ArrayList源码阅读jdk1.8

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

//默认长度
private static final int DEFAULT_CAPACITY = 10;

//空的数组
private static final Object[] EMPTY_ELEMENTDATA = {};

private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};

//实际存储元素的缓存数组，如果第一次添加的时候为空，那么会扩展到默认大小
transient Object[] elementData; // non-private to simplify nested class access

//实际存储的元素个数
private int size;

//初始化缓存数组，将设置长度为传入的长度
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);
}
}

//如果没有传入，设置缓存数组为空数组，长度为0
public ArrayList() {
this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
}

//接收一个集合，
public ArrayList(Collection<? extends E> c) {
elementData = c.toArray();
if ((size = elementData.length) != 0) {
// c.toArray might (incorrectly) not return Object[] (see 6260652)
if (elementData.getClass() != Object[].class)
elementData = Arrays.copyOf(elementData, size, Object[].class);
} else {
// replace with empty array.
this.elementData = EMPTY_ELEMENTDATA;
}
}

(bug:6260652)原因：由于Arrays.asList的toArray()实现和List的toArray()实现的不同导致的

//Arrays$ArraysList.toArray()的方法,所以数组是什么类型就转换成什么类型
private final E[] a;
@Override
public Object[] toArray() {
return a.clone();
}

//ArrayList的toArray如下
transient Object[] elementData;

public Object[] toArray() {
return Arrays.copyOf(elementData, size);
}

//样例如下:
List<String> test = Arrays.asList("abc");
ArrayList<String> strings = new ArrayList<>();
Object[] object1 = test.toArray();
System.out.println(object1.getClass());
//class [Ljava.lang.String;

List<String> arraysTest = new ArrayList<String>(test);
Object[] object2 = arraysTest.toArray();
System.out.println(object2.getClass());
//class [Ljava.lang.Object;

//缩小当前的数组长度到元素大小,会造成一次复制,
//并且要把modCount:监控是否有修改,用于fail-fast
public void trimToSize() {
modCount++;
if (size < elementData.length) {
elementData = (size == 0)
? EMPTY_ELEMENTDATA
: Arrays.copyOf(elementData, size);
}
}

//扩容到指定的大小
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;
//如果需要的能力,比最小扩容大,就扩容
if (minCapacity > minExpand) {
ensureExplicitCapacity(minCapacity);
}
}
//计算大小，如果是空的取最大值
private static int calculateCapacity(Object[] elementData, int minCapacity) {
if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
return Math.max(DEFAULT_CAPACITY, minCapacity);
}
return minCapacity;
}

private void ensureCapacityInternal(int minCapacity) {
ensureExplicitCapacity(calculateCapacity(elementData, minCapacity));
}
//首先把修改modCount标记++,然后如果需要的大小,比元素的大小大,那么扩容.
private void ensureExplicitCapacity(int minCapacity) {
modCount++;

// overflow-conscious code
if (minCapacity - elementData.length > 0)
grow(minCapacity);
}

//数组安全判断大小为int最大值减去8
private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;

//将原来的长度扩展为1.5倍,与需要的容量比较,如果还是小于,那么就扩展成需要的容量,如果需要的容量减去最大数组值大于0,要进行最大能力判断.
private void grow(int minCapacity) {
// overflow-conscious code
int oldCapacity = elementData.length;
int newCapacity = oldCapacity + (oldCapacity >> 1);
if (newCapacity - minCapacity < 0)
newCapacity = minCapacity;
if (newCapacity - MAX_ARRAY_SIZE > 0)
newCapacity = hugeCapacity(minCapacity);
// minCapacity is usually close to size, so this is a win:
elementData = Arrays.copyOf(elementData, newCapacity);
}
/
1fff7
/大容量的扩容，判断是否会内存溢出。
//如果minCapacity = Integer.MAX_VALUE +1,
//mark = (minCapacity  - Integer.MAX_VALUE) >0
private static int hugeCapacity(int minCapacity) {
if (minCapacity < 0) // overflow
throw new OutOfMemoryError();
return (minCapacity > MAX_ARRAY_SIZE) ?
Integer.MAX_VALUE :
MAX_ARRAY_SIZE;
}

//返回数组内实际存放的元素个数
public int size() {
return size;
}

public boolean isEmpty() {
return size == 0;
}

//是否包含该元素，利用的equals
public boolean contains(Object o) {
return indexOf(o) >= 0;
}

//遍历判断分为null和非null两种情况，本质是遍历数据缓冲数组，顺序从前往后遍历
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;
}

//同上，从后往前遍历
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;
}

//拷贝一个数组返回，是一个新的对象
public Object clone() {
try {
ArrayList<?> v = (ArrayList<?>) super.clone();
v.elementData = Arrays.copyOf(elementData, size);
v.modCount = 0;
return v;
} catch (CloneNotSupportedException e) {
// this shouldn't happen, since we are Cloneable
throw new InternalError(e);
}
}

//返回一个copy出来的数组，对外可以随意修改，不影响当前list引用
public Object[] toArray() {
return Arrays.copyOf(elementData, size);
}

//转换成一个指定的类型，如果传入的数组长度小于原数组，那么直接使用原数组的长度去做复制。
public <T> T[] toArray(T[] a) {
if (a.length < size)
// Make a new array of a's runtime type, but my contents:
return (T[]) Arrays.copyOf(elementData, size, a.getClass());
System.arraycopy(elementData, 0, a, 0, size);
if (a.length > size)
a[size] = null;
return a;
}

//获取指定位置的元素
@SuppressWarnings("unchecked")
E elementData(int index) {
return (E) elementData[index];
}

//先判断范围，仅仅判断是不是大于size，如果超过，那么抛出异常
public E get(int index) {
rangeCheck(index);

return elementData(index);
}

//将指定位置的元素替换成传入的，并且返回旧的元素
public E set(int index, E element) {
rangeCheck(index);

E oldValue = elementData(index);
elementData[index] = element;
return oldValue;
}

//先检查长度，ensureCapacityInternal方法。并且在该方法中修改modCount，如果需要扩容就扩容
public boolean add(E e) {
ensureCapacityInternal(size + 1);  // Increments modCount!!
elementData[size++] = e;
return true;
}

//判断范围,是否大于size与小于0，移动数组位置，然后复制
public void add(int index, E element) {
rangeCheckForAdd(index);

ensureCapacityInternal(size + 1);  // Increments modCount!!
System.arraycopy(elementData, index, elementData, index + 1,
size - index);
elementData[index] = element;
size++;
}

//判断范围，计算需要移动的个数，如果是最后一位就不需要移动，否则移动元素并且要把最后一位设置为null，以便gc去回收
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;
}
//fastRemove是remove(int index)的简化版，移除匹配的第一个对象
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;
}

//参考remove(int index),简化版
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
}

//遍历把对象设置为null
public void clear() {
modCount++;

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

size = 0;
}

//添加一个集合元素c到list的队尾,不判断c是否为空集合，都执行操作
public boolean addAll(Collection<? extends E> c) {
Object[] a = c.toArray();
int numNew = a.length;
ensureCapacityInternal(size + numNew);  // Increments modCount
System.arraycopy(a, 0, elementData, size, numNew);
size += numNew;
return numNew != 0;
}

//将集合元素添加到指定的位置
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;
}

//计算移除后是否需要移动，先移动元素，然后把最后多余的引用设置为null，并改变大小size
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
int newSize = size - (toIndex-fromIndex);
for (int i = newSize; i < size; i++) {
elementData[i] = null;
}
size = newSize;
}

//判断范围，使用函数get,set,remove,不检查负数，负数由数组来报错
private void rangeCheck(int index) {
if (index >= size)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}

//判断范围，添加方法使用。为了throw early?(待完全查看)
private void rangeCheckForAdd(int index) {
if (index > size || index < 0)
throw new ndexOutOfBoundsException(outOfBoundsMsg(index));
}

//异常抛出错误
private String outOfBoundsMsg(int index) {
return "Index: "+index+", Size: "+size;
}

//移除集合c中包含的元素，关键是传入的false参数
public boolean removeAll(Collection<?> c) {
Objects.requireNonNull(c);
return batchRemove(c, false);
}

//取交集，和上面的相反
public boolean retainAll(Collection<?> c) {
Objects.requireNonNull(c);
return batchRemove(c, true);
}
//移除和取交集的核心方法，通过参数complement去控制，不监测c的null值，需要调用方控制
private boolean batchRemove(Collection<?> c, boolean complement) {
final Object[] elementData = this.elementData;
int r = 0, w = 0;
boolean modified = false;
try {
//遍历集合，r为变量标志，根据complement的不同，把匹配到的元素放到elementData 的开始。
for (; r < size; r++)
if (c.contains(elementData[r]) == complement)
elementData[w++] = elementData[r];
} finally {
// Preserve behavioral compatibility with AbstractCollection,
// even if c.contains() throws.
//此处为了保证如果操作中途抛出异常，尽量恢复数组内还未操作的元素。
if (r != size) {
System.arraycopy(elementData, r,
elementData, w,
size - r);
w += size - r;
}
//此处判断是否需要缩小数组，并且移除没用的元素，防止内存泄漏
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;
}

//由于elementData被修饰为不可序列化的，通过如下方法写入流中
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();
}
}

//作用同上，读取用
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();
}
}
}
//返回一个从指定位置开始的listIterator迭代器
public ListIterator<E> listIterator(int index) {
if (index < 0 || index > size)
throw new IndexOutOfBoundsException("Index: "+index);
return new ListItr(index);
}

//返回从0开始的listIterator迭代器
public ListIterator<E> listIterator() {
return new ListItr(0);
}

//返回一个迭代器，都是fail-faster
public Iterator<E> iterator() {
return new Itr();
}

//迭代器，
private class Itr implements Iterator<E> {
//下一个元素的返回位置
int cursor;       // index of next element to return
//当前元素返回的位置
int lastRet = -1; // index of last element returned; -1 if no such
//创建的时候，记录list的操作数量，用于判断是不是被操作了
int expectedModCount = modCount;

Itr() {}
//是否有下一个
public boolean hasNext() {
return cursor != size;
}
//需要正确处理多线程并发时候的问题
@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;
//问题：感觉此处还是有多线程问题，当i>=元素长度时
return (E) elementData[lastRet = i];
}
//删除已经返回的上一个元素，需要谨慎处理cursor、lastRet、expectedModCount
public void remove() {
if (lastRet < 0)
throw new IllegalStateException();
checkForComodification();

try {
ArrayList.this.remove(lastRet);
cursor = lastRet;
lastRet = -1;
expectedModCount = modCount;
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}
//TODO：没太理解这个方法干吗的。
@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();
}
//检查是否被操作，通过判断modCount
final void checkForComodification() {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
}
}

//返回一个ListIterator，增加了元素操作功能，并且具备往前遍历的功能
private class ListItr extends Itr implements ListIterator<E> {
ListItr(int index) {
super();
cursor = index;
}
//cursor 不为0则有前一个。cursor 只有+操作
public boolean hasPrevious() {
return cursor != 0;
}

public int nextIndex() {
return cursor;
}

public int previousIndex() {
return cursor - 1;
}
//遍历前一个，要注意cursor和lastRet的变化
@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();
}
}
}

//生成一个子列，子列的操作会反应到主列中
public List<E> subList(int fromIndex, int toIndex) {
subListRangeCheck(fromIndex, toIndex, size);
return new SubList(this, 0, fromIndex, toIndex);
}
//子列的范围校验
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 {
//实际的list的引用
private final AbstractList<E> parent;
//fromIndex的偏移
private final int parentOffset;
//队列的偏移
private final int offset;
//子列的元素个数
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;
}
//设置元素，逻辑同上，只是使用的索引位置不同。
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);
}
//委托父类的方法处理
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();
}
//根据子列的偏移量生成了一个迭代器
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();
}
};
}
//子列再生产子列，注意偏移量
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();
}
}

//返回一个可以并行操作的ArrayListSpliterator
@Override
public Spliterator<E> spliterator() {
return new ArrayListSpliterator<>(this, 0, -1, 0);
}

Spliterator：是一个实现并行处理的接口，参考网上的内容得到引用网址：https://blog.csdn.net/lh513828570/article/details/56673804

static final class ArrayListSpliterator<E> implements Spliterator<E> {

//保存list引用
private final ArrayList<E> list;
//索引位置
private int index; // current index, modified on advance/split
//list结束为止，默认为-1，使用的时候通过getFence()初始化
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;
}
//获取list的最后的位置
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;
}
//尝试切割list，新产生的ArrayListSpliterator是前半,留下的是后半
public ArrayListSpliterator<E> trySplit() {
//hi：末尾，lo：开头，mid：中间位置
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);
}
//传入一个执行动作action，执行一次
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;
}
//剩下的所以元素遍历执行action，需要比较和tryAdvance的区别。
//如果已经执行过forEachRemaining或tryAdvance，index会增加。
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++;
}
}