Arraylist 源码解读-一一网

public static native void arraycopy(Object src,int srcPos, Object dest, int destPos,int length);
src – 源数组。 srcPos – 源数组中的起始位置。 dest – 目标数组。 destPos – 目标数据中的起始位置。 length – 要复制的数组元素的数量。该方法用了native关键字，说明调用的是其他语言写的底层函数
（1）ListIterator有add()方法，可以向List中添加对象，而Iterator不能
（2）ListIterator和Iterator都有hasNext()和next()方法，可以实现顺序向后遍历，但是ListIterator有hasPrevious()和previous()方法，可以实现逆向（顺序向前）遍历。 // Iterator就不可以。
（3）ListIterator可以定位当前的索引位置，nextIndex()和previousIndex()可以实现。Iterator没有此功能。（4）都可实现删除对象，但是ListIterator可以实现对象的修改，set()方法可以实现。Iierator仅能遍历，不能修改。

package java.util;

import java.util.function.Consumer;
import java.util.function.Predicate;
import java.util.function.UnaryOperator;
import sun.misc.SharedSecrets;

/**

@author Josh Bloch
@author Neal Gafter
@see Collection
@see List
@see LinkedList
@see Vector
@since 1.2

public class ArrayList extends AbstractList
implements List, RandomAccess, Cloneable, java.io.Serializable
{
private static final long serialVersionUID = 8683452581122892189L;

/**
 * Default initial capacity. 默认容量
 */
private static final int DEFAULT_CAPACITY = 10;

/**
 * Shared empty array instance used for empty instances. 存储空间 默认是空数组
 */
private static final Object[] EMPTY_ELEMENTDATA = {};

/**
 * Shared empty array instance used for default sized empty instances. We
 * distinguish this from EMPTY_ELEMENTDATA to know how much to inflate when
 * first element is added.
 */
private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};

/**
 * The array buffer into which the elements of the ArrayList are stored.
 * The capacity of the ArrayList is the length of this array buffer. Any
 * empty ArrayList with elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA
 * will be expanded to DEFAULT_CAPACITY when the first element is added.
 */
transient Object[] elementData; // non-private to simplify nested class access

/**
 * The size of the ArrayList (the number of elements it contains).
 *
 * @serial
 */
private int size;
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创建一个固定大小的集合

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);
    }
}
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初始化一个空集合

public ArrayList()
{
    this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
}
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创建一个带有数据的集合

public ArrayList(Collection<? extends E> c)
{
    Object[] a = c.toArray();
    if ((size = a.length) != 0) {
        if (c.getClass() == ArrayList.class) {
            elementData = a;
        } else {
            elementData = Arrays.copyOf(a, size, Object[].class);
        }
    } else {
        // replace with empty array.
        elementData = EMPTY_ELEMENTDATA;
    }
}
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压缩数组中的容量让数组开辟的空间=真实存放的元素的数量数可以节约内存

public void trimToSize()
{
    //修改次数+1
    modCount++;
    if (size < elementData.length)
    {
        // 如果集合中存放的数据 数量 <数组开辟的容量
        elementData = (size == 0)
                ? EMPTY_ELEMENTDATA
                : Arrays.copyOf(elementData, size);
        // 复制数组到一个新数组
    }
}

/**
 * Increases the capacity of this <tt>ArrayList</tt> instance, if
 * necessary, to ensure that it can hold at least the number of elements
 * specified by the minimum capacity argument.
 *
 * @param   minCapacity   the desired minimum capacity
 */
public void ensureCapacity(int minCapacity) {
    int minExpand = (elementData != DEFAULTCAPACITY_EMPTY_ELEMENTDATA)
            // any size if not default element table
            ? 0
            // larger than default for default empty table. It's already
            // supposed to be at default size.
            : DEFAULT_CAPACITY;

    if (minCapacity > minExpand) {
        ensureExplicitCapacity(minCapacity);
    }
}
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minCapacity = size+1

计算容量

private static int calculateCapacity(Object[] elementData, int minCapacity)
{
    // 如果是空数组 
    if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA)
    {
        // 返回10 和传入值的最大值 
        return Math.max(DEFAULT_CAPACITY, minCapacity);
    }
    // 如果不是空数组 返回传入的值 minCapacity
    return minCapacity;
}

/**
 minCapacity = size+1;
 **/
private void ensureCapacityInternal(int minCapacity)
{
    //  ulateCapacity(elementData, minCapacity) 等于size+1
    ensureExplicitCapacity(calculateCapacity(elementData, minCapacity));
}

/**
 如果增加数据后导致容量不足  判断是否要扩容 在ad方法调用的时候 会调用这个函数
 */
private void ensureExplicitCapacity(int minCapacity)
{
    // 修改次数+1
    modCount++;
    // overflow-conscious code
    if (minCapacity - elementData.length > 0)
        // 扩容
        grow(minCapacity);
}

/**
 * The maximum size of array to allocate.
 * Some VMs reserve some header words in an array.
 * Attempts to allocate larger arrays may result in
 * OutOfMemoryError: Requested array size exceeds VM limit
 */
private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
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当数组是空的时候minCapacity =10 当数组不是空的时候 minCapacity = size+1

就是添加后元素的个数扩容

private void grow(int minCapacity)
{
    // overflow-conscious code
    int oldCapacity = elementData.length;
    // 新的容量是原来的1.5
    int newCapacity = oldCapacity + (oldCapacity >> 1);
    if (newCapacity - minCapacity < 0)
        // 添加第一个元素的时候 会执行这里 newCapacity =10;
        newCapacity = minCapacity;
    if (newCapacity - MAX_ARRAY_SIZE > 0)
        newCapacity = hugeCapacity(minCapacity);
    // 扩容  elementData 老数组 newCapacity 新数组的容量 
    // 创建一个新的数组 然后把原来数组存放的数据填充到新数组
    elementData = Arrays.copyOf(elementData, newCapacity);

    /**
     public static byte[] copyOf(byte[] original, int newLength) {
     // 创建一个新容量的数组 newLength= 容量大小
     byte[] copy = new byte[newLength];
     System.arraycopy(original, 0, copy, 0,
     Math.min(original.length, newLength));
     return copy; }*/
}


private static int hugeCapacity(int minCapacity)
{
    if (minCapacity < 0) // overflow
        throw new OutOfMemoryError();
    return (minCapacity > MAX_ARRAY_SIZE) ?
            Integer.MAX_VALUE :
            MAX_ARRAY_SIZE;
}
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判断集合中元素数量

public int size()
{
    return size;
}
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判断集合是否空

public boolean isEmpty()
{
    return size == 0;
}
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判断某个元素是否在集合中

利用查询元素在数组下标的值判断是否有这个值

public boolean contains(Object o)
{
    return indexOf(o) >= 0;
}
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查询元素在数组中那个位置下标值index

如果没有返回-1

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;
}
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倒序查询某个元素在数组中的下标位置index

如果查询失败返回-1

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;
}
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Object类的clone 方法是浅复制

ArrayList.clone 方法是浅复制

public Object clone()
{
    try {
        // 复制一个数组  指针v 指向 --->和原来一个数组指向一样的堆空间
        ArrayList<?> v = (ArrayList<?>) super.clone();
        // 所以复制一份数组 Arrays.copyOf(elementData, size); 返回一个新的数组
        // V.elementData 指针指向 新的数组
        v.elementData = Arrays.copyOf(elementData, size);
        v.modCount = 0;
        // 返回v
        return v;
    } catch (CloneNotSupportedException e) {
        // this shouldn't happen, since we are Cloneable
        throw new InternalError(e);
    }
}
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把list集合转为数组其实就是调用System.arraycopy（）

方法生成一个新的Object[] 数组

public Object[] toArray()
{
    return Arrays.copyOf(elementData, size);
}
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把集合转成任意数组这是个泛型方法

@SuppressWarnings("unchecked")
public <T> T[] toArray(T[] a)
{
    if (a.length < size)
        // 如果传的数组元素个数小于 复制数组  把 复制数组的数据全部复制一遍
        return (T[]) Arrays.copyOf(elementData, size, a.getClass());
    // 如果 大于也是全部复制
    System.arraycopy(elementData, 0, a, 0, size);
    if (a.length > size)
        a[size] = null;
    return a;
}

// Positional Access Operations
// 内部使用函数 get 指定位置的数据
@SuppressWarnings("unchecked")
E elementData(int index)
{
    return (E) elementData[index];
}
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通过下标获取数据

public E get(int index)
{
    // 校验index 是否数组下标越界
    rangeCheck(index);

    return elementData(index);
}
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替换index 位置的值返回替换前的值

public E set(int index, E element)
{

    // 校验index 是否数组下标越界
    rangeCheck(index);

    E oldValue = elementData(index);
    elementData[index] = element;
    return oldValue;
}
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添加数据要验证是否扩容

public boolean add(E e)
{
    // 校验是否要扩容
    ensureCapacityInternal(size + 1);
    // 数量加+1
    elementData[size++] = e;
    return true;
}
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添加指定位置index 数据

public void add(int index, E element)
{
    rangeCheckForAdd(index);

    ensureCapacityInternal(size + 1);

    // 移动位置
    System.arraycopy(elementData, index, elementData, index + 1,
            size - index);
    elementData[index] = element;
    size++;
}
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删除Index 位置的下标

返回删除index 位置的value

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; // clear to let GC do its work

    return oldValue;
}
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删除某个值

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;
}
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删除指定位置Index 值

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
}
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清空集合存放的数据

public void clear()
{
    modCount++;

    // clear to let GC do its work
    for (int i = 0; i < size; i++)
        elementData[i] = null;

    size = 0;
}
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合并2个集合中的数据

c 要合并的集合

public boolean addAll(Collection<? extends E> c)
{
    // 把集合转数组
    Object[] a = c.toArray();
    // 数组元素个数
    int numNew = a.length;
    // 验证是否要扩容
    ensureCapacityInternal(size + numNew);  // Increments modCount
    // 复制数组从index =size 出开始复制
    System.arraycopy(a, 0, elementData, size, numNew);
    size += numNew;
    return numNew != 0;
}
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从指定位置插入数据

public boolean addAll(int index, Collection<? extends E> c)
{
    rangeCheckForAdd(index);

    Object[] a = c.toArray();
    int numNew = a.length;
    ensureCapacityInternal(size + numNew);  // Increments modCount

    int numMoved = size - index;
    if (numMoved > 0)
        System.arraycopy(elementData, index, elementData, index + numNew,
                numMoved);

    System.arraycopy(a, 0, elementData, index, numNew);
    size += numNew;
    return numNew != 0;
}
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* 删除范围内的数据 fromIndex toIndex 1 2 3 4 5

子类方法不包含 toIndex

protected void removeRange(int fromIndex, int toIndex)
{
    modCount++;
    // 
    int numMoved = size - toIndex;
    System.arraycopy(elementData, toIndex, elementData, fromIndex,
            numMoved);

    // clear to let GC do its work
    // toIndex-fromIndex 表示删除元素个数  nexSize 剩下的数量
    int newSize = size - (toIndex-fromIndex);
    for (int i = newSize; i < size; i++) {
        elementData[i] = null;
    }
    size = newSize;
}
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校验index 值异常抛出异常

private void rangeCheck(int index)
{
    if (index >= size)
        throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
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校验index值

private void rangeCheckForAdd(int index)
{
    if (index > size || index < 0)
        throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
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异常提示信息

private String outOfBoundsMsg(int index)
{
    return "Index: "+index+", Size: "+size;
}
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批量删除

public boolean removeAll(Collection<?> c)
{
    Objects.requireNonNull(c);
    return batchRemove(c, false);
}

/**
 * Retains only the elements in this list that are contained in the
 * specified collection.  In other words, removes from this list all
 * of its elements that are not contained in the specified collection.
 *
 * @param c collection containing elements to be retained in this list
 * @return {@code true} if this list changed as a result of the call
 * @throws ClassCastException if the class of an element of this list
 *         is incompatible with the specified collection
 * (<a href="https://juejin.cn/post/Collection.html#optional-restrictions">optional</a>)
 * @throws NullPointerException if this list contains a null element and the
 *         specified collection does not permit null elements
 * (<a href="https://juejin.cn/post/Collection.html#optional-restrictions">optional</a>),
 *         or if the specified collection is null
 * @see Collection#contains(Object)
 */
public boolean retainAll(Collection<?> c)
{
    Objects.requireNonNull(c);
    return batchRemove(c, true);
}

private boolean batchRemove(Collection<?> c, boolean complement)
{
    // 原数组
    final Object[] elementData = this.elementData;
    int r = 0, w = 0;
    boolean modified = false;
    try {
        // elementData 遍历数组 
        for (; r < size; r++)
            // 如果在集合中 
            if (c.contains(elementData[r]) == complement)
                elementData[w++] = elementData[r];
    } finally {
        // Preserve behavioral compatibility with AbstractCollection,
        // even if c.contains() throws.
        if (r != size) {
            System.arraycopy(elementData, r,
                    elementData, w,
                    size - r);
            w += size - r;
        }
        if (w != size) {
            // clear to let GC do its work
            for (int i = w; i < size; i++)
                elementData[i] = null;
            modCount += size - w;
            size = w;
            modified = true;
        }
    }
    return modified;
}

/**
 * Save the state of the <tt>ArrayList</tt> instance to a stream (that
 * is, serialize it).
 *
 * @serialData The length of the array backing the <tt>ArrayList</tt>
 *             instance is emitted (int), followed by all of its elements
 *             (each an <tt>Object</tt>) in the proper order.
 */
private void writeObject(java.io.ObjectOutputStream s)
        throws java.io.IOException{
    // Write out element count, and any hidden stuff
    int expectedModCount = modCount;
    s.defaultWriteObject();

    // Write out size as capacity for behavioural compatibility with clone()
    s.writeInt(size);

    // Write out all elements in the proper order.
    for (int i=0; i<size; i++) {
        s.writeObject(elementData[i]);
    }

    if (modCount != expectedModCount) {
        throw new ConcurrentModificationException();
    }
}

/**
 * Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
 * deserialize it).
 */
private void readObject(java.io.ObjectInputStream s)
        throws java.io.IOException, ClassNotFoundException {
    elementData = EMPTY_ELEMENTDATA;

    // Read in size, and any hidden stuff
    s.defaultReadObject();

    // Read in capacity
    s.readInt(); // ignored

    if (size > 0) {
        // be like clone(), allocate array based upon size not capacity
        int capacity = calculateCapacity(elementData, size);
        SharedSecrets.getJavaOISAccess().checkArray(s, Object[].class, capacity);
        ensureCapacityInternal(size);

        Object[] a = elementData;
        // Read in all elements in the proper order.
        for (int i=0; i<size; i++) {
            a[i] = s.readObject();
        }
    }
}

/**
 ListIterator 迭代器 比 Iterator 强大
 */
public ListIterator<E> listIterator(int index)
{
    if (index < 0 || index > size)
        throw new IndexOutOfBoundsException("Index: "+index);
    return new ListItr(index);
}

/**
 * 创建ListItr对象   ListItr extends Itr implements ListIterator
 这个对象有迭代器Iterator的方法和增加了部分Iterator迭代器没有的方法
 创建ListIterator 迭代器 对象
 */
public ListIterator<E> listIterator()
{
    return new ListItr(0);
}

/**
 * 集合迭代器Iterator
 */
public Iterator<E> iterator()
{
    return new Itr();
}

/**
 *  集合迭代器Iterator实现类
 */
private class Itr implements Iterator<E>
{

    // 下一个元素下标位置 默认值是0
    int cursor;       // index of next element to return
    // 取到值的下标位置 = cursor-1  这个值其实没啥用
    int lastRet = -1; // index of last element returned; -1 if no such
    int expectedModCount = modCount;

    Itr() {}

    public boolean hasNext()
    {
        // 判断集合中是否遍历完了 
        return cursor != size;
    }

    // 从下标index =0 index=1 到index=size-1 顺序取值
    @SuppressWarnings("unchecked")
    public E next()
    {
        checkForComodification();
        int i = cursor;
        if (i >= size)
            throw new NoSuchElementException();
        Object[] elementData = ArrayList.this.elementData;
        if (i >= elementData.length)
            throw new ConcurrentModificationException();
        cursor = i + 1;
        return (E) elementData[lastRet = i];
    }

    // 删除数据  其实就是调用remove(index) 方法 然后移动游标
    public void remove()
    {
        if (lastRet < 0)
            throw new IllegalStateException();
        // 校验是否有并发修改的情况 
        checkForComodification();

        try {
            // 调用集合中remove(index) 指定下标的方法
            ArrayList.this.remove(lastRet);
            // 当前游标数量-1 不然删除不了后面相同的数据
            cursor = lastRet;
            // 恢复原来默认值
            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++]);
        }
        // update once at end of iteration to reduce heap write traffic
        cursor = i;
        lastRet = i - 1;
        checkForComodification();
    }

    // 判断是否存在并发修改的情况
    final void checkForComodification() {
        if (modCount != expectedModCount)
            throw new ConcurrentModificationException();
    }
}

/**
 *  ListItr 继承了 Itr 迭代器 有hasNext next remove 等方法 
 增加了部分不 Itr 没有的方法
 */
private class ListItr extends Itr implements ListIterator<E>
{
    ListItr(int index) {
        super();
        // 默认cursor = 0
        cursor = index;
    }

    public boolean hasPrevious()
    {
        return cursor != 0;
    }

    /** 获取cursor 值*/
    public int nextIndex()
    {
        return cursor;
    }

    /** 获取cursor 值 -1 */
    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];
    }

    // 在遍历的过程中 替换值
    public void set(E e)
    {
        if (lastRet < 0)
            throw new IllegalStateException();
        checkForComodification();

        try {
            ArrayList.this.set(lastRet, e);
        } catch (IndexOutOfBoundsException ex) {
            throw new ConcurrentModificationException();
        }
    }

    // 在遍历的过程中添加元素 添加元素的位置是index=cursor
    public void add(E e)
    {
        checkForComodification();

        try {
            //添加的index
            int i = cursor;
            // 在某个index 位置添加元素
            ArrayList.this.add(i, e);
            // 跳过添加的元素
            cursor = i + 1;
            lastRet = -1;
            expectedModCount = modCount;
        } catch (IndexOutOfBoundsException ex) {
            throw new ConcurrentModificationException();
        }
    }
}

/**
 * Returns a view of the portion of this list between the specified
 * {@code fromIndex}, inclusive, and {@code toIndex}, exclusive.  (If
 * {@code fromIndex} and {@code toIndex} are equal, the returned list is
 * empty.)  The returned list is backed by this list, so non-structural
 * changes in the returned list are reflected in this list, and vice-versa.
 * The returned list supports all of the optional list operations.
 *
 * <p>This method eliminates the need for explicit range operations (of
 * the sort that commonly exist for arrays).  Any operation that expects
 * a list can be used as a range operation by passing a subList view
 * instead of a whole list.  For example, the following idiom
 * removes a range of elements from a list:
 * <pre>
 *      list.subList(from, to).clear();
 * </pre>
 * Similar idioms may be constructed for {@link #indexOf(Object)} and
 * {@link #lastIndexOf(Object)}, and all of the algorithms in the
 * {@link Collections} class can be applied to a subList.
 *
 * <p>The semantics of the list returned by this method become undefined if
 * the backing list (i.e., this list) is <i>structurally modified</i> in
 * any way other than via the returned list.  (Structural modifications are
 * those that change the size of this list, or otherwise perturb it in such
 * a fashion that iterations in progress may yield incorrect results.)
 *
 * @throws IndexOutOfBoundsException {@inheritDoc}
 * @throws IllegalArgumentException {@inheritDoc}
 */
public List<E> subList(int fromIndex, int toIndex) {
    subListRangeCheck(fromIndex, toIndex, size);
    return new SubList(this, 0, fromIndex, toIndex);
}

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 + ")");
}

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);
    }
}


// 遍历集合
@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="https://juejin.cn/post/Spliterator.html#binding">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++;
}
复制代码

}

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