java.util.ArrayList是實現List接口的可調整大小的數組實現。實現所有可選的列表操作，可以存儲所有類型元素，包括null。除了實現List接口之外，這個類還提供了一些方法來操作內部用於存儲列表的數組的大小。（這個類大致相當於Vector，只是它是非同步的）。
類名
public class ArrayList<E> extends AbstractList<E>
implements List<E>, RandomAccess, Cloneable, java.io.Serializable
變量
//默認初始容量。
private static final int DEFAULT_CAPACITY = 10;
//用於空實例的共享空數組實例
private static final Object[] EMPTY_ELEMENTDATA = {};
/**
* 用於默認大小的空實例的共享空數組實例。
* 我們將其與空的元素數據區分開來，以知道在添加第一個元素時要擴容多少。
*/
private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};
/**
* 存儲ArrayList元素的數組緩衝區。ArrayList的容量是此數組緩衝區的長度。
* 添加第一個元素時，elementData==DEFAULTCAPACITY_EMPTY_ELEMENTDATA,
* ArrayList大小爲DEFAULT_CAPACITY。
*/
transient Object[] elementData;
/**
* ArrayList的大小（它包含的元素數）。
*/
private int size;
add(E e)
/**
* 添加元素
*/
public boolean add(E e) {
//是否需要擴容
ensureCapacityInternal(size + 1);
elementData[size++] = e;
return true;
}
在添加一個元素時，先調用ensureCapacityInternal方法進行擴容，
private void ensureCapacityInternal(int minCapacity) {
if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);
}
ensureExplicitCapacity(minCapacity);
}
private void ensureExplicitCapacity(int minCapacity) {
modCount++;
// overflow-conscious code
if (minCapacity - elementData.length > 0)
grow(minCapacity);
}
/**
* 增加容量以確保它至少可以容納由最小容量參數指定的元素數
*/
private void grow(int minCapacity) {
// list的大小
int oldCapacity = elementData.length;
//擴容1.5倍後的大小，oldCapacity >> 1相當於oldCapacity/2
int newCapacity = oldCapacity + (oldCapacity >> 1);
if (newCapacity - minCapacity < 0)
newCapacity = minCapacity;
if (newCapacity - MAX_ARRAY_SIZE > 0)
newCapacity = hugeCapacity(minCapacity);
// 構建新的長度的數組
elementData = Arrays.copyOf(elementData, newCapacity);
}
//和最大容量比較
private static int hugeCapacity(int minCapacity) {
if (minCapacity < 0) // overflow
throw new OutOfMemoryError();
return (minCapacity > MAX_ARRAY_SIZE) ?
Integer.MAX_VALUE :
MAX_ARRAY_SIZE;
}
get(int index)
// 獲取指定位置元素
public E get(int index) {
//判斷index是否
rangeCheck(index);
return elementData(index);
}
remove(int index)
public E remove(int index) {
//判斷index是否越界
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;
}
addAll(Collection<? extends E> c)
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;
}
fail-fast 機制
即快速失敗機制，是java集合(Collection)中的一種錯誤檢測機制。當在迭代集合的過程中該集合在結構上發生改變的時候，就有可能會發生fail-fast，即拋出ConcurrentModificationException異常。fail-fast機制並不保證在不同步的修改下一定會拋出異常，它只是盡最大努力去拋出，所以這種機制一般僅用於檢測bug。
List<String> list = new ArrayList<String>();
for (int i = 0; i < 10; i++) {
list.add(i + "");
}
for (String s : list){
if ("1".equals(s)){
list.remove(s);
}
}
如上，當在以上for循環中刪除元素時，會報如下錯誤：
Spliterator
在jdk1.8中新增了一個Spliterator接口，是Java爲了並行遍歷數據源中的元素而設計的迭代器。可以按順序或並行方式對流使用Spliterator。在1.8的ArrayList中也實現了這個接口。
List<String> arrs = new ArrayList<>();
arrs.add("a");
arrs.add("b");
arrs.add("c");
arrs.add("d");
arrs.add("e");
arrs.add("f");
Spliterator<String> p = arrs.spliterator();
//此時p爲a b c d e f
Spliterator<String> q = p.trySplit();
//此時p爲d e f q爲a b c
Spliterator<String> j = p.trySplit();
//此時p爲e f q爲a b c j爲d
p.forEachRemaining(s -> System.out.print(s + " "));
System.out.println();
q.forEachRemaining(s -> System.out.print(s + " "));
System.out.println();
j.forEachRemaining(s -> System.out.print(s + " "));
源碼（1.8）
public class ArrayList<E> extends AbstractList<E>
implements List<E>, RandomAccess, Cloneable, java.io.Serializable
{
private static final long serialVersionUID = 8683452581122892189L;
//默認初始容量。
private static final int DEFAULT_CAPACITY = 10;
//用於空實例的共享空數組實例
private static final Object[] EMPTY_ELEMENTDATA = {};
/**
* 用於默認大小的空實例的共享空數組實例。
* 我們將其與空的元素數據區分開來，以知道在添加第一個元素時要擴容多少。
*/
private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};
/**
* 存儲ArrayList元素的數組緩衝區。ArrayList的容量是此數組緩衝區的長度。
* 添加第一個元素時，elementData==DEFAULTCAPACITY_EMPTY_ELEMENTDATA,
* ArrayList大小爲DEFAULT_CAPACITY。
*/
transient Object[] elementData;
/**
* ArrayList的大小（它包含的元素數）。
*/
private int size;
/**
* 構造具有指定初始容量的空列表
*
* @param initialCapacity 初始容量
*/
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);
}
}
/**
* 構造初始容量爲10的空列表。
*/
public ArrayList() {
this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
}
/**
* 構造包含指定集合的元素的列表
*/
public ArrayList(Collection<? extends E> c) {
elementData = c.toArray();
if ((size = elementData.length) != 0) {
// c.toArray可能不是Object[]
if (elementData.getClass() != Object[].class)
elementData = Arrays.copyOf(elementData, size, Object[].class);
} else {
// 替換成空數組.
this.elementData = EMPTY_ELEMENTDATA;
}
}
/**
* 將此ArrayList實例的容量修剪爲列表的當前大小。
* 應用程序可以使用此操作最小化ArrayList實例的存儲.
*/
public void trimToSize() {
modCount++;
if (size < elementData.length) {
elementData = (size == 0)
? EMPTY_ELEMENTDATA
: Arrays.copyOf(elementData, size);
}
}
/**
* 必要時增加此ArrayList實例的容量
* @param minCapacity 所需的最小容量
*/
public void ensureCapacity(int minCapacity) {
int minExpand = (elementData != DEFAULTCAPACITY_EMPTY_ELEMENTDATA)
// 如果不是默認空數組
? 0
// 默認值
: DEFAULT_CAPACITY;
if (minCapacity > minExpand) {
ensureExplicitCapacity(minCapacity);
}
}
private void ensureCapacityInternal(int minCapacity) {
if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);
}
ensureExplicitCapacity(minCapacity);
}
private void ensureExplicitCapacity(int minCapacity) {
modCount++;
// overflow-conscious code
if (minCapacity - elementData.length > 0)
grow(minCapacity);
}
/**
* 最大容量
*/
private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
/**
* 增加容量以確保它至少可以容納由最小容量參數指定的元素數
*/
private void grow(int minCapacity) {
// list的大小
int oldCapacity = elementData.length;
//擴容1.5倍後的大小，oldCapacity >> 1相當於oldCapacity/2
int newCapacity = oldCapacity + (oldCapacity >> 1);
if (newCapacity - minCapacity < 0)
newCapacity = minCapacity;
if (newCapacity - MAX_ARRAY_SIZE > 0)
newCapacity = hugeCapacity(minCapacity);
// 構建新的長度的數組
elementData = Arrays.copyOf(elementData, newCapacity);
}
//和最大容量比較
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list大小
*/
public int size() {
return size;
}
/**
* 判斷有沒有元素
*/
public boolean isEmpty() {
return size == 0;
}
/**
* 是否包含某個對象
*/
public boolean contains(Object o) {
return indexOf(o) >= 0;
}
/**
* 返回此列表中指定元素第一次出現的索引，
* 如果此列表不包含該元素，則返回-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;
}
/**
* 返回此列表中指定元素最一次出現的索引，
* 如果此列表不包含該元素，則返回-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;
}
/**
* 返回此ArrayList實例的淺層副本。（不會複製元素本身。）
*/
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);
}
}
/**
* 返回一個數組
*
* 返回的數組將是“安全的”，因爲此列表不維護對它的引用。
*（換句話說，這個方法必須分配一個新數組）。
* 因此，調用者可以自由地修改返回的數組。
*/
public Object[] toArray() {
return Arrays.copyOf(elementData, size);
}
/**
* 返回一個數組，該數組按正確的順序，包含此列表中的所有元素；
* 如果列表符合指定的數組，則返回該列表。
* 否則，將使用指定數組的運行時類型和此列表的大小分配新數組。
*/
@SuppressWarnings("unchecked")
public <T> T[] toArray(T[] a) {
if (a.length < size)
// 創建運行時類型的新數組:
return (T[]) Arrays.copyOf(elementData, size, a.getClass());
System.arraycopy(elementData, 0, a, 0, size);
if (a.length > size)
a[size] = null;
return a;
}
// 獲取指定位置元素
@SuppressWarnings("unchecked")
E elementData(int index) {
return (E) elementData[index];
}
// 獲取指定位置元素
public E get(int index) {
//判斷index是否
rangeCheck(index);
return elementData(index);
}
/**
* 修改指定位置元素的值.
*/
public E set(int index, E element) {
//判斷index是否越界
rangeCheck(index);
E oldValue = elementData(index);
elementData[index] = element;
return oldValue;
}
/**
* 添加元素
*/
public boolean add(E e) {
//是否需要擴容
ensureCapacityInternal(size + 1);
elementData[size++] = e;
return true;
}
/**
* 在指定位置插入元素
*/
public void add(int index, E element) {
//判斷index是否越界
rangeCheckForAdd(index);
//是否需要擴容
ensureCapacityInternal(size + 1); // Increments modCount!!
System.arraycopy(elementData, index, elementData, index + 1,
size - index);
elementData[index] = element;
size++;
}
/**
* 刪除指定位置元素
*/
public E remove(int index) {
//判斷index是否越界
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;
}
/**
* 從列表中刪除指定元素的第一個匹配項（如果存在）。
*/
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;
}
/*
* 私有刪除方法.
*/
private void fastRemove(int index) {
modCount++;
int numMoved = size - index - 1;
if (numMoved > 0)
//將index後面的元素前移一位
System.arraycopy(elementData, index+1, elementData, index,
numMoved);
//將最後一位設置成null，由GC回收
elementData[--size] = null; // clear to let GC do its work
}
/**
* 刪除所有元素
*/
public void clear() {
modCount++;
// clear to let GC do its work
for (int i = 0; i < size; i++)
elementData[i] = null;
size = 0;
}
/**
* 將指定集合中的所有元素追加到此列表的末尾
*/
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;
}
/**
* 將指定集合中的所有元素追加到此列表的index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;
}
/**
* 刪除指定範圍的元素
*/
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;
}
/**
* 檢查給定索引是否在範圍內
*/
private void rangeCheck(int index) {
if (index >= size)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
/**
* add和addAll使用的rangeCheck版本。
*/
private void rangeCheckForAdd(int index) {
if (index > size || index < 0)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
/**
* 構造IndexOutboundsException詳細消息
*/
private String outOfBoundsMsg(int index) {
return "Index: "+index+", Size: "+size;
}
/**
* 從該列表中刪除指定集合中包含的所有元素.
*/
public boolean removeAll(Collection<?> c) {
Objects.requireNonNull(c);
return batchRemove(c, false);
}
/**
* 從該列表中刪除指定集合中未包含的所有元素。
*/
public boolean retainAll(Collection<?> c) {
Objects.requireNonNull(c);
return batchRemove(c, true);
}
private boolean batchRemove(Collection<?> c, boolean complement) {
final Object[] elementData = this.elementData;
int r = 0, w = 0;
boolean modified = false;
try {
for (; r < size; r++)
if (c.contains(elementData[r]) == complement)
elementData[w++] = elementData[r];
} finally {
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;
}
/**
* 序列化list
*/
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();
}
}
/**
* 反序列化list
*/
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
ensureCapacityInternal(size);
Object[] a = elementData;
// Read in all elements in the proper order.
for (int i=0; i<size; i++) {
a[i] = s.readObject();
}
}
}
/**
* 從列表中的指定位置開始，返回此列表中元素的列表迭代器.
*/
public ListIterator<E> listIterator(int index) {
if (index < 0 || index > size)
throw new IndexOutOfBoundsException("Index: "+index);
return new ListItr(index);
}
public ListIterator<E> listIterator() {
return new ListItr(0);
}
/**
* 以適當的順序返回此列表中元素的迭代器.
*/
public Iterator<E> iterator() {
return new Itr();
}
/**
* An optimized version of AbstractList.Itr
*/
private class Itr implements Iterator<E> {
int cursor; // index of next element to return
int lastRet = -1; // index of last element returned; -1 if no such
int expectedModCount = modCount;
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();
}
}
@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();
}
final void checkForComodification() {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
}
}
/**
* An optimized version of AbstractList.ListItr
*/
private class ListItr extends Itr implements ListIterator<E> {
ListItr(int index) {
super();
cursor = index;
}
public boolean hasPrevious() {
return cursor != 0;
}
public int nextIndex() {
return cursor;
}
public int previousIndex() {
return cursor - 1;
}
@SuppressWarnings("unchecked")
public E previous() {
checkForComodification();
int i = cursor - 1;
if (i < 0)
throw new NoSuchElementException();
Object[] elementData = ArrayList.this.elementData;
if (i >= elementData.length)
throw new ConcurrentModificationException();
cursor = i;
return (E) elementData[lastRet = i];
}
public void set(E e) {
if (lastRet < 0)
throw new IllegalStateException();
checkForComodification();
try {
ArrayList.this.set(lastRet, e);
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}
public void add(E e) {
checkForComodification();
try {
int i = cursor;
ArrayList.this.add(i, e);
cursor = i + 1;
lastRet = -1;
expectedModCount = modCount;
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}
}
/**
* 返回指定範圍的list
*/
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);
}
}
@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();
}
}
/**
* 在此列表中的元素上創建一個late-binding和fail-fast的鏈接拆分器。
* @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> {
/*
* 如果ArrayList是不可變的，或者在結構上是不可變的（沒有添加、刪除等），
* 我們可以用Arrays.spliterator實現它們的拆分器。
* 相反，我們在遍歷過程中檢測儘可能多的干擾，而不犧牲很多性能。
* 我們主要依靠模態計數。它們不能保證檢測到併發衝突，
* 有時對線程內干擾過於保守，但檢測到的問題足夠值得在實踐中使用。
* 爲了實現這一點，我們（1）延遲初始化fence和expectedModCount，
* 直到我們需要提交給我們正在檢查的狀態的最新點；從而提高精度。
*（這不適用於創建具有當前非惰性值的拆分器的子列表）。
*（2） 我們只在forEach（對性能最敏感的方法）末尾執行一次ConcurrentModificationException檢查。
* 當使用forEach（與迭代器相反）時，我們通常只能在操作後檢測干擾，
* 而不是之前。進一步的CME觸發檢查適用於所有其他可能違反假設的情況，
* 例如給定其size（）的elementData數組爲空或太小，這可能是由於干擾造成的。
* 這允許forEach的內部循環運行而無需進一步檢查，並簡化了lambda解析。
* 雖然這需要進行多次檢查，但請注意，在list.stream（）.forEach（a）的常見情況下，
* 除了forEach本身之外，不會在任何地方進行檢查或其他計算。
* 其他不常使用的方法無法利用大多數這些流線型。
*/
//用於存放ArrayList對象
private final ArrayList<E> list;
private int index; //當前位置，advance/split操作時會修改
private int fence; //結束位置，-1 表示到最後一個元素
private int expectedModCount; //用於存放list的modCount
/** 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;
}
//獲取結束位置
private int getFence() { // 第一次調用時初始化fence爲list的大小
int hi; // (a specialized variant appears in method forEach)
ArrayList<E> lst;
if ((hi = fence) < 0) {
//list 爲 null時，fence=0
if ((lst = list) == null)
hi = fence = 0;
else {
//否則 賦值爲list的大小
expectedModCount = lst.modCount;
hi = fence = lst.size;
}
}
return hi;
}
//分割list，返回一個新分割出的spliterator實例
public ArrayListSpliterator<E> trySplit() {
//計算中間位置
int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
//當lo>=mid,表示不能再分割，返回null
//當lo<mid時,可分割，切割（lo，mid）出去，同時更新index=mid
return (lo >= mid) ? null : // divide range in half unless too small
new ArrayListSpliterator<E>(list, lo, index = mid,
expectedModCount);
}
//返回true 時，只表示可能還有元素未處理
//返回false 時，沒有剩餘元素處理了
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);
//遍歷時，如果結構發生變更，報錯
if (list.modCount != expectedModCount)
throw new ConcurrentModificationException();
return true;
}
return false;
}
//順序遍歷處理所有剩下的元素
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++;
}
}
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