ArrayList 源码精读（JDK 11 中文注释版）
返回建议阅读顺序：
- 先看 JDK 8 版本的源码精读，理解主干实现；
- 再查看本页，注意对比：
- 构造方法与
ensureCapacity的行为差异； equals/hashCode、removeIf/replaceAll等新方法的实现；- 对
SubList、Spliterator等类的改动。
- 构造方法与
/*
* 本文件基于 JDK 11 的 ArrayList 源码，加入中文注释，帮助理解其实现。
* 代码结构与官方源码保持一致，仅在关键位置补充中文说明。
*/
package java.util;
import java.util.function.Consumer;
import java.util.function.Predicate;
import java.util.function.UnaryOperator;
import jdk.internal.misc.SharedSecrets;
/**
* ArrayList：基于可扩容数组实现的 {@code List}。
*
* 主要特性：
* 1）底层是 Object[] 顺序存储，支持随机访问，get/set O(1)。
* 2）支持自动扩容，默认容量 10，扩容策略为 1.5 倍左右。
* 3）非线程安全，多线程并发修改需外部加锁或用 Collections.synchronizedList。
* 4）迭代器 / Spliterator / forEach / removeIf / replaceAll / sort 等都具备 fail-fast 能力，通过 modCount 检测并发修改。
*
* 与 JDK8/JDK7 相比，JDK11 关键差异：
* - 扩容逻辑抽取为 grow/newCapacity，ensureCapacity 逻辑稍有精简。
* - indexOf/lastIndexOf 提取 indexOfRange/lastIndexOfRange，SubList 重构为“树状子列表”，支持嵌套。
* - 使用 jdk.internal.misc.SharedSecrets 替代 sun.misc.SharedSecrets 做安全检查。
*/
public class ArrayList<E> extends AbstractList<E>
implements List<E>, RandomAccess, Cloneable, java.io.Serializable
{
// 序列化版本号
private static final long serialVersionUID = 8683452581122892189L;
/**
* 默认初始容量：10
*/
private static final int DEFAULT_CAPACITY = 10;
/**
* 共享空数组：用于“显式容量为 0” 的 ArrayList（如 new ArrayList(0)、从空集合构造）。
*/
private static final Object[] EMPTY_ELEMENTDATA = {};
/**
* 默认空数组：用于无参构造创建的 ArrayList。
* 与 EMPTY_ELEMENTDATA 区分，是为了首次 add 时知道要扩容到多少（DEFAULT_CAPACITY）。
*/
private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};
/**
* 真实存储元素的数组：
* - 容量 = elementData.length
* - 当 elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA 时，首次添加元素会扩至 DEFAULT_CAPACITY
*
* 非 private，方便内部嵌套类（如 SubList、ArrayListSpliterator）直接访问。
*/
transient Object[] elementData;
/**
* 实际元素个数（逻辑大小）
*
* @serial
*/
private int size;
// ====================== 构造方法 ======================
/**
* 指定初始容量的构造。
*
* - initialCapacity > 0：直接 new Object[initialCapacity]
* - initialCapacity == 0：使用 EMPTY_ELEMENTDATA
* - initialCapacity < 0：抛 IllegalArgumentException
*/
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);
}
}
/**
* 无参构造：延迟分配真实容量。
*
* 初始时使用 DEFAULTCAPACITY_EMPTY_ELEMENTDATA，首次 add 时扩容到 DEFAULT_CAPACITY。
*/
public ArrayList() {
this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
}
/**
* 使用指定集合元素构造 ArrayList。
*
* 注意：
* - 先直接用 c.toArray() 的结果作为 elementData；
* - 若 size > 0 且返回的不是 Object[]，则通过 Arrays.copyOf 强制拷贝为 Object[]；
* - 若 size == 0，则回退到 EMPTY_ELEMENTDATA。
*/
public ArrayList(Collection<? extends E> c) {
elementData = c.toArray();
if ((size = elementData.length) != 0) {
// 防御：c.toArray 可能不是 Object[]（某些错误实现），因此确保类型正确
if (elementData.getClass() != Object[].class)
elementData = Arrays.copyOf(elementData, size, Object[].class);
} else {
this.elementData = EMPTY_ELEMENTDATA;
}
}
// ====================== 容量管理 ======================
/**
* trimToSize：将容量裁剪到当前 size，释放多余空间。
*/
public void trimToSize() {
modCount++;
if (size < elementData.length) {
elementData = (size == 0)
? EMPTY_ELEMENTDATA
: Arrays.copyOf(elementData, size);
}
}
/**
* ensureCapacity：如有必要，增加容量到不少于 minCapacity。
*
* 逻辑：
* - 若 minCapacity > elementData.length，且不是“默认空表且要求不超过默认容量”的情况，则：
* - modCount++；
* - 调用 grow(minCapacity) 扩容。
*/
public void ensureCapacity(int minCapacity) {
if (minCapacity > elementData.length
&& !(elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA
&& minCapacity <= DEFAULT_CAPACITY)) {
modCount++;
grow(minCapacity);
}
}
/**
* 能够分配的最大数组长度（预留一部分头信息空间）。
*/
private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
/**
* grow：扩容至至少 minCapacity。
*
* 由 newCapacity 计算新容量，再通过 Arrays.copyOf 完成扩容。
*/
private Object[] grow(int minCapacity) {
return elementData = Arrays.copyOf(elementData,
newCapacity(minCapacity));
}
/**
* grow() 无参版本：默认按 size+1 来计算最小容量，多用于 add 时自动扩容。
*/
private Object[] grow() {
return grow(size + 1);
}
/**
* newCapacity：根据旧容量/默认容量/最大容量等综合计算新的扩容大小。
*
* 规则：
* 1）基础新容量 = oldCapacity + oldCapacity/2（即 1.5 倍）；
* 2）如果 1.5 倍仍 < minCapacity：
* - 若当前是默认空表 DEFAULTCAPACITY_EMPTY_ELEMENTDATA，则返回 max(DEFAULT_CAPACITY, minCapacity)；
* - 若 minCapacity < 0，则溢出，抛 OutOfMemoryError；
* - 否则直接返回 minCapacity；
* 3）若 1.5 倍 > MAX_ARRAY_SIZE，则通过 hugeCapacity 进行上限裁剪；
* 4）否则返回 newCapacity。
*/
private int newCapacity(int minCapacity) {
// overflow-conscious code
int oldCapacity = elementData.length;
int newCapacity = oldCapacity + (oldCapacity >> 1);
if (newCapacity - minCapacity <= 0) {
if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA)
return Math.max(DEFAULT_CAPACITY, minCapacity);
if (minCapacity < 0) // overflow
throw new OutOfMemoryError();
return minCapacity;
}
return (newCapacity - MAX_ARRAY_SIZE <= 0)
? newCapacity
: hugeCapacity(minCapacity);
}
/**
* hugeCapacity：处理 minCapacity 非常大的极端情况。
*/
private static int hugeCapacity(int minCapacity) {
if (minCapacity < 0) // overflow
throw new OutOfMemoryError();
return (minCapacity > MAX_ARRAY_SIZE)
? Integer.MAX_VALUE
: MAX_ARRAY_SIZE;
}
// ====================== 基本查询 ======================
public int size() {
return size;
}
public boolean isEmpty() {
return size == 0;
}
public boolean contains(Object o) {
return indexOf(o) >= 0;
}
/**
* indexOf：返回第一次出现 o 的下标，不存在返回 -1。
* 委托给 indexOfRange，在 [0, size) 范围查找。
*/
public int indexOf(Object o) {
return indexOfRange(o, 0, size);
}
/**
* indexOfRange：在 [start, end) 区间查找元素 o。
* 内部通用实现，支持 SubList 等场景复用。
*/
int indexOfRange(Object o, int start, int end) {
Object[] es = elementData;
if (o == null) {
for (int i = start; i < end; i++) {
if (es[i] == null) {
return i;
}
}
} else {
for (int i = start; i < end; i++) {
if (o.equals(es[i])) {
return i;
}
}
}
return -1;
}
/**
* lastIndexOf：从后往前查找最后一次出现的位置。
*/
public int lastIndexOf(Object o) {
return lastIndexOfRange(o, 0, size);
}
/**
* lastIndexOfRange：在 [start, end) 区间倒序查找。
*/
int lastIndexOfRange(Object o, int start, int end) {
Object[] es = elementData;
if (o == null) {
for (int i = end - 1; i >= start; i--) {
if (es[i] == null) {
return i;
}
}
} else {
for (int i = end - 1; i >= start; i--) {
if (o.equals(es[i])) {
return i;
}
}
}
return -1;
}
/**
* 浅拷贝：新 ArrayList 拥有自己的 elementData 数组，但内部元素引用不复制。
*/
public Object clone() {
try {
ArrayList<?> v = (ArrayList<?>) super.clone();
v.elementData = Arrays.copyOf(elementData, size);
v.modCount = 0;
return v;
} catch (CloneNotSupportedException e) {
// 理论上不会发生，因为实现了 Cloneable
throw new InternalError(e);
}
}
public Object[] toArray() {
return Arrays.copyOf(elementData, size);
}
@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;
}
// ====================== 按索引访问/修改 ======================
@SuppressWarnings("unchecked")
E elementData(int index) {
return (E) elementData[index];
}
@SuppressWarnings("unchecked")
static <E> E elementAt(Object[] es, int index) {
return (E) es[index];
}
public E get(int index) {
// JDK11 使用 Objects.checkIndex 做越界检查
Objects.checkIndex(index, size);
return elementData(index);
}
public E set(int index, E element) {
Objects.checkIndex(index, size);
E oldValue = elementData(index);
elementData[index] = element;
return oldValue;
}
/**
* 私有 helper：add(e) 拆分出来的真正插入逻辑，便于 JIT 内联优化。
*/
private void add(E e, Object[] elementData, int s) {
if (s == elementData.length)
elementData = grow();
elementData[s] = e;
size = s + 1;
}
/**
* 尾部追加一个元素。
*/
public boolean add(E e) {
modCount++;
add(e, elementData, size);
return true;
}
/**
* 在指定下标 index 插入一个元素。
*/
public void add(int index, E element) {
rangeCheckForAdd(index);
modCount++;
final int s;
Object[] elementData;
if ((s = size) == (elementData = this.elementData).length)
elementData = grow();
System.arraycopy(elementData, index,
elementData, index + 1,
s - index);
elementData[index] = element;
size = s + 1;
}
/**
* 删除指定下标的元素，并返回旧值。
*/
public E remove(int index) {
Objects.checkIndex(index, size);
final Object[] es = elementData;
@SuppressWarnings("unchecked") E oldValue = (E) es[index];
fastRemove(es, index);
return oldValue;
}
// ====================== equals / hashCode ======================
public boolean equals(Object o) {
if (o == this) {
return true;
}
if (!(o instanceof List)) {
return false;
}
final int expectedModCount = modCount;
// 快速路径：如果 o 也是 ArrayList，使用 equalsArrayList；否则用 equalsRange
boolean equal = (o.getClass() == ArrayList.class)
? equalsArrayList((ArrayList<?>) o)
: equalsRange((List<?>) o, 0, size);
checkForComodification(expectedModCount);
return equal;
}
/**
* equalsRange：与另一个 List 在 [from, to) 区间进行逐元素比较。
*/
boolean equalsRange(List<?> other, int from, int to) {
final Object[] es = elementData;
if (to > es.length) {
throw new ConcurrentModificationException();
}
var oit = other.iterator();
for (; from < to; from++) {
if (!oit.hasNext() || !Objects.equals(es[from], oit.next())) {
return false;
}
}
return !oit.hasNext();
}
/**
* equalsArrayList：当对方也是 ArrayList 时的优化版本。
*/
private boolean equalsArrayList(ArrayList<?> other) {
final int otherModCount = other.modCount;
final int s = size;
boolean equal;
if (equal = (s == other.size)) {
final Object[] otherEs = other.elementData;
final Object[] es = elementData;
if (s > es.length || s > otherEs.length) {
throw new ConcurrentModificationException();
}
for (int i = 0; i < s; i++) {
if (!Objects.equals(es[i], otherEs[i])) {
equal = false;
break;
}
}
}
other.checkForComodification(otherModCount);
return equal;
}
/**
* 用 expectedModCount 做 fail-fast 检测。
*/
private void checkForComodification(final int expectedModCount) {
if (modCount != expectedModCount) {
throw new ConcurrentModificationException();
}
}
/**
* hashCode：按照 List 规范，迭代计算 hash。
*/
public int hashCode() {
int expectedModCount = modCount;
int hash = hashCodeRange(0, size);
checkForComodification(expectedModCount);
return hash;
}
int hashCodeRange(int from, int to) {
final Object[] es = elementData;
if (to > es.length) {
throw new ConcurrentModificationException();
}
int hashCode = 1;
for (int i = from; i < to; i++) {
Object e = es[i];
hashCode = 31 * hashCode + (e == null ? 0 : e.hashCode());
}
return hashCode;
}
// ====================== 删除与清空 ======================
/**
* 删除第一次出现的指定元素。
*/
public boolean remove(Object o) {
final Object[] es = elementData;
final int size = this.size;
int i = 0;
found: {
if (o == null) {
for (; i < size; i++)
if (es[i] == null)
break found;
} else {
for (; i < size; i++)
if (o.equals(es[i]))
break found;
}
return false;
}
fastRemove(es, i);
return true;
}
/**
* fastRemove：不做下标检查的内部快速删除。
*/
private void fastRemove(Object[] es, int i) {
modCount++;
final int newSize;
if ((newSize = size - 1) > i)
System.arraycopy(es, i + 1, es, i, newSize - i);
es[size = newSize] = null;
}
/**
* 清空整个列表。
*/
public void clear() {
modCount++;
final Object[] es = elementData;
for (int to = size, i = size = 0; i < to; i++)
es[i] = null;
}
// ====================== addAll / removeRange ======================
public boolean addAll(Collection<? extends E> c) {
Object[] a = c.toArray();
modCount++;
int numNew = a.length;
if (numNew == 0)
return false;
Object[] elementData;
final int s;
if (numNew > (elementData = this.elementData).length - (s = size))
elementData = grow(s + numNew);
System.arraycopy(a, 0, elementData, s, numNew);
size = s + numNew;
return true;
}
public boolean addAll(int index, Collection<? extends E> c) {
rangeCheckForAdd(index);
Object[] a = c.toArray();
modCount++;
int numNew = a.length;
if (numNew == 0)
return false;
Object[] elementData;
final int s;
if (numNew > (elementData = this.elementData).length - (s = size))
elementData = grow(s + numNew);
int numMoved = s - index;
if (numMoved > 0)
System.arraycopy(elementData, index,
elementData, index + numNew,
numMoved);
System.arraycopy(a, 0, elementData, index, numNew);
size = s + numNew;
return true;
}
/**
* 删除区间 [fromIndex, toIndex) 元素。
*/
protected void removeRange(int fromIndex, int toIndex) {
if (fromIndex > toIndex) {
throw new IndexOutOfBoundsException(
outOfBoundsMsg(fromIndex, toIndex));
}
modCount++;
shiftTailOverGap(elementData, fromIndex, toIndex);
}
/**
* shiftTailOverGap：将 [hi, size) 区间整体左移到 lo 开始位置，并清空尾部无用元素。
*/
private void shiftTailOverGap(Object[] es, int lo, int hi) {
System.arraycopy(es, hi, es, lo, size - hi);
for (int to = size, i = (size -= hi - lo); i < to; i++)
es[i] = null;
}
// ====================== 下标检查与错误信息 ======================
private void rangeCheckForAdd(int index) {
if (index > size || index < 0)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
private String outOfBoundsMsg(int index) {
return "Index: "+index+", Size: "+size;
}
private static String outOfBoundsMsg(int fromIndex, int toIndex) {
return "From Index: " + fromIndex + " > To Index: " + toIndex;
}
// ====================== 批量删除 / retainAll ======================
public boolean removeAll(Collection<?> c) {
return batchRemove(c, false, 0, size);
}
public boolean retainAll(Collection<?> c) {
return batchRemove(c, true, 0, size);
}
/**
* batchRemove：批量删除/保留，支持指定区间 [from, end)。
*
* complement = false：删除 c 中包含的元素；
* complement = true ：仅保留 c 中包含的元素。
*/
boolean batchRemove(Collection<?> c, boolean complement,
final int from, final int end) {
Objects.requireNonNull(c);
final Object[] es = elementData;
int r;
// 优化：先跳过前面一串“幸存元素”
for (r = from;; r++) {
if (r == end)
return false;
if (c.contains(es[r]) != complement)
break;
}
int w = r++;
try {
for (Object e; r < end; r++)
if (c.contains(e = es[r]) == complement)
es[w++] = e;
} catch (Throwable ex) {
// 若 c.contains 抛异常，保持行为与 AbstractCollection 一致
System.arraycopy(es, r, es, w, end - r);
w += end - r;
throw ex;
} finally {
modCount += end - w;
shiftTailOverGap(es, w, end);
}
return true;
}
// ====================== 自定义序列化 ======================
private void writeObject(java.io.ObjectOutputStream s)
throws java.io.IOException {
int expectedModCount = modCount;
s.defaultWriteObject();
// 为兼容 clone 行为，这里写 size 作为 capacity
s.writeInt(size);
for (int i=0; i<size; i++) {
s.writeObject(elementData[i]);
}
if (modCount != expectedModCount) {
throw new ConcurrentModificationException();
}
}
private void readObject(java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException {
// 读取 size、modCount 等字段
s.defaultReadObject();
// 读取 capacity（被忽略，仅保持序列化协议兼容）
s.readInt(); // ignored
if (size > 0) {
// 类似 clone：根据 size 分配数组，而不是 capacity
SharedSecrets.getJavaObjectInputStreamAccess().checkArray(s, Object[].class, size);
Object[] elements = new Object[size];
for (int i = 0; i < size; i++) {
elements[i] = s.readObject();
}
elementData = elements;
} else if (size == 0) {
elementData = EMPTY_ELEMENTDATA;
} else {
throw new java.io.InvalidObjectException("Invalid size: " + size);
}
}
// ====================== 迭代器 ======================
public ListIterator<E> listIterator(int index) {
rangeCheckForAdd(index);
return new ListItr(index);
}
public ListIterator<E> listIterator() {
return new ListItr(0);
}
public Iterator<E> iterator() {
return new Itr();
}
/**
* Itr：单向迭代器。
*/
private class Itr implements Iterator<E> {
int cursor; // 下一个要返回元素的下标
int lastRet = -1; // 上次返回元素的下标，-1 表示还没返回过
int expectedModCount = modCount;
Itr() {}
public boolean hasNext() {
return cursor != size;
}
@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];
}
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();
}
}
/**
* JDK8 引入的 forEachRemaining，在 JDK11 中继续保留。
*/
@Override
public void forEachRemaining(Consumer<? super E> action) {
Objects.requireNonNull(action);
final int size = ArrayList.this.size;
int i = cursor;
if (i < size) {
final Object[] es = elementData;
if (i >= es.length)
throw new ConcurrentModificationException();
for (; i < size && modCount == expectedModCount; i++)
action.accept(elementAt(es, i));
cursor = i;
lastRet = i - 1;
checkForComodification();
}
}
final void checkForComodification() {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
}
}
/**
* ListItr：双向迭代器，在 Itr 基础上扩展 previous / set / add 等能力。
*/
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();
}
}
}
// ====================== SubList 视图（JDK11 重构版） ======================
public List<E> subList(int fromIndex, int toIndex) {
subListRangeCheck(fromIndex, toIndex, size);
return new SubList<>(this, fromIndex, toIndex);
}
private static class SubList<E> extends AbstractList<E> implements RandomAccess {
private final ArrayList<E> root; // 指向最顶层的 ArrayList
private final SubList<E> parent; // 上一级 SubList，可为 null
private final int offset; // 在 root.elementData 中的偏移
private int size; // 当前子列表的长度
/**
* 构造“根”SubList：直接基于 ArrayList。
*/
public SubList(ArrayList<E> root, int fromIndex, int toIndex) {
this.root = root;
this.parent = null;
this.offset = fromIndex;
this.size = toIndex - fromIndex;
this.modCount = root.modCount;
}
/**
* 构造“嵌套”SubList：基于另一 SubList 再裁剪子范围。
*/
private SubList(SubList<E> parent, int fromIndex, int toIndex) {
this.root = parent.root;
this.parent = parent;
this.offset = parent.offset + fromIndex;
this.size = toIndex - fromIndex;
this.modCount = root.modCount;
}
public E set(int index, E element) {
Objects.checkIndex(index, size);
checkForComodification();
E oldValue = root.elementData(offset + index);
root.elementData[offset + index] = element;
return oldValue;
}
public E get(int index) {
Objects.checkIndex(index, size);
checkForComodification();
return root.elementData(offset + index);
}
public int size() {
checkForComodification();
return size;
}
public void add(int index, E element) {
rangeCheckForAdd(index);
checkForComodification();
root.add(offset + index, element);
updateSizeAndModCount(1);
}
public E remove(int index) {
Objects.checkIndex(index, size);
checkForComodification();
E result = root.remove(offset + index);
updateSizeAndModCount(-1);
return result;
}
protected void removeRange(int fromIndex, int toIndex) {
checkForComodification();
root.removeRange(offset + fromIndex, offset + toIndex);
updateSizeAndModCount(fromIndex - toIndex);
}
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();
root.addAll(offset + index, c);
updateSizeAndModCount(cSize);
return true;
}
public void replaceAll(UnaryOperator<E> operator) {
root.replaceAllRange(operator, offset, offset + size);
}
public boolean removeAll(Collection<?> c) {
return batchRemove(c, false);
}
public boolean retainAll(Collection<?> c) {
return batchRemove(c, true);
}
private boolean batchRemove(Collection<?> c, boolean complement) {
checkForComodification();
int oldSize = root.size;
boolean modified =
root.batchRemove(c, complement, offset, offset + size);
if (modified)
updateSizeAndModCount(root.size - oldSize);
return modified;
}
public boolean removeIf(Predicate<? super E> filter) {
checkForComodification();
int oldSize = root.size;
boolean modified = root.removeIf(filter, offset, offset + size);
if (modified)
updateSizeAndModCount(root.size - oldSize);
return modified;
}
public Object[] toArray() {
checkForComodification();
return Arrays.copyOfRange(root.elementData, offset, offset + size);
}
@SuppressWarnings("unchecked")
public <T> T[] toArray(T[] a) {
checkForComodification();
if (a.length < size)
return (T[]) Arrays.copyOfRange(
root.elementData, offset, offset + size, a.getClass());
System.arraycopy(root.elementData, offset, a, 0, size);
if (a.length > size)
a[size] = null;
return a;
}
public boolean equals(Object o) {
if (o == this) {
return true;
}
if (!(o instanceof List)) {
return false;
}
boolean equal = root.equalsRange((List<?>)o, offset, offset + size);
checkForComodification();
return equal;
}
public int hashCode() {
int hash = root.hashCodeRange(offset, offset + size);
checkForComodification();
return hash;
}
public int indexOf(Object o) {
int index = root.indexOfRange(o, offset, offset + size);
checkForComodification();
return index >= 0 ? index - offset : -1;
}
public int lastIndexOf(Object o) {
int index = root.lastIndexOfRange(o, offset, offset + size);
checkForComodification();
return index >= 0 ? index - offset : -1;
}
public boolean contains(Object o) {
return indexOf(o) >= 0;
}
public Iterator<E> iterator() {
return listIterator();
}
public ListIterator<E> listIterator(int index) {
checkForComodification();
rangeCheckForAdd(index);
return new ListIterator<E>() {
int cursor = index;
int lastRet = -1;
int expectedModCount = root.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 = root.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 = root.elementData;
if (offset + i >= elementData.length)
throw new ConcurrentModificationException();
cursor = i;
return (E) elementData[offset + (lastRet = i)];
}
public void forEachRemaining(Consumer<? super E> action) {
Objects.requireNonNull(action);
final int size = SubList.this.size;
int i = cursor;
if (i < size) {
final Object[] es = root.elementData;
if (offset + i >= es.length)
throw new ConcurrentModificationException();
for (; i < size && modCount == expectedModCount; i++)
action.accept(elementAt(es, offset + i));
cursor = i;
lastRet = i - 1;
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 = root.modCount;
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}
public void set(E e) {
if (lastRet < 0)
throw new IllegalStateException();
checkForComodification();
try {
root.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 = root.modCount;
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}
final void checkForComodification() {
if (root.modCount != expectedModCount)
throw new ConcurrentModificationException();
}
};
}
public List<E> subList(int fromIndex, int toIndex) {
subListRangeCheck(fromIndex, toIndex, size);
return new SubList<>(this, fromIndex, toIndex);
}
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 (root.modCount != modCount)
throw new ConcurrentModificationException();
}
/**
* 更新当前 SubList 及其所有祖先 SubList 的 size / modCount。
*/
private void updateSizeAndModCount(int sizeChange) {
SubList<E> slist = this;
do {
slist.size += sizeChange;
slist.modCount = root.modCount;
slist = slist.parent;
} while (slist != null);
}
public Spliterator<E> spliterator() {
checkForComodification();
// SubList 使用单独的 Spliterator 实现，而不是 ArrayListSpliterator（但内部也会使用它）
return new Spliterator<E>() {
private int index = offset; // 当前遍历位置
private int fence = -1; // -1 表示尚未初始化；初始化后为 offset+size
private int expectedModCount;
private int getFence() {
int hi;
if ((hi = fence) < 0) {
expectedModCount = modCount;
hi = fence = offset + size;
}
return hi;
}
public ArrayList<E>.ArrayListSpliterator trySplit() {
int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
// 使用根 ArrayList 的 Spliterator 实现
return (lo >= mid) ? null :
root.new ArrayListSpliterator(lo, index = mid, expectedModCount);
}
public boolean tryAdvance(Consumer<? super E> action) {
Objects.requireNonNull(action);
int hi = getFence(), i = index;
if (i < hi) {
index = i + 1;
@SuppressWarnings("unchecked") E e = (E)root.elementData[i];
action.accept(e);
if (root.modCount != expectedModCount)
throw new ConcurrentModificationException();
return true;
}
return false;
}
public void forEachRemaining(Consumer<? super E> action) {
Objects.requireNonNull(action);
int i, hi, mc;
ArrayList<E> lst = root;
Object[] a;
if ((a = lst.elementData) != null) {
if ((hi = fence) < 0) {
mc = modCount;
hi = offset + 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 getFence() - index;
}
public int characteristics() {
return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED;
}
};
}
}
// ====================== JDK8+ Lambda 增强 ======================
@Override
public void forEach(Consumer<? super E> action) {
Objects.requireNonNull(action);
final int expectedModCount = modCount;
final Object[] es = elementData;
final int size = this.size;
for (int i = 0; modCount == expectedModCount && i < size; i++)
action.accept(elementAt(es, i));
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
}
@Override
public Spliterator<E> spliterator() {
return new ArrayListSpliterator(0, -1, 0);
}
/**
* ArrayListSpliterator：基于下标的延迟绑定 Spliterator，实现流式遍历。
*/
final class ArrayListSpliterator implements Spliterator<E> {
private int index; // 当前下标
private int fence; // -1 表示未初始化，初始化后为 size
private int expectedModCount;
ArrayListSpliterator(int origin, int fence, int expectedModCount) {
this.index = origin;
this.fence = fence;
this.expectedModCount = expectedModCount;
}
private int getFence() {
int hi;
if ((hi = fence) < 0) {
expectedModCount = modCount;
hi = fence = size;
}
return hi;
}
public ArrayListSpliterator trySplit() {
int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
return (lo >= mid) ? null :
new ArrayListSpliterator(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)elementData[i];
action.accept(e);
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
return true;
}
return false;
}
public void forEachRemaining(Consumer<? super E> action) {
int i, hi, mc;
Object[] a;
if (action == null)
throw new NullPointerException();
if ((a = elementData) != null) {
if ((hi = fence) < 0) {
mc = modCount;
hi = 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 (modCount == mc)
return;
}
}
throw new ConcurrentModificationException();
}
public long estimateSize() {
return getFence() - index;
}
public int characteristics() {
return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED;
}
}
// ====================== removeIf / replaceAll / sort（JDK8+） ======================
// 简易 bitset 工具，用 long[] 表示哪些元素需要删除
private static long[] nBits(int n) {
return new long[((n - 1) >> 6) + 1];
}
private static void setBit(long[] bits, int i) {
bits[i >> 6] |= 1L << i;
}
private static boolean isClear(long[] bits, int i) {
return (bits[i >> 6] & (1L << i)) == 0;
}
@Override
public boolean removeIf(Predicate<? super E> filter) {
return removeIf(filter, 0, size);
}
/**
* removeIf：从区间 [i, end) 中删除所有满足 filter 的元素。
*
* 分两阶段：
* 1）遍历记录要删除的元素位置到 bitset，确保 filter 的异常不会破坏集合；
* 2）第二次遍历，将未标记的元素向左压缩，最后清理尾部。
*/
boolean removeIf(Predicate<? super E> filter, int i, final int end) {
Objects.requireNonNull(filter);
int expectedModCount = modCount;
final Object[] es = elementData;
// 先跳过前面一串“不需要删除”的元素
for (; i < end && !filter.test(elementAt(es, i)); i++)
;
if (i < end) {
final int beg = i;
final long[] deathRow = nBits(end - beg);
deathRow[0] = 1L; // 第一个要删的元素
for (i = beg + 1; i < end; i++)
if (filter.test(elementAt(es, i)))
setBit(deathRow, i - beg);
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
modCount++;
int w = beg;
for (i = beg; i < end; i++)
if (isClear(deathRow, i - beg))
es[w++] = es[i];
shiftTailOverGap(es, w, end);
return true;
} else {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
return false;
}
}
@Override
public void replaceAll(UnaryOperator<E> operator) {
replaceAllRange(operator, 0, size);
modCount++;
}
/**
* replaceAllRange：在区间 [i, end) 上对每个元素执行 operator 替换。
*/
private void replaceAllRange(UnaryOperator<E> operator, int i, int end) {
Objects.requireNonNull(operator);
final int expectedModCount = modCount;
final Object[] es = elementData;
for (; modCount == expectedModCount && i < end; i++)
es[i] = operator.apply(elementAt(es, i));
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
}
@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++;
}
// 仅用于调试不变式检查
void checkInvariants() {
// assert size >= 0;
// assert size == elementData.length || elementData[size] == null;
}
}