abstractlist.java

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      {
        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.
  /** The original list. */
  final AbstractList backingList;
  /** The index of the first element of the sublist. */
  final int offset;
  /** The size of the sublist. */
  int size;

  /**
   * Construct the sublist.
   *
   * @param backing the list this comes from
   * @param fromIndex the lower bound, inclusive
   * @param toIndex the upper bound, exclusive
   */
  SubList(AbstractList backing, int fromIndex, int toIndex)
  {
    backingList = backing;
    modCount = backing.modCount;
    offset = fromIndex;
    size = toIndex - fromIndex;
  }

  /**
   * This method checks the two modCount fields to ensure that there has
   * not been a concurrent modification, returning if all is okay.
   *
   * @throws ConcurrentModificationException if the backing list has been
   *         modified externally to this sublist
   */
  // This can be inlined. Package visible, for use by iterator.
  void checkMod()
  {
    if (modCount != backingList.modCount)
      throw new ConcurrentModificationException();
  }

  /**
   * This method checks that a value is between 0 and size (inclusive). If
   * it is not, an exception is thrown.
   *
   * @param index the value to check
   * @throws IndexOutOfBoundsException if the value is out of range
   */
  // This will get inlined, since it is private.
  private void checkBoundsInclusive(int index)
  {
    if (index < 0 || index > size)
      throw new IndexOutOfBoundsException("Index: " + index + ", Size:"
                                          + size);
  }

  /**
   * This method checks that a value is between 0 (inclusive) and size
   * (exclusive). If it is not, an exception is thrown.
   *
   * @param index the value to check
   * @throws IndexOutOfBoundsException if the value is out of range
   */
  // This will get inlined, since it is private.
  private void checkBoundsExclusive(int index)
  {
    if (index < 0 || index >= size)
      throw new IndexOutOfBoundsException("Index: " + index + ", Size:"
                                          + size);
  }

  /**
   * Specified by AbstractList.subList to return the private field size.
   *
   * @return the sublist size
   */
  public int size()
  {
    checkMod();
    return size;
  }

  /**
   * Specified by AbstractList.subList to delegate to the backing list.
   *
   * @param index the location to modify
   * @param o the new value
   * @return the old value
   */
  public Object set(int index, Object o)
  {
    checkMod();
    checkBoundsExclusive(index);
    return backingList.set(index + offset, o);
  }

  /**
   * Specified by AbstractList.subList to delegate to the backing list.
   *
   * @param index the location to get from
   * @return the object at that location
   */
  public Object get(int index)
  {
    checkMod();
    checkBoundsExclusive(index);
    return backingList.get(index + offset);
  }

  /**
   * Specified by AbstractList.subList to delegate to the backing list.
   *
   * @param index the index to insert at
   * @param o the object to add
   */
  public void add(int index, Object o)
  {
    checkMod();
    checkBoundsInclusive(index);
    backingList.add(index + offset, o);
    size++;
    modCount = backingList.modCount;
  }

  /**
   * Specified by AbstractList.subList to delegate to the backing list.
   *
   * @param index the index to remove
   * @return the removed object
   */
  public Object remove(int index)
  {
    checkMod();
    checkBoundsExclusive(index);
    Object o = backingList.remove(index + offset);
    size--;
    modCount = backingList.modCount;
    return o;
  }

  /**
   * Specified by AbstractList.subList to delegate to the backing list.
   * This does no bounds checking, as it assumes it will only be called
   * by trusted code like clear() which has already checked the bounds.
   *
   * @param fromIndex the lower bound, inclusive
   * @param toIndex the upper bound, exclusive
   */
  protected void removeRange(int fromIndex, int toIndex)
  {
    checkMod();

    backingList.removeRange(offset + fromIndex, offset + toIndex);
    size -= toIndex - fromIndex;
    modCount = backingList.modCount;
  }

  /**
   * Specified by AbstractList.subList to delegate to the backing list.
   *
   * @param index the location to insert at
   * @param c the collection to insert
   * @return true if this list was modified, in other words, c is non-empty
   */
  public boolean addAll(int index, Collection c)
  {
    checkMod();
    checkBoundsInclusive(index);
    int csize = c.size();
    boolean result = backingList.addAll(offset + index, c);
    size += csize;
    modCount = backingList.modCount;
    return result;
  }

  /**
   * Specified by AbstractList.subList to return addAll(size, c).
   *
   * @param c the collection to insert
   * @return true if this list was modified, in other words, c is non-empty
   */
  public boolean addAll(Collection c)
  {
    return addAll(size, c);
  }

  /**
   * Specified by AbstractList.subList to return listIterator().
   *
   * @return an iterator over the sublist
   */
  public Iterator iterator()
  {
    return listIterator();
  }

  /**
   * Specified by AbstractList.subList to return a wrapper around the
   * backing list's iterator.
   *
   * @param index the start location of the iterator
   * @return a list iterator over the sublist
   */
  public ListIterator listIterator(final int index)
  {
    checkMod();
    checkBoundsInclusive(index);

    return new ListIterator()
    {
      private final ListIterator i = backingList.listIterator(index + offset);
      private int position = index;

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

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

      public Object next()
      {
        if (position == size)
          throw new NoSuchElementException();
        position++;
        return i.next();
      }

      public Object previous()
      {
        if (position == 0)
          throw new NoSuchElementException();
        position--;
        return i.previous();
      }

      public int nextIndex()
      {
        return i.nextIndex() - offset;
      }

      public int previousIndex()
      {
        return i.previousIndex() - offset;
      }

      public void remove()
      {
        i.remove();
        size--;
        position = nextIndex();
        modCount = backingList.modCount;
      }

      public void set(Object o)
      {
        i.set(o);
      }

      public void add(Object o)
      {
        i.add(o);
        size++;
        position++;
        modCount = backingList.modCount;
      }

      // Here is the reason why the various modCount fields are mostly
      // ignored in this wrapper listIterator.
      // If the backing listIterator is failfast, then the following holds:
      //   Using any other method on this list will call a corresponding
      //   method on the backing list *after* the backing listIterator
      //   is created, which will in turn cause a ConcurrentModException
      //   when this listIterator comes to use the backing one. So it is
      //   implicitly failfast.
      // If the backing listIterator is NOT failfast, then the whole of
      //   this list isn't failfast, because the modCount field of the
      //   backing list is not valid. It would still be *possible* to
      //   make the iterator failfast wrt modifications of the sublist
      //   only, but somewhat pointless when the list can be changed under
      //   us.
      // Either way, no explicit handling of modCount is needed.
      // However modCount = backingList.modCount must be executed in add
      // and remove, and size must also be updated in these two methods,
      // since they do not go through the corresponding methods of the subList.
    };
  }
} // class SubList

/**
 * This class is a RandomAccess version of SubList, as required by
 * {@link AbstractList#subList(int, int)}.
 *
 * @author Eric Blake <[e-mail]>
 */
final class RandomAccessSubList extends SubList
  implements RandomAccess
{
  /**
   * Construct the sublist.
   *
   * @param backing the list this comes from
   * @param fromIndex the lower bound, inclusive
   * @param toIndex the upper bound, exclusive
   */
  RandomAccessSubList(AbstractList backing, int fromIndex, int toIndex)
  {
    super(backing, fromIndex, toIndex);
  }
} // class RandomAccessSubList