001/* 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache License, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 */ 017package org.apache.commons.collections4.iterators; 018 019import java.util.Iterator; 020import java.util.NoSuchElementException; 021 022import org.apache.commons.collections4.Predicate; 023import org.apache.commons.collections4.functors.TruePredicate; 024 025/** 026 * Decorates an {@link Iterator} using an optional predicate to filter elements. 027 * <p> 028 * This iterator decorates the underlying iterator, only allowing through 029 * those elements that match the specified {@link Predicate Predicate}. 030 * </p> 031 * 032 * @param <E> the type of elements returned by this iterator. 033 * @since 1.0 034 */ 035public class FilterIterator<E> implements IteratorOperations<E> { 036 037 /** The iterator to be filtered. */ 038 private Iterator<? extends E> iterator; 039 040 /** The predicate to filter elements. */ 041 private Predicate<? super E> predicate = TruePredicate.truePredicate(); 042 043 /** The next object in the iteration. */ 044 private E nextObject; 045 046 /** Whether the next object has been calculated yet. */ 047 private boolean nextObjectSet; 048 049 /** 050 * Constructs a new {@code FilterIterator} that will not function 051 * until {@link #setIterator(Iterator) setIterator} is invoked. 052 */ 053 public FilterIterator() { 054 } 055 056 /** 057 * Constructs a new {@code FilterIterator} that will not function 058 * until {@link #setPredicate(Predicate) setPredicate} is invoked. 059 * 060 * @param iterator the iterator to use 061 */ 062 public FilterIterator(final Iterator<? extends E> iterator) { 063 this.iterator = iterator; 064 } 065 066 /** 067 * Constructs a new {@code FilterIterator} that will use the 068 * given iterator and predicate. 069 * 070 * @param iterator the iterator to use 071 * @param predicate the predicate to use, null accepts all values. 072 */ 073 public FilterIterator(final Iterator<? extends E> iterator, final Predicate<? super E> predicate) { 074 this.iterator = iterator; 075 this.predicate = safePredicate(predicate); 076 } 077 078 /** 079 * Gets the iterator this iterator is using. 080 * 081 * @return the underlying iterator. 082 */ 083 public Iterator<? extends E> getIterator() { 084 return iterator; 085 } 086 087 /** 088 * Gets the predicate this iterator is using. 089 * 090 * @return the filtering predicate. 091 */ 092 public Predicate<? super E> getPredicate() { 093 return predicate; 094 } 095 096 /** 097 * Returns true if the underlying iterator contains an object that 098 * matches the predicate. 099 * 100 * @return true if there is another object that matches the predicate 101 * @throws NullPointerException if either the iterator or predicate are null 102 */ 103 @Override 104 public boolean hasNext() { 105 return nextObjectSet || setNextObject(); 106 } 107 108 /** 109 * Returns the next object that matches the predicate. 110 * 111 * @return the next object which matches the given predicate 112 * @throws NullPointerException if either the iterator or predicate are null 113 * @throws NoSuchElementException if there are no more elements that 114 * match the predicate 115 */ 116 @Override 117 public E next() { 118 if (!nextObjectSet && !setNextObject()) { 119 throw new NoSuchElementException(); 120 } 121 nextObjectSet = false; 122 return nextObject; 123 } 124 125 /** 126 * Removes from the underlying collection of the base iterator the last 127 * element returned by this iterator. 128 * This method can only be called 129 * if {@code next()} was called, but not after 130 * {@code hasNext()}, because the {@code hasNext()} call 131 * changes the base iterator. 132 * 133 * @throws IllegalStateException if {@code hasNext()} has already 134 * been called. 135 */ 136 @Override 137 public void remove() { 138 if (nextObjectSet) { 139 throw new IllegalStateException("remove() cannot be called"); 140 } 141 iterator.remove(); 142 } 143 144 private Predicate<? super E> safePredicate(final Predicate<? super E> predicate) { 145 return predicate != null ? predicate : TruePredicate.truePredicate(); 146 } 147 148 /** 149 * Sets the iterator for this iterator to use. 150 * If iteration has started, this effectively resets the iterator. 151 * 152 * @param iterator the iterator to use 153 */ 154 public void setIterator(final Iterator<? extends E> iterator) { 155 this.iterator = iterator; 156 nextObject = null; 157 nextObjectSet = false; 158 } 159 160 /** 161 * Sets nextObject to the next object. If there are no more 162 * objects, then return false. Otherwise, return true. 163 */ 164 private boolean setNextObject() { 165 while (iterator.hasNext()) { 166 final E object = iterator.next(); 167 if (predicate.test(object)) { 168 nextObject = object; 169 nextObjectSet = true; 170 return true; 171 } 172 } 173 return false; 174 } 175 176 /** 177 * Sets the predicate this the iterator to use where null accepts all values. 178 * 179 * @param predicate the predicate to use, null accepts all values. 180 */ 181 public void setPredicate(final Predicate<? super E> predicate) { 182 this.predicate = safePredicate(predicate); 183 nextObject = null; 184 nextObjectSet = false; 185 } 186 187}