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;
023
024/**
025 * Decorates another {@link Iterator} using a predicate to filter elements.
026 * <p>
027 * This iterator decorates the underlying iterator, only allowing through
028 * those elements that match the specified {@link Predicate Predicate}.
029 *
030 * @since 1.0
031 */
032public class FilterIterator<E> implements Iterator<E> {
033
034    /** The iterator being used */
035    private Iterator<? extends E> iterator;
036    /** The predicate being used */
037    private Predicate<? super E> predicate;
038    /** The next object in the iteration */
039    private E nextObject;
040    /** Whether the next object has been calculated yet */
041    private boolean nextObjectSet = false;
042
043    //-----------------------------------------------------------------------
044    /**
045     * Constructs a new <code>FilterIterator</code> that will not function
046     * until {@link #setIterator(Iterator) setIterator} is invoked.
047     */
048    public FilterIterator() {
049        super();
050    }
051
052    /**
053     * Constructs a new <code>FilterIterator</code> that will not function
054     * until {@link #setPredicate(Predicate) setPredicate} is invoked.
055     *
056     * @param iterator  the iterator to use
057     */
058    public FilterIterator(final Iterator<? extends E> iterator) {
059        super();
060        this.iterator = iterator;
061    }
062
063    /**
064     * Constructs a new <code>FilterIterator</code> that will use the
065     * given iterator and predicate.
066     *
067     * @param iterator  the iterator to use
068     * @param predicate  the predicate to use
069     */
070    public FilterIterator(final Iterator<? extends E> iterator, final Predicate<? super E> predicate) {
071        super();
072        this.iterator = iterator;
073        this.predicate = predicate;
074    }
075
076    //-----------------------------------------------------------------------
077    /**
078     * Returns true if the underlying iterator contains an object that
079     * matches the predicate.
080     *
081     * @return true if there is another object that matches the predicate
082     * @throws NullPointerException if either the iterator or predicate are null
083     */
084    @Override
085    public boolean hasNext() {
086        return nextObjectSet || setNextObject();
087    }
088
089    /**
090     * Returns the next object that matches the predicate.
091     *
092     * @return the next object which matches the given predicate
093     * @throws NullPointerException if either the iterator or predicate are null
094     * @throws NoSuchElementException if there are no more elements that
095     *  match the predicate
096     */
097    @Override
098    public E next() {
099        if (!nextObjectSet && !setNextObject()) {
100            throw new NoSuchElementException();
101        }
102        nextObjectSet = false;
103        return nextObject;
104    }
105
106    /**
107     * Removes from the underlying collection of the base iterator the last
108     * element returned by this iterator.
109     * This method can only be called
110     * if <code>next()</code> was called, but not after
111     * <code>hasNext()</code>, because the <code>hasNext()</code> call
112     * changes the base iterator.
113     *
114     * @throws IllegalStateException if <code>hasNext()</code> has already
115     *  been called.
116     */
117    @Override
118    public void remove() {
119        if (nextObjectSet) {
120            throw new IllegalStateException("remove() cannot be called");
121        }
122        iterator.remove();
123    }
124
125    //-----------------------------------------------------------------------
126    /**
127     * Gets the iterator this iterator is using.
128     *
129     * @return the iterator
130     */
131    public Iterator<? extends E> getIterator() {
132        return iterator;
133    }
134
135    /**
136     * Sets the iterator for this iterator to use.
137     * If iteration has started, this effectively resets the iterator.
138     *
139     * @param iterator  the iterator to use
140     */
141    public void setIterator(final Iterator<? extends E> iterator) {
142        this.iterator = iterator;
143        nextObject = null;
144        nextObjectSet = false;
145    }
146
147    //-----------------------------------------------------------------------
148    /**
149     * Gets the predicate this iterator is using.
150     *
151     * @return the predicate
152     */
153    public Predicate<? super E> getPredicate() {
154        return predicate;
155    }
156
157    /**
158     * Sets the predicate this the iterator to use.
159     *
160     * @param predicate  the predicate to use
161     */
162    public void setPredicate(final Predicate<? super E> predicate) {
163        this.predicate = predicate;
164        nextObject = null;
165        nextObjectSet = false;
166    }
167
168    //-----------------------------------------------------------------------
169    /**
170     * Set nextObject to the next object. If there are no more
171     * objects then return false. Otherwise, return true.
172     */
173    private boolean setNextObject() {
174        while (iterator.hasNext()) {
175            final E object = iterator.next();
176            if (predicate.evaluate(object)) {
177                nextObject = object;
178                nextObjectSet = true;
179                return true;
180            }
181        }
182        return false;
183    }
184
185}