java源码--AbstractList

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);
    }
}