abstractlist.java

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        if (knownMod != modCount)
          throw new ConcurrentModificationException();
      }

      public boolean hasNext()
      {
        checkMod();
        return pos < size;
      }

      public Object next()
      {
        checkMod();
        if (pos == size)
          throw new NoSuchElementException();
        last = pos;
        return get(pos++);
      }

      public void remove()
      {
        checkMod();
        if (last < 0)
          throw new IllegalStateException();
        AbstractList.this.remove(last);
        pos--;
        size--;
        last = -1;
        knownMod = modCount;
      }
    };
  }

  /**
   * Obtain the last index at which a given object is to be found in this
   * list. This implementation grabs listIterator(size()), then searches
   * backwards for a match or returns -1.
   *
   * @return the greatest integer n such that <code>o == null ? get(n) == null
   *         : o.equals(get(n))</code>, or -1 if there is no such index
   */
  public int lastIndexOf(Object o)
  {
    int pos = size();
    ListIterator itr = listIterator(pos);
    while (--pos >= 0)
      if (equals(o, itr.previous()))
        return pos;
    return -1;
  }

  /**
   * Obtain a ListIterator over this list, starting at the beginning. This
   * implementation returns listIterator(0).
   *
   * @return a ListIterator over the elements of this list, in order, starting
   *         at the beginning
   */
  public ListIterator listIterator()
  {
    return listIterator(0);
  }

  /**
   * Obtain a ListIterator over this list, starting at a given position.
   * A first call to next() would return the same as get(index), and a
   * first call to previous() would return the same as get(index - 1).
   * <p>
   *
   * This implementation uses size(), get(int), set(int, Object),
   * add(int, Object), and remove(int) of the backing list, and does not
   * support remove, set, or add unless the list does. This implementation
   * is fail-fast if you correctly maintain modCount.
   *
   * @param index the position, between 0 and size() inclusive, to begin the
   *        iteration from
   * @return a ListIterator over the elements of this list, in order, starting
   *         at index
   * @throws IndexOutOfBoundsException if index &lt; 0 || index &gt; size()
   * @see #modCount
   */
  public ListIterator listIterator(final int index)
  {
    if (index < 0 || index > size())
      throw new IndexOutOfBoundsException("Index: " + index + ", Size:"
                                          + size());

    return new ListIterator()
    {
      private int knownMod = modCount;
      private int position = index;
      private int lastReturned = -1;
      private int size = size();

      // This will get inlined, since it is private.
      private void checkMod()
      {
        if (knownMod != modCount)
          throw new ConcurrentModificationException();
      }

      public boolean hasNext()
      {
        checkMod();
        return position < size;
      }

      public boolean hasPrevious()
      {
        checkMod();
        return position > 0;
      }

      public Object next()
      {
        checkMod();
        if (position == size)
          throw new NoSuchElementException();
        lastReturned = position;
        return get(position++);
      }

      public Object previous()
      {
        checkMod();
        if (position == 0)
          throw new NoSuchElementException();
        lastReturned = --position;
        return get(lastReturned);
      }

      public int nextIndex()
      {
        checkMod();
        return position;
      }

      public int previousIndex()
      {
        checkMod();
        return position - 1;
      }

      public void remove()
      {
        checkMod();
        if (lastReturned < 0)
          throw new IllegalStateException();
        AbstractList.this.remove(lastReturned);
        size--;
        position = lastReturned;
        lastReturned = -1;
        knownMod = modCount;
      }

      public void set(Object o)
      {
        checkMod();
        if (lastReturned < 0)
          throw new IllegalStateException();
        AbstractList.this.set(lastReturned, o);
      }

      public void add(Object o)
      {
        checkMod();
        AbstractList.this.add(position++, o);
        size++;
        lastReturned = -1;
        knownMod = modCount;
      }
    };
  }

  /**
   * Remove the element at a given position in this list (optional operation).
   * Shifts all remaining elements to the left to fill the gap. This
   * implementation always throws an UnsupportedOperationException.
   * If you want fail-fast iterators, be sure to increment modCount when
   * overriding this.
   *
   * @param index the position within the list of the object to remove
   * @return the object that was removed
   * @throws UnsupportedOperationException if this list does not support the
   *         remove operation
   * @throws IndexOutOfBoundsException if index &lt; 0 || index &gt;= size()
   * @see #modCount
   */
  public Object remove(int index)
  {
    throw new UnsupportedOperationException();
  }

  /**
   * Remove a subsection of the list. This is called by the clear and
   * removeRange methods of the class which implements subList, which are
   * difficult for subclasses to override directly. Therefore, this method
   * should be overridden instead by the more efficient implementation, if one
   * exists. Overriding this can reduce quadratic efforts to constant time
   * in some cases!
   * <p>
   *
   * This implementation first checks for illegal or out of range arguments. It
   * then obtains a ListIterator over the list using listIterator(fromIndex).
   * It then calls next() and remove() on this iterator repeatedly, toIndex -
   * fromIndex times.
   *
   * @param fromIndex the index, inclusive, to remove from.
   * @param toIndex the index, exclusive, to remove to.
   */
  protected void removeRange(int fromIndex, int toIndex)
  {
    ListIterator itr = listIterator(fromIndex);
    for (int index = fromIndex; index < toIndex; index++)
      {
        itr.next();
        itr.remove();
      }
  }

  /**
   * Replace an element of this list with another object (optional operation).
   * This implementation always throws an UnsupportedOperationException.
   *
   * @param index the position within this list of the element to be replaced
   * @param o the object to replace it with
   * @return the object that was replaced
   * @throws UnsupportedOperationException if this list does not support the
   *         set operation
   * @throws IndexOutOfBoundsException if index &lt; 0 || index &gt;= size()
   * @throws ClassCastException if o cannot be added to this list due to its
   *         type
   * @throws IllegalArgumentException if o cannot be added to this list for
   *         some other reason
   */
  public Object set(int index, Object o)
  {
    throw new UnsupportedOperationException();
  }

  /**
   * Obtain a List view of a subsection of this list, from fromIndex
   * (inclusive) to toIndex (exclusive). If the two indices are equal, the
   * sublist is empty. The returned list should be modifiable if and only
   * if this list is modifiable. Changes to the returned list should be
   * reflected in this list. If this list is structurally modified in
   * any way other than through the returned list, the result of any subsequent
   * operations on the returned list is undefined.
   * <p>
   *
   * This implementation returns a subclass of AbstractList. It stores, in
   * private fields, the offset and size of the sublist, and the expected
   * modCount of the backing list. If the backing list implements RandomAccess,
   * the sublist will also.
   * <p>
   *
   * The subclass's <code>set(int, Object)</code>, <code>get(int)</code>,
   * <code>add(int, Object)</code>, <code>remove(int)</code>,
   * <code>addAll(int, Collection)</code> and
   * <code>removeRange(int, int)</code> methods all delegate to the
   * corresponding methods on the backing abstract list, after
   * bounds-checking the index and adjusting for the offset. The
   * <code>addAll(Collection c)</code> method merely returns addAll(size, c).
   * The <code>listIterator(int)</code> method returns a "wrapper object"
   * over a list iterator on the backing list, which is created with the
   * corresponding method on the backing list. The <code>iterator()</code>
   * method merely returns listIterator(), and the <code>size()</code> method
   * merely returns the subclass's size field.
   * <p>
   *
   * All methods first check to see if the actual modCount of the backing
   * list is equal to its expected value, and throw a
   * ConcurrentModificationException if it is not. 
   *
   * @param fromIndex the index that the returned list should start from
   *        (inclusive)
   * @param toIndex the index that the returned list should go to (exclusive)
   * @return a List backed by a subsection of this list
   * @throws IndexOutOfBoundsException if fromIndex &lt; 0
   *         || toIndex &gt; size()
   * @throws IllegalArgumentException if fromIndex &gt; toIndex
   * @see ConcurrentModificationException
   * @see RandomAccess
   */
  public List subList(int fromIndex, int toIndex)
  {
    // This follows the specification of AbstractList, but is inconsistent
    // with the one in List. Don't you love Sun's inconsistencies?
    if (fromIndex > toIndex)
      throw new IllegalArgumentException(fromIndex + " > " + toIndex);
    if (fromIndex < 0 || toIndex > size())
      throw new IndexOutOfBoundsException();

    if (this instanceof RandomAccess)
      return new RandomAccessSubList(this, fromIndex, toIndex);
    return new SubList(this, fromIndex, toIndex);
  }

} // class AbstractList


/**
 * This class follows the implementation requirements set forth in
 * {@link AbstractList#subList(int, int)}. It matches Sun's implementation
 * by using a non-public top-level class in the same package.
 *
 * @author Original author unknown
 * @author Eric Blake <[e-mail]>
 */
class SubList extends AbstractList
{
  // Package visible, for use by iterator.