
    }
  }
  //使用指定參數(shù)設置數(shù)組容量
  public void ensureCapacity(int minCapacity) {
    //如果數(shù)組為空，容量預取0，否則去默認值(10)
    int minExpand = (elementData != DEFAULTCAPACITY_EMPTY_ELEMENTDATA)? 0: DEFAULT_CAPACITY;
    //若參數(shù)大于預設的容量，在使用該參數(shù)進一步設置數(shù)組容量
    if (minCapacity > minExpand) {
      ensureExplicitCapacity(minCapacity);
    }
  }
  //用于添加元素時，確保數(shù)組容量
  private void ensureCapacityInternal(int minCapacity) {
    //使用默認值和參數(shù)中較大者作為容量預設值
    if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
      minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);
    }
    ensureExplicitCapacity(minCapacity);
  }
  //如果參數(shù)大于數(shù)組容量，就增加數(shù)組容量
  private void ensureExplicitCapacity(int minCapacity) {
    modCount++;
    if (minCapacity - elementData.length > 0)
      grow(minCapacity);
  }
  //數(shù)組的最大容量，可能會導致內存溢出(VM內存限制)
  private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
  //增加容量，以確保它可以至少持有由參數(shù)指定的元素的數(shù)目
  private void grow(int minCapacity) {
    int oldCapacity = elementData.length;
    //預設容量增加一半
    int newCapacity = oldCapacity + (oldCapacity >> 1);
    //取與參數(shù)中的較大值
    if (newCapacity - minCapacity < 0)//即newCapacity<minCapacity
      newCapacity = minCapacity;
    //若預設值大于默認的最大值檢查是否溢出
    if (newCapacity - MAX_ARRAY_SIZE > 0)
      newCapacity = hugeCapacity(minCapacity);
    elementData = Arrays.copyOf(elementData, newCapacity);
  }
  //檢查是否溢出，若沒有溢出，返回最大整數(shù)值(java中的int為4字節(jié)，所以最大為0x7fffffff)或默認最大值
  private static int hugeCapacity(int minCapacity) {
    if (minCapacity < 0) //溢出
      throw new OutOfMemoryError();
    return (minCapacity > MAX_ARRAY_SIZE) ? Integer.MAX_VALUE : MAX_ARRAY_SIZE;
  }
  //返回數(shù)組大小
  public int size() {
    return size;
  }
  //是否為空
  public boolean isEmpty() {
    return size == 0;
  }
  //是否包含一個數(shù) 返回bool
  public boolean contains(Object o) {
    return indexOf(o) >= 0;
  }
  //返回一個值在數(shù)組首次出現(xiàn)的位置，會根據是否為null使用不同方式判斷。不存在就返回-1。時間復雜度為O(N)
  public int indexOf(Object o) {
    if (o == null) {
      for (int i = 0; i < size; i++)
        if (elementData[i]==null)
          return i;
    } else {
      for (int i = 0; i < size; i++)
        if (o.equals(elementData[i]))
          return i;
    }
    return -1;
  }
  //返回一個值在數(shù)組最后一次出現(xiàn)的位置，不存在就返回-1。時間復雜度為O(N)
  public int lastIndexOf(Object o) {
    if (o == null) {
      for (int i = size-1; i >= 0; i--)
        if (elementData[i]==null)
          return i;
    } else {
      for (int i = size-1; i >= 0; i--)
        if (o.equals(elementData[i]))
          return i;
    }
    return -1;
  }
  //返回副本，元素本身沒有被復制，復制過程數(shù)組發(fā)生改變會拋出異常
  public Object clone() {
    try {
      ArrayList<?> v = (ArrayList<?>) super.clone();
      v.elementData = Arrays.copyOf(elementData, size);
      v.modCount = 0;
      return v;
    } catch (CloneNotSupportedException e) {
      throw new InternalError(e);
    }
  }
  //轉換為Object數(shù)組，使用Arrays.copyOf()方法
  public Object[] toArray() {
    return Arrays.copyOf(elementData, size);
  }
  //返回一個數(shù)組，使用運行時確定類型，該數(shù)組包含在這個列表中的所有元素（從第一到最后一個元素）
  //返回的數(shù)組容量由參數(shù)和本數(shù)組中較大值確定
  @SuppressWarnings("unchecked")
  public <T> T[] toArray(T[] a) {
    if (a.length < size)
      return (T[]) Arrays.copyOf(elementData, size, a.getClass());
    System.arraycopy(elementData, 0, a, 0, size);
    if (a.length > size)
      a[size] = null;
    return a;
  }
  //返回指定位置的值，因為是數(shù)組，所以速度特別快
  @SuppressWarnings("unchecked")
  E elementData(int index) {
    return (E) elementData[index];
  }
  //返回指定位置的值，但是會檢查這個位置數(shù)否超出數(shù)組長度
  public E get(int index) {
    rangeCheck(index);
    return elementData(index);
  }
  //設置指定位置為一個新值，并返回之前的值，會檢查這個位置是否超出數(shù)組長度
  public E set(int index, E element) {
    rangeCheck(index);
    E oldValue = elementData(index);
    elementData[index] = element;
    return oldValue;
  }
  //添加一個值，首先會確保容量
  public boolean add(E e) {
    ensureCapacityInternal(size + 1);
    elementData[size++] = e;
    return true;
  }
  //指定位置添加一個值，會檢查添加的位置和容量
  public void add(int index, E element) {
    rangeCheckForAdd(index);
    ensureCapacityInternal(size + 1);
    //public static void arraycopy(Object src, int srcPos, Object dest, int destPos, int length) 
    //src:源數(shù)組； srcPos:源數(shù)組要復制的起始位置； dest:目的數(shù)組； destPos:目的數(shù)組放置的起始位置； length:復制的長度
    System.arraycopy(elementData, index, elementData, index + 1,size - index);
    elementData[index] = element;
    size++;
  }
  //刪除指定位置的值，會檢查添加的位置，返回之前的值
  public E remove(int index) {
    rangeCheck(index);
    modCount++;
    E oldValue = elementData(index);
    int numMoved = size - index - 1;
    if (numMoved > 0) System.arraycopy(elementData, index+1, elementData, index,numMoved);
    elementData[--size] = null; //便于垃圾回收期回收
    return oldValue;
  }
  //刪除指定元素首次出現(xiàn)的位置
  public boolean remove(Object o) {
    if (o == null) {
      for (int index = 0; index < size; index++)
        if (elementData[index] == null) {
          fastRemove(index);
          return true;
        }
    } else {
      for (int index = 0; index < size; index++)
        if (o.equals(elementData[index])) {
          fastRemove(index);
          return true;
        }
    }
    return false;
  }
  //快速刪除指定位置的值，之所以叫快速，應該是不需要檢查和返回值，因為只內部使用
  private void fastRemove(int index) {
    modCount++;
    int numMoved = size - index - 1;
    if (numMoved > 0)
      System.arraycopy(elementData, index+1, elementData, index,numMoved);
    elementData[--size] = null; // clear to let GC do its work
  }
  //清空數(shù)組，把每一個值設為null,方便垃圾回收(不同于reset，數(shù)組默認大小有改變的話不會重置)
  public void clear() {
    modCount++;
    for (int i = 0; i < size; i++) elementData[i] = null;
    size = 0;
  }
  //添加一個集合的元素到末端，若要添加的集合為空返回false
  public boolean addAll(Collection<? extends E> c) {
    Object[] a = c.toArray();
    int numNew = a.length;
    ensureCapacityInternal(size + numNew); 
    System.arraycopy(a, 0, elementData, size, numNew);
    size += numNew;
    return numNew != 0;
  }
  //功能同上，從指定位置開始添加
  public boolean addAll(int index, Collection<? extends E> c) {
    rangeCheckForAdd(index);
    Object[] a = c.toArray();  //要添加的數(shù)組
    int numNew = a.length;   //要添加的數(shù)組長度
    ensureCapacityInternal(size + numNew); //確保容量
    int numMoved = size - index;//不會移動的長度(前段部分)
    if (numMoved > 0)      //有不需要移動的，就通過自身復制，把數(shù)組后部分需要移動的移動到正確位置
      System.arraycopy(elementData, index, elementData, index + numNew,numMoved);
    System.arraycopy(a, 0, elementData, index, numNew); //新的數(shù)組添加到改變后的原數(shù)組中間
    size += numNew;
    return numNew != 0;
  }
  //刪除指定范圍元素。參數(shù)為開始刪的位置和結束位置
  protected void removeRange(int fromIndex, int toIndex) {
    modCount++;
    int numMoved = size - toIndex; //后段保留的長度
    System.arraycopy(elementData, toIndex, elementData, fromIndex,numMoved);
    int newSize = size - (toIndex-fromIndex);
    for (int i = newSize; i < size; i++) {
      elementData[i] = null;
    }
    size = newSize;
  }
  //檢查數(shù)否超出數(shù)組長度 用于添加元素時
  private void rangeCheck(int index) {
    if (index >= size)
      throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
  }
  //檢查是否溢出
  private void rangeCheckForAdd(int index) {
    if (index > size || index < 0)
      throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
  }
  //拋出的異常的詳情
  private String outOfBoundsMsg(int index) {
    return "Index: "+index+", Size: "+size;
  }
  //刪除指定集合的元素
  public boolean removeAll(Collection<?> c) {
    Objects.requireNonNull(c);//檢查參數(shù)是否為null
    return batchRemove(c, false);
  }
  //僅保留指定集合的元素
  public boolean retainAll(Collection<?> c) {
    Objects.requireNonNull(c);
    return batchRemove(c, true);
  }
  /**
   * 源碼解讀 BY http://anxpp.com/
   * @param complement true時從數(shù)組保留指定集合中元素的值，為false時從數(shù)組刪除指定集合中元素的值。
   * @return 數(shù)組中重復的元素都會被刪除(而不是僅刪除一次或幾次)，有任何刪除操作都會返回true
   */
  private boolean batchRemove(Collection<?> c, boolean complement) {
    final Object[] elementData = this.elementData;
    int r = 0, w = 0;
    boolean modified = false;
    try {
      //遍歷數(shù)組，并檢查這個集合是否包含對應的值，移動要保留的值到數(shù)組前面，w最后值為要保留的元素的數(shù)量
      //簡單點：若保留，就將相同元素移動到前段；若刪除，就將不同元素移動到前段
      for (; r < size; r++)
        if (c.contains(elementData[r]) == complement)
          elementData[w++] = elementData[r];
    }finally {//確保異常拋出前的部分可以完成期望的操作，而未被遍歷的部分會被接到后面
      //r!=size表示可能出錯了：c.contains(elementData[r])拋出異常
      if (r != size) {
        System.arraycopy(elementData, r,elementData, w,size - r);
        w += size - r;
      }
      //如果w==size：表示全部元素都保留了，所以也就沒有刪除操作發(fā)生，所以會返回false；反之，返回true，并更改數(shù)組
      //而w!=size的時候，即使try塊拋出異常，也能正確處理異常拋出前的操作，因為w始終為要保留的前段部分的長度，數(shù)組也不會因此亂序
      if (w != size) {
        for (int i = w; i < size; i++)
          elementData[i] = null;
        modCount += size - w;//改變的次數(shù)
        size = w;  //新的大小為保留的元素的個數(shù)
        modified = true;
      }
    }
    return modified;
  }
  //保存數(shù)組實例的狀態(tài)到一個流（即它序列化）。寫入過程數(shù)組被更改會拋出異常
  private void writeObject(java.io.ObjectOutputStream s) throws java.io.IOException{
    int expectedModCount = modCount;
    s.defaultWriteObject(); //執(zhí)行默認的反序列化/序列化過程。將當前類的非靜態(tài)和非瞬態(tài)字段寫入此流
    // 寫入大小
    s.writeInt(size);
    // 按順序寫入所有元素
    for (int i=0; i<size; i++) {
      s.writeObject(elementData[i]);
    }
    if (modCount != expectedModCount) {
      throw new ConcurrentModificationException();
    }
  }
  //上面是寫，這個就是讀了。
  private void readObject(java.io.ObjectInputStream s) throws java.io.IOException, ClassNotFoundException {
    elementData = EMPTY_ELEMENTDATA;
    // 執(zhí)行默認的序列化/反序列化過程
    s.defaultReadObject();
    // 讀入數(shù)組長度
    s.readInt();
    if (size > 0) {
      ensureCapacityInternal(size);
      Object[] a = elementData;
      //讀入所有元素
      for (int i=0; i<size; i++) {
        a[i] = s.readObject();
      }
    }
  }
  //返回ListIterator，開始位置為指定參數(shù)
  public ListIterator<E> listIterator(int index) {
    if (index < 0 || index > size)
      throw new IndexOutOfBoundsException("Index: "+index);
    return new ListItr(index);
  }
  //返回ListIterator，開始位置為0
  public ListIterator<E> listIterator() {
    return new ListItr(0);
  }
  //返回普通迭代器
  public Iterator<E> iterator() {
    return new Itr();
  }
  //通用的迭代器實現(xiàn)
  private class Itr implements Iterator<E> {
    int cursor;    //游標，下一個元素的索引，默認初始化為0
    int lastRet = -1; //上次訪問的元素的位置
    int expectedModCount = modCount;//迭代過程不運行修改數(shù)組，否則就拋出異常
    //是否還有下一個
    public boolean hasNext() {
      return cursor != size;
    }
    //下一個元素
    @SuppressWarnings("unchecked")
    public E next() {
      checkForComodification();//檢查數(shù)組是否被修改
      int i = cursor;
      if (i >= size)
        throw new NoSuchElementException();
      Object[] elementData = ArrayList.this.elementData;
      if (i >= elementData.length)
        throw new ConcurrentModificationException();
      cursor = i + 1; //向后移動游標
      return (E) elementData[lastRet = i];  //設置訪問的位置并返回這個值
    }
    //刪除元素
    public void remove() {
      if (lastRet < 0)
        throw new IllegalStateException();
      checkForComodification();//檢查數(shù)組是否被修改
      try {
        ArrayList.this.remove(lastRet);
        cursor = lastRet;
        lastRet = -1;
        expectedModCount = modCount;
      } catch (IndexOutOfBoundsException ex) {
        throw new ConcurrentModificationException();
      }
    }
    @Override
    @SuppressWarnings("unchecked")
    public void forEachRemaining(Consumer<? super E> consumer) {
      Objects.requireNonNull(consumer);
      final int size = ArrayList.this.size;
      int i = cursor;
      if (i >= size) {
        return;
      }
      final Object[] elementData = ArrayList.this.elementData;
      if (i >= elementData.length) {
        throw new ConcurrentModificationException();
      }
      while (i != size && modCount == expectedModCount) {
        consumer.accept((E) elementData[i++]);
      }
      cursor = i;
      lastRet = i - 1;
      checkForComodification();
    }
    //檢查數(shù)組是否被修改
    final void checkForComodification() {
      if (modCount != expectedModCount)
        throw new ConcurrentModificationException();
    }
  }
  //ListIterator迭代器實現(xiàn)
  private class ListItr extends Itr implements ListIterator<E> {
    ListItr(int index) {
      super();
      cursor = index;
    }
    public boolean hasPrevious() {
      return cursor != 0;
    }
    public int nextIndex() {
      return cursor;
    }
    public int previousIndex() {
      return cursor - 1;
    }
    @SuppressWarnings("unchecked")
    public E previous() {
      checkForComodification();
      int i = cursor - 1;
      if (i < 0)
        throw new NoSuchElementException();
      Object[] elementData = ArrayList.this.elementData;
      if (i >= elementData.length)
        throw new ConcurrentModificationException();
      cursor = i;
      return (E) elementData[lastRet = i];
    }
    public void set(E e) {
      if (lastRet < 0)
        throw new IllegalStateException();
      checkForComodification();
      try {
        ArrayList.this.set(lastRet, e);
      } catch (IndexOutOfBoundsException ex) {
        throw new ConcurrentModificationException();
      }
    }
    public void add(E e) {
      checkForComodification();
      try {
        int i = cursor;
        ArrayList.this.add(i, e);
        cursor = i + 1;
        lastRet = -1;
        expectedModCount = modCount;
      } catch (IndexOutOfBoundsException ex) {
        throw new ConcurrentModificationException();
      }
    }
  }
  //返回指定范圍的子數(shù)組
  public List<E> subList(int fromIndex, int toIndex) {
    subListRangeCheck(fromIndex, toIndex, size);
    return new SubList(this, 0, fromIndex, toIndex);
  }
  //安全檢查
  static void subListRangeCheck(int fromIndex, int toIndex, int size) {
    if (fromIndex < 0)
      throw new IndexOutOfBoundsException("fromIndex = " + fromIndex);
    if (toIndex > size)
      throw new IndexOutOfBoundsException("toIndex = " + toIndex);
    if (fromIndex > toIndex)
      throw new IllegalArgumentException("fromIndex(" + fromIndex +
                        ") > toIndex(" + toIndex + ")");
  }
  //子數(shù)組
  private class SubList extends AbstractList<E> implements RandomAccess {
    private final AbstractList<E> parent;
    private final int parentOffset;
    private final int offset;
    int size;
    SubList(AbstractList<E> parent,int offset, int fromIndex, int toIndex) {
      this.parent = parent;
      this.parentOffset = fromIndex;
      this.offset = offset + fromIndex;
      this.size = toIndex - fromIndex;
      this.modCount = ArrayList.this.modCount;
    }
    public E set(int index, E e) {
      rangeCheck(index);
      checkForComodification();
      E oldValue = ArrayList.this.elementData(offset + index);
      ArrayList.this.elementData[offset + index] = e;
      return oldValue;
    }
    public E get(int index) {
      rangeCheck(index);
      checkForComodification();
      return ArrayList.this.elementData(offset + index);
    }
    public int size() {
      checkForComodification();
      return this.size;
    }
    public void add(int index, E e) {
      rangeCheckForAdd(index);
      checkForComodification();
      parent.add(parentOffset + index, e);
      this.modCount = parent.modCount;
      this.size++;
    }
    public E remove(int index) {
      rangeCheck(index);
      checkForComodification();
      E result = parent.remove(parentOffset + index);
      this.modCount = parent.modCount;
      this.size--;
      return result;
    }
    protected void removeRange(int fromIndex, int toIndex) {
      checkForComodification();
      parent.removeRange(parentOffset + fromIndex,parentOffset + toIndex);
      this.modCount = parent.modCount;
      this.size -= toIndex - fromIndex;
    }
    public boolean addAll(Collection<? extends E> c) {
      return addAll(this.size, c);
    }
    public boolean addAll(int index, Collection<? extends E> c) {
      rangeCheckForAdd(index);
      int cSize = c.size();
      if (cSize==0)
        return false;
      checkForComodification();
      parent.addAll(parentOffset + index, c);
      this.modCount = parent.modCount;
      this.size += cSize;
      return true;
    }
    public Iterator<E> iterator() {
      return listIterator();
    }
    public ListIterator<E> listIterator(final int index) {
      checkForComodification();
      rangeCheckForAdd(index);
      final int offset = this.offset;
      return new ListIterator<E>() {
        int cursor = index;
        int lastRet = -1;
        int expectedModCount = ArrayList.this.modCount;
        public boolean hasNext() {
          return cursor != SubList.this.size;
        }
        @SuppressWarnings("unchecked")
        public E next() {
          checkForComodification();
          int i = cursor;
          if (i >= SubList.this.size)
            throw new NoSuchElementException();
          Object[] elementData = ArrayList.this.elementData;
          if (offset + i >= elementData.length)
            throw new ConcurrentModificationException();
          cursor = i + 1;
          return (E) elementData[offset + (lastRet = i)];
        }
        public boolean hasPrevious() {
          return cursor != 0;
        }
        @SuppressWarnings("unchecked")
        public E previous() {
          checkForComodification();
          int i = cursor - 1;
          if (i < 0)
            throw new NoSuchElementException();
          Object[] elementData = ArrayList.this.elementData;
          if (offset + i >= elementData.length)
            throw new ConcurrentModificationException();
          cursor = i;
          return (E) elementData[offset + (lastRet = i)];
        }
        @SuppressWarnings("unchecked")
        public void forEachRemaining(Consumer<? super E> consumer) {
          Objects.requireNonNull(consumer);
          final int size = SubList.this.size;
          int i = cursor;
          if (i >= size) {
            return;
          }
          final Object[] elementData = ArrayList.this.elementData;
          if (offset + i >= elementData.length) {
            throw new ConcurrentModificationException();
          }
          while (i != size && modCount == expectedModCount) {
            consumer.accept((E) elementData[offset + (i++)]);
          }
          // update once at end of iteration to reduce heap write traffic
          lastRet = cursor = i;
          checkForComodification();
        }
        public int nextIndex() {
          return cursor;
        }
        public int previousIndex() {
          return cursor - 1;
        }
        public void remove() {
          if (lastRet < 0)
            throw new IllegalStateException();
          checkForComodification();
          try {
            SubList.this.remove(lastRet);
            cursor = lastRet;
            lastRet = -1;
            expectedModCount = ArrayList.this.modCount;
          } catch (IndexOutOfBoundsException ex) {
            throw new ConcurrentModificationException();
          }
        }
        public void set(E e) {
          if (lastRet < 0)
            throw new IllegalStateException();
          checkForComodification();
          try {
            ArrayList.this.set(offset + lastRet, e);
          } catch (IndexOutOfBoundsException ex) {
            throw new ConcurrentModificationException();
          }
        }
        public void add(E e) {
          checkForComodification();
          try {
            int i = cursor;
            SubList.this.add(i, e);
            cursor = i + 1;
            lastRet = -1;
            expectedModCount = ArrayList.this.modCount;
          } catch (IndexOutOfBoundsException ex) {
            throw new ConcurrentModificationException();
          }
        }
        final void checkForComodification() {
          if (expectedModCount != ArrayList.this.modCount)
            throw new ConcurrentModificationException();
        }
      };
    }
    public List<E> subList(int fromIndex, int toIndex) {
      subListRangeCheck(fromIndex, toIndex, size);
      return new SubList(this, offset, fromIndex, toIndex);
    }
    private void rangeCheck(int index) {
      if (index < 0 || index >= this.size)
        throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
    }
    private void rangeCheckForAdd(int index) {
      if (index < 0 || index > this.size)
        throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
    }
    private String outOfBoundsMsg(int index) {
      return "Index: "+index+", Size: "+this.size;
    }
    private void checkForComodification() {
      if (ArrayList.this.modCount != this.modCount)
        throw new ConcurrentModificationException();
    }
    public Spliterator<E> spliterator() {
      checkForComodification();
      return new ArrayListSpliterator<E>(ArrayList.this, offset,offset + this.size, this.modCount);
    }
  }
  @Override
  public void forEach(Consumer<? super E> action) {
    Objects.requireNonNull(action);
    final int expectedModCount = modCount;
    @SuppressWarnings("unchecked")
    final E[] elementData = (E[]) this.elementData;
    final int size = this.size;
    for (int i=0; modCount == expectedModCount && i < size; i++) {
      action.accept(elementData[i]);
    }
    if (modCount != expectedModCount) {
      throw new ConcurrentModificationException();
    }
  }
  /**
   * Creates a <em><a href="Spliterator.html#binding" rel="external nofollow" >late-binding</a></em>
   * and <em>fail-fast</em> {@link Spliterator} over the elements in this
   * list.
   *
   * <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
   * {@link Spliterator#SUBSIZED}, and {@link Spliterator#ORDERED}.
   * Overriding implementations should document the reporting of additional
   * characteristic values.
   *
   * @return a {@code Spliterator} over the elements in this list
   * @since 1.8
   */
  @Override
  public Spliterator<E> spliterator() {
    return new ArrayListSpliterator<>(this, 0, -1, 0);
  }
  /** Index-based split-by-two, lazily initialized Spliterator */
  static final class ArrayListSpliterator<E> implements Spliterator<E> {
    /*
     * If ArrayLists were immutable, or structurally immutable (no
     * adds, removes, etc), we could implement their spliterators
     * with Arrays.spliterator. Instead we detect as much
     * interference during traversal as practical without
     * sacrificing much performance. We rely primarily on
     * modCounts. These are not guaranteed to detect concurrency
     * violations, and are sometimes overly conservative about
     * within-thread interference, but detect enough problems to
     * be worthwhile in practice. To carry this out, we (1) lazily
     * initialize fence and expectedModCount until the latest
     * point that we need to commit to the state we are checking
     * against; thus improving precision. (This doesn't apply to
     * SubLists, that create spliterators with current non-lazy
     * values). (2) We perform only a single
     * ConcurrentModificationException check at the end of forEach
     * (the most performance-sensitive method). When using forEach
     * (as opposed to iterators), we can normally only detect
     * interference after actions, not before. Further
     * CME-triggering checks apply to all other possible
     * violations of assumptions for example null or too-small
     * elementData array given its size(), that could only have
     * occurred due to interference. This allows the inner loop
     * of forEach to run without any further checks, and
     * simplifies lambda-resolution. While this does entail a
     * number of checks, note that in the common case of
     * list.stream().forEach(a), no checks or other computation
     * occur anywhere other than inside forEach itself. The other
     * less-often-used methods cannot take advantage of most of
     * these streamlinings.
     */
    private final ArrayList<E> list;
    private int index; // current index, modified on advance/split
    private int fence; // -1 until used; then one past last index
    private int expectedModCount; // initialized when fence set
    /** Create new spliterator covering the given range */
    ArrayListSpliterator(ArrayList<E> list, int origin, int fence,
               int expectedModCount) {
      this.list = list; // OK if null unless traversed
      this.index = origin;
      this.fence = fence;
      this.expectedModCount = expectedModCount;
    }
    private int getFence() { // initialize fence to size on first use
      int hi; // (a specialized variant appears in method forEach)
      ArrayList<E> lst;
      if ((hi = fence) < 0) {
        if ((lst = list) == null)
          hi = fence = 0;
        else {
          expectedModCount = lst.modCount;
          hi = fence = lst.size;
        }
      }
      return hi;
    }
    public ArrayListSpliterator<E> trySplit() {
      int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
      return (lo >= mid) ? null : // divide range in half unless too small
        new ArrayListSpliterator<E>(list, lo, index = mid,
                      expectedModCount);
    }
    public boolean tryAdvance(Consumer<? super E> action) {
      if (action == null)
        throw new NullPointerException();
      int hi = getFence(), i = index;
      if (i < hi) {
        index = i + 1;
        @SuppressWarnings("unchecked") E e = (E)list.elementData[i];
        action.accept(e);
        if (list.modCount != expectedModCount)
          throw new ConcurrentModificationException();
        return true;
      }
      return false;
    }
    public void forEachRemaining(Consumer<? super E> action) {
      int i, hi, mc; // hoist accesses and checks from loop
      ArrayList<E> lst; Object[] a;
      if (action == null)
        throw new NullPointerException();
      if ((lst = list) != null && (a = lst.elementData) != null) {
        if ((hi = fence) < 0) {
          mc = lst.modCount;
          hi = lst.size;
        }
        else
          mc = expectedModCount;
        if ((i = index) >= 0 && (index = hi) <= a.length) {
          for (; i < hi; ++i) {
            @SuppressWarnings("unchecked") E e = (E) a[i];
            action.accept(e);
          }
          if (lst.modCount == mc)
            return;
        }
      }
      throw new ConcurrentModificationException();
    }
    public long estimateSize() {
      return (long) (getFence() - index);
    }
    public int characteristics() {
      return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED;
    }
  }
  @Override
  public boolean removeIf(Predicate<? super E> filter) {
    Objects.requireNonNull(filter);
    // figure out which elements are to be removed
    // any exception thrown from the filter predicate at this stage
    // will leave the collection unmodified
    int removeCount = 0;
    final BitSet removeSet = new BitSet(size);
    final int expectedModCount = modCount;
    final int size = this.size;
    for (int i=0; modCount == expectedModCount && i < size; i++) {
      @SuppressWarnings("unchecked")
      final E element = (E) elementData[i];
      if (filter.test(element)) {
        removeSet.set(i);
        removeCount++;
      }
    }
    if (modCount != expectedModCount) {
      throw new ConcurrentModificationException();
    }
    // shift surviving elements left over the spaces left by removed elements
    final boolean anyToRemove = removeCount > 0;
    if (anyToRemove) {
      final int newSize = size - removeCount;
      for (int i=0, j=0; (i < size) && (j < newSize); i++, j++) {
        i = removeSet.nextClearBit(i);
        elementData[j] = elementData[i];
      }
      for (int k=newSize; k < size; k++) {
        elementData[k] = null; // Let gc do its work
      }
      this.size = newSize;
      if (modCount != expectedModCount) {
        throw new ConcurrentModificationException();
      }
      modCount++;
    }
    return anyToRemove;
  }
  @Override
  @SuppressWarnings("unchecked")
  public void replaceAll(UnaryOperator<E> operator) {
    Objects.requireNonNull(operator);
    final int expectedModCount = modCount;
    final int size = this.size;
    for (int i=0; modCount == expectedModCount && i < size; i++) {
      elementData[i] = operator.apply((E) elementData[i]);
    }
    if (modCount != expectedModCount) {
      throw new ConcurrentModificationException();
    }
    modCount++;
  }
  @Override
  @SuppressWarnings("unchecked")
  public void sort(Comparator<? super E> c) {
    final int expectedModCount = modCount;
    Arrays.sort((E[]) elementData, 0, size, c);
    if (modCount != expectedModCount) {
      throw new ConcurrentModificationException();
    }
    modCount++;
  }
}