nulliterator.java

来自「RESIN 3.2 最新源码」· Java 代码 · 共 92 行

/*
 * Copyright (c) 1998-2008 Caucho Technology -- all rights reserved
 *
 * This file is part of Resin(R) Open Source
 *
 * Each copy or derived work must preserve the copyright notice and this
 * notice unmodified.
 *
 * Resin Open Source is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * Resin Open Source 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, or any warranty
 * of NON-INFRINGEMENT.  See the GNU General Public License for more
 * details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Resin Open Source; if not, write to the
 *   Free SoftwareFoundation, Inc.
 *   59 Temple Place, Suite 330
 *   Boston, MA 02111-1307  USA
 *
 * @author Scott Ferguson
 */

package com.caucho.util;

import java.util.ListIterator;

/**
 * A null iterator
 */
public class NullIterator<E> implements ListIterator<E> {
  private static NullIterator _singleton;

  public static NullIterator create()
  {
    if (_singleton == null)
      _singleton = new NullIterator();

    return _singleton;
  }

  public boolean hasNext()
  {
    return false;
  }

  public E next()
  {
    return null;
  }

  public int nextIndex()
  {
    return -1;
  }

  public boolean hasPrevious()
  {
    return false;
  }

  public E previous()
  {
    return null;
  }

  public int previousIndex()
  {
    return -1;
  }

  public void add(E o)
  {
    throw new UnsupportedOperationException();
  }

  public void set(E o)
  {
    throw new UnsupportedOperationException();
  }

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