    001/*
    002 * Copyright (c) 2016-2018 Chris K Wensel <chris@wensel.net>. All Rights Reserved.
    003 *
    004 * Project and contact information: http://www.cascading.org/
    005 *
    006 * This file is part of the Cascading project.
    007 *
    008 * Licensed under the Apache License, Version 2.0 (the "License");
    009 * you may not use this file except in compliance with the License.
    010 * You may obtain a copy of the License at
    011 *
    012 *     http://www.apache.org/licenses/LICENSE-2.0
    013 *
    014 * Unless required by applicable law or agreed to in writing, software
    015 * distributed under the License is distributed on an "AS IS" BASIS,
    016 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    017 * See the License for the specific language governing permissions and
    018 * limitations under the License.
    019 */
    020
    021package cascading.util;
    022
    023import java.util.Arrays;
    024import java.util.Iterator;
    025import java.util.LinkedList;
    026
    027/**
    028 *
    029 */
    030public abstract class LazyIterable<V, T> implements Iterable<T>
    031  {
    032  LinkedList<T> cache;
    033  Iterable<V> iterable;
    034
    035  public LazyIterable( V... values )
    036    {
    037    this( Arrays.asList( values ) );
    038    }
    039
    040  public LazyIterable( boolean enableCache, V... values )
    041    {
    042    this( enableCache, Arrays.asList( values ) );
    043    }
    044
    045  public LazyIterable( Iterable<V> iterable )
    046    {
    047    this( true, iterable );
    048    }
    049
    050  public LazyIterable( boolean enableCache, Iterable<V> iterable )
    051    {
    052    if( enableCache )
    053      this.cache = new LinkedList<>();
    054
    055    this.iterable = iterable;
    056    }
    057
    058  @Override
    059  public Iterator<T> iterator()
    060    {
    061    if( cache != null && !cache.isEmpty() )
    062      return cache.iterator();
    063
    064    final Iterator<V> iterator = iterable.iterator();
    065
    066    return new Iterator<T>()
    067      {
    068      @Override
    069      public boolean hasNext()
    070        {
    071        return iterator.hasNext();
    072        }
    073
    074      @Override
    075      public T next()
    076        {
    077        T converted = convert( iterator.next() );
    078
    079        if( cache != null )
    080          cache.add( converted );
    081
    082        return converted;
    083        }
    084
    085      @Override
    086      public void remove()
    087        {
    088        iterator.remove();
    089        }
    090      };
    091    }
    092
    093  protected abstract T convert( V next );
    094  }