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/*
* 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 org.apache.commons.collections4.iterators;
import java.util.ListIterator;
import java.util.NoSuchElementException;
import org.apache.commons.collections4.Predicate;
/**
* Decorates another {@link ListIterator} using a predicate to filter elements.
*
* This iterator decorates the underlying iterator, only allowing through
* those elements that match the specified {@link Predicate Predicate}.
*
* @since 2.0
*/
public class FilterListIterator implements ListIterator {
/** The iterator being used */
private ListIterator iterator;
/** The predicate being used */
private Predicate predicate;
/**
* The value of the next (matching) object, when
* {@link #nextObjectSet} is true.
*/
private E nextObject;
/**
* Whether or not the {@link #nextObject} has been set
* (possibly to null).
*/
private boolean nextObjectSet = false;
/**
* The value of the previous (matching) object, when
* {@link #previousObjectSet} is true.
*/
private E previousObject;
/**
* Whether or not the {@link #previousObject} has been set
* (possibly to null).
*/
private boolean previousObjectSet = false;
/**
* The index of the element that would be returned by {@link #next}.
*/
private int nextIndex = 0;
//-----------------------------------------------------------------------
/**
* Constructs a new FilterListIterator that will not function
* until {@link #setListIterator(ListIterator) setListIterator}
* and {@link #setPredicate(Predicate) setPredicate} are invoked.
*/
public FilterListIterator() {
super();
}
/**
* Constructs a new FilterListIterator that will not
* function until {@link #setPredicate(Predicate) setPredicate} is invoked.
*
* @param iterator the iterator to use
*/
public FilterListIterator(final ListIterator iterator ) {
super();
this.iterator = iterator;
}
/**
* Constructs a new FilterListIterator.
*
* @param iterator the iterator to use
* @param predicate the predicate to use
*/
public FilterListIterator(final ListIterator iterator, final Predicate predicate) {
super();
this.iterator = iterator;
this.predicate = predicate;
}
/**
* Constructs a new FilterListIterator that will not function
* until {@link #setListIterator(ListIterator) setListIterator} is invoked.
*
* @param predicate the predicate to use.
*/
public FilterListIterator(final Predicate predicate) {
super();
this.predicate = predicate;
}
//-----------------------------------------------------------------------
/**
* Not supported.
* @param o the element to insert
*/
@Override
public void add(final E o) {
throw new UnsupportedOperationException("FilterListIterator.add(Object) is not supported.");
}
@Override
public boolean hasNext() {
return nextObjectSet || setNextObject();
}
@Override
public boolean hasPrevious() {
return previousObjectSet || setPreviousObject();
}
@Override
public E next() {
if (!nextObjectSet && !setNextObject()) {
throw new NoSuchElementException();
}
nextIndex++;
final E temp = nextObject;
clearNextObject();
return temp;
}
@Override
public int nextIndex() {
return nextIndex;
}
@Override
public E previous() {
if (!previousObjectSet && !setPreviousObject()) {
throw new NoSuchElementException();
}
nextIndex--;
final E temp = previousObject;
clearPreviousObject();
return temp;
}
@Override
public int previousIndex() {
return nextIndex-1;
}
/** Not supported. */
@Override
public void remove() {
throw new UnsupportedOperationException("FilterListIterator.remove() is not supported.");
}
/**
* Not supported.
* @param o the element with which to replace the last element returned by
* {@code next} or {@code previous}
*/
@Override
public void set(final E o) {
throw new UnsupportedOperationException("FilterListIterator.set(Object) is not supported.");
}
//-----------------------------------------------------------------------
/**
* Gets the iterator this iterator is using.
*
* @return the iterator.
*/
public ListIterator getListIterator() {
return iterator;
}
/**
* Sets the iterator for this iterator to use.
* If iteration has started, this effectively resets the iterator.
*
* @param iterator the iterator to use
*/
public void setListIterator(final ListIterator iterator) {
this.iterator = iterator;
}
//-----------------------------------------------------------------------
/**
* Gets the predicate this iterator is using.
*
* @return the predicate.
*/
public Predicate getPredicate() {
return predicate;
}
/**
* Sets the predicate this the iterator to use.
*
* @param predicate the transformer to use
*/
public void setPredicate(final Predicate predicate) {
this.predicate = predicate;
}
//-----------------------------------------------------------------------
private void clearNextObject() {
nextObject = null;
nextObjectSet = false;
}
private boolean setNextObject() {
// if previousObjectSet,
// then we've walked back one step in the
// underlying list (due to a hasPrevious() call)
// so skip ahead one matching object
if (previousObjectSet) {
clearPreviousObject();
if (!setNextObject()) {
return false;
}
clearNextObject();
}
if (iterator == null) {
return false;
}
while (iterator.hasNext()) {
final E object = iterator.next();
if (predicate.evaluate(object)) {
nextObject = object;
nextObjectSet = true;
return true;
}
}
return false;
}
private void clearPreviousObject() {
previousObject = null;
previousObjectSet = false;
}
private boolean setPreviousObject() {
// if nextObjectSet,
// then we've walked back one step in the
// underlying list (due to a hasNext() call)
// so skip ahead one matching object
if (nextObjectSet) {
clearNextObject();
if (!setPreviousObject()) {
return false;
}
clearPreviousObject();
}
if (iterator == null) {
return false;
}
while (iterator.hasPrevious()) {
final E object = iterator.previous();
if (predicate.evaluate(object)) {
previousObject = object;
previousObjectSet = true;
return true;
}
}
return false;
}
}