public class ArrayList extends AbstractList implements List, RandomAccess, Cloneable, java.io.Serializable
{private static final long serialVersionUID = 8683452581122892189L;//默认的初始容量为10
private static final int DEFAULT_CAPACITY = 10;private static final Object[] EMPTY_ELEMENTDATA ={};private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA ={};transientObject[] elementData;//ArrayList中实际数据的数量
private intsize;public ArrayList(int initialCapacity) //带初始容量大小的构造函数
{if (initialCapacity > 0) //初始容量大于0,实例化数组
{this.elementData = newObject[initialCapacity];
}else if (initialCapacity == 0) //初始化等于0，将空数组赋给elementData
{this.elementData =EMPTY_ELEMENTDATA;
}else //初始容量小于，抛异常
{throw new IllegalArgumentException("Illegal Capacity: "+initialCapacity);
}
}public ArrayList() //无参构造函数,默认容量为10
{this.elementData =DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
}public ArrayList(Collection extends E> c) //创建一个包含collection的ArrayList
{
elementData= c.toArray(); //返回包含c所有元素的数组
if ((size = elementData.length) != 0)
{if (elementData.getClass() != Object[].class)
elementData= Arrays.copyOf(elementData, size, Object[].class);//复制指定数组，使elementData具有指定长度
}else{//c中没有元素
this.elementData =EMPTY_ELEMENTDATA;
}
}//将当前容量值设为当前实际元素大小
public voidtrimToSize()
{
modCount++;if (size
{
elementData= (size == 0)?EMPTY_ELEMENTDATA:Arrays.copyOf(elementData, size);
}
}//将集合的capacit增加minCapacity
public void ensureCapacity(intminCapacity)
{int minExpand = (elementData != DEFAULTCAPACITY_EMPTY_ELEMENTDATA)?0:DEFAULT_CAPACITY;if (minCapacity >minExpand)
{
ensureExplicitCapacity(minCapacity);
}
}private void ensureCapacityInternal(intminCapacity)
{if (elementData ==DEFAULTCAPACITY_EMPTY_ELEMENTDATA)
{
minCapacity=Math.max(DEFAULT_CAPACITY, minCapacity);
}
ensureExplicitCapacity(minCapacity);
}private void ensureExplicitCapacity(intminCapacity)
{
modCount++;if (minCapacity - elementData.length > 0)
grow(minCapacity);
}private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;private void grow(intminCapacity)
{int oldCapacity =elementData.length;
//注意此处扩充capacity的方式是将其向右一位再加上原来的数，实际上是扩充了1.5倍int newCapacity = oldCapacity + (oldCapacity >> 1);if (newCapacity - minCapacity < 0)
newCapacity=minCapacity;if (newCapacity - MAX_ARRAY_SIZE > 0)
newCapacity=hugeCapacity(minCapacity);
elementData=Arrays.copyOf(elementData, newCapacity);
}private static int hugeCapacity(intminCapacity)
{if (minCapacity < 0) //overflow
throw newOutOfMemoryError();return (minCapacity > MAX_ARRAY_SIZE) ?Integer.MAX_VALUE :
MAX_ARRAY_SIZE;
}//返回ArrayList的大小
public intsize()
{returnsize;
}//判断ArrayList是否为空
public booleanisEmpty() {return size == 0;
}//判断ArrayList中是否包含Object(o)
public booleancontains(Object o) {return indexOf(o) >= 0;
}//正向查找，返回ArrayList中元素Object(o)的索引位置
public intindexOf(Object o)
{if (o == null) {for (int i = 0; i < size; i++)if (elementData[i]==null)returni;
}else{for (int i = 0; i < size; i++)if(o.equals(elementData[i]))returni;
}return -1;
}//逆向查找，返回返回ArrayList中元素Object(o)的索引位置
public intlastIndexOf(Object o) {if (o == null) {for (int i = size-1; i >= 0; i--)if (elementData[i]==null)returni;
}else{for (int i = size-1; i >= 0; i--)if(o.equals(elementData[i]))returni;
}return -1;
}//返回此 ArrayList实例的浅拷贝。
publicObject clone()
{try{
ArrayList> v = (ArrayList>) super.clone();
v.elementData=Arrays.copyOf(elementData, size);
v.modCount= 0;returnv;
}catch(CloneNotSupportedException e) {//this shouldn't happen, since we are Cloneable
throw newInternalError(e);
}
}//返回一个包含ArrayList中所有元素的数组
publicObject[] toArray() {returnArrays.copyOf(elementData, size);
}
@SuppressWarnings("unchecked")public T[] toArray(T[] a) {if (a.length
System.arraycopy(elementData,0, a, 0, size);if (a.length >size)
a[size]= null;returna;
}
@SuppressWarnings("unchecked")
E elementData(intindex) {return(E) elementData[index];
}//返回至指定索引的值
public E get(intindex)
{
rangeCheck(index);//检查给定的索引值是否越界
returnelementData(index);
}//将指定索引上的值替换为新值，并返回旧值
public E set(intindex, E element)
{
rangeCheck(index);
E oldValue=elementData(index);
elementData[index]=element;returnoldValue;
}//将指定的元素添加到此列表的尾部
public booleanadd(E e)
{
ensureCapacityInternal(size+ 1);
elementData[size++] =e;return true;
}//将element添加到ArrayList的指定位置
public void add(intindex, E element) {
rangeCheckForAdd(index);
ensureCapacityInternal(size+ 1);//从指定源数组中复制一个数组，复制从指定的位置开始，到目标数组的指定位置结束。//arraycopy(被复制的数组, 从第几个元素开始复制, 要复制到的数组, 从第几个元素开始粘贴, 一共需要复制的元素个数)//即在数组elementData从index位置开始，复制到index+1位置,共复制size-index个元素
System.arraycopy(elementData, index, elementData, index + 1,size -index);
elementData[index]=element;
size++;
}//删除ArrayList指定位置的元素
public E remove(intindex)
{
rangeCheck(index);
modCount++;
E oldValue=elementData(index);int numMoved = size - index - 1;if (numMoved > 0)
System.arraycopy(elementData, index+1, elementData, index,numMoved);
elementData[--size] = null; //将原数组最后一个位置置为null
returnoldValue;
}//移除ArrayList中首次出现的指定元素(如果存在)。
public booleanremove(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;
}//快速删除指定位置的元素
private void fastRemove(intindex)
{
modCount++;int numMoved = size - index - 1;if (numMoved > 0)
System.arraycopy(elementData, index+1, elementData, index, numMoved);
elementData[--size] = null;
}//清空ArrayList，将全部的元素设为null
public voidclear()
{
modCount++;for (int i = 0; i < size; i++)
elementData[i]= null;
size= 0;
}//按照c的迭代器所返回的元素顺序，将c中的所有元素添加到此列表的尾部
public boolean addAll(Collection extends E>c) {
Object[] a=c.toArray();int numNew =a.length;
ensureCapacityInternal(size+ numNew); //Increments modCount
System.arraycopy(a, 0, elementData, size, numNew);
size+=numNew;return numNew != 0;
}//从指定位置index开始，将指定c中的所有元素插入到此列表中
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)//先将ArrayList中从index开始的numMoved个元素移动到起始位置为index+numNew的后面去
System.arraycopy(elementData, index, elementData, index +numNew, numMoved);//再将c中的numNew个元素复制到起始位置为index的存储空间中去
System.arraycopy(a, 0, elementData, index, numNew);
size+=numNew;return numNew != 0;
}//删除fromIndex到toIndex之间的全部元素
protected void removeRange(int fromIndex, inttoIndex)
{
modCount++;//numMoved为删除索引后面的元素个数
int numMoved = size -toIndex;//将删除索引后面的元素复制到以fromIndex为起始位置的存储空间中去
System.arraycopy(elementData, toIndex, elementData, fromIndex,numMoved);int newSize = size - (toIndex-fromIndex);//将ArrayList后面(toIndex-fromIndex)个元素置为null
for (int i = newSize; i < size; i++)
{
elementData[i]= null;
}
size=newSize;
}//检查索引是否越界
private void rangeCheck(intindex)
{if (index >=size)throw newIndexOutOfBoundsException(outOfBoundsMsg(index));
}private void rangeCheckForAdd(intindex)
{if (index > size || index < 0)throw newIndexOutOfBoundsException(outOfBoundsMsg(index));
}private String outOfBoundsMsg(intindex) {return "Index: "+index+", Size: "+size;
}//删除ArrayList中包含在c中的元素
public boolean removeAll(Collection>c)
{
Objects.requireNonNull(c);return batchRemove(c, false);
}//删除ArrayList中除包含在c中的元素，和removeAll相反
public boolean retainAll(Collection>c)
{
Objects.requireNonNull(c);//检查指定对象是否为空
return batchRemove(c, true);
}private boolean batchRemove(Collection> c, booleancomplement) {final Object[] elementData = this.elementData;int r = 0, w = 0;boolean modified = false;try{for (; r < size; r++)if (c.contains(elementData[r]) == complement) //判断c中是否有elementData[r]元素
elementData[w++] =elementData[r];
}finally{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;
}
}returnmodified;
}//将ArrayList的“容量，所有的元素值”都写入到输出流中
private void writeObject(java.io.ObjectOutputStream s) throwsjava.io.IOException
{int expectedModCount =modCount;
s.defaultWriteObject();//写入数组大小
s.writeInt(size);//写入所有数组的元素
for (int i=0; i
s.writeObject(elementData[i]);
}if (modCount !=expectedModCount) {throw newConcurrentModificationException();
}
}//先将ArrayList的“大小”读出，然后将“所有的元素值”读出
private voidreadObject(java.io.ObjectInputStream s)throwsjava.io.IOException, ClassNotFoundException {
elementData=EMPTY_ELEMENTDATA;
s.defaultReadObject();
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
a[i]=s.readObject();
}
}
}
