ArrayList : 类图
image
RandomAccess：标记接口，表示支持快速访问，实现方式为顺序表，查询更快
Cloneable：标记接口，表明可以克隆，需要实现重写clone方法，在没有实现Cloneable接口时调用clone方法会抛出CloneNotSupportedException
①调用super.clone属于浅拷贝：不拷贝对象包含的引用
②修改得到clone对象的值：深拷贝
Serializable：标记接口，表明该对象可以序列化。可以通过ObjectOutputStream.writeObject把对象写到一个文件，再通过ObjectInputStream.readObject方法把对象读出来。
①序列化不能保存静态变量
②transient关键字：阻止变量序列化
③SerializableUID：判断类和对象的版本，在网络传输中如果SerializableUID不一致则反序列化不能执行
Iterable：接口，表明可迭代，实现iterable方法
Iterator：迭代器接口，自定义迭代器是使用
Collection：接口，定义了集合的共性功能
List：接口，内容允许重复，扩充了Collection
AbstractCollection : 抽象类，允许null元素，toArray()遍历完后，如果有新的元素调用finishToArray
AbstractList ： 允许null元素，subList
/*https://blog.csdn.net/xiaojie_570/article/details/79640367*/
public class ArrayList<E> extends AbstractList<E>
implements List<E>, RandomAccess, Cloneable, java.io.Serializable
{
/*标记类和对象的版本*/
private static final long serialVersionUID = 8683452581122892189L;
/*默认的容量10*/
private static final int DEFAULT_CAPACITY = 10;
/*空elementData，共享空数组实例，用于空实例*/
private static final Object[] EMPTY_ELEMENTDATA = {};
/*默认空elementData，和EMPTY_ELEMENTDATA的区别：当第一个元素被加入进来的时候它知道如何扩张*/
private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};
/**
* 用来储存元素，数组实现，查询速度快
* 空的实例的默认容量是elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA
* 当第一个元素加入时容量变成DEFAULT_CAPACITY
* transient：防止序列化, 重写了writeObject
* */
transient Object[] elementData; // non-private to simplify nested class access
/*包含元素的数量*/
private int size;
/* 构造函数，指定初始化容量 */
public ArrayList(int initialCapacity) {
if (initialCapacity > 0) {
this.elementData = new Object[initialCapacity];
} else if (initialCapacity == 0) {
this.elementData = EMPTY_ELEMENTDATA;
} else {//负数的时候抛出IllegalArgumentException
throw new IllegalArgumentException("Illegal Capacity: "+
initialCapacity);
}
}
/*默认构造器*/
public ArrayList() {
this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
}
/*构造函数，初始化一个集合Collection*/
public ArrayList(Collection<? extends E> c) {
elementData = c.toArray();
if ((size = elementData.length) != 0) {
/*see 6260652 编号代表JDK bug库中的编号*/
/*https://blog.csdn.net/huzhigenlaohu/article/details/51702737*/
/*
* 假如我们有1个Object[]数组，并不代表着我们可以将Object对象存进去，这取决于数组中元素实际的类型。
* List<String> list = Arrays.asList("abc");需要注意，可以知道返回的实际类型是java.util.Arrays$ArrayList，而不是ArrayList。
* 调用Object[] objArray = list.toArray();返回是String[]数组，所以我们不能将Object对象，放到objArray数组中。
* */
// c.toArray might (incorrectly) not return Object[] (see 6260652)
if (elementData.getClass() != Object[].class)
/*这个方法就是用来创建1个Object[]数组，这样数组中就可以存放任意对象了。*/
elementData = Arrays.copyOf(elementData, size, Object[].class);
} else {
// replace with empty array.
this.elementData = EMPTY_ELEMENTDATA;
}
}
/*作用去掉预留元素位置*/
public void trimToSize() {
/* 继承自AbstractList，记录了ArrayList结构性变化的次数。*/
modCount++;
if (size < elementData.length) {
elementData = (size == 0)
? EMPTY_ELEMENTDATA
: Arrays.copyOf(elementData, size);
}
}
/*增加list的容量，如果需要就扩容到minCapacity*/
public void ensureCapacity(int minCapacity) {
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;
if (minCapacity > minExpand) {
ensureExplicitCapacity(minCapacity);
}
}
/*增加list的容量*/
private void ensureCapacityInternal(int minCapacity) {
if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);
}
ensureExplicitCapacity(minCapacity);
}
/*判断是否需要扩容*/
private void ensureExplicitCapacity(int minCapacity) {
modCount++;
// overflow-conscious code
/*防止溢出*/
if (minCapacity - elementData.length > 0)
/*进行扩容*/
grow(minCapacity);
}
/*ArrayList最大容量 防止：OutOfMemoryError: Requested array size exceeds VM limit*/
private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
/*扩容的实际操作函数*/
private void grow(int minCapacity) {
// overflow-conscious code
int oldCapacity = elementData.length;
int newCapacity = oldCapacity + (oldCapacity >> 1);/*默认扩容至原来的1.5倍*/
if (newCapacity - minCapacity < 0)
newCapacity = minCapacity;
if (newCapacity - MAX_ARRAY_SIZE > 0)/*如果要扩容的大于MAX_ARRAY_SIZE*/
newCapacity = hugeCapacity(minCapacity);/*扩容到Integer.MAX_VALUE */
// minCapacity is usually close to size, so this is a win:
elementData = Arrays.copyOf(elementData, newCapacity);
}
/*最大容量Integer.MAX_VALUE */
private static int hugeCapacity(int minCapacity) {
if (minCapacity < 0) // overflow
throw new OutOfMemoryError();
return (minCapacity > MAX_ARRAY_SIZE) ?
Integer.MAX_VALUE :
MAX_ARRAY_SIZE;
}
/*返回list里面的元素数量*/
public int size() {
return size;
}
/*判断list是否为空*/
public boolean isEmpty() {
return size == 0;
}
/*判断是否包含指定元素*/
public boolean contains(Object o) {
return indexOf(o) >= 0;
}
/*返回指定元素的最小索引*/
public int indexOf(Object o) {
if (o == null) {/*可以包含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;
}
/*返回指定元素的最大索引*/
public int lastIndexOf(Object o) {
if (o == null) {/*可以包含空值*/
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;
}
/*重写clone完成深拷贝*/
public Object clone() {
try {
ArrayList<?> v = (ArrayList<?>) super.clone();
v.elementData = Arrays.copyOf(elementData, size);
v.modCount = 0;/*将新的modCount数量=0*/
return v;
} catch (CloneNotSupportedException e) {
// this shouldn't happen, since we are Cloneable
throw new InternalError(e);
}
}
/*返回包含list所有元素数组*/
public Object[] toArray() {
return Arrays.copyOf(elementData, size);
}
/*将集合中的元素转换为泛型类型的数组，存储在参数中返回*/
@SuppressWarnings("unchecked")
public <T> T[] toArray(T[] a) {
if (a.length < size)/*当传入的数组不足以容纳list内所有的元素时*/
// 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)/*当传入的数组过大时*/
a[size] = null;
return a;
}
// Positional Access Operations
/*获取指定位置的元素,默认修饰符*/
@SuppressWarnings("unchecked")
E elementData(int index) {
return (E) elementData[index];
}
/*获取指定位置的元素*/
public E get(int index) {
rangeCheck(index);/*价差index是否越界，抛出IndexOutOfBoundsException*/
return elementData(index);
}
/*修改指定位置的元素*/
public E set(int index, E element) {
rangeCheck(index);
E oldValue = elementData(index);
elementData[index] = element;
return oldValue;/*返回修改之前的元素*/
}
/*添加元素*/
public boolean add(E e) {
/*无论是否添加成功modCount++*/
ensureCapacityInternal(size + 1); // Increments modCount!!
elementData[size++] = e;/*在数组的尾部添加元素*/
return true;/*返回是否添加成功*/
}
/*指定位置添加元素*/
public void add(int index, E element) {
rangeCheckForAdd(index);
ensureCapacityInternal(size + 1); // Increments modCount!!
System.arraycopy(elementData, index, elementData, index + 1,
size - index);
elementData[index] = element;
size++;
}
/*删除指定位置的元素*/
public E remove(int index) {
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; // clear to let GC do its work
return oldValue;/*返回要删除的元素*/
}
/*删除指定元素,删除第一个指定元素*/
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;/*返回是否包含这个元素*/
}
/*删除指定位置的元素，修饰符private*/
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*/
public void clear() {
modCount++;
// clear to let GC do its work
for (int i = 0; i < size; i++)
elementData[i] = null;
size = 0;
}
/*批量添加数据,如果传入的集合是null抛出NullPointerException*/
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;//是否添加数据
}
/*批量添加数据到index位置开始，IndexOutOfBoundsException，NullPointerException*/
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;
}
/*删除指定范围的数据
* 抛出IndexOutOfBoundsException
* ({fromIndex < 0 ||fromIndex >= size() ||toIndex > size() ||toIndex < fromIndex})
* */
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;
}
/*检查index是否越界*/
private void rangeCheck(int index) {
if (index >= size)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
/*检查index是否有效*/
private void rangeCheckForAdd(int index) {
if (index > size || index < 0)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
/*数组越界信息*/
private String outOfBoundsMsg(int index) {
return "Index: "+index+", Size: "+size;
}
/*批量删除指定的元素，求差集*/
public boolean removeAll(Collection<?> c) {
Objects.requireNonNull(c);/*判断c是否为空，如果是则抛出NullPointerException*/
/*如果c中的元素不兼容list内的元素抛出ClassCastException*/
return batchRemove(c, false);/*批量删除元素*/
}
/*保存所有c中的元素，删除其他元素，求交集*/
public boolean retainAll(Collection<?> c) {
Objects.requireNonNull(c);/*判断c是否为空，如果是则抛出NullPointerException*/
/*如果c中的元素不兼容list内的元素抛出ClassCastException*/
return batchRemove(c, true);
}
/*真正求差集和交集的操作函数 * */
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++)
/*
* complement=false：删除c内的元素，求差集
* complement=true：保留c内的元素，删除其他元素，求交集
* false==false ：true
* true == false ：false
* */
if (c.contains(elementData[r]) == complement)
elementData[w++] = elementData[r];
} finally {
// Preserve behavioral compatibility with AbstractCollection,
// even if c.contains() throws.
if (r != size) {/*整理数组*/
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;/*返回是否修改*/
}
/*重写的序列化方法*/
private void writeObject(java.io.ObjectOutputStream s)
throws java.io.IOException{
// Write out element count, and any hidden stuff
int expectedModCount = modCount;/*序列化过程中时候有新的元素插入或者修改list结构*/
s.defaultWriteObject();/*调用默认的序列化方法*/
// Write out size as capacity for behavioural compatibility with clone()
s.writeInt(size);
// Write out all elements in the proper order.
/* 因为transient Object[] elementData;所以一默认的序列化方法不会序列化elementData*/
for (int i=0; i<size; i++) {
/*序列化实际保存的元素*/
s.writeObject(elementData[i]);
}
if (modCount != expectedModCount) {
throw new ConcurrentModificationException();
}
}
/*重写的反序列化函数*/
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
/*读取保存的数据元素*/
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();
}
}
}
/*创建迭代器指定起始位置*/
public ListIterator<E> listIterator(int index) {
if (index < 0 || index > size)
throw new IndexOutOfBoundsException("Index: "+index);
return new ListItr(index);
}
/*创建迭代器默认其实位置0*/
public ListIterator<E> listIterator() {
return new ListItr(0);
}
/*重写的list的 返回一个自定义的Iterator*/
public Iterator<E> iterator() {
return new Itr();
}
/*实现自身迭代器*/
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();
}
}
/*实现ListIterator，使用list实例化对象时使用*/
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();
}
}
}
/*返回指定下标范围的List*/
public List<E> subList(int fromIndex, int toIndex) {
subListRangeCheck(fromIndex, toIndex, size);
return new SubList(this, 0, fromIndex, toIndex);
}
/*subList下标范围检查*/
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 + ")");
}
/*
*内部类SubList
* https://blog.csdn.net/Pengjx2014/article/details/78944416#arraylist%E7%9A%84%E8%BF%AD%E4%BB%A3%E5%99%A8%E5%AE%9E%E7%8E%B0sublist
* subList不是从ArrayList复制一份，而是SubList指向的实例是ArrayList的一段映射，
* ArrayList的修改和SubList的修改是对同一个底层数组的修改
* 功能和ArrayList类似
* */
private class SubList extends AbstractList<E> implements RandomAccess {
private final AbstractList<E> parent;// 引用原始的宿主 ArrayList
private final int parentOffset;//宿主ArrayList起始索引，默认0
private final int offset;// 切片位置
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;/*AbstractList继承来的*/
}
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);
}
}
/*
https://www.w3resource.com/java-tutorial/arraylist/arraylist_foreach.php
定义一个实现里Consumer接口的类
*/
@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++) {
/*对每一个元素执行自定义的action中实现的accept方法*/
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);
}
/*
* https://blog.csdn.net/Pengjx2014/article/details/78944416#arraylist%E7%9A%84spliterator%E8%BF%AD%E4%BB%A3%E5%99%A8arraylistspliterator
* Spliterator是一个可分割迭代器，Spliterator就是为了并行遍历元素而设计的一个迭代器
* */
static final class ArrayListSpliterator<E> implements Spliterator<E> {
//用于存放ArrayList对象
private final ArrayList<E> list;
//起始位置（包含），advance/split操作时会修改
private int index; // current index, modified on advance/split
//结束位置（不包含），-1 表示到最后一个元素
private int fence; // -1 until used; then one past last index
//用于存放list的modCount
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;
}
/*获取结束位置（存在意义：首次初始化石需对fence和expectedModCount进行赋值）*/
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;
}
}
/*
按照一定规则过滤集合中的元素
定义一个实现里Consumer接口的类
https://blog.csdn.net/qq_33829547/article/details/80277956
*/
@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)) {/*对每一个元素执行test*/
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;
}
/*
* https://www.cnblogs.com/gxl1995/p/7534171344218b3784f1beb90d621337.html
* UnaryOperator 接受一个什么类型的参数，返回一个什么类型的参数
* 对数组中的每一个元素进行一系列的操作，返回同样的元素，
* 如果 List<Student> lists 将list集合中的每一个student姓名改为张三
* 使用这个方法就非常方便
*/
@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++;
}
/*根据 Comparator条件进行排序*/
@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++;
}
}
