有些东西还没做学习，学习完后补充
/*
* Copyright (c) 1997, 2017, Oracle and/or its affiliates. All rights reserved.
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*
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*/package java.util;
import java.util.function.Consumer;
import java.util.function.Predicate;
import java.util.function.UnaryOperator;
import sun.misc.SharedSecrets;
/**
* Resizable-array implementation of the List interface.Implements
* all optional list operations, and permits all elements, including
* null.In addition to implementing the 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
* Vector, except that it is unsynchronized.)
*
* The size, isEmpty, get, set,
* iterator, and listIterator operations run in constant
* time.The add operation runs in amortized constant time,
* 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 LinkedList implementation.
*
* Each ArrayList instance has a capacity.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.
*
* 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 amount of incremental reallocation.
*
* Note that this implementation is not synchronized.
* If multiple threads access an ArrayList instance concurrently,
* and at least one of the threads modifies the list structurally, it
* must 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:
*List list = Collections.synchronizedList(new ArrayList(...));
*
* * The iterators returned by this class's {@link #iterator() iterator} and
* {@link #listIterator(int) listIterator} methods are fail-fast:
* 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.
*
* 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:the fail-fast behavior of iterators
* should be used only to detect bugs.
*
* This class is a member of the
*
* Java Collections Framework.
*
* @authorJosh Bloch
* @authorNeal Gafter
* @seeCollection
* @seeList
* @seeLinkedList
* @seeVector
* @since1.2
*/public class ArrayList extends AbstractList
implements List, RandomAccess, Cloneable, java.io.Serializable
{
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 = https://www.it610.com/article/{};
/**
* 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.
*
* @paraminitialCapacitythe initial capacity of the list
* @throws IllegalArgumentException if the specified initial capacity
*is negative
*/
public ArrayList(int initialCapacity) {
//构造函数，指定数组大小
if (initialCapacity> 0) {
this.elementData = https://www.it610.com/article/new Object[initialCapacity];
} else if (initialCapacity == 0) {
this.elementData = EMPTY_ELEMENTDATA;
//赋值为空数组
} else {
throw new IllegalArgumentException("Illegal Capacity: "+
initialCapacity);
}
}/**
* Constructs an empty list with an initial capacity of ten.
*/
public ArrayList() {
this.elementData = https://www.it610.com/article/DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
//默认为空数组{}
}/**
* 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 c) {
elementData = https://www.it610.com/article/c.toArray();
if ((size = elementData.length) != 0) {
// c.toArray might (incorrectly) not return Object[] (see 6260652)
if (elementData.getClass() != Object[].class)
elementData = Arrays.copyOf(elementData, size, Object[].class);
//由于toArray的原因，可能出现返回的数组不是Object类型
/*
可以百度JavaBug6260652，主要的问题就是Arrays.asList方法
源码如下：
public static List asList(T... a) {
return new ArrayList<>(a);
}
可以看到返回的是一个ArrayList，这个ArrayList是Arrays内部定义的
再来看ArrayList的源码
ArrayList(E[] array) {
a = Objects.requireNonNull(array);
}
可以看到调用了Objects的方法，再来定位到该方法
public static T requireNonNull(T obj) {
if (obj == null)
throw new NullPointerException();
return obj;
}
该方法就是返回原始对象，类型就是原始对象的类型
可以看到在ArrayList(Collection c)方法中， elementData = https://www.it610.com/article/c.toArray();
开始elementData直接就赋值为c.toArray();
我们来查看Array中的ArrayList的toArray方法
public Object[] toArray() {
return a.clone();
}
可以看到就是返回a的副本所以最终会导致elementData的类型被改变
我们看一下elementData的原始类型是什么
transient Object[] elementData;
可以看到elementData原本是Object的，可以保存任意值，如果类型发生
改变，那么将只能存储指定类型的值，显然这是不行的*/
} else {
// replace with empty array.
this.elementData = EMPTY_ELEMENTDATA;
}
}/**
* Trims the capacity of this ArrayList instance to be the
* list's current size.An application can use this operation to minimize
* the storage of an ArrayList instance.
*/
public void trimToSize() {//去除elementData空白的元素，将大小变为size
modCount++;
if (size < elementData.length) {
elementData = https://www.it610.com/article/(size == 0)
? EMPTY_ELEMENTDATA
: Arrays.copyOf(elementData, size);
}
}/**
* Increases the capacity of this ArrayList instance, if
* necessary, to ensure that it can hold at least the number of elements
* specified by the minimum capacity argument.
*
* @paramminCapacitythe desired minimum capacity
*/
public void ensureCapacity(int minCapacity) {//确保数据的大小可以存储size+1个元素
int minExpand = (elementData != DEFAULTCAPACITY_EMPTY_ELEMENTDATA)
// any size if not default element table
? 0
// larger than default for default empty table. It's already
// supposed to be at default size.
: DEFAULT_CAPACITY;
//10if (minCapacity > minExpand) {
ensureExplicitCapacity(minCapacity);
}
}private static int calculateCapacity(Object[] elementData, int minCapacity) {//计算容量
if (elementData =https://www.it610.com/article/= DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {//如果数组还是空的，返回默认容量10和minCapacity的最大值
return Math.max(DEFAULT_CAPACITY, minCapacity);
}
return minCapacity;
}private void ensureCapacityInternal(int minCapacity) {
ensureExplicitCapacity(calculateCapacity(elementData, minCapacity));
}private void ensureExplicitCapacity(int minCapacity) {
modCount++;
// overflow-conscious code
if (minCapacity - elementData.length> 0)//如果此时数组容量小于要存储数据的容量，进行扩容
grow(minCapacity);
}/**
* The maximum size of array to allocate.
* 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;
/**
* 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
*/
private void grow(int minCapacity) {
// overflow-conscious code
int oldCapacity = elementData.length;
int newCapacity = oldCapacity + (oldCapacity >> 1);
//将容量变为原来的1.5倍
if (newCapacity - minCapacity < 0)//如果1.5倍还是不能存储，将容量变为minCapacity
newCapacity = minCapacity;
if (newCapacity - MAX_ARRAY_SIZE > 0)//MAX_ARRAY_SIZE=int最大值-8
newCapacity = hugeCapacity(minCapacity);
// minCapacity is usually close to size, so this is a win:
elementData = https://www.it610.com/article/Arrays.copyOf(elementData, newCapacity);
}private static int hugeCapacity(int minCapacity) {//数组的最大容量为int的最大值
if (minCapacity < 0) // overflow
throw new OutOfMemoryError();
return (minCapacity> MAX_ARRAY_SIZE) ?
Integer.MAX_VALUE :
MAX_ARRAY_SIZE;
}/**
* Returns the number of elements in this list.
*
* @return the number of elements in this list
*/
public int size() {
return size;
}/**
* Returns true if this list contains no elements.
*
* @return true if this list contains no elements
*/
public boolean isEmpty() {
return size == 0;
}/**
* Returns true if this list contains the specified element.
* More formally, returns true if and only if this list contains
* at least one element e such that
* (o==null
?
e==null
:
o.equals(e)).
*
* @param o element whose presence in this list is to be tested
* @return 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 i such that
* (o==null
?
get(i)==null
:
o.equals(get(i))),
* or -1 if there is no such index.
*/
public int indexOf(Object o) {//从前往后for循环遍历查找元素
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;
}/**
* 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 i such that
* (o==null
?
get(i)==null
:
o.equals(get(i))),
* or -1 if there is no such index.
*/
public int lastIndexOf(Object o) {//从后往前佛如循环查找元素
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 ArrayList instance.(The
* elements themselves are not copied.)
*
* @return a clone of this ArrayList instance
*/
public Object clone() {//深拷贝
try {
ArrayList v = (ArrayList) super.clone();
v.elementData = https://www.it610.com/article/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).
*
* 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.
*
* 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.
*
* 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
* null.(This is useful in determining the length of the
* list only 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[] 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) {//得到指定下标的值
return (E) elementData[index];
}/**
* Returns the element at the specified position in this list.
*
* @paramindex index of the element to return
* @return the element at the specified position in this list
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public E get(int index) {//得到指定下标的值
rangeCheck(index);
//检测index是否越界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) {//设置指定下标的值
rangeCheck(index);
E oldValue = https://www.it610.com/article/elementData(index);
elementData[index] = element;
return oldValue;
}/**
* Appends the specified element to the end of this list.
*
* @param e element to be appended to this list
* @return true (as specified by {@link Collection#add})
*/
public boolean add(E e) {//添加元素
ensureCapacityInternal(size + 1);
// Increments modCount!!
elementData[size++] = e;
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) {//在指定下标处，插入值，数组要后移，耗时操作
rangeCheckForAdd(index);
ensureCapacityInternal(size + 1);
// Increments modCount!!
System.arraycopy(elementData, index, elementData, index + 1,
size - index);
elementData[index] = element;
size++;
}/**
* 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) {//移除指定下标的值
rangeCheck(index);
modCount++;
E oldValue = https://www.it610.com/article/elementData(index);
int numMoved = size - index - 1;
//计算index后有多少个元素
if (numMoved> 0)
System.arraycopy(elementData, index+1, elementData, index,
numMoved);
elementData[--size] = null;
// clear to let GC do its workreturn oldValue;
}/**
* 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
* i such that
* (o==null
?
get(i)==null
:
o.equals(get(i)))
* (if such an element exists).Returns 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 true if this list contained the specified element
*/
public boolean remove(Object o) {//移除指定元素
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++)//for循环遍历，找到元素
if (o.equals(elementData[index])) {
fastRemove(index);
return true;
}
}
return false;
}/*
* Private remove method that skips bounds checking and does not
* return the value removed.
*/
private void fastRemove(int index) {//和remove(index)同理
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
}/**
* Removes all of the elements from this list.The list will
* be empty after this call returns.
*/
public void clear() {//清除所有元素
modCount++;
// clear to let GC do its work
for (int i = 0;
i < size;
i++)//将数组赋值为null，存储的引用对象不再被引用等待垃圾回收器的回收
elementData[i] = null;
size = 0;
}/**
* 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 true if this list changed as a result of the call
* @throws NullPointerException if the specified collection is null
*/
public boolean addAll(Collection c) {//批量添加元素
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;
}/**
* 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 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 c) {//指定下标处添加
rangeCheckForAdd(index);
Object[] a = c.toArray();
int numNew = a.length;
ensureCapacityInternal(size + numNew);
// Increments modCountint 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;
}/**
* 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 ||
*fromIndex >= size() ||
*toIndex > size() ||
*toIndex < fromIndex})
*/
protected void removeRange(int fromIndex, int toIndex) {//移除区域内的元素
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;
}/**
* Checks if the given index is in range.If not, throws an appropriate
* runtime exception.This method does *not* check if the index is
* negative: It is always used immediately prior to an array access,
* which throws an ArrayIndexOutOfBoundsException if index is negative.
*/
private void rangeCheck(int index) {
if (index >= size)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}/**
* 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;
}/**
* 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
* (optional)
* @throws NullPointerException if this list contains a null element and the
*specified collection does not permit null elements
* (optional),
*or if the specified collection is null
* @see Collection#contains(Object)
*/
public boolean removeAll(Collection c) {//移除集合c中包含的元素
Objects.requireNonNull(c);
return batchRemove(c, false);
}/**
* 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
* (optional)
* @throws NullPointerException if this list contains a null element and the
*specified collection does not permit null elements
* (optional),
*or if the specified collection is null
* @see Collection#contains(Object)
*/
public boolean retainAll(Collection c) {//保留集合c中包含的元素
Objects.requireNonNull(c);
return batchRemove(c, true);
}private boolean batchRemove(Collection c, boolean complement) {
final Object[] elementData = https://www.it610.com/article/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 {
// Preserve behavioral compatibility with AbstractCollection,
// even if c.contains() throws.
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;
}/**
* Save the state of the ArrayList instance to a stream (that
* is, serialize it).
*
* @serialData The length of the array backing the ArrayList
*instance is emitted (int), followed by all of its elements
*(each an Object) in the proper order.
*/
private void writeObject(java.io.ObjectOutputStream s)//序列化
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;
i++) {
s.writeObject(elementData[i]);
}if (modCount != expectedModCount) {
throw new ConcurrentModificationException();
}
}/**
* Reconstitute the ArrayList instance from a stream (that is,
* deserialize it).
*/
private void readObject(java.io.ObjectInputStream s)//序列化
throws java.io.IOException, ClassNotFoundException {
elementData = https://www.it610.com/article/EMPTY_ELEMENTDATA;
// Read in size, and any hidden stuff
s.defaultReadObject();
// Read in capacity
s.readInt();
// ignoredif (size> 0) {
// be like clone(), allocate array based upon size not capacity
int capacity = calculateCapacity(elementData, size);
SharedSecrets.getJavaOISAccess().checkArray(s, Object[].class, capacity);
ensureCapacityInternal(size);
Object[] a = elementData;
// Read in all elements in the proper order.
for (int i=0;
i;
i++) {
a[i] = s.readObject();
}
}
}/**
* 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.
*
* The returned list iterator is fail-fast.
*
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public ListIterator listIterator(int index) {
if (index < 0 || index > size)
throw new IndexOutOfBoundsException("Index: "+index);
return new ListItr(index);
}/**
* Returns a list iterator over the elements in this list (in proper
* sequence).
*
* The returned list iterator is fail-fast.
*
* @see #listIterator(int)
*/
public ListIterator listIterator() {
return new ListItr(0);
}/**
* Returns an iterator over the elements in this list in proper sequence.
*
* The returned iterator is fail-fast.
*
* @return an iterator over the elements in this list in proper sequence
*/
public Iterator iterator() {
return new Itr();
}/**
* An optimized version of AbstractList.Itr
*/
private class Itr implements Iterator {//迭代器
int cursor;
// index of next element to return
int lastRet = -1;
// index of last element returned;
-1 if no such
int expectedModCount = modCount;
Itr() {}public boolean hasNext() {
return cursor != size;
}@SuppressWarnings("unchecked")
public E next() {//实现next方法
checkForComodification();
int i = cursor;
if (i >= size)
throw new NoSuchElementException();
Object[] elementData = https://www.it610.com/article/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 consumer) {
Objects.requireNonNull(consumer);
final int size = ArrayList.this.size;
int i = cursor;
if (i >= size) {
return;
}
final Object[] elementData = https://www.it610.com/article/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 {
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 = https://www.it610.com/article/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.
*
* 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:
*
*list.subList(from, to).clear();
*
* 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.
*
* The semantics of the list returned by this method become undefined if
* the backing list (i.e., this list) is structurally modified 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 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 implements RandomAccess {
private final AbstractList parent;
private final int parentOffset;
private final int offset;
int size;
SubList(AbstractList 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 = https://www.it610.com/article/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 c) {
return addAll(this.size, c);
}public boolean addAll(int index, Collection 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 iterator() {
return listIterator();
}public ListIterator listIterator(final int index) {
checkForComodification();
rangeCheckForAdd(index);
final int offset = this.offset;
return new ListIterator() {
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 = https://www.it610.com/article/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 = https://www.it610.com/article/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 consumer) {
Objects.requireNonNull(consumer);
final int size = SubList.this.size;
int i = cursor;
if (i >= size) {
return;
}
final Object[] elementData = https://www.it610.com/article/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 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 spliterator() {
checkForComodification();
return new ArrayListSpliterator(ArrayList.this, offset,
offset + this.size, this.modCount);
}
}@Override
public void forEach(Consumer action) {
Objects.requireNonNull(action);
final int expectedModCount = modCount;
@SuppressWarnings("unchecked")
final E[] elementData = https://www.it610.com/article/(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();
}
}/**
* Creates a late-binding
* and fail-fast {@link Spliterator} over the elements in this
* list.
*
* 【ArrayList的简单了解】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 spliterator() {
return new ArrayListSpliterator<>(this, 0, -1, 0);
}/** Index-based split-by-two, lazily initialized Spliterator */
static final class ArrayListSpliterator implements Spliterator {/*
* 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 final ArrayList list;
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/** Create new spliterator covering the givenrange */
ArrayListSpliterator(ArrayList list, int origin, int fence,
int expectedModCount) {
this.list = list;
// OK if null unless traversed
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)
ArrayList lst;
if ((hi = fence) < 0) {
if ((lst = list) == null)
hi = fence = 0;
else {
expectedModCount = lst.modCount;
hi = fence = lst.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(list, lo, index = mid,
expectedModCount);
}public boolean tryAdvance(Consumer action) {
if (action == null)
throw new NullPointerException();
int hi = getFence(), i = index;
if (i < hi) {
index = i + 1;
@SuppressWarnings("unchecked") E e = (E)list.elementData[i];
action.accept(e);
if (list.modCount != expectedModCount)
throw new ConcurrentModificationException();
return true;
}
return false;
}public void forEachRemaining(Consumer action) {
int i, hi, mc;
// hoist accesses and checks from loop
ArrayList 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 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 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 c) {
final int expectedModCount = modCount;
Arrays.sort((E[]) elementData, 0, size, c);
if (modCount != expectedModCount) {
throw new ConcurrentModificationException();
}
modCount++;
}
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