Iterator Utils : Iterator « Collections « Java Tutorial

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2. Collections
3. Iterator

/*
 * Distributed as part of debuggen v.0.1.0
 *
 * Copyright (C) 2005 Machinery For Change, Inc.
 *
 * Author: Steve Waldman <swaldman@mchange.com>
 *
 * This library is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License version 2.1, as 
 * published by the Free Software Foundation.
 *
 * This software is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this software; see the file LICENSE.  If not, write to the
 * Free Software Foundation, Inc., 59 Temple Place, Suite 330,
 * Boston, MA 02111-1307, USA.
 */



import java.util.*;
import java.lang.reflect.Array;

public final class IteratorUtils
{
    public final static Iterator EMPTY_ITERATOR = new Iterator()
    {
  public boolean hasNext()
  { return false; }

  public Object next()
  { throw new NoSuchElementException(); }

  public void remove()
  { throw new IllegalStateException(); }
    };

    public static Iterator oneElementUnmodifiableIterator(final Object elem)
    {
  return new Iterator()
      {
    boolean shot = false;

    public boolean hasNext() { return (!shot); }

    public Object next()
    {
        if (shot)
      throw new NoSuchElementException();
        else
      {
          shot = true;
          return elem;
      }
    }

    public void remove()
    { throw new UnsupportedOperationException("remove() not supported."); }
      };
    }

    public static boolean equivalent(Iterator ii, Iterator jj)
    {
  while (true)
      {
    boolean ii_hasnext = ii.hasNext();
    boolean jj_hasnext = jj.hasNext();
    if (ii_hasnext ^ jj_hasnext)
        return false;
    else if (ii_hasnext)
        {
      Object iiNext = ii.next();
      Object jjNext = jj.next();
      if (iiNext == jjNext)
          continue;
      else if (iiNext == null)
          return false;
      else if (!iiNext.equals(jjNext))
          return false;
        }
    else return true;
      }
    }

    public static ArrayList toArrayList(Iterator ii, int initial_capacity)
    {
  ArrayList out = new ArrayList(initial_capacity);
  while (ii.hasNext())
      out.add(ii.next());
  return out;
    }

    /**
     * Fills an array with the contents of an iterator. If the array is too small,
     * it will contain the first portion of the iterator. If the array can contain
     * more elements than the iterator, extra elements are left untouched, unless
     * null_terminate is set to true, in which case the element immediately following
     * the last from the iterator is set to null. (This method is intended to make
     * it easy to implement Collection.toArray(Object[] oo) methods...
     *
     * @param null_terminate iff there is extra space in the array, set the element
     *        immediately after the last from the iterator to null.
     */
    public static void fillArray(Iterator ii, Object[] fillMe, boolean null_terminate)
    {
  int i = 0;
  int len = fillMe.length;
  while ( i < len && ii.hasNext() )
      fillMe[ i++ ] = ii.next();
  if (null_terminate && i < len)
      fillMe[i] = null;
    }

    public static void fillArray(Iterator ii, Object[] fillMe)
    { fillArray( ii, fillMe, false); }

    /**
     * @param null_terminate iff there is extra space in the array, set the element
     *        immediately after the last from the iterator to null.
     */
    public static Object[] toArray(Iterator ii, int array_size, Class componentClass, boolean null_terminate)
    {
  Object[] out = (Object[]) Array.newInstance( componentClass, array_size );
  fillArray(ii, out, null_terminate);
  return out;
    }

    public static Object[] toArray(Iterator ii, int array_size, Class componentClass)
    { return toArray( ii, array_size, componentClass, false ); }

    /**
     * Designed to help implement Collection.toArray(Object[] )methods... does
     * the right thing if you can express an iterator and know the size of your
     * Collection.
     */
    public static Object[] toArray(Iterator ii, int ii_size, Object[] maybeFillMe)
    {
  if (maybeFillMe.length >= ii_size)
      {
    fillArray( ii, maybeFillMe, true );
    return maybeFillMe;
      }
  else
      {
    Class componentType = maybeFillMe.getClass().getComponentType(); 
    return toArray( ii, ii_size, componentType );
      }
    }

    private IteratorUtils()
    {}
}