本文介绍了Java集合类中ArrayList类
本文是源码分fan析yi系列文的第三篇
##ArrayList
查看ArrayList源码,发现ArrayList(类)----实现----> AbstractList(类)----实现---->AbstractCollection(类)
同时,AbstractList----实现----> List(接口)-----实现----Collection(接口)
package cn.lawfree.orgcode;
import java.util.AbstractList;
import java.util.Arrays;
import java.util.BitSet;
import java.util.Collection;
import java.util.Comparator;
import java.util.ConcurrentModificationException;
import java.util.List;
import java.util.ListIterator;
import java.util.NoSuchElementException;
import java.util.Objects;
import java.util.RandomAccess;
import java.util.Spliterator;
import java.util.function.Consumer;
import java.util.function.Predicate;
import java.util.function.UnaryOperator;
/**
* List接口的可变数组实现.实现了所有可选列表操作，并允许包括null在内的所有元素。除了实现List接口外，
* 此类还提供一些方法来操作内部用来存储列表的数组的大小。（此类大致上等同于Vector类，除了此类是不同步的。）
*
* size、isEmpty、get、set、iterator和listIterator操作都以固定时间运行。add操作以分摊的固定时间运行，
* 也就是说，添加n个元素需要O(n)时间。其他所有操作都以线性时间运行（大体上讲）。与用于LinkedList实现的常数因子相比， 此实现的常数因子较低。
*
* 每个ArrayList实例都有一个容量。该容量是指用来存储list元素的数组的大小。它总是至少等于列表的大小。随着向ArrayList
* 中不断添加元素，其容量也自动增长。并未指定增长策略的细节，因为这不只是添加元素会带来分摊固定时间开销那样简单。
*
* 在添加大量元素前，应用程序可以使用ensureCapacity操作来增加ArrayList实例的容量。这可以减少递增式再分配的数量。
*
* 注意，此实现不是同步的。如果多个线程同时访问一个ArrayList实例，而其中至少一个线程从结构上修改了列表，那么它必须保持外部同步。
* （结构上的修改是指任何添加或删除一个或多个元素的操作，或者显式调整底层数组的大小；仅仅设置元素的值不是结构上的修改。）
* 这一般通过对自然封装该列表的对象进行同步操作来完成。如果不存在这样的对象，则应该使用Collections.synchronizedList
* 方法将该列表“包装”起来。这最好在创建时完成，以防止意外对列表进行不同步的访问： List list =
* Collections.synchronizedList(new ArrayList(…));
*
* 注意，迭代器的快速失败行为无法得到保证，因为一般来说，不可能对是否出现不同步并发修改做出任何硬性保证。
* 快速失败迭代器会尽最大努力抛出ConcurrentModificationException。因此，为提高这类迭代器的正确性而编写一个依赖于此异常
* 的程序是错误的做法：迭代器的快速失败行为应该仅用于检测bug。
*
* 此类是Java Collections Framework的成员。
*
* 总结: (1)底层：ArrayList是List接口的大小可变数组的实现。 (2)是否允许null：ArrayList允许null元素。
* (3)时间复杂度：size、isEmpty、get、set、iterator和listIterator方法都以固定时间运行，时间复杂度为O(1)。add和remove方法需要O(n)时间。与用于LinkedList实现的常数因子相比，此实现的常数因子较低。
* (4)容量：ArrayList的容量可以自动增长。 (5)是否同步：ArrayList不是同步的。
* (6)迭代器：ArrayList的iterator和listIterator方法返回的迭代器是fail-fast的。
*/
public class ArrayList<E> extends AbstractList<E> implements List<E>, RandomAccess, Cloneable, java.io.Serializable {
private static final long serialVersionUID = 8683452581122892189L;
/**
* 默认初始化的容量大小
*/
private static final int DEFAULT_CAPACITY = 10;
/**
* 为空的实例例对象提供一个空数组
*/
private static final Object[] EMPTY_ELEMENTDATA = {};
/**
* 为空的实例对象提供一个空数组.该数组与EMPTY_ELEMENTDATA的区别就在于当第一个元素添加进来的时候它知道如何扩张. (add(E
* e)中的第一行代码中的所在的函数就是这句话的实现。)
*/
private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};
/**
* ArrayList的元素被存储在数组缓冲区中.ArrayList的容量就是数组的缓存量, 任何一个用elementData ==
* DEFAULTCAPACITY_EMPTY_ELEMENTDATA的空ArrayList将在第一个元素被加进来时扩张,
*
* elementData数组用来存储ArrayList中的元素，从这个可以看出，ArrayList是底层是借组于数组来实现的。
*/
transient Object[] elementData; // non-private to simplify nested class access
/**
* ArrayList的大小(它包含的元素个数).
*/
private int size;
/**
* 创建任何一个由指定初始容量的空List 从源码可以看到，就是根据参数的大小作为容量来实例化底层的数组对象。当参数小于0时，抛异常。
* 当参数等于0时，用空的常量数组对象EMPTY_ELEMENTDATA来初始化底层数组elementData。
*/
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);
}
}
/**
* 创建一个空List,这时它的初始容量为10
*/
public ArrayList() {
this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
}
/**
* 创建一个包含着给定集合中的元素的list,按照它们在迭代器中的顺序返回.
*
* @param c
* 元素将被放入队列中的这个集合.
* @throws NullPointerException
* 指定集合为空
*/
public ArrayList(Collection<? extends E> c) {
elementData = 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);
} else {
// replace with empty array.
this.elementData = EMPTY_ELEMENTDATA;
}
}
/**
* 将ArrayList实例对象的容量修剪为当前队列的大小. 一个用处是缩小ArrayList对象的存储
*/
public void trimToSize() {
modCount++;
if (size < elementData.length) {
elementData = (size == 0) ? EMPTY_ELEMENTDATA : Arrays.copyOf(elementData, size);
}
}
/**
* 增加ArrayList实例对象的容量,如果有必要,确保有一个参数,它作为给定的最小容量.
*
* @param minCapacity
* the desired minimum capacity
*/
public void ensureCapacity(int minCapacity) {
// 如果elementData等于DEFAULTCAPACITY_EMPTY_ELEMENTDATA，最小扩容量为DEFAULT_CAPACITY，否则为0
int minExpand = (elementData != DEFAULTCAPACITY_EMPTY_ELEMENTDATA) ? 0
// larger than default for default empty table. It's already
// supposed to be at default size.
: DEFAULT_CAPACITY;
// 如果想要的最小容量大于最小扩容量，则使用想要的最小容量。
if (minCapacity > minExpand) {
ensureExplicitCapacity(minCapacity);
}
}
/**
* 数组容量检查，不够时则进行扩容，只供类内部使用。
*
* @param 想要的最小容量
*/
private void ensureCapacityInternal(int minCapacity) {
if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);
}
ensureExplicitCapacity(minCapacity);
}
/**
* 数组容量检查，不够时则进行扩容，只供类内部使用
*
* @param 想要的最小容量
*/
private void ensureExplicitCapacity(int minCapacity) {
modCount++;
// 确保指定的最小容量 > 数组缓冲区当前的长度
if (minCapacity - elementData.length > 0)
// 扩容
grow(minCapacity);
}
/**
* 分派给arrays的最大容量 减8,
* 因为某些VM会在数组中保留一些头字，尝试分配这个最大存储容量，可能会导致array容量大于VM的limit，最终导致OutOfMemoryError。
*/
private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
/**
* 扩容，保证ArrayList至少能存储minCapacity个元素 第一次扩容，逻辑为newCapacity = oldCapacity +
* (oldCapacity >>
* 1);即在原有的容量基础上增加一半。第一次扩容后，如果容量还是小于minCapacity，就将容量扩充为minCapacity。
*
* @param minCapacity
* 想要的最小容量
*/
private void grow(int minCapacity) {
// 获取当前数组的容量
int oldCapacity = elementData.length;
// 扩容。新的容量=当前容量+当前容量/2.即将当前容量增加一半。
int newCapacity = oldCapacity + (oldCapacity >> 1);
// 如果扩容后的容量还是小于想要的最小容量
if (newCapacity - minCapacity < 0)
// 将扩容后的容量再次扩容为想要的最小容量
newCapacity = minCapacity;
// 如果扩容后的容量大于临界值，则进行大容量分配
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);
}
/**
* 进行大容量分配
*/
private static int hugeCapacity(int minCapacity) {
// 如果minCapacity<0，抛出异常
if (minCapacity < 0) // overflow
throw new OutOfMemoryError();
// 如果想要的容量大于MAX_ARRAY_SIZE，则分配Integer.MAX_VALUE，否则分配MAX_ARRAY_SIZE
return (minCapacity > MAX_ARRAY_SIZE) ? Integer.MAX_VALUE : MAX_ARRAY_SIZE;
}
/**
* 1 进行空间检查，决定是否进行扩容，以及确定最少需要的容量 2.如果确定扩容，就执行grow(int
* minCapacity)，minCapacity为最少需要的容量 3.第一次扩容，逻辑为newCapacity = oldCapacity +
* (oldCapacity >> 1);即在原有的容量基础上增加一半。
* 4.第一次扩容后，如果容量还是小于minCapacity，就将容量扩充为minCapacity。
* 5.对扩容后的容量进行判断，如果大于允许的最大容量MAX_ARRAY_SIZE，则将容量再次调整为MAX_ARRAY_SIZE。至此扩容操作结束。
*/
public int size() {
return size;
}
public boolean isEmpty() {
return size == 0;
}
public boolean contains(Object o) {
return indexOf(o) >= 0;
}
/**
* 返回指定元素在这个list中第一次出现的位置索引,如果list不包含这个元素,返回-1.
* 准确地讲:返回指定元素在list中出现的最小索引,当list里面没有则返回-1.
*/
public int indexOf(Object o) {
if (o == null) {
for (int i = 0; i < size; i++)
if (elementData[i] == null)
return i;
} else {
for (int i = 0; i < size; i++)
if (o.equals(elementData[i]))
return i;
}
return -1;
}
/**
* 返回指定元素在list中最后出现的位置,如果不存在,就返回-1. 正式说法是:返回指定元素的最高索引值,若没有就返回-1.
*/
public int lastIndexOf(Object o) {
if (o == null) {
for (int i = size - 1; i >= 0; i--)
if (elementData[i] == null)
return i;
} else {
for (int i = size - 1; i >= 0; i--)
if (o.equals(elementData[i]))
return i;
}
return -1;
}
/**
* 返回一个数组实例的浅拷贝.(这个元素本身不被复制)
*
* 发现这个方法的底层是Arrays.copyOf(elementData, size); public static <T> T[] copyOf(T[]
* original, int newLength) { return (T[]) copyOf(original, newLength,
* original.getClass()); } 我来强翻一波源码: 复制给定的数组,必要的话截断或者用nulls填补,因此这个复制是有指定的大小的.
* 这两个数组包含相等的值,对所有索引,在原数组和复制数组都是有效的. 复制的数组包含空时,任意索引在复制数组中有效而在原数组中无效.
* 这样的索引当且仅当指定的长度比原数组的更大.作为结果的数组是新类型的
*
* 简单来说:copyOf()在内部新建一个数组，调用arrayCopy()将original内容复制到copy中去，
* 并且长度为newLength。返回copy;
*
* 发现 Arrays.copyOf()底层是copyOf(original, newLength, original.getClass())
*
*/
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);
}
}
/**
* 返回一个包含着这个list中的所有元素的数组,它的顺序就是从前到后.
*/
public Object[] toArray() {
return Arrays.copyOf(elementData, size);
}
@SuppressWarnings("unchecked")
public <T> T[] toArray(T[] a) {
if (a.length < size)
// Make a new array of a's runtime type, but my contents:
return (T[]) Arrays.copyOf(elementData, size, a.getClass());
System.arraycopy(elementData, 0, a, 0, size);
if (a.length > size)
a[size] = null;
return a;
}
// 位置操作
@SuppressWarnings("unchecked")
E elementData(int index) {
return (E) elementData[index];
}
/**
* Returns the element at the specified position in this list. 返回list中指定位置上的元素
*/
public E get(int index) {
rangeCheck(index);
return elementData(index);
}
/**
* 用指定的元素去替换指定位置上的元素
*/
public E set(int index, E element) {
rangeCheck(index);// 就是判断index>size?继续:抛异常
E oldValue = elementData(index);
elementData[index] = element;// 指定值赋给数组的指定位置
return oldValue;
}
/**
* 将指定元素添加到list最后
*/
public boolean add(E e) {
ensureCapacityInternal(size + 1); // 一定要先扩容
elementData[size++] = e;
return true;
}
/**
* 在list的指定位置上插入指定元素. 他后面的元素将向后移一位
*/
public void add(int index, E element) {
// 越界检查
rangeCheckForAdd(index);
// 确认list容量，如果不够，容量加1。注意：只加1，保证资源不被浪费
ensureCapacityInternal(size + 1); // Increments modCount!!
// 对数组进行复制处理，目的就是空出index的位置插入element，并将index后的元素位移一个位置
System.arraycopy(elementData, index, elementData, index + 1, size - index);
// 将指定的index位置赋值为element
elementData[index] = element;
// 实际容量+1
size++;
}
/**
* 删除list中位置为指定索引index的元素 索引之后的元素向左移一位
*/
public E remove(int index) {
// 检查索引是否越界。如果参数指定索引index>=size，抛出一个越界异常
rangeCheck(index);
// 结构性修改次数+1
modCount++;
// 记录索引为inde处的元素
E oldValue = elementData(index);
// 删除指定元素后，需要左移的元素个数
int numMoved = size - index - 1;
// 如果有需要左移的元素，就移动（移动后，该删除的元素就已经被覆盖了）
if (numMoved > 0)
System.arraycopy(elementData, index + 1, elementData, index, numMoved);
// size减一，然后将索引为size-1处的元素置为null。为了让GC起作用，必须显式的为最后一个位置赋null值
elementData[--size] = null; // clear to let GC do its work
// 返回被删除的元素
return oldValue;
}
/**
* 移除在这个list中指定第一次出现的指定元素. 如果list不包含这个元素,那么将不会改变list.
* 准确说法:移除在list中最低索引的指定元素.如果list中包含指定元素,移除成功,返回true
*/
public boolean remove(Object o) {
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++)
if (o.equals(elementData[index])) {
fastRemove(index);
return true;
}
}
return false;
}
/*
* 快速删除索引为index的元素。该方法会跳过越界检查。
*/
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
}
/**
* 清空list中所有元素,该方法执行后list将为空,底层数组为空.
*/
public void clear() {
modCount++;
// clear to let GC do its work
for (int i = 0; i < size; i++)
elementData[i] = null;
size = 0;
}
/**
* 在list集合末尾添加指定的集合中的所有元素,其顺序就是指定数组中迭代的顺序.
*
* 看看底层的System.arraycopy方法: public static native void arraycopy(Object src, int
* srcPos, Object dest, int destPos, int length);
*
* 复制指定源数组src到目标数组dest。复制从src的srcPos索引开始，复制的个数是length，复制到dest的索引从destPos开始。
*/
public boolean addAll(Collection<? extends E> c) {
Object[] a = c.toArray();// 先将c转换为一个Obeject类型的数组a
int numNew = a.length;// 得到a的长度
ensureCapacityInternal(size + numNew); // 扩容,扩容大小为a的长度
System.arraycopy(a, 0, elementData, size, numNew);//
size += numNew;
return numNew != 0;
}
/**
* 在制定index位置插入指定集合中所有的元素。index后的元素右移。新插入的元素和指定集合中的元素顺序相同。
*/
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;
if (numMoved > 0)
System.arraycopy(elementData, index, elementData, index + numNew, numMoved);
System.arraycopy(a, 0, elementData, index, numNew);
size += numNew;
return numNew != 0;
}
/**
* 删除list中从索引fromIndex到endIndex的所有元素。endIndex后的元素左移
*/
protected void removeRange(int fromIndex, int toIndex) {
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;
}
private void rangeCheck(int index) {
if (index >= size)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
/**
* 被add和 addAll方法使用的索引越界检查方法
*/
private void rangeCheckForAdd(int index) {
if (index > size || index < 0)// 且index<0
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
/**
* 返回异常消息,当IndexOutOfBoundsException
*/
private String outOfBoundsMsg(int index) {
return "Index: " + index + ", Size: " + size;
}
/**
* 移除list中指定集合c
*
* @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
* 如果list中元素和指定集合c中的元素不相容,集合c不一定是其子集,只要有交集即可
* @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 看个例子: public static void
* main(String[] args) { Integer[] ins = { 1, 2, 3, 4, 5, 6 };
* List<Integer> list = new ArrayList<Integer>(Arrays.asList(ins));
*
* boolean a = list.removeAll(Arrays.asList(1, 2, 3));
* System.out.println(a + " " + list);//true [4, 5, 6]
*
* boolean b = list.removeAll(Arrays.asList(1, 2, 3, null));
* System.out.println(b + " " + list);//false [4, 5, 6]
*
* boolean c = list.removeAll(Arrays.asList(1, 2, 4, 8));
* System.out.println(c + " " + list);//true [5, 6]
*
* boolean d = list.removeAll(Arrays.asList(1, 2, 3.5));
* System.out.println(d + " " + list);//false [5, 6]
*
* boolean f = list.removeAll(Arrays.asList(7.5, "a", false));
* System.out.println(f + " " + list);//false [5, 6] }
*
*/
public boolean removeAll(Collection<?> c) {
Objects.requireNonNull(c);
return batchRemove(c, false);
}
/**
* 只保留list和指定集合c中共有的元素，其他的元素都删除
*/
public boolean retainAll(Collection<?> c) {
Objects.requireNonNull(c);
return batchRemove(c, true);
}
/**
* 批量删除
*
* @param c
* 指定集合
* @param complement
* 是否取补集
*/
private boolean batchRemove(Collection<?> c, boolean complement) {
final Object[] elementData = 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;
}
/**
* 序列化list
* elementData数组是使用transient修饰的，那么elementData的序列化是怎么实现的呢？ArrayList使用了自定义的序列化方式。
*/
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();
}
}
/**
* 反序列化ArrayList
*/
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();
}
}
}
/**
* 返回一个所有元素的list迭代器(顺次),从list中指定的位置开始. 返回list迭代器，并使迭代器准备好返回索引为index的元素 该迭代器是
* fail-fast 机制的
*
* @throws IndexOutOfBoundsException
* {@inheritDoc}
*/
public ListIterator<E> listIterator(int index) {
if (index < 0 || index > size)
throw new IndexOutOfBoundsException("Index: " + index);
return new ListItr(index);
}
/**
* * 返回list迭代器，并使迭代器准备好返回索引为index的元素 该迭代器是 fail-fast 机制的
*/
public ListIterator<E> listIterator() {
return new ListItr(0);
}
/**
* 返回一个迭代器 该迭代器是 fail-fast 机制的
*/
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();
}
}
}
/**
* 获取从 fromIndex 到 toIndex 之间的子集合(左闭右开区间) 对该子集合的操作，会影响原有集合 当调用了 subList()
* 后，若对原有集合进行删除操作时，会抛出异常 java.util.ConcurrentModificationException
*/
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();
}
}
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++;
}
}
