前言
ArrayList就是动态数组，其实就是Array的复杂版本，它提供了动态的添加元素和删除元素的方法，其实现了Collection 和 List接口，能够灵活的设置数组的大小。
同时还实现了 RandomAccess、Cloneable、Serializable 接口，所以ArrayList 是支持快速访问、复制、序列化的。
一、ArrayList构造方法
通过源码的分析，我们可以看到ArrayList有三种构造方法
- 空的构造函数
- 根据传入的数值大小，创建指定长度的数组
- 通过传入Collection元素列表进行生成
/**
* 默认初始化容量
*/
private static final int DEFAULT_CAPACITY = 10;
/**
* 共享的空数组（集合）实例
*/
private static final Object[] EMPTY_ELEMENTDATA = {};
/**
* 用于默认大小的空实例的共享空数组实例。我们
* 将其与EMPTY_ELEMENTDATA区分开来，以便知道何时膨胀多少
* 添加第一个元素。
*
* 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 = {};
/**
* 存储元素的数组，数组的元素个数即 list 的大小
*/
transient Object[] elementData; // non-private to simplify nested class access
/**
* 集合元素个数
*
* @serial
*/
private int size;
/**
* 带初始化容量的构造函数
*
* @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);
}
}
/**
* 无参构造函数，默认初始容量 10
*/
public ArrayList() {
this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
}
/**
* 构造包含指定元素的列表,集合的迭代器返回它们的顺序。
*
* 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
* C元素的集合放置在这个列表中
* @throws NullPointerException if the specified collection is null
*/
public ArrayList(Collection<? extends E> c) {
elementData = c.toArray();
if ((size = elementData.length) != 0) {
// 类型检查,判断数组的类型
if (elementData.getClass() != Object[].class)
/**
* 将数组内容拷贝到长度为 size 中的新数组中去，并返回
* Arrays.copyOf() 底层调用 System.arraycopy() 方法：浅拷贝、线程不安全
* Arrays.copyOf()对应System.arraycopy()
* System.arraycopy()对应到JVM 函数JVM_ArrayCopy
* {"arraycopy", "(" OBJ "I" OBJ "II)V", (void *)&JVM_ArrayCopy},
*/
elementData = Arrays.copyOf(elementData, size, Object[].class);
} else {
// replace with empty array. 替换为空数组。;
this.elementData = EMPTY_ELEMENTDATA;
}
}二、ArrayList解析
1.ArrayList优缺点
#### 优点
> ArrayList底层是以数组实现，是一种随机访问模式，再加上它实现了RandomAccess接口，因此在执行get方法的时候很快。
> ArrayList在顺序添加元素的时候非常场面，只是往数组中添加了一个元素而已，根据下标遍历元素，效率高。
> 可以自动扩容，默认为每次扩容为原来的1.5倍
#### 缺点
数组里面（除了末尾）插入和删除元素效率不高，因为需要移动大量的元素
> ArrayList在小于扩容容量的情况下，其实增加操作效率非常高，在涉及扩容的情况下，添加操作效率确实低，删除操作需要移位拷贝。
> 同时因为ArrayList中增加（扩容）或者删除元素要调用System.arrayCopy()这种效率很低的方法进行处理，所以遇到数据量略大 或者 需要频繁插入和删除操作的时候，效率就比较低了，如果遇到上述的场景，那么就需要使用LinkedList来代替 。
> 因为ArrayList的优点在于构造好数组后，频繁的访问元素的效率非常高。
2.ArrayList和Vector的区别
首先List接口一共有三个实现类：ArrayList、Vector、LinkedList
Vector 和 ArrayList一样，都是通过数组来实现的，不同的是 Vector支持线程的同步，也就是说某一个时刻下，只有一个线程能够写Vector，避免了多线程同时写而引起的不一致的问题，但实现同步需要很高的代Synchronized 因此，Vector的效率比ArrayList慢 。
同时Vector 和 ArrayList的扩容机制有差异的，Vector每次扩容为数组长度的一倍，而ArrayList则是原来数组长度的1.5倍。
3.ArrayList扩容机制
3.1.add方法
// 将指定的元素加到列表的末尾
public boolean add(E e) {
// 添加元素之前，先调用ensureCapacityInternal方法
ensureCapacityInternal(size + 1); // Increments modCount!!
// 这里看到的ArrayList添加元素的实质相当于为数组赋值
elementData[size++] = e;
return true;
}3.2.ensureCapacityInternal方法
// 当add进一个元素的时候，minCapacity为1，此时取两者的最大值
// 得到最小的扩容量
private void ensureCapacityInternal(int minCapacity) {
// 当一开始是默认空的列表
if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
// 获取默认的容量和传入参数的最大值
// DEFAULT_CAPACITY: 10 , minCapacity: 1
minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);
}
ensureExplicitCapacity(minCapacity);
}3.3.ensureExplicitCapacity方法
// 判断是否需要扩容
private void ensureExplicitCapacity(int minCapacity) {
modCount++;
// overflow-conscious code
if (minCapacity - elementData.length > 0)
// 调用grow方法进行扩容
grow(minCapacity);
}3.4.grow方法
// 需要分配的数组大小
private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
private void grow(int minCapacity) {
// 集合的容量
int oldCapacity = elementData.length;
// 新的集合的容量（在这里运用了位运算，位运算是计算机最快的，右移一位，所以新容量是1.5倍）
// 当添加元素的时候，大于当前数组的长度，就会触发grow操作，该操作将会对数组进行扩容
int newCapacity = oldCapacity + (oldCapacity >> 1);
// 如果新容量小于添加的集合的容量，则把该容量替换
if (newCapacity - minCapacity < 0)
newCapacity = minCapacity;
/** 如果新容量大于 MAX_ARRAY_SIZE,进入(执行) `hugeCapacity()` 方法来比较 minCapacity 和
* MAX_ARRAY_SIZE，如果minCapacity大于最大容量，则新容量则为`Integer.MAX_VALUE`，否则，
* 新容量大小则为 MAX_ARRAY_SIZE 即为 `Integer.MAX_VALUE - 8`。
**/
if (newCapacity - MAX_ARRAY_SIZE > 0)
newCapacity = hugeCapacity(minCapacity);
// minCapacity is usually close to size, so this is a win:
// 将原数组copy到新的数组中
// 将原来的数组长度，进行扩容到1.5倍，然后在执行拷贝命令，将旧数组中的内容，拷贝到新的数组中，实现元素的扩容操作。
elementData = Arrays.copyOf(elementData, newCapacity);
}
/** 如果新容量大于 MAX_ARRAY_SIZE,进入(执行) `hugeCapacity()` 方法来比较 minCapacity 和
* MAX_ARRAY_SIZE，如果minCapacity大于最大容量，则新容量则为`Integer.MAX_VALUE`，否则，
* 新容量大小则为 MAX_ARRAY_SIZE 即为 `Integer.MAX_VALUE - 8`。
*/
private static int hugeCapacity(int minCapacity) {
if (minCapacity < 0) // overflow
throw new OutOfMemoryError();
return (minCapacity > MAX_ARRAY_SIZE) ?
Integer.MAX_VALUE :
MAX_ARRAY_SIZE;
}3.5.Arrays.copyOf方法
public static <T,U> T[] copyOf(U[] original, int newLength, Class<? extends T[]> newType) {
@SuppressWarnings("unchecked")
T[] copy = ((Object)newType == (Object)Object[].class)
? (T[]) new Object[newLength]
: (T[]) Array.newInstance(newType.getComponentType(), newLength);
System.arraycopy(original, 0, copy, 0,
Math.min(original.length, newLength));
return copy;
}总结
ArrayList扩容机制梳理
- 当我们add进第一个元素到ArrayList的时候，elementData.length为0（因为还是一个空的list，有种懒加载的感觉？？），但是此时执行了ensureCapacityInternal() 方法，通过默认的比较，此时会得到minCapacity为10，此时minCapacity - elementData.length > 0满足，所以会进入grow(minCapacity)方法。
- 当add第二个元素的时候，minCapacity为2，此时elementData.length()在添加第一个元素后，扩容变成了10，此时minCapacity - elementData.length > 0 不成立，所以不会进入（执行）grow(minCapacity)方法。 - 同时我们继续添加元素 3,4 .... 11，到第11个元素的时候，minCapacity(11) 比 10更大，那么会触发grow操作。
下面给出ArrayList源码文件(部分带注释，有需要的可以看下，没有就可以Exit)。
/**
* 知识点总结：
* 1.Arrays.copyof()：
* https://juejin.im/post/5aa32725f265da2373140df3
* https://segmentfault.com/a/1190000009922279
* System.arraycopy为 JVM 内部固有方法，它通过手工编写汇编或其他优化方法来进行
* Java 数组拷贝，这种方式比起直接在 Java 上进行 for 循环或 clone 是更加高效的。数组越大体现地越明显。
* System.arraycopy是对内存直接进行复制，减少了for循环过程中的寻址时间，从而提高了效能。
* 2.modCount 作用：记录被修改的数次，保证在迭代时的正确性
* 3.ArrayList 可添加 null 值，源码中 null 与非 null 采取两种方式处理（比如遍历）
* 4.subList
*/
package java.util;
import java.util.function.Consumer;
import java.util.function.Predicate;
import java.util.function.UnaryOperator;
public class ArrayList<E> extends AbstractList<E>
implements List<E>, RandomAccess, Cloneable, java.io.Serializable
{
private static final long serialVersionUID = 8683452581122892189L;
/**
* 默认初始化容量
*/
private static final int DEFAULT_CAPACITY = 10;
/**
* 共享的空数组（集合）实例
*/
private static final Object[] EMPTY_ELEMENTDATA = {};
/**
* 用于默认大小的空实例的共享空数组实例。我们
* 将其与EMPTY_ELEMENTDATA区分开来，以便知道何时膨胀多少
* 添加第一个元素。
*
* 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 = {};
/**
* 存储元素的数组，数组的元素个数即 list 的大小
*/
transient Object[] elementData; // non-private to simplify nested class access
/**
* 集合元素个数
*
* @serial
*/
private int size;
/**
* 带初始化容量的构造函数
*
* @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);
}
}
/**
* 无参构造函数，默认初始容量 10
*/
public ArrayList() {
this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
}
/**
* 构造包含指定元素的列表,集合的迭代器返回它们的顺序。
*
* 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
* C元素的集合放置在这个列表中
* @throws NullPointerException if the specified collection is null
*/
public ArrayList(Collection<? extends E> c) {
elementData = c.toArray();
if ((size = elementData.length) != 0) {
// 类型检查,判断数组的类型
if (elementData.getClass() != Object[].class)
/**
* 将数组内容拷贝到长度为 size 中的新数组中去，并返回
* Arrays.copyOf() 底层调用 System.arraycopy() 方法：浅拷贝、线程不安全
* Arrays.copyOf()对应System.arraycopy()
* System.arraycopy()对应到JVM 函数JVM_ArrayCopy
* {"arraycopy", "(" OBJ "I" OBJ "II)V", (void *)&JVM_ArrayCopy},
*/
elementData = Arrays.copyOf(elementData, size, Object[].class);
} else {
// replace with empty array. 替换为空数组。;
this.elementData = EMPTY_ELEMENTDATA;
}
}
/**
* 阀内件的能力 ArrayList 实例列表的当前大小
* 应用程序可以使用该操作来 最小化存储的 ArrayList 实例数组列表
* 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.
*/
public void trimToSize() {
// 修改的次数
modCount++;
if (size < elementData.length) {
elementData = (size == 0)
? EMPTY_ELEMENTDATA
: Arrays.copyOf(elementData, size);
}
}
/**
* 增加集合能力 ArrayList 实例数组列表,
* 如果有必要,以确保它可以容纳至少最低容量参数指定的元素的个数。;
*
* 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.
*
* @param minCapacity the desired minimum capacity
* 所需的最小容量;
*/
public void ensureCapacity(int minCapacity) {
// 比较 数据(elementData) 和 默认大小的空实例的共享空数组实例(DEFAULTCAPACITY_EMPTY_ELEMENTDATA)
int minExpand = (elementData != DEFAULTCAPACITY_EMPTY_ELEMENTDATA)
// any size if not default element table 任何大小如果不是默认元素表
? 0
// larger than default for default empty table. It's already
// supposed to be at default size.
// 默认初始化容量
: DEFAULT_CAPACITY;
// 所需的最小容量(minCapacity) 大于 数组的容量(minExpand)
if (minCapacity > minExpand) {
// 扩容判断
ensureExplicitCapacity(minCapacity);
}
}
private void ensureCapacityInternal(int minCapacity) {
// 判空
if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
// 取最大值
minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);
}
// 扩容判断
ensureExplicitCapacity(minCapacity);
}
private void ensureExplicitCapacity(int minCapacity) {
modCount++;
// 数组所需的最小容量 大于 当前数组的大小
// 当数组存不下新元素时，对数组进行扩容
if (minCapacity - elementData.length > 0)
// 扩容
grow(minCapacity);
}
/**
* 数组最大数量
* 2<sup>31</sup>-1-8.
* OutOfMemoryError: Requested array size exceeds VM limit
*/
private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
/**
* 数组扩容
*
* @param minCapacity the desired minimum capacity
* 期望的最小容量
*/
private void grow(int minCapacity) {
// overflow-conscious code
int oldCapacity = elementData.length;
// 数组容量被扩大为原来的 1.5 倍
int newCapacity = oldCapacity + (oldCapacity >> 1);
if (newCapacity - minCapacity < 0)
newCapacity = minCapacity;
// MAX_ARRAY_SIZE = 2<sup>31</sup>-1-8
if (newCapacity - MAX_ARRAY_SIZE > 0)
newCapacity = hugeCapacity(minCapacity);
// minCapacity is usually close to size, so this is a win:
elementData = Arrays.copyOf(elementData, newCapacity);
}
private static int hugeCapacity(int minCapacity) {
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 <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;
}
/**
* 是否包含某个元素
*
* @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;
}
/**
* 顺序遍历整个数组，返回第一个出现该元素的 index
*
* @param o
* @return
*/
public int indexOf(Object o) {
// 对 null 单独处理
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;
}
/**
* 倒序遍历整个数组，返回最后一个出现该元素的 index
*
* @param o
* @return
*/
public int lastIndexOf(Object o) {
if (o == null) {
for (int i = size-1; i >= 0; i--)
if (elementData[i]==null)
return i;
} else {
for (int i = size-1; i >= 0; i--)
if (o.equals(elementData[i]))
return i;
}
return -1;
}
/**
* 返回集合实例的浅拷贝对象 (元素本身并没有拷贝->指向已经存在的元素)
*
* @return a clone of this <tt>ArrayList</tt> 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);
}
}
/**
* ArrayList 转数组
*
* <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);
}
/**
* ArrayList 转一个指定的数组
*
* <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.)
*
* @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:
// 疑问1：为什么是 size 不是 length，可以使用测试证明
return (T[]) Arrays.copyOf(elementData, size, a.getClass());
System.arraycopy(elementData, 0, a, 0, size);
if (a.length > size)
a[size] = null;
return a;
}
/**
* 根据角标获取元素
*
* @param index
* @return
*/
@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) {
// 角标范围检查
rangeCheck(index);
return elementData(index);
}
/**
* 替换指定位置的元素
*
* @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) {
rangeCheck(index);
E oldValue = elementData(index);
elementData[index] = element;
// 返回被替换的元素
return oldValue;
}
/**
* 添加元素
*
* @param e element to be appended to this list
* @return <tt>true</tt> (as specified by {@link Collection#add})
*/
public boolean add(E e) {
// Increments modCount!! 增量 修改次数(modCount)
ensureCapacityInternal(size + 1);
elementData[size++] = e;
return true;
}
/**
* 在指定位置插入元素，移动当前位于该位置的元素（如果有）和右边的任何后续元素（在其索引中加1）。
*
* @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) {
// 角标范围检查
rangeCheckForAdd(index);
// Increments modCount!! 增量 修改次数(modCount)
ensureCapacityInternal(size + 1);
// 浅拷贝，把指定 index 位置及以后的元素向后移动
System.arraycopy(elementData, index, elementData, index + 1,
size - index);
// 把新增的元素插入到指定位置上
elementData[index] = element;
size++;
}
/**
* 移除指定位置的元素，将所有后续元素左移，并返回被移除的元素
*
* @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) {
rangeCheck(index);
modCount++;
E oldValue = elementData(index);
int numMoved = size - index - 1;
// 当移除的不是最后一个元素时，将后面的元素向前移动
if (numMoved > 0)
System.arraycopy(elementData, index+1, elementData, index,
numMoved);
// clear to let GC do its work 清除，让GC完成它的工作
elementData[--size] = null;
return oldValue;
}
/**
* 移除当前 list 中第一个匹配项，不匹配时，元素不变动，返回 true/false
*
* <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).
*
* @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) {
// 对 null 与不为 null 分两种形式进行判断
if (o == null) {
for (int index = 0; index < size; index++)
if (elementData[index] == null) {
// 根据角标移除元素
fastRemove(index);
return true;
}
} else {
for (int index = 0; index < size; index++)
if (o.equals(elementData[index])) {
fastRemove(index);
return true;
}
}
return false;
}
/**
* 移除指定角标的元素
*
* @param index
*/
private void fastRemove(int index) {
modCount++;
int numMoved = size - index - 1;
// 当移除的不是最后一个元素时，将后面的元素向前移动
if (numMoved > 0)
System.arraycopy(elementData, index+1, elementData, index,
numMoved);
// clear to let GC do its work
elementData[--size] = null;
}
/**
* 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
// 循环数组将把所有元素置为 null，让 GC 进行垃圾回收
for (int i = 0; i < size; i++)
elementData[i] = null;
// 把集合 size 置为 0
size = 0;
}
/**
* 把指定集合中的所有元素追加到当前 list
*
* @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();
// 追加的元素个数
int numNew = a.length;
// Increments modCount 增量 修改次数(modCount)
ensureCapacityInternal(size + numNew);
System.arraycopy(a, 0, elementData, size, numNew);
// 更新 list size
size += numNew;
return numNew != 0;
}
/**
* 在指定的位置将集合中的元素添加到 list
*
* @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;
// Increments modCount 增量 修改次数(modCount)
ensureCapacityInternal(size + numNew);
int numMoved = size - index;
// 在 index 位置将后面元素右移
if (numMoved > 0)
System.arraycopy(elementData, index, elementData, index + numNew,
numMoved);
// 将集合中的元素拷贝到 list
System.arraycopy(a, 0, elementData, index, numNew);
// 更新 list size
size += numNew;
return numNew != 0;
}
/**
* 删除指定起始与终止位置之间的元素
*
* @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++;
// 后面未删除的元素个数
int numMoved = size - toIndex;
System.arraycopy(elementData, toIndex, elementData, fromIndex,
numMoved);
// clear to let GC do its work
// 删除后的元素个数
int newSize = size - (toIndex-fromIndex);
for (int i = newSize; i < size; i++) {
elementData[i] = null;
}
// 更新 list size
size = newSize;
}
/**
* 范围检查
*/
private void rangeCheck(int index) {
if (index >= size)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
/**
* 范围检查
* 用于添加和添加ALL的rangeCheck的一种版本
* A version of rangeCheck used by add and addAll.
*/
private void rangeCheckForAdd(int index) {
if (index > size || index < 0)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
/**
* IndexOutOfBoundsException 异常信息
*
* 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;
}
/**
* 在list 中移除指定集合中包含的所有元素
*
* @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) {
// 判 null 检查
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
* (<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);
}
/**
* 批量删除 list 与指定集合中重复的元素
*
* @param c
* @param complement
* @return
*/
private boolean batchRemove(Collection<?> c, boolean complement) {
final Object[] elementData = this.elementData;
// r：遍历 elementData 数组的角标 w: 当 c 中不包含 elementData 数组中的元素时，重构 elementData 数组角标
int r = 0, w = 0;
boolean modified = false;
try {
//遍历，移除 elementData 在 c 中包含的元素
for (; r < size; r++)
// 当 c 中不包含 elementData 数组中的元素时，重构 elementData 数组
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;
}
// 当 c 中有包含 elementData 数组中的元素时，把 w 角标后面的元素置 null
// w = elementData 中删除后剩余的元素个数
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 <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
*/
private class Itr implements Iterator<E> {
int cursor; // index of next element to return
int lastRet = -1; // index of last element returned; -1 if no such
int expectedModCount = modCount;
public boolean hasNext() {
return cursor != size;
}
@SuppressWarnings("unchecked")
public E next() {
checkForComodification();
int i = cursor;
if (i >= size)
throw new NoSuchElementException();
Object[] elementData = ArrayList.this.elementData;
if (i >= elementData.length)
throw new ConcurrentModificationException();
cursor = i + 1;
return (E) elementData[lastRet = i];
}
public void remove() {
if (lastRet < 0)
throw new IllegalStateException();
checkForComodification();
try {
ArrayList.this.remove(lastRet);
cursor = lastRet;
lastRet = -1;
expectedModCount = modCount;
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}
@Override
@SuppressWarnings("unchecked")
public void forEachRemaining(Consumer<? super E> consumer) {
Objects.requireNonNull(consumer);
final int size = ArrayList.this.size;
int i = cursor;
if (i >= size) {
return;
}
final Object[] elementData = ArrayList.this.elementData;
if (i >= elementData.length) {
throw new ConcurrentModificationException();
}
while (i != size && modCount == expectedModCount) {
consumer.accept((E) elementData[i++]);
}
// update once at end of iteration to reduce heap write traffic
cursor = i;
lastRet = i - 1;
checkForComodification();
}
final void checkForComodification() {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
}
}
/**
* An optimized version of AbstractList.ListItr
*/
private class ListItr extends Itr implements ListIterator<E> {
ListItr(int index) {
super();
cursor = index;
}
public boolean hasPrevious() {
return cursor != 0;
}
public int nextIndex() {
return cursor;
}
public int previousIndex() {
return cursor - 1;
}
@SuppressWarnings("unchecked")
public E previous() {
checkForComodification();
int i = cursor - 1;
if (i < 0)
throw new NoSuchElementException();
Object[] elementData = ArrayList.this.elementData;
if (i >= elementData.length)
throw new ConcurrentModificationException();
cursor = i;
return (E) elementData[lastRet = i];
}
public void set(E e) {
if (lastRet < 0)
throw new IllegalStateException();
checkForComodification();
try {
ArrayList.this.set(lastRet, e);
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}
public void add(E e) {
checkForComodification();
try {
int i = cursor;
ArrayList.this.add(i, e);
cursor = i + 1;
lastRet = -1;
expectedModCount = modCount;
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}
}
/**
* 返回列表中部分数据视图
*
* 如果对原 list 调用 subList(int fromIndex, int toIndex) 方法：
* 1.原 list 可以进行修改与查询操作，但是修改后 subList 中对应的元素值也会对应改变（index 不超过 subList 的大小），如果对原 list
* 执行删除与添加时会报 ConcurrentModificationException 并发修改异常
* 2.如果对 subList 执行增删改操作会对原 list 执行同样的操作
*
*
* <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);
}
/**
* 角标检查
*
* @param fromIndex
* @param toIndex
* @param size
*/
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);
}
}
/**
* 据说有小伙伴使用 forEach 删除元素时报了并发修改异常？重点画一下，咳咳～
* 这里以移除元素为例
*
* @param action
*/
@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;
// 在移除元素时 modCount 会自增，在移除元素之前 expectedModCount = modCount
for (int i=0; modCount == expectedModCount && i < size; i++) {
action.accept(elementData[i]);
}
// 在移除元素之后 modCount 显然就变大了，拿着改变之前的值与改变之后的值做比较肯定是不一样的
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.
*
* 如果ArrayLists是不可变的，或者是结构不可变的（没有*添加、删除等），我们可以用数组.spliterator.
* 相反，我们在遍历过程中尽可能多地检测到*干扰，而不会牺牲太多性能。我们主要依靠“模式计数”。
* 它们不能保证检测到并发性*冲突，有时对线程内的*冲突过于保守，但检测到的问题足够*值得在实践中使用。
* 为了实现这一点，我们（1）懒洋洋地初始化fence和expectedModCount，直到我们需要提交给我
* 们正在检查的状态的最新*点；从而提高精度。（这不适用于*子列表，它使用当前的非惰性*值创建拆分器）。
* （2） 我们只在forEach*结尾执行一个*ConcurrentModificationException检查（对性能最敏感的方法）。
* 当使用forEach*（与迭代器相反）时，我们通常只能在操作之后而不是之前检测*干扰。此外，CME触发检查
* 适用于所有其他可能的*违反假设的情况，例如给定其size（）的*elementData数组为空或太小，这可能是
* 由于干扰而*发生的。这允许forEach的内部循环*运行而无需进一步检查，*简化了lambda解析。虽然这需要
* *多次检查，但请注意在*的常见情况下list.stream列表（1）forEach（a），除了forEach本身之外，
* 任何地方都不进行检查或其他计算。其他不常用的方法不能充分利用这些流线型
*/
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++;
}
}
以上。