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 }