package java.util;
// ArrayList源码分析，ArrayList即使用数组实现的列表，是一种线性表
public class ArrayList<E> extends AbstractList<E>
implements List<E>, RandomAccess, Cloneable, java.io.Serializable
{
private static final long serialVersionUID = 8683452581122892189L;
/**
* Default initial capacity.
* 默认初始化容量
*/
private static final int DEFAULT_CAPACITY = 10;
/**
* Shared empty array instance used for empty instances.
* 共享的数组实例，供所有空列表(size==0，即elementData的长度为0)的实例使用
* 作用是提供一个标记指针，判断当前列表是否为空列表
*/
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.
* 共享的空数组实例，供所有默认长度空列表(通过构造函数ArrayList()创建的)实例使用.
* 对比DEFAULTCAPACITY_EMPTY_ELEMENTDATA和EMPTY_ELEMENTDATA，可以获得当第一个
* 元素被添加至列表时，需要扩充多少内存空间.
* 作用是提供一个标记指针，判断当前列表是否为一个默认容量的空数组
*/
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.
* 列表元素所存储的缓冲数组.
* 列表的容量即该缓冲数组的长度.
* 所有 elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA 的空列表，当第一个
* 元素被添加时，会将elementData的容量扩充为默认容量 DEFAULT_CAPACITY
*/
// non-private to simplify nested class access
// 非私有，简化嵌套类访问权限. transient用来表示该域不是该对象串行化的一部分
transient Object[] elementData;
/**
* The size of the ArrayList (the number of elements it contains).
* 列表的大小(列表所存储元素的总和)
* @serial
*/
private int size;
/**
* Constructs an empty list with the specified initial capacity.
* 构造一个指定初始容量的空列表
*
* @param initialCapacity the initial capacity of the list
* @throws IllegalArgumentException if the specified initial capacity
* is negative
*/
public ArrayList(int initialCapacity) {
//当初始化容量参数值大于0时，为elementData分配相应的内存空间
if (initialCapacity > 0) {
this.elementData = new Object[initialCapacity];
//当初始化容量参数值为0时，elementData DEFAULTCAPACITY_EMPTY_ELEMENTDATA 空数组
} else if (initialCapacity == 0) {
this.elementData = EMPTY_ELEMENTDATA;
//当初始化容量参数小于0时，抛出异常
} else {
throw new IllegalArgumentException("Illegal Capacity: "+
initialCapacity);
}
}
/**
* Constructs an empty list with an initial capacity of ten.
* 构造一个初始容量为10的空列表
*/
public ArrayList() {
//elementData 置成EMPTY_ELEMENTDATA 空数组
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.
* 通过一个包含一些元素的指定的集合，通过迭代器按顺序地取出这些元素，用来构造一个列表
*
* @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) {
//调用集合c.toArray，方法获得一个元素素组
elementData = c.toArray();
//将列表大小置为elmentData的长度，如果长度不为0
if ((size = elementData.length) != 0) {
// c.toArray might (incorrectly) not return Object[] (see 6260652)
/* 这个注释比较有意思了，意思是 c.toArray方法可能返回一个错误的Object[].
* 这是JDK的一个BUG JDK-6260652
* 在调用Arrays.asList("Larry", "Moe", "Curly")时，返回的并不是java.util.Arralist
* 而是Arrays的静态嵌套类 java.util.Arrays$ArrayList的实例
* java.util.Arrays$ArrayList实现了Collection接口，
* 调用java.util.Arrays$ArrayList.toArray()时，可能会返回错误的Object[]
* 源码: (注意这里的ArrayList 为Arrays的静态嵌套类，与java.util.Arralist不同)
* //Arrays:
* public static <T> List<T> asList(T... a) {
* return new ArrayList<>(a);
* }
*
* //Arrays.ArrayList
* ArrayList(E[] array) {
* //直接将成员变量a置成了array
* a = Objects.requireNonNull(array);
* }
*
* public Object[] toArray(){
* //toArray的时候，也只是将传进来的数组拷贝一份给返回了，虽说向上转型为Object[]
* //但返回数组仍然会为原始的数组类型，所以elementData.getClass()!= Object[].class
* //若所以elementData数组为String[]类型的数组，此时elementData.getClass()==String[].class
* //那么执行elementData[i] = new Object();时
* //是无法将Object向下转型为String存放的，会抛出ArrayStoreException异常
* return a.clone();
* }
* 为了防止上述问题，在elementData.getClass()!= Object[].class时，用Arrays.copyOf方法，将
* elementData转换为一个真正的Object数组
*/
if (elementData.getClass() != Object[].class)
elementData = Arrays.copyOf(elementData, size, Object[].class);
}
//如果长度为0
else {
// replace with empty array.
// elementData替换为空数组EMPTY_ELEMENTDATA
this.elementData = EMPTY_ELEMENTDATA;
}
}
/**
* Trims the capacity of this <tt>ArrayList</tt> instance to be the
* list‘s current size. An application can use this operation to minimize
* the storage of an <tt>ArrayList</tt> instance.
* 将列表容量修剪为列表的当前大小。该操作可将ArrayList实例的占用的存储空间减小到最少.
*/
public void trimToSize() {
/* modCount为AbstractList的一个成员变量，用来标记列表被修改的次数，实现fast-fail机制
* fast-fail--快速失败，它是Java集合的一种错误检测机制。
* 当多个线程对集合进行结构上的改变的操作时，有可能会产生fail-fast机制。
* 记住是有可能，而不是一定。例如：假设存在两个线程（线程1、线程2），
* 线程1通过Iterator在遍历集合A中的元素，在某个时候线程2修改了集合A的结构（是结构上面的修改，
* 而不是简单的修改集合元素的内容），那么这个时候程序就会抛出
* ConcurrentModificationException 异常，从而产生fail-fast机制。
*/
modCount++;
//当列表实际长度小于容量时
if (size < elementData.length) {
//若为空列表，则将elementData置为空数组EMPTY_ELEMENTDATA
//反之拷贝一个长度为size的数组，赋值为elementData
elementData = (size == 0)
? EMPTY_ELEMENTDATA
: Arrays.copyOf(elementData, size);
}
}
/**
* Increases the capacity of this <tt>ArrayList</tt> instance, if
* necessary, to ensure that it can hold at least the number of elements
* specified by the minimum capacity argument.
* 必要时,为ArrayList实例扩充容量, 来确保当前ArrayList能容纳下minCapacity参数
* 所指定的最小数量的元素
*
* @param minCapacity the desired minimum capacity
* 所需的最小容量，即最少能容纳新添加元素的容量
*/
public void ensureCapacity(int minCapacity) {
//如果当前列表不为默认容量的空列表，minExpand(最小扩充容量)为0
//如果当前列表为默认容量的空列表，minExpand(最小扩充容量)为默认容量10
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;
//如果所需的最小容量比最小扩充容量要大
if (minCapacity > minExpand) {
//确保正确的容量
ensureExplicitCapacity(minCapacity);
}
}
//确保容量，内部函数
private void ensureCapacityInternal(int minCapacity) {
//如果当前列表为默认容量空列表
if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
//minCapacity小于DEFAULT_CAPACITY时，取DEFAULT_CAPACITY
minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);
}
ensureExplicitCapacity(minCapacity);
}
//确保明确的容量
private void ensureExplicitCapacity(int minCapacity) {
modCount++;
// overflow-conscious code
// 当前列表容量不够时，扩充容量
if (minCapacity - elementData.length > 0)
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
* 创建一个数组允许被分配的最大内存容量
* 一些虚拟机会在数组头部存储数组的元信息(引用Java Memory management中的描述)：
* 1.Class--指向数组Class类型的指针，如果为整形数组，则指向int[].class
* 2.Flags--一些标志的集合，描述对象的状态、哈希码、对象的类型（即是否为一个数组）
* 3.Lock --对象的同步信息，也就是说，对象是否正在同步
* 4.Size --数组长度
* 尝试分配更大长度的数组可能引起 OutOfMemoryError :
* 请求的数组长度超出虚拟机限制
* Integer.MAX_VALUE = 0x7fffffff
* 减去8即排除需要存储元数据的内存开销
*/
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.
* 为列表扩容，来确保其能容纳参数minCapacity所指定数量的元素
*
* @param minCapacity the desired minimum capacity
*/
private void grow(int minCapacity) {
// overflow-conscious code
int oldCapacity = elementData.length;
// 尝试扩充新容量为原来的1.5倍
int newCapacity = oldCapacity + (oldCapacity >> 1);
// 扩充1.5倍不够，就将新容量置成最小所需的容量
if (newCapacity - minCapacity < 0)
newCapacity = minCapacity;
// 不好了，新容量超出了虚拟机单数组大小限制了！
if (newCapacity - MAX_ARRAY_SIZE > 0)
newCapacity = hugeCapacity(minCapacity);
// minCapacity is usually close to size, so this is a win:
// minCapacity 通常与列表的大小十分接近，所以这是一场胜利：
// 直接创建一个新的数组，将原来数组的数据拷贝进去
// WTF! 没有realloc没有free?? 就是这么简单粗暴...
elementData = Arrays.copyOf(elementData, newCapacity);
}
/* Arrays.copyOf源码贴下
* public static <T,U> T[] copyOf(U[] original, int newLength
* , Class<? extends T[]> newType) {
* @SuppressWarnings("unchecked")
* //直接创建一个新的newType类型的数组，把原数组数据拷贝进去
* T[] copy = ((Object)newType == (Object)Object[].class)
* //碎碎念下，C语言里，新建变量指定长度的数组也蛮想这样写的...
* ? (T[]) new Object[newLength]
* : (T[]) Array.newInstance(newType.getComponentType(), newLength);
* System.arraycopy(original, 0, copy, 0,
* Math.min(original.length, newLength));
* return copy;
* }
*/
private static int hugeCapacity(int minCapacity) {
//minCapacity都小于0了，扩充容量超出了最大正整数值，堆栈溢出
if (minCapacity < 0) // overflow
throw new OutOfMemoryError();
//扩充后大于Integer.MAX_VALUE-8，返回Integer.MAX_VALUE
//反之返回MAX_ARRAY_SIZE
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 <tt>true</tt> if this list contains no elements.
*
* @return <tt>true</tt> if this list contains no elements
*/
public boolean isEmpty() {
return size == 0;
}
/**
* Returns <tt>true</tt> if this list contains the specified element.
* More formally, returns <tt>true</tt> if and only if this list contains
* at least one element <tt>e</tt> such that
* <tt>(o==null ? e==null : o.equals(e))</tt>.
*
* @param o element whose presence in this list is to be tested
* @return <tt>true</tt> 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 <tt>i</tt> such that
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
* or -1 if there is no such index.
* 返回第一个等于参数对象的序号，没有则返回-1
*/
public int indexOf(Object o) {
//万恶的null
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 <tt>i</tt> such that
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
* or -1 if there is no such index.
* 返回最后一个等于参数对象的序号，没有则返回-1，从后往前找而已
*/
public int lastIndexOf(Object o) {
//万恶的null
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 <tt>ArrayList</tt> instance. (The
* elements themselves are not copied.)
*
* @return a clone of this <tt>ArrayList</tt> instance
* 虽说建了个新ArrayList实例，存的东西还是浅拷贝呢
*/
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() {
//复制一个吧
//比Arrays.ArrayList.toArray的直接clone要科学
//elementData是一个真的Object[]
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
* <tt>null</tt>. (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.)
* 将elementData存进传进来的参数数组中
*
* @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:
// 参数数组长度不够，创建一个新的数组，复制数据并返回
return (T[]) Arrays.copyOf(elementData, size, a.getClass());
//长度够的话，直接写进参数数组好了
System.arraycopy(elementData, 0, a, 0, size);
//参数数组长度比列表大小要大的话，在size处标记null
if (a.length > size)
a[size] = null;
return a;
}
// Positional Access Operations
@SuppressWarnings("unchecked")
E elementData(int index) {
return (E) elementData[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) {
//序号范围检查
rangeCheck(index);
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) {
//序号范围检查
rangeCheck(index);
E oldValue = elementData(index);
elementData[index] = element;
return oldValue;
}
/**
* Appends the specified element to the end of this list.
* 在列表最后添加一个元素 push!
* @param e element to be appended to this list
* @return <tt>true</tt> (as specified by {@link Collection#add})
*/
public boolean add(E e) {
ensureCapacityInternal(size + 1); // Increments modCount!!
// 这个函数，已经增加了modCount
//push
elementData[size++] = e;
return true;
}
/*
arraycopy(Object src, 原数组
int srcPos, 从原数组位置开始复制
Object dest, 目标数组
int destPos, 从目标数组的位置开始粘贴
int length); 复制多少个元素
*/
/**
* 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).
* 在指定位置添加元素
* @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) {
//序号范围检查
rangeCheckForAdd(index);
ensureCapacityInternal(size + 1); // Increments modCount!! 怨念..
//把index，及index后的元素都向后移动一个位置，线性存储我看出来了
System.arraycopy(elementData, index, elementData, index + 1,
size - index);
//index置成element
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) {
//序号范围检查
rangeCheck(index);
modCount++;
//把删除的对象取出来，作返回值
E oldValue = elementData(index);
//把index后的元素向前移动一个位置
int numMoved = size - index - 1;
if (numMoved > 0)
System.arraycopy(elementData, index+1, elementData, index,
numMoved);
//删除最后一个元素，取消引用，回收内存
elementData[--size] = null; // clear to let GC do its work
return 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
* <tt>i</tt> such that
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>
* (if such an element exists). Returns <tt>true</tt> if this list
* contained the specified element (or equivalently, if this list
* changed as a result of the call).
* 从列表中删除指定对象，由于存在对象才会删除，所以跳过了范围检查
*
* @param o element to be removed from this list, if present
* @return <tt>true</tt> if this list contained the specified element
*/
public boolean remove(Object o) {
//万恶的null
if (o == null) {
for (int index = 0; index < size; index++)
if (elementData[index] == null) {
fastRemove(index);
return true;
}
} else {
//如果存了多个相同对象的话，还是会只删除第一个的
for (int index = 0; index < size; index++)
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) {
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() {
modCount++;
// clear to let GC do its work
// 对每个元素取消引用，回收内存
for (int i = 0; i < size; i++)
elementData[i] = null;
//列表大小置0
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.)
* 将参数集合插入列表
* @param c collection containing elements to be added to this list
* @return <tt>true</tt> 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();
int numNew = a.length;
ensureCapacityInternal(size + numNew); // Increments modCount
//将集合转为数组，拷贝到列表最后
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.
* 将参数集合插入列表指定位置
* @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 <tt>true</tt> 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();
int numNew = a.length;
ensureCapacityInternal(size + numNew); // Increments modCount
int numMoved = size - index;
//将从index开始，的numNew个元素移动到列表末尾
if (numMoved > 0)
System.arraycopy(elementData, index, elementData, index + numNew,
numMoved);
//将参数集合填充到中间位置
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.)
* 删除一段范围的元素
* @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) {
modCount++;
int numMoved = size - toIndex;
//将toIndex后的元素向前移动到fromIndex的位置
System.arraycopy(elementData, toIndex, elementData, fromIndex,
numMoved);
// 列表末尾toIndex-fromIndex个元素取消引用，释放内存
// 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) {
//范围检查
if (index >= size)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
/**
* A version of rangeCheck used by add and addAll.
*/
private void rangeCheckForAdd(int index) {
//插入返回检查，index<0
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.
* 删除所有集合参数所包含的元素
*
* @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) {
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.
* 保留集合所包含的元素
* @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) {
Objects.requireNonNull(c);
return batchRemove(c, true);
}
private boolean batchRemove(Collection<?> c, boolean complement) {
//elementData的引用，声明为final，不允许修改这个引用地址
final Object[] elementData = this.elementData;
int r = 0, w = 0;
boolean modified = false;
try {
//遍历elementData
for (; r < size; r++)
//removeAll complement为假：即如果集合不包含这个元素，则保留元素
//retainAll complement为真：即如果集合包含这个元素，则保留元素
if (c.contains(elementData[r]) == complement)
//将当前元素按顺序写入elementData，从0开始. r>=w，所以这里没啥问题
elementData[w++] = elementData[r];
} finally {
// Preserve behavioral compatibility with AbstractCollection,
// even if c.contains() throws.
// 即使c.contains()抛出异常，也保持结果与AbstractCollectiony的行为一致
// r!= size , 即在遍历列表时抛出了异常,把r后的元素拷贝至w位置后
if (r != size) {
System.arraycopy(elementData, r,
elementData, w,
size - r);
//w加上末尾补充的元素数量
w += size - r;
}
//剩余元素数量与size不一致的时候
if (w != size) {
// clear to let GC do its work
// 清除w位置后的引用，释放内存
for (int i = w; i < size; i++)
elementData[i] = null;
modCount += size - w;
size = w;
modified = true;
}
}
return modified;
}
/**
* Save the state of the <tt>ArrayList</tt> instance to a stream (that
* is, serialize it).
*
* @serialData The length of the array backing the <tt>ArrayList</tt>
* instance is emitted (int), followed by all of its elements
* (each an <tt>Object</tt>) in the proper order.
*/
private void writeObject(java.io.ObjectOutputStream s)
throws java.io.IOException{
// Write out element count, and any hidden stuff
int expectedModCount = modCount;
s.defaultWriteObject();
// Write out size as capacity for behavioural compatibility with clone()
s.writeInt(size);
// Write out all elements in the proper order.
for (int i=0; i<size; i++) {
s.writeObject(elementData[i]);
}
if (modCount != expectedModCount) {
throw new ConcurrentModificationException();
}
}
/**
* Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
* deserialize it).
*/
private void readObject(java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException {
elementData = EMPTY_ELEMENTDATA;
// Read in size, and any hidden stuff
s.defaultReadObject();
// Read in capacity
s.readInt(); // ignored
if (size > 0) {
// be like clone(), allocate array based upon size not capacity
ensureCapacityInternal(size);
Object[] a = elementData;
// Read in all elements in the proper order.
for (int i=0; i<size; i++) {
a[i] = s.readObject();
}
}
}
/**
* 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) {
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).
*
* <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
* AbstractList.Itr的优化版本
*/
private class Itr implements Iterator<E> {
// index of next element to return
// 下个返回元素的位置
int cursor;
// index of last element returned; -1 if no such
// 最后一个返回元素的位置，如果不存在则标记为-1
int lastRet = -1;
// 期望的修改次数，如果modCount没有按照预期变化，会抛出异常,实现fast-fail机制
int expectedModCount = modCount;
public boolean hasNext() {
return cursor != size;
}
//返回下个元素
@SuppressWarnings("unchecked")
public E next() {
//检查操作时列表是否被修改了
checkForComodification();
int i = cursor;
if (i >= size)
throw new NoSuchElementException();
Object[] elementData = ArrayList.this.elementData;
if (i >= elementData.length)
throw new ConcurrentModificationException();
//下个返回元素的位置置成i+1
cursor = i + 1;
//lastRet置成i，返回第i个元素
return (E) elementData[lastRet = i];
}
//删除
public void remove() {
//迭代完毕了，无法再删除了
if (lastRet < 0)
throw new IllegalStateException();
//检查操作时列表是否被修改了
checkForComodification();
try {
//删除当前返回的最后一个元素
ArrayList.this.remove(lastRet);
//下个返回元素的位置置为lastRet
cursor = lastRet;
//标记最后一个返回元素为-1，因为已经删掉了
lastRet = -1;
//重置expectedModCount
expectedModCount = modCount;
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}
//为每个剩余元素执行给定的操作，实现Consumer接口
@Override
@SuppressWarnings("unchecked")
public void forEachRemaining(Consumer<? super E> consumer) {
Objects.requireNonNull(consumer);
final int size = ArrayList.this.size;
int i = cursor;
if (i >= size) {
return;
}
final Object[] elementData = ArrayList.this.elementData;
if (i >= elementData.length) {
throw new ConcurrentModificationException();
}
while (i != size && modCount == expectedModCount) {
consumer.accept((E) elementData[i++]);
}
// update once at end of iteration to reduce heap write traffic
cursor = i;
lastRet = i - 1;
checkForComodification();
}
//检查操作时列表是否被修改了
final void checkForComodification() {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
}
}
/**
* An optimized version of AbstractList.ListItr
* AbstractList.ListItr的优化版本
*/
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, 0, fromIndex, toIndex);
}
static void subListRangeCheck(int fromIndex, int toIndex, int size) {
if (fromIndex < 0)
throw new IndexOutOfBoundsException("fromIndex = " + fromIndex);
if (toIndex > size)
throw new IndexOutOfBoundsException("toIndex = " + toIndex);
if (fromIndex > toIndex)
throw new IllegalArgumentException("fromIndex(" + fromIndex +
") > toIndex(" + toIndex + ")");
}
private class SubList extends AbstractList<E> implements RandomAccess {
private final AbstractList<E> parent;
private final int parentOffset;
private final int offset;
int size;
SubList(AbstractList<E> parent,
int offset, int fromIndex, int toIndex) {
this.parent = parent;
this.parentOffset = fromIndex;
this.offset = offset + fromIndex;
this.size = toIndex - fromIndex;
this.modCount = ArrayList.this.modCount;
}
public E set(int index, E e) {
rangeCheck(index);
checkForComodification();
E oldValue = ArrayList.this.elementData(offset + index);
ArrayList.this.elementData[offset + index] = e;
return oldValue;
}
public E get(int index) {
rangeCheck(index);
checkForComodification();
return ArrayList.this.elementData(offset + index);
}
public int size() {
checkForComodification();
return this.size;
}
public void add(int index, E e) {
rangeCheckForAdd(index);
checkForComodification();
parent.add(parentOffset + index, e);
this.modCount = parent.modCount;
this.size++;
}
public E remove(int index) {
rangeCheck(index);
checkForComodification();
E result = parent.remove(parentOffset + index);
this.modCount = parent.modCount;
this.size--;
return result;
}
protected void removeRange(int fromIndex, int toIndex) {
checkForComodification();
parent.removeRange(parentOffset + fromIndex,
parentOffset + toIndex);
this.modCount = parent.modCount;
this.size -= toIndex - fromIndex;
}
public boolean addAll(Collection<? extends E> c) {
return addAll(this.size, c);
}
public boolean addAll(int index, Collection<? extends E> c) {
rangeCheckForAdd(index);
int cSize = c.size();
if (cSize==0)
return false;
checkForComodification();
parent.addAll(parentOffset + index, c);
this.modCount = parent.modCount;
this.size += cSize;
return true;
}
public Iterator<E> iterator() {
return listIterator();
}
public ListIterator<E> listIterator(final int index) {
checkForComodification();
rangeCheckForAdd(index);
final int offset = this.offset;
return new ListIterator<E>() {
int cursor = index;
int lastRet = -1;
int expectedModCount = ArrayList.this.modCount;
public boolean hasNext() {
return cursor != SubList.this.size;
}
@SuppressWarnings("unchecked")
public E next() {
checkForComodification();
int i = cursor;
if (i >= SubList.this.size)
throw new NoSuchElementException();
Object[] elementData = ArrayList.this.elementData;
if (offset + i >= elementData.length)
throw new ConcurrentModificationException();
cursor = i + 1;
return (E) elementData[offset + (lastRet = i)];
}
public boolean hasPrevious() {
return cursor != 0;
}
@SuppressWarnings("unchecked")
public E previous() {
checkForComodification();
int i = cursor - 1;
if (i < 0)
throw new NoSuchElementException();
Object[] elementData = ArrayList.this.elementData;
if (offset + i >= elementData.length)
throw new ConcurrentModificationException();
cursor = i;
return (E) elementData[offset + (lastRet = i)];
}
@SuppressWarnings("unchecked")
public void forEachRemaining(Consumer<? super E> consumer) {
Objects.requireNonNull(consumer);
final int size = SubList.this.size;
int i = cursor;
if (i >= size) {
return;
}
final Object[] elementData = ArrayList.this.elementData;
if (offset + i >= elementData.length) {
throw new ConcurrentModificationException();
}
while (i != size && modCount == expectedModCount) {
consumer.accept((E) elementData[offset + (i++)]);
}
// update once at end of iteration to reduce heap write traffic
lastRet = cursor = i;
checkForComodification();
}
public int nextIndex() {
return cursor;
}
public int previousIndex() {
return cursor - 1;
}
public void remove() {
if (lastRet < 0)
throw new IllegalStateException();
checkForComodification();
try {
SubList.this.remove(lastRet);
cursor = lastRet;
lastRet = -1;
expectedModCount = ArrayList.this.modCount;
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}
public void set(E e) {
if (lastRet < 0)
throw new IllegalStateException();
checkForComodification();
try {
ArrayList.this.set(offset + lastRet, e);
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}
public void add(E e) {
checkForComodification();
try {
int i = cursor;
SubList.this.add(i, e);
cursor = i + 1;
lastRet = -1;
expectedModCount = ArrayList.this.modCount;
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}
final void checkForComodification() {
if (expectedModCount != ArrayList.this.modCount)
throw new ConcurrentModificationException();
}
};
}
public List<E> subList(int fromIndex, int toIndex) {
subListRangeCheck(fromIndex, toIndex, size);
return new SubList(this, offset, fromIndex, toIndex);
}
private void rangeCheck(int index) {
if (index < 0 || index >= this.size)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
private void rangeCheckForAdd(int index) {
if (index < 0 || index > this.size)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
private String outOfBoundsMsg(int index) {
return "Index: "+index+", Size: "+this.size;
}
private void checkForComodification() {
if (ArrayList.this.modCount != this.modCount)
throw new ConcurrentModificationException();
}
public Spliterator<E> spliterator() {
checkForComodification();
return new ArrayListSpliterator<E>(ArrayList.this, offset,
offset + this.size, this.modCount);
}
}
@Override
public void forEach(Consumer<? super E> action) {
Objects.requireNonNull(action);
final int expectedModCount = modCount;
@SuppressWarnings("unchecked")
final E[] elementData = (E[]) this.elementData;
final int size = this.size;
for (int i=0; modCount == expectedModCount && i < size; i++) {
action.accept(elementData[i]);
}
if (modCount != expectedModCount) {
throw new ConcurrentModificationException();
}
}
/**
* 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<>(this, 0, -1, 0);
}
/** Index-based split-by-two, lazily initialized Spliterator */
static final class ArrayListSpliterator<E> 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 final ArrayList<E> 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 given range */
ArrayListSpliterator(ArrayList<E> list, int origin, int fence,
int expectedModCount) {
this.list = list; // OK if null unless traversed
this.index = origin;
this.fence = fence;
this.expectedModCount = expectedModCount;
}
private int getFence() { // initialize fence to size on first use
int hi; // (a specialized variant appears in method forEach)
ArrayList<E> lst;
if ((hi = fence) < 0) {
if ((lst = list) == null)
hi = fence = 0;
else {
expectedModCount = lst.modCount;
hi = fence = lst.size;
}
}
return hi;
}
public ArrayListSpliterator<E> trySplit() {
int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
return (lo >= mid) ? null : // divide range in half unless too small
new ArrayListSpliterator<E>(list, 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)list.elementData[i];
action.accept(e);
if (list.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
ArrayList<E> lst; Object[] a;
if (action == null)
throw new NullPointerException();
if ((lst = list) != null && (a = lst.elementData) != null) {
if ((hi = fence) < 0) {
mc = lst.modCount;
hi = lst.size;
}
else
mc = expectedModCount;
if ((i = index) >= 0 && (index = hi) <= a.length) {
for (; i < hi; ++i) {
@SuppressWarnings("unchecked") E e = (E) a[i];
action.accept(e);
}
if (lst.modCount == mc)
return;
}
}
throw new ConcurrentModificationException();
}
public long estimateSize() {
return (long) (getFence() - index);
}
public int characteristics() {
return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED;
}
}
@Override
public boolean removeIf(Predicate<? super E> filter) {
Objects.requireNonNull(filter);
// figure out which elements are to be removed
// any exception thrown from the filter predicate at this stage
// will leave the collection unmodified
int removeCount = 0;
final BitSet removeSet = new BitSet(size);
final int expectedModCount = modCount;
final int size = this.size;
for (int i=0; modCount == expectedModCount && i < size; i++) {
@SuppressWarnings("unchecked")
final E element = (E) elementData[i];
if (filter.test(element)) {
removeSet.set(i);
removeCount++;
}
}
if (modCount != expectedModCount) {
throw new ConcurrentModificationException();
}
// shift surviving elements left over the spaces left by removed elements
final boolean anyToRemove = removeCount > 0;
if (anyToRemove) {
final int newSize = size - removeCount;
for (int i=0, j=0; (i < size) && (j < newSize); i++, j++) {
i = removeSet.nextClearBit(i);
elementData[j] = elementData[i];
}
for (int k=newSize; k < size; k++) {
elementData[k] = null; // Let gc do its work
}
this.size = newSize;
if (modCount != expectedModCount) {
throw new ConcurrentModificationException();
}
modCount++;
}
return anyToRemove;
}
@Override
@SuppressWarnings("unchecked")
public void replaceAll(UnaryOperator<E> operator) {
Objects.requireNonNull(operator);
final int expectedModCount = modCount;
final int size = this.size;
for (int i=0; modCount == expectedModCount && i < size; i++) {
elementData[i] = operator.apply((E) elementData[i]);
}
if (modCount != expectedModCount) {
throw new ConcurrentModificationException();
}
modCount++;
}
@Override
@SuppressWarnings("unchecked")
public void sort(Comparator<? super E> c) {
final int expectedModCount = modCount;
Arrays.sort((E[]) elementData, 0, size, c);
if (modCount != expectedModCount) {
throw new ConcurrentModificationException();
}
modCount++;
}
}
时间： 2024-10-27 03:19:45