package java.util;
public abstract class AbstractList<E> extends AbstractCollection<E> implements List<E> {
/**
*唯一的构造函数。(对于子类构造函数的调用，通常是隐式的。)
*/
protected AbstractList() {
}
//添加元素，调用add(size(), e)
public boolean add(E e) {
add(size(), e);
return true;
}
/**
* 唯一的抽象函数*/
abstract public E get(int index);
/**
* 获取集合中的函数
* {@code UnsupportedOperationException}.*/
public E set(int index, E element) {
throw new UnsupportedOperationException();
}
/**
* 添加元素*/
public void add(int index, E element) {
throw new UnsupportedOperationException();
}
/**
* 删除元素*/
public E remove(int index) {
throw new UnsupportedOperationException();
}
// Search Operations 搜索操作
/**
* 列表循环，找出元素第一次出现的位置*/
public int indexOf(Object o) {
ListIterator<E> it = listIterator();
if (o==null) {
while (it.hasNext())
if (it.next()==null)
return it.previousIndex();
} else {
while (it.hasNext())
if (o.equals(it.next()))
return it.previousIndex();
}
return -1;
}
/**
* 列表循环，找出元素最后一次出现的位置*/
public int lastIndexOf(Object o) {
ListIterator<E> it = listIterator(size());
if (o==null) {
while (it.hasPrevious())
if (it.previous()==null)
return it.nextIndex();
} else {
while (it.hasPrevious())
if (o.equals(it.previous()))
return it.nextIndex();
}
return -1;
}
// Bulk Operations 批量操作
/**
* Removes all of the elements from this list (optional operation).*/
public void clear() {
removeRange(0, size());
}
/**
* 集合中添加集合*/
public boolean addAll(int index, Collection<? extends E> c) {
rangeCheckForAdd(index); //效验index在范围之内 0< index < size()
boolean modified = false;
for (E e : c) { //循环添加
add(index++, e);
modified = true;
}
return modified;
}
// Iterators 迭代器
/**
* 按适当的顺序对列表中的元素返回一个迭代器。
* @return an iterator over the elements in this list in proper sequence
*/
public Iterator<E> iterator() {
return new Itr();
}
public ListIterator<E> listIterator() {
return listIterator(0);
}
/**
* 此实现返回一个简单的实现，类的实现的扩展*/
public ListIterator<E> listIterator(final int index) {
rangeCheckForAdd(index); //检查下标是否越界
return new ListItr(index);
}
private class Itr implements Iterator<E> {
/**
* 对next的后续调用将返回的元素的索引。
*/
int cursor = 0;
/**
* 最近一次调用next时，在返回的元素的索引
* 之前的。如果此元素被调用删除，则重置为-1
*/
int lastRet = -1;
/**
* 迭代器认为支持列表应该具有的modCount值。如果违背了这个期望，迭代器就会检测到并发修改
*/
int expectedModCount = modCount;
//是否有下一个
public boolean hasNext() {
return cursor != size();
}
//返回当前元素，游标跳到下一个元素
public E next() {
checkForComodification();
try {
int i = cursor;
E next = get(i); // 获取当前元素
lastRet = i; // 当前元素索引
cursor = i + 1; //游标指定下一个元素
return next;
} catch (IndexOutOfBoundsException e) {
checkForComodification();
throw new NoSuchElementException();
}
}
// 删除集合内容
public void remove() {
if (lastRet < 0)
throw new IllegalStateException();
checkForComodification();
try {
AbstractList.this.remove(lastRet); //删除当前索引元素
if (lastRet < cursor)
cursor--; //游标后退一个索引值
lastRet = -1;
expectedModCount = modCount;
} catch (IndexOutOfBoundsException e) {
throw new ConcurrentModificationException();
}
}
// 防止两个线程同时对列表进行操作，一个读，一个修改，这样可能会出现我要读的元素刚好被删了，此时会发生异常。并发异常
final void checkForComodification() {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
}
}
private class ListItr extends Itr implements ListIterator<E> {
ListItr(int index) {
cursor = index; //当前游标值
}
//是否有前一个元素
public boolean hasPrevious() {
return cursor != 0;
}
// 前一个元素值
public E previous() {
checkForComodification(); //检查当前列表元素没有被修改过，并发异常
try {
int i = cursor - 1; //上一个索引值
E previous = get(i); //上一个元素
lastRet = cursor = i; //当前游标值
return previous;
} catch (IndexOutOfBoundsException e) {
checkForComodification();
throw new NoSuchElementException();
}
}
public int nextIndex() {
return cursor;
}
//是否有上一个元素
public int previousIndex() {
return cursor-1;
}
public void set(E e) {
if (lastRet < 0)
throw new IllegalStateException();
checkForComodification(); // 检验并发异常
try {
AbstractList.this.set(lastRet, e); //修改当前元素
expectedModCount = modCount;
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}
public void add(E e) {
checkForComodification();//检验并发异常
try {
int i = cursor;
AbstractList.this.add(i, e);
lastRet = -1;
cursor = i + 1;
expectedModCount = modCount;
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}
}
//判断是否实现了RandomAccess接口，此接口的作用：https://www.cnblogs.com/yeya/p/9950723.html
public List<E> subList(int fromIndex, int toIndex) {
return (this instanceof RandomAccess ?
new RandomAccessSubList<>(this, fromIndex, toIndex) :
new SubList<>(this, fromIndex, toIndex));
}
// Comparison and hashing 比较和散列
public boolean equals(Object o) {
if (o == this)
return true;
if (!(o instanceof List))
return false;
ListIterator<E> e1 = listIterator();
ListIterator<?> e2 = ((List<?>) o).listIterator();
while (e1.hasNext() && e2.hasNext()) {
E o1 = e1.next();
Object o2 = e2.next();
if (!(o1==null ? o2==null : o1.equals(o2)))
return false;
}
return !(e1.hasNext() || e2.hasNext());
}
public int hashCode() {
int hashCode = 1;
for (E e : this)
hashCode = 31*hashCode + (e==null ? 0 : e.hashCode());
return hashCode;
}
//从该列表中删除其索引位于之间的所有元素
protected void removeRange(int fromIndex, int toIndex) {
ListIterator<E> it = listIterator(fromIndex);
for (int i=0, n=toIndex-fromIndex; i<n; i++) {
it.next();
it.remove();
}
}
protected transient int modCount = 0;
//检查范围
private void rangeCheckForAdd(int index) {
if (index < 0 || index > size())
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
private String outOfBoundsMsg(int index) {
return "Index: "+index+", Size: "+size();
}
}
class SubList<E> extends AbstractList<E> {
private final AbstractList<E> l; //一个AbstractList类的引用，代表的是要被截取的List
private final int offset; //下标移动量
private int size; //元素个数
SubList(AbstractList<E> list, int fromIndex, int toIndex) {
//数据效验
if (fromIndex < 0)
throw new IndexOutOfBoundsException("fromIndex = " + fromIndex);
if (toIndex > list.size())
throw new IndexOutOfBoundsException("toIndex = " + toIndex);
if (fromIndex > toIndex)
throw new IllegalArgumentException("fromIndex(" + fromIndex +
") > toIndex(" + toIndex + ")");
l = list; //内容
offset = fromIndex; //开始下标
size = toIndex - fromIndex; //大小
this.modCount = l.modCount;
}
public E set(int index, E element) {
rangeCheck(index);//检查下标是否越界
checkForComodification(); //检查并发异常
return l.set(index+offset, element);
}
public E get(int index) {
rangeCheck(index); //是否越界
checkForComodification(); //并发异常
return l.get(index+offset);
}
public int size() {
checkForComodification(); //并发异常
return size;
}
public void add(int index, E element) {
rangeCheckForAdd(index);
checkForComodification();
l.add(index+offset, element);
this.modCount = l.modCount;
size++;
}
public E remove(int index) {
rangeCheck(index);
checkForComodification();
E result = l.remove(index+offset);
this.modCount = l.modCount;
size--;
return result;
}
protected void removeRange(int fromIndex, int toIndex) {
checkForComodification();
l.removeRange(fromIndex+offset, toIndex+offset);
this.modCount = l.modCount;
size -= (toIndex-fromIndex);
}
public boolean addAll(Collection<? extends E> c) {
return addAll(size, c);
}
public boolean addAll(int index, Collection<? extends E> c) {
rangeCheckForAdd(index);
int cSize = c.size();
if (cSize==0)
return false;
checkForComodification();
l.addAll(offset+index, c);
this.modCount = l.modCount;
size += cSize;
return true;
}
public Iterator<E> iterator() {
return listIterator();
}
public ListIterator<E> listIterator(final int index) {
checkForComodification();
rangeCheckForAdd(index);
return new ListIterator<E>() {
private final ListIterator<E> i = l.listIterator(index+offset);
public boolean hasNext() {
return nextIndex() < size;
}
public E next() {
if (hasNext())
return i.next();
else
throw new NoSuchElementException();
}
public boolean hasPrevious() {
return previousIndex() >= 0;
}
public E previous() {
if (hasPrevious())
return i.previous();
else
throw new NoSuchElementException();
}
public int nextIndex() {
return i.nextIndex() - offset;
}
public int previousIndex() {
return i.previousIndex() - offset;
}
public void remove() {
i.remove();
SubList.this.modCount = l.modCount;
size--;
}
public void set(E e) {
i.set(e);
}
public void add(E e) {
i.add(e);
SubList.this.modCount = l.modCount;
size++;
}
};
}
public List<E> subList(int fromIndex, int toIndex) {
return new SubList<>(this, fromIndex, toIndex);
}
//越界异常
private void rangeCheck(int index) {
if (index < 0 || index >= size)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
//在添加元素时，越界异常，与上面不同的是参数不能等于本对象元素大小
private void rangeCheckForAdd(int index) {
if (index < 0 || index > size)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
//越界文字提醒
private String outOfBoundsMsg(int index) {
return "Index: "+index+", Size: "+size;
}
//这个方法是判断是否出现并发异常的方法，判断的依据就是两个modCount是否一致。
private void checkForComodification() {
if (this.modCount != l.modCount)
throw new ConcurrentModificationException();
}
}
class RandomAccessSubList<E> extends SubList<E> implements RandomAccess {
RandomAccessSubList(AbstractList<E> list, int fromIndex, int toIndex) {
super(list, fromIndex, toIndex);
}
public List<E> subList(int fromIndex, int toIndex) {
return new RandomAccessSubList<>(this, fromIndex, toIndex);
}
}
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