ArrayList
1 Introduction
It inherits from AbstractList and implements the List interface. The bottom layer realizes the dynamic change of capacity based on array. null is not allowed.
At the same time, RandomAccess, Cloneable and Serializable interfaces are also implemented, so ArrayList supports fast access, replication and serialization.
-
RandomAccess:
Flag interface. The List collection that implements this interface supports fast random access. In other words, the collection that implements this interface supports fast random access policy.
If it is a List that implements this interface, using the for loop to get data is better than using the iterator to get data. -
Cloneable:
Cloning interface is also a tag interface. Only after this interface is implemented, and then override the clone method in the Object in the class, and then call the clone method through the class, can cloning succeed. If this interface is not implemented, a clonenotsupportedexception (cloning is not supported) exception will be thrown.The role of clonable interface and in-depth understanding of deep and shallow cloning
-
Serializable:
An object serialization interface. Only when a class implements the Serializable interface can its objects be serialized
What is serialization? See the IO chapter
2 source code opening description
Adjustable array implementation of the List interface. Implement all optional List operations and allow all elements, including null. In addition to implementing the List interface, this class also provides methods to manipulate the internal array size used to store the List. (this class is roughly equivalent to Vector, but it is non thread safe.)
The size, isEmpty, get, set, iterator, and listIterator operations run in constant time. The addition operation runs in a flat constant time, that is, it takes O(n) time to add n elements. All other operations run in linear time (roughly speaking). Compared with the LinkedList implementation, the constant factor is low.
Each ArrayList instance has a capacity. Capacity is the size of the array used to store the elements in the list. It is always at least as large as the list size. When an element is added to the ArrayList, its capacity automatically increases. Apart from the fact that the amortized time cost of adding elements is constant, no details of the growth strategy are specified.
An application can increase the capacity of an ArrayList instance before adding a large number of elements using the ensureCapacity operation. This may reduce the number of incremental reassignments.
Note that this implementation is not synchronous. If multiple threads access an ArrayList instance at the same time, and at least one thread has structurally modified the list, it must be synchronized externally. (structure modification is any operation of adding or deleting one or more elements, or explicitly adjusting the size of the background array; setting the value of the element alone is not a structural modification.) This is usually done by synchronizing some objects of the naturally encapsulated list. If such an object does not exist, you should use Collections to "wrap" the list. synchronizedList method. This is best done at creation time to prevent accidental asynchronous access to the list:
List = set. Synchronizedlist (New ArrayList(...);
The iterator returned by the iterator and listIterator methods of this class fails quickly: if the structure of the list is modified at any time after the iterator is created, the iterator will throw a ConcurrentModificationException except through the iterator's own remove or add methods. Therefore, in the face of concurrent modifications, the iterator will fail quickly and cleanly, rather than risking arbitrary and uncertain behavior at an uncertain time in the future.
Note that the fast failure behavior of iterators cannot be guaranteed, because generally speaking, it is impossible to make any hard guarantee in the presence of asynchronous concurrent modifications. The fast failure iterator will try its best to throw a ConcurrentModificationException. Therefore, it is wrong to write a program that depends on this exception to ensure its correctness: the fast failure behavior of the iterator can only be used to detect bug s.
This class is a member of the Java Collections Framework.
Since: 1.2
See: Collection, List, LinkedList, Vector
Author: Josh Bloch, Neal Gafter
Type parameters: – the type of elements in this list
3 member variables
The bottom layer of ArrayList is based on array to realize the dynamic change of capacity
// Size of the array list (number of elements included) private int size; // Actual number of elements transient Object[] elementData;
size refers to the actual number of elements in elementData
elementData.length is the collection capacity, indicating the maximum number of elements that can be accommodated
The default initial capacity size is 10
private static final int DEFAULT_CAPACITY = 10;
This variable is defined in AbstractList. Record the number of operations on the List. It is mainly used in Iterator to prevent the set from being modified during iteration
protected transient int modCount = 0;
The following two variables are used in the constructor
When adding an element for the first time, you know whether the collection capacity is initialized from an empty constructor or a parameter constructor, so as to confirm how to expand the capacity
/**
* Shared empty array instance used for empty instances.
*/
private static final Object[] EMPTY_ELEMENTDATA = {};
/**
* Shared empty array instance used for default sized empty instances. We
* distinguish this from EMPTY_ELEMENTDATA to know how much to inflate when
* first element is added.
*/
private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};
4 three construction methods
non-parameter constructor
/**
* Constructs an empty list with an initial capacity of ten.
* Construct an empty list with an initial capacity of 10
*/
public ArrayList() {
this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
}
Although the comment says that an empty list with an initial capacity of 10 is constructed, the default capability here is_ EMPTY_ Elementdata is a null value
In fact, the capacity is expanded to 10 when adding elements for the first time
The parameterized constructor passes an integer to confirm the capacity of the collection
If constructed in this way, the array size will be initialized, but the size of the list does not change, because the size of the list returns 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);
}
}
When initialCapacity is greater than zero, initialize an object array with the size of initialCapacity and assign it to elementData
When initialCapacity is zero, empty is set_ elementData is assigned to elementData
Constructor to construct an ArrayList using the specified Collection
public ArrayList(Collection<? extends E> c) {
Object[] a = c.toArray();
if ((size = a.length) != 0) {
if (c.getClass() == ArrayList.class) {
elementData = a;
} else {
elementData = Arrays.copyOf(a, size, Object[].class);
}
} else {
// replace with empty array.
elementData = EMPTY_ELEMENTDATA;
}
}
5. Some concluding remarks
ArrayList is an array list. It is characterized by fast query and access of elements and slow insertion and deletion
And thread unsafe
Expansion mode
If the default construction is adopted during construction, the bottom layer will be assigned an empty array by default, so the array capacity is 0
The default default is assigned only when adding add to the data_ Capacity = initial capacity of 10.
During capacity expansion, it is realized through array capacity expansion. When adding, it is found that the set is full
It will redefine an array with a length of 1.5 times that of the original array, assign the data of the original array to the new array, and then modify the address point to the new array
Changes from version 1.7
During initialization, this(10) will be called before 1.7 for real initialization. The capacity is 10, but after 1.7, the nonparametric construction defaults to the way of empty array
During capacity expansion, the new version has higher efficiency and adopts displacement operation
3 / 2 + 1 at 1.7
1.8 direct is 3 / 2 (bit operation)
New element
You can specify the subscript position to add or add directly
Before adding an element, check the length. If the length is not enough, it needs to be expanded. The size increases by + 1
If the specified subscript is added, the efficiency will become lower. Why?
When adding by specifying subscript, one more array with length + 1 will be copied, and the elements after subscript + 1 will be assigned
After vacating the location, add the specified new element to the specified location
delete
The speed at which ArraysList is inserted and deleted depends on how far away the element making the change is from the end array
Because it inserts and deletes the same array in copy
Is ArrayList suitable for queues
Queues are generally FIFO (first in, first out). If ArrayList is used as a queue, you need to add data at the end of the array, delete the array at the head of the array, and vice versa.
However, in any case, there will always be an operation involving the data relocation of the array, which is more performance-consuming.
Conclusion: ArrayList is not suitable for queue.
Are arrays suitable for queues
Arrays are very appropriate.
For example, the internal implementation of ArrayBlockingQueue is a ring queue. It is a fixed length queue, which is internally implemented by a fixed length array.
In addition, the famous Disruptor open source Library is also an ultra-high performance queue implemented by ring array. The specific principle is not explained and is more complex.
Simply put, two offsets are used to mark the read position and write position of the array. If they exceed the length, they will be folded back to the beginning of the array, provided that they are fixed length arrays.
How do you compare the traversal performance of ArrayList and LinkedList?
In terms of traversing ArrayList, it is much faster than LinkedList. The biggest advantage of ArrayList traversal is the continuity of memory. The internal cache structure of CPU will cache continuous memory fragments, which can greatly reduce the performance overhead of reading memory.
6 common methods
Look at the API, no explanation, no explanation
Source attachment
/*
* Copyright (c) 1997, 2019, Oracle and/or its affiliates. All rights reserved.
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*
*
*/
package java.util;
import java.util.function.Consumer;
import java.util.function.Predicate;
import java.util.function.UnaryOperator;
import jdk.internal.access.SharedSecrets;
import jdk.internal.util.ArraysSupport;
/**
* Resizable-array implementation of the {@code List} interface. Implements
* all optional list operations, and permits all elements, including
* {@code null}. In addition to implementing the {@code List} interface,
* this class provides methods to manipulate the size of the array that is
* used internally to store the list. (This class is roughly equivalent to
* {@code Vector}, except that it is unsynchronized.)
*
* <p>The {@code size}, {@code isEmpty}, {@code get}, {@code set},
* {@code iterator}, and {@code listIterator} operations run in constant
* time. The {@code add} operation runs in <i>amortized constant time</i>,
* that is, adding n elements requires O(n) time. All of the other operations
* run in linear time (roughly speaking). The constant factor is low compared
* to that for the {@code LinkedList} implementation.
*
* <p>Each {@code ArrayList} instance has a <i>capacity</i>. The capacity is
* the size of the array used to store the elements in the list. It is always
* at least as large as the list size. As elements are added to an ArrayList,
* its capacity grows automatically. The details of the growth policy are not
* specified beyond the fact that adding an element has constant amortized
* time cost.
*
* <p>An application can increase the capacity of an {@code ArrayList} instance
* before adding a large number of elements using the {@code ensureCapacity}
* operation. This may reduce the amount of incremental reallocation.
*
* <p><strong>Note that this implementation is not synchronized.</strong>
* If multiple threads access an {@code ArrayList} instance concurrently,
* and at least one of the threads modifies the list structurally, it
* <i>must</i> be synchronized externally. (A structural modification is
* any operation that adds or deletes one or more elements, or explicitly
* resizes the backing array; merely setting the value of an element is not
* a structural modification.) This is typically accomplished by
* synchronizing on some object that naturally encapsulates the list.
*
* If no such object exists, the list should be "wrapped" using the
* {@link Collections#synchronizedList Collections.synchronizedList}
* method. This is best done at creation time, to prevent accidental
* unsynchronized access to the list:<pre>
* List list = Collections.synchronizedList(new ArrayList(...));</pre>
*
* <p id="fail-fast">
* The iterators returned by this class's {@link #iterator() iterator} and
* {@link #listIterator(int) listIterator} methods are <em>fail-fast</em>:
* if the list is structurally modified at any time after the iterator is
* created, in any way except through the iterator's own
* {@link ListIterator#remove() remove} or
* {@link ListIterator#add(Object) add} methods, the iterator will throw a
* {@link ConcurrentModificationException}. Thus, in the face of
* concurrent modification, the iterator fails quickly and cleanly, rather
* than risking arbitrary, non-deterministic behavior at an undetermined
* time in the future.
*
* <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
* as it is, generally speaking, impossible to make any hard guarantees in the
* presence of unsynchronized concurrent modification. Fail-fast iterators
* throw {@code ConcurrentModificationException} on a best-effort basis.
* Therefore, it would be wrong to write a program that depended on this
* exception for its correctness: <i>the fail-fast behavior of iterators
* should be used only to detect bugs.</i>
*
* <p>This class is a member of the
* <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">
* Java Collections Framework</a>.
*
* @param <E> the type of elements in this list
*
* @author Josh Bloch
* @author Neal Gafter
* @see Collection
* @see List
* @see LinkedList
* @see Vector
* @since 1.2
*/
public class ArrayList<E> extends AbstractList<E>
implements List<E>, RandomAccess, Cloneable, java.io.Serializable
{
@java.io.Serial
private static final long serialVersionUID = 8683452581122892189L;
/**
* Default initial capacity.
*/
private static final int DEFAULT_CAPACITY = 10;
/**
* Shared empty array instance used for empty instances.
*/
private static final Object[] EMPTY_ELEMENTDATA = {};
/**
* Shared empty array instance used for default sized empty instances. We
* distinguish this from EMPTY_ELEMENTDATA to know how much to inflate when
* first element is added.
*/
private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};
/**
* The array buffer into which the elements of the ArrayList are stored.
* The capacity of the ArrayList is the length of this array buffer. Any
* empty ArrayList with elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA
* will be expanded to DEFAULT_CAPACITY when the first element is added.
*/
transient Object[] elementData; // non-private to simplify nested class access
/**
* The size of the ArrayList (the number of elements it contains).
*
* @serial
*/
private int size;
/**
* Constructs an empty list with the specified initial capacity.
*
* @param initialCapacity the initial capacity of the list
* @throws IllegalArgumentException if the specified initial capacity
* is negative
*/
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);
}
}
/**
* Constructs an empty list with an initial capacity of ten.
*/
public ArrayList() {
this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
}
/**
* Constructs a list containing the elements of the specified
* collection, in the order they are returned by the collection's
* iterator.
*
* @param c the collection whose elements are to be placed into this list
* @throws NullPointerException if the specified collection is null
*/
public ArrayList(Collection<? extends E> c) {
Object[] a = c.toArray();
if ((size = a.length) != 0) {
if (c.getClass() == ArrayList.class) {
elementData = a;
} else {
elementData = Arrays.copyOf(a, size, Object[].class);
}
} else {
// replace with empty array.
elementData = EMPTY_ELEMENTDATA;
}
}
/**
* Trims the capacity of this {@code ArrayList} instance to be the
* list's current size. An application can use this operation to minimize
* the storage of an {@code ArrayList} instance.
*/
public void trimToSize() {
modCount++;
if (size < elementData.length) {
elementData = (size == 0)
? EMPTY_ELEMENTDATA
: Arrays.copyOf(elementData, size);
}
}
/**
* Increases the capacity of this {@code ArrayList} instance, if
* necessary, to ensure that it can hold at least the number of elements
* specified by the minimum capacity argument.
*
* @param minCapacity the desired minimum capacity
*/
public void ensureCapacity(int minCapacity) {
if (minCapacity > elementData.length
&& !(elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA
&& minCapacity <= DEFAULT_CAPACITY)) {
modCount++;
grow(minCapacity);
}
}
/**
* Increases the capacity to ensure that it can hold at least the
* number of elements specified by the minimum capacity argument.
*
* @param minCapacity the desired minimum capacity
* @throws OutOfMemoryError if minCapacity is less than zero
*/
private Object[] grow(int minCapacity) {
int oldCapacity = elementData.length;
if (oldCapacity > 0 || elementData != DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
int newCapacity = ArraysSupport.newLength(oldCapacity,
minCapacity - oldCapacity, /* minimum growth */
oldCapacity >> 1 /* preferred growth */);
return elementData = Arrays.copyOf(elementData, newCapacity);
} else {
return elementData = new Object[Math.max(DEFAULT_CAPACITY, minCapacity)];
}
}
private Object[] grow() {
return grow(size + 1);
}
/**
* Returns the number of elements in this list.
*
* @return the number of elements in this list
*/
public int size() {
return size;
}
/**
* Returns {@code true} if this list contains no elements.
*
* @return {@code true} if this list contains no elements
*/
public boolean isEmpty() {
return size == 0;
}
/**
* Returns {@code true} if this list contains the specified element.
* More formally, returns {@code true} if and only if this list contains
* at least one element {@code e} such that
* {@code Objects.equals(o, e)}.
*
* @param o element whose presence in this list is to be tested
* @return {@code true} if this list contains the specified element
*/
public boolean contains(Object o) {
return indexOf(o) >= 0;
}
/**
* Returns the index of the first occurrence of the specified element
* in this list, or -1 if this list does not contain the element.
* More formally, returns the lowest index {@code i} such that
* {@code Objects.equals(o, get(i))},
* or -1 if there is no such index.
*/
public int indexOf(Object o) {
return indexOfRange(o, 0, size);
}
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;
}
/**
* Returns the index of the last occurrence of the specified element
* in this list, or -1 if this list does not contain the element.
* More formally, returns the highest index {@code i} such that
* {@code Objects.equals(o, get(i))},
* or -1 if there is no such index.
*/
public int lastIndexOf(Object o) {
return lastIndexOfRange(o, 0, size);
}
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;
}
/**
* Returns a shallow copy of this {@code ArrayList} instance. (The
* elements themselves are not copied.)
*
* @return a clone of this {@code ArrayList} instance
*/
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);
}
}
/**
* Returns an array containing all of the elements in this list
* in proper sequence (from first to last element).
*
* <p>The returned array will be "safe" in that no references to it are
* maintained by this list. (In other words, this method must allocate
* a new array). The caller is thus free to modify the returned array.
*
* <p>This method acts as bridge between array-based and collection-based
* APIs.
*
* @return an array containing all of the elements in this list in
* proper sequence
*/
public Object[] toArray() {
return Arrays.copyOf(elementData, size);
}
/**
* Returns an array containing all of the elements in this list in proper
* sequence (from first to last element); the runtime type of the returned
* array is that of the specified array. If the list fits in the
* specified array, it is returned therein. Otherwise, a new array is
* allocated with the runtime type of the specified array and the size of
* this list.
*
* <p>If the list fits in the specified array with room to spare
* (i.e., the array has more elements than the list), the element in
* the array immediately following the end of the collection is set to
* {@code null}. (This is useful in determining the length of the
* list <i>only</i> if the caller knows that the list does not contain
* any null elements.)
*
* @param a the array into which the elements of the list are to
* be stored, if it is big enough; otherwise, a new array of the
* same runtime type is allocated for this purpose.
* @return an array containing the elements of the list
* @throws ArrayStoreException if the runtime type of the specified array
* is not a supertype of the runtime type of every element in
* this list
* @throws NullPointerException if the specified array is null
*/
@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];
}
/**
* Returns the element at the specified position in this list.
*
* @param index index of the element to return
* @return the element at the specified position in this list
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public E get(int index) {
Objects.checkIndex(index, size);
return elementData(index);
}
/**
* Replaces the element at the specified position in this list with
* the specified element.
*
* @param index index of the element to replace
* @param element element to be stored at the specified position
* @return the element previously at the specified position
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
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;
}
/**
* Appends the specified element to the end of this list.
*
* @param e element to be appended to this list
* @return {@code true} (as specified by {@link Collection#add})
*/
public boolean add(E e) {
modCount++;
add(e, elementData, size);
return true;
}
/**
* Inserts the specified element at the specified position in this
* list. Shifts the element currently at that position (if any) and
* any subsequent elements to the right (adds one to their indices).
*
* @param index index at which the specified element is to be inserted
* @param element element to be inserted
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
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;
}
/**
* Removes the element at the specified position in this list.
* Shifts any subsequent elements to the left (subtracts one from their
* indices).
*
* @param index the index of the element to be removed
* @return the element that was removed from the list
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
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;
}
/**
* {@inheritDoc}
*/
public boolean equals(Object o) {
if (o == this) {
return true;
}
if (!(o instanceof List)) {
return false;
}
final int expectedModCount = modCount;
// ArrayList can be subclassed and given arbitrary behavior, but we can
// still deal with the common case where o is ArrayList precisely
boolean equal = (o.getClass() == ArrayList.class)
? equalsArrayList((ArrayList<?>) o)
: equalsRange((List<?>) o, 0, size);
checkForComodification(expectedModCount);
return equal;
}
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();
}
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;
}
private void checkForComodification(final int expectedModCount) {
if (modCount != expectedModCount) {
throw new ConcurrentModificationException();
}
}
/**
* {@inheritDoc}
*/
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;
}
/**
* Removes the first occurrence of the specified element from this list,
* if it is present. If the list does not contain the element, it is
* unchanged. More formally, removes the element with the lowest index
* {@code i} such that
* {@code Objects.equals(o, get(i))}
* (if such an element exists). Returns {@code true} if this list
* contained the specified element (or equivalently, if this list
* changed as a result of the call).
*
* @param o element to be removed from this list, if present
* @return {@code true} if this list contained the specified element
*/
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;
}
/**
* Private remove method that skips bounds checking and does not
* return the value removed.
*/
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;
}
/**
* Removes all of the elements from this list. The list will
* be empty after this call returns.
*/
public void clear() {
modCount++;
final Object[] es = elementData;
for (int to = size, i = size = 0; i < to; i++)
es[i] = null;
}
/**
* Appends all of the elements in the specified collection to the end of
* this list, in the order that they are returned by the
* specified collection's Iterator. The behavior of this operation is
* undefined if the specified collection is modified while the operation
* is in progress. (This implies that the behavior of this call is
* undefined if the specified collection is this list, and this
* list is nonempty.)
*
* @param c collection containing elements to be added to this list
* @return {@code true} if this list changed as a result of the call
* @throws NullPointerException if the specified collection is null
*/
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;
}
/**
* 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.
*
* @param index index at which to insert the first element from the
* specified collection
* @param c collection containing elements to be added to this list
* @return {@code true} if this list changed as a result of the call
* @throws IndexOutOfBoundsException {@inheritDoc}
* @throws NullPointerException if the specified collection is null
*/
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;
}
/**
* Removes from this list all of the elements whose index is between
* {@code fromIndex}, inclusive, and {@code toIndex}, exclusive.
* Shifts any succeeding elements to the left (reduces their index).
* This call shortens the list by {@code (toIndex - fromIndex)} elements.
* (If {@code toIndex==fromIndex}, this operation has no effect.)
*
* @throws IndexOutOfBoundsException if {@code fromIndex} or
* {@code toIndex} is out of range
* ({@code fromIndex < 0 ||
* toIndex > size() ||
* toIndex < fromIndex})
*/
protected void removeRange(int fromIndex, int toIndex) {
if (fromIndex > toIndex) {
throw new IndexOutOfBoundsException(
outOfBoundsMsg(fromIndex, toIndex));
}
modCount++;
shiftTailOverGap(elementData, fromIndex, toIndex);
}
/** Erases the gap from lo to hi, by sliding down following elements. */
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;
}
/**
* A version of rangeCheck used by add and addAll.
*/
private void rangeCheckForAdd(int index) {
if (index > size || index < 0)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
/**
* Constructs an IndexOutOfBoundsException detail message.
* Of the many possible refactorings of the error handling code,
* this "outlining" performs best with both server and client VMs.
*/
private String outOfBoundsMsg(int index) {
return "Index: "+index+", Size: "+size;
}
/**
* A version used in checking (fromIndex > toIndex) condition
*/
private static String outOfBoundsMsg(int fromIndex, int toIndex) {
return "From Index: " + fromIndex + " > To Index: " + toIndex;
}
/**
* Removes from this list all of its elements that are contained in the
* specified collection.
*
* @param c collection containing elements to be removed from this list
* @return {@code true} if this list changed as a result of the call
* @throws ClassCastException if the class of an element of this list
* is incompatible with the specified collection
* (<a href="Collection.html#optional-restrictions">optional</a>)
* @throws NullPointerException if this list contains a null element and the
* specified collection does not permit null elements
* (<a href="Collection.html#optional-restrictions">optional</a>),
* or if the specified collection is null
* @see Collection#contains(Object)
*/
public boolean removeAll(Collection<?> c) {
return batchRemove(c, false, 0, size);
}
/**
* Retains only the elements in this list that are contained in the
* specified collection. In other words, removes from this list all
* of its elements that are not contained in the specified collection.
*
* @param c collection containing elements to be retained in this list
* @return {@code true} if this list changed as a result of the call
* @throws ClassCastException if the class of an element of this list
* is incompatible with the specified collection
* (<a href="Collection.html#optional-restrictions">optional</a>)
* @throws NullPointerException if this list contains a null element and the
* specified collection does not permit null elements
* (<a href="Collection.html#optional-restrictions">optional</a>),
* or if the specified collection is null
* @see Collection#contains(Object)
*/
public boolean retainAll(Collection<?> c) {
return batchRemove(c, true, 0, size);
}
boolean batchRemove(Collection<?> c, boolean complement,
final int from, final int end) {
Objects.requireNonNull(c);
final Object[] es = elementData;
int r;
// Optimize for initial run of survivors
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) {
// 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;
shiftTailOverGap(es, w, end);
}
return true;
}
/**
* Saves the state of the {@code ArrayList} instance to a stream
* (that is, serializes it).
*
* @param s the stream
* @throws java.io.IOException if an I/O error occurs
* @serialData The length of the array backing the {@code ArrayList}
* instance is emitted (int), followed by all of its elements
* (each an {@code Object}) in the proper order.
*/
@java.io.Serial
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 behavioral 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();
}
}
/**
* Reconstitutes the {@code ArrayList} instance from a stream (that is,
* deserializes it).
* @param s the stream
* @throws ClassNotFoundException if the class of a serialized object
* could not be found
* @throws java.io.IOException if an I/O error occurs
*/
@java.io.Serial
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);
}
}
/**
* Returns a list iterator over the elements in this list (in proper
* sequence), starting at the specified position in the list.
* The specified index indicates the first element that would be
* returned by an initial call to {@link ListIterator#next next}.
* An initial call to {@link ListIterator#previous previous} would
* return the element with the specified index minus one.
*
* <p>The returned list iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
*
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public ListIterator<E> listIterator(int index) {
rangeCheckForAdd(index);
return new ListItr(index);
}
/**
* Returns a list iterator over the elements in this list (in proper
* sequence).
*
* <p>The returned list iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
*
* @see #listIterator(int)
*/
public ListIterator<E> listIterator() {
return new ListItr(0);
}
/**
* Returns an iterator over the elements in this list in proper sequence.
*
* <p>The returned iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
*
* @return an iterator over the elements in this list in proper sequence
*/
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;
// 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();
}
}
/**
* 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();
}
}
}
/**
* Returns a view of the portion of this list between the specified
* {@code fromIndex}, inclusive, and {@code toIndex}, exclusive. (If
* {@code fromIndex} and {@code toIndex} are equal, the returned list is
* empty.) The returned list is backed by this list, so non-structural
* changes in the returned list are reflected in this list, and vice-versa.
* The returned list supports all of the optional list operations.
*
* <p>This method eliminates the need for explicit range operations (of
* the sort that commonly exist for arrays). Any operation that expects
* a list can be used as a range operation by passing a subList view
* instead of a whole list. For example, the following idiom
* removes a range of elements from a list:
* <pre>
* list.subList(from, to).clear();
* </pre>
* Similar idioms may be constructed for {@link #indexOf(Object)} and
* {@link #lastIndexOf(Object)}, and all of the algorithms in the
* {@link Collections} class can be applied to a subList.
*
* <p>The semantics of the list returned by this method become undefined if
* the backing list (i.e., this list) is <i>structurally modified</i> in
* any way other than via the returned list. (Structural modifications are
* those that change the size of this list, or otherwise perturb it in such
* a fashion that iterations in progress may yield incorrect results.)
*
* @throws IndexOutOfBoundsException {@inheritDoc}
* @throws IllegalArgumentException {@inheritDoc}
*/
public List<E> subList(int fromIndex, int toIndex) {
subListRangeCheck(fromIndex, toIndex, size);
return new SubList<>(this, fromIndex, toIndex);
}
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;
/**
* Constructs a sublist of an arbitrary 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;
}
/**
* Constructs a sublist of another SubList.
*/
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 = parent.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 = SubList.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 = 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 && root.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 = SubList.this.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 = SubList.this.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;
}
};
}
}
/**
* @throws NullPointerException {@inheritDoc}
*/
@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();
}
/**
* 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();
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);
// TODO(8203662): remove increment of modCount from ...
modCount++;
}
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++;
}
void checkInvariants() {
// assert size >= 0;
// assert size == elementData.length || elementData[size] == null;
}
}