AbstractSequentialList.java

/* AbstractSequentialList.java -- List implementation for sequential access
   Copyright (C) 1998, 1999, 2000, 2001 Free Software Foundation, Inc.

This file is part of GNU Classpath.

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it under the terms of the GNU General Public License as published by
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General Public License for more details.

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02111-1307 USA.

Linking this library statically or dynamically with other modules is
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permission to link this library with independent modules to produce an
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package java.util;

/**
 * Abstract superclass to make it easier to implement the List interface when
 * backed by a sequential-access store, such as a linked list. For random
 * access data, use AbstractList. This class implements the random access
 * methods (<code>get</code>, <code>set</code>, <code>add</code>, and
 * <code>remove</code>) atop the list iterator, opposite of AbstractList's
 * approach of implementing the iterator atop random access.
 * <p>
 *
 * To implement a list, you need an implementation for <code>size()</code>
 * and <code>listIterator</code>.  With just <code>hasNext</code>,
 * <code>next</code>, <code>hasPrevious</code>, <code>previous</code>,
 * <code>nextIndex</code>, and <code>previousIndex</code>, you have an
 * unmodifiable list. For a modifiable one, add <code>set</code>, and for
 * a variable-size list, add <code>add</code> and <code>remove</code>.
 * <p>
 *
 * The programmer should provide a no-argument constructor, and one that
 * accepts another Collection, as recommended by the Collection interface.
 * Unfortunately, there is no way to enforce this in Java.
 *
 * @author Original author unknown
 * @author Bryce McKinlay
 * @author Eric Blake <ebb9@email.byu.edu>
 * @see Collection
 * @see List
 * @see AbstractList
 * @see AbstractCollection
 * @see ListIterator
 * @see LinkedList
 * @since 1.2
 * @status updated to 1.4
 */
public abstract class AbstractSequentialList extends AbstractList
{
  /**
   * The main constructor, for use by subclasses.
   */
  protected AbstractSequentialList()
  {
  }

  /**
   * Returns a ListIterator over the list, starting from position index.
   * Subclasses must provide an implementation of this method.
   *
   * @param index the starting position of the list
   * @return the list iterator
   * @throws IndexOutOfBoundsException if index &lt; 0 || index &gt; size()
   */
  public abstract ListIterator listIterator(int index);

  /**
   * Insert an element into the list at a given position (optional operation).
   * This shifts all existing elements from that position to the end one
   * index to the right. This version of add has no return, since it is
   * assumed to always succeed if there is no exception. This iteration
   * uses listIterator(index).add(o).
   *
   * @param index the location to insert the item
   * @param o the object to insert
   * @throws UnsupportedOperationException if this list does not support the
   *         add 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 void add(int index, Object o)
  {
    listIterator(index).add(o);
  }

  /**
   * Insert the contents of a collection into the list at a given position
   * (optional operation). Shift all elements at that position to the right
   * by the number of elements inserted. This operation is undefined if
   * this list is modified during the operation (for example, if you try
   * to insert a list into itself).
   * <p>
   *
   * This implementation grabs listIterator(index), then proceeds to use add
   * for each element returned by c's iterator. Sun's online specs are wrong,
   * claiming that this also calls next(): listIterator.add() correctly
   * skips the added element.
   *
   * @param index the location to insert the collection
   * @param c the collection to insert
   * @return true if the list was modified by this action, that is, if c is
   *         non-empty
   * @throws UnsupportedOperationException if this list does not support the
   *         addAll operation
   * @throws IndexOutOfBoundsException if index &lt; 0 || index &gt; size()
   * @throws ClassCastException if some element of c cannot be added to this
   *         list due to its type
   * @throws IllegalArgumentException if some element of c cannot be added
   *         to this list for some other reason
   * @throws NullPointerException if the specified collection is null
   * @see #add(int, Object)
   */
  public boolean addAll(int index, Collection c)
  {
    Iterator ci = c.iterator();
    int size = c.size();
    ListIterator i = listIterator(index);
    for (int pos = size; pos > 0; pos--)
      i.add(ci.next());
    return size > 0;
  }

  /**
   * Get the element at a given index in this list. This implementation
   * returns listIterator(index).next().
   *
   * @param index the index of the element to be returned
   * @return the element at index index in this list
   * @throws IndexOutOfBoundsException if index &lt; 0 || index &gt;= size()
   */
  public Object get(int index)
  {
    // This is a legal listIterator position, but an illegal get.
    if (index == size())
      throw new IndexOutOfBoundsException("Index: " + index + ", Size:"
                                          + size());
    return listIterator(index).next();
  }

  /**
   * Obtain an Iterator over this list, whose sequence is the list order. This
   * implementation returns listIterator().
   *
   * @return an Iterator over the elements of this list, in order
   */
  public Iterator iterator()
  {
    return listIterator();
  }

  /**
   * 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 uses listIterator(index) and ListIterator.remove().
   *
   * @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()
   */
  public Object remove(int index)
  {
    // This is a legal listIterator position, but an illegal remove.
    if (index == size())
      throw new IndexOutOfBoundsException("Index: " + index + ", Size:"
                                          + size());
    ListIterator i = listIterator(index);
    Object removed = i.next();
    i.remove();
    return removed;
  }

  /**
   * Replace an element of this list with another object (optional operation).
   * This implementation uses listIterator(index) and ListIterator.set(o).
   *
   * @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)
  {
    // This is a legal listIterator position, but an illegal set.
    if (index == size())
      throw new IndexOutOfBoundsException("Index: " + index + ", Size:"
                                          + size());
    ListIterator i = listIterator(index);
    Object old = i.next();
    i.set(o);
    return old;
  }
}