ArrayList，
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ArrayList，
//fail-fast:list发生结构性修改 iterator抛出异常，行为无法保证
public class ArrayList<E> extends AbstractList<E>
implements List<E>, RandomAccess, Cloneable, java.io.Serializable
{
private static final long serialVersionUID = 8683452581122892189L;
//默认capacity
private static final int DEFAULT_CAPACITY = 10;
private static final Object[] EMPTY_ELEMENTDATA = {};
//与EMPTY_ELEMENTDATA区分
private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};
//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
private int size;
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);
}
}
//第一个元素添加时扩展至DEFAULT_CAPACITY=10
public ArrayList() {
this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
}
public ArrayList(Collection<? extends E> c) {
elementData = c.toArray();
if ((size = elementData.length) != 0) {
// defend against c.toArray (incorrectly) not returning Object[]
// (see e.g. https://bugs.openjdk.java.net/browse/JDK-6260652)
if (elementData.getClass() != Object[].class)
//返回Object对象
elementData = Arrays.copyOf(elementData, size, Object[].class);
} else {
this.elementData = EMPTY_ELEMENTDATA;
}
}
//消减到最小size
public void trimToSize() {
modCount++;
if (size < elementData.length) {
elementData = (size == 0)
? EMPTY_ELEMENTDATA
: Arrays.copyOf(elementData, size);
}
}
public void ensureCapacity(int minCapacity) {
if (minCapacity > elementData.length
//保证不为默认空数组、大于DEFAULT_CAPACITY
&& !(elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA
&& minCapacity <= DEFAULT_CAPACITY)) {
modCount++;
grow(minCapacity);
}
}
/**
* The maximum size of array to allocate (unless necessary).
* 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;
private Object[] grow(int minCapacity) {
return elementData = Arrays.copyOf(elementData,
newCapacity(minCapacity));
}
private Object[] grow() {
return grow(size + 1);
}
/**
* Returns a capacity at least as large as the given minimum capacity.
* Returns the current capacity increased by 50% if that suffices.
* Will not return a capacity greater than MAX_ARRAY_SIZE unless
* the given minimum capacity is greater than MAX_ARRAY_SIZE.
*/
private int newCapacity(int minCapacity) {
// overflow-conscious code
int oldCapacity = elementData.length;
//1.5倍
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);
}
private static int hugeCapacity(int minCapacity) {
if (minCapacity < 0) // overflow
throw new OutOfMemoryError();
return (minCapacity > MAX_ARRAY_SIZE)
? Integer.MAX_VALUE
: MAX_ARRAY_SIZE;
}
public int size() {
return size;
}
public boolean isEmpty() {
return size == 0;
}
public boolean contains(Object o) {
return indexOf(o) >= 0;
}
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;
}
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;
}
/**
* Returns a shallow copy of this {@code ArrayList} instance. (The
* elements themselves are not copied.)
*/
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);
}
}
public Object[] toArray() {
return Arrays.copyOf(elementData, size);
}
@SuppressWarnings("unchecked")
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;
}
// Positional Access Operations
@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) {
//有HotSpot Virtual Machine注解，可能但并不保证会以replaces the annotated method
//with hand-written
//assembly and/or hand-written compiler IR -- a compiler intrinsic -- to improve
//performance
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;
}
/**
* This helper method split out from add(E) to keep method
* bytecode size under 35 (the -XX:MaxInlineSize default value),
* which helps when add(E) is called in a C1-compiled loop.
*/
private void add(E e, Object[] elementData, int s) {
if (s == elementData.length)
elementData = grow();
elementData[s] = e;
size = s + 1;
}
public boolean add(E e) {
modCount++;
add(e, elementData, size);
return true;
}
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;
}
public E remove(int index) {
Objects.checkIndex(index, size);
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;
}
public boolean remove(Object o) {
if (o == null) {
for (int index = 0; index < size; index++)
if (elementData[index] == null) {
//与remove区别：无边界检查、删除值返回
fastRemove(index);
return true;
}
} else {
for (int index = 0; index < size; index++)
if (o.equals(elementData[index])) {
fastRemove(index);
return true;
}
}
return false;
}
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
}
public void clear() {
modCount++;
final Object[] es = elementData;
for (int to = size, i = size = 0; i < to; i++)
es[i] = null;
}
public boolean addAll(Collection<? extends E> c) {
//List.toArray()
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;
}
/**
* Inserts all of the elements in the specified collection into this
* list, starting at the specified position. Shifts the element
* currently at that position (if any) and any subsequent elements to
* the right (increases their indices). The new elements will appear
* in the list in the order that they are returned by the
* specified collection's iterator.
*/
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;
//右移原数组元素
if (numMoved > 0)
System.arraycopy(elementData, index,
elementData, index + numNew,
numMoved);
System.arraycopy(a, 0, elementData, index, numNew);
size = s + numNew;
return true;
}
protected void removeRange(int fromIndex, int toIndex) {
if (fromIndex > toIndex) {
throw new IndexOutOfBoundsException(
outOfBoundsMsg(fromIndex, toIndex));
}
modCount++;
shiftTailOverGap(elementData, fromIndex, toIndex);
}
private void shiftTailOverGap(Object[] es, int lo, int hi) {
//hi后元素前移至lo
System.arraycopy(es, hi, es, lo, size - hi);
for (int to = size, i = (size -= hi - lo); i < to; i++)
es[i] = null;
}
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;
}
public boolean removeAll(Collection<?> c) {
return batchRemove(c, false, 0, size);
}
public boolean retainAll(Collection<?> c) {
return batchRemove(c, true, 0, size);
}
//complement为true则保留c中元素，删除其他
boolean batchRemove(Collection<?> c, boolean complement,
final int from, final int end) {
//c==null则抛出空指针异常
Objects.requireNonNull(c);
final Object[] es = elementData;
final boolean modified;
int r;
// Optimize for initial run of survivors
for (r = from; r < end && c.contains(es[r]) == complement; r++)
;
if (modified = (r < end)) {
int w = r++;
try {
for (Object e; r < end; r++)
if (c.contains(e = es[r]) == complement)
es[w++] = e;
} catch (Throwable ex) {
// Preserve behavioral compatibility with AbstractCollection,
// even if c.contains() throws.
System.arraycopy(es, r, es, w, end - r);
w += end - r;
throw ex;
} finally {
modCount += end - w;
//消除空位
shiftTailOverGap(es, w, end);
}
}
return modified;
}
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();
}
}
private void readObject(java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException {
// Read in size, and any hidden stuff
s.defaultReadObject();
// Read in capacity
s.readInt(); // ignored
if (size > 0) {
// like clone(), allocate array based upon size not capacity
SharedSecrets.getJavaObjectInputStreamAccess().checkArray(s, Object[].class, size);
Object[] elements = new Object[size];
// Read in all elements in the proper order.
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);
}
}
public ListIterator<E> listIterator(int index) {
rangeCheckForAdd(index);
return new ListItr(index);
}
public ListIterator<E> listIterator() {
//扩展了Itr()
return new ListItr(0);
}
public Iterator<E> iterator() {
//实现了Iterator<E>
return new 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;
// prevent creating a synthetic constructor
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();
}
}
@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));
// update once at end to reduce heap write traffic
cursor = i;
lastRet = i - 1;
checkForComodification();
}
}
final void checkForComodification() {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
}
}
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();
}
}
}
public List<E> subList(int fromIndex, int toIndex) {
subListRangeCheck(fromIndex, toIndex, size);
return new SubList<>(this, fromIndex, toIndex);
}
//改动对底层进行
private static class SubList<E> extends AbstractList<E> implements RandomAccess {
private final ArrayList<E> root;
private final SubList<E> parent;
private final int offset;
private int size;
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;
}
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 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 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));
// update once at end to reduce heap write traffic
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();
}
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();
// ArrayListSpliterator not used here due to late-binding
return new Spliterator<E>() {
private int index = offset; // current index, modified on advance/split
private int fence = -1; // -1 until used; then one past last index
private int expectedModCount; // initialized when fence set
private int getFence() { // initialize fence to size on first use
int hi; // (a specialized variant appears in method forEach)
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;
// ArrayListSpliterator can be used here as the source is already bound
return (lo >= mid) ? null : // divide range in half unless too small
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; // hoist accesses and checks from loop
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;
}
};
}
}
@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();
}
//待补
/**
* Creates a <em><a href="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(0, -1, 0);
}
/** Index-based split-by-two, lazily initialized Spliterator */
final class ArrayListSpliterator 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 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
/** Creates new spliterator covering the given range. */
ArrayListSpliterator(int origin, int fence, int expectedModCount) {
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)
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 : // divide range in half unless too small
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; // hoist accesses and checks from loop
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;
}
}
// A tiny bit set implementation
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;
}
/**
* @throws NullPointerException {@inheritDoc}
*/
@Override
public boolean removeIf(Predicate<? super E> filter) {
return removeIf(filter, 0, size);
}
/**
* Removes all elements satisfying the given predicate, from index
* i (inclusive) to index end (exclusive).
*/
boolean removeIf(Predicate<? super E> filter, int i, final int end) {
Objects.requireNonNull(filter);
int expectedModCount = modCount;
final Object[] es = elementData;
// Optimize for initial run of survivors
for (; i < end && !filter.test(elementAt(es, i)); i++)
;
// Tolerate predicates that reentrantly access the collection for
// read (but writers still get CME), so traverse once to find
// elements to delete, a second pass to physically expunge.
if (i < end) {
final int beg = i;
final long[] deathRow = nBits(end - beg);
deathRow[0] = 1L; // set bit 0
for (i = beg + 1; i < end; i++)
if (filter.test(elementAt(es, i)))
setBit(deathRow, i - beg);
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
expectedModCount++;
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) {
Objects.requireNonNull(operator);
final int expectedModCount = modCount;
final Object[] es = elementData;
final int size = this.size;
for (int i = 0; modCount == expectedModCount && i < size; i++)
es[i] = operator.apply(elementAt(es, 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++;
}
void checkInvariants() {
// assert size >= 0;
// assert size == elementData.length || elementData[size] == null;
}
}
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