content: /*
   * Licensed to the Apache Software Foundation (ASF) under one
   * or more contributor license agreements.  See the NOTICE file
   * distributed with this work for additional information
   * regarding copyright ownership.  The ASF licenses this file
   * to you under the Apache License, Version 2.0 (the
   * "License"); you may not use this file except in compliance
   * with the License.  You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing,
   * software distributed under the License is distributed on an
   * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
   * KIND, either express or implied.  See the License for the
   * specific language governing permissions and limitations
   * under the License.
   */
  
  package com.aliyun.odps;
  
  import java.util.Iterator;
  import java.util.LinkedList;
  import java.util.List;
  import java.util.NoSuchElementException;
  
  /**
   * 支持通过{@link #list()}自定义的Iterator
   */
  public abstract class ListIterator<E> implements Iterator<E> {
  
    /**
     * 获取数据
     *
     * @return 返回null表示迭代结束
     */
    protected abstract List<E> list();
  
    public List<E> list(String marker, long maxItems) {
      return list();
    }
  
    public String getMarker() {
      // marker = empty string => end of loop
      return null;
    }
  
    private LinkedList<E> cache = new LinkedList<E>();
  
    @Override
    public boolean hasNext() {
      while (cache.size() == 0) {
        List<E> list = list();
        if (list == null) {
          return false;
        } else {
          cache.addAll(list);
        }
      }
      return cache.size() > 0;
    }
  
    @Override
    public E next() {
      if (!hasNext()) {
        throw new NoSuchElementException();
      }
      return cache.pollFirst();
    }
  
    @Override
    public void remove() {
      throw new RuntimeException("Method not supported.");
    }
  
  }
  