org.apache.commons.collections4.iterators.FilterIterator Maven / Gradle / Ivy
Show all versions of commons-collections4 Show documentation
/*
* 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.Iterator;
import java.util.NoSuchElementException;
import org.apache.commons.collections4.Predicate;
/**
* Decorates another {@link Iterator} 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 1.0
*/
public class FilterIterator implements Iterator {
/** The iterator being used */
private Iterator iterator;
/** The predicate being used */
private Predicate predicate;
/** The next object in the iteration */
private E nextObject;
/** Whether the next object has been calculated yet */
private boolean nextObjectSet = false;
//-----------------------------------------------------------------------
/**
* Constructs a new FilterIterator that will not function
* until {@link #setIterator(Iterator) setIterator} is invoked.
*/
public FilterIterator() {
super();
}
/**
* Constructs a new FilterIterator that will not function
* until {@link #setPredicate(Predicate) setPredicate} is invoked.
*
* @param iterator the iterator to use
*/
public FilterIterator(final Iterator iterator) {
super();
this.iterator = iterator;
}
/**
* Constructs a new FilterIterator that will use the
* given iterator and predicate.
*
* @param iterator the iterator to use
* @param predicate the predicate to use
*/
public FilterIterator(final Iterator iterator, final Predicate predicate) {
super();
this.iterator = iterator;
this.predicate = predicate;
}
//-----------------------------------------------------------------------
/**
* Returns true if the underlying iterator contains an object that
* matches the predicate.
*
* @return true if there is another object that matches the predicate
* @throws NullPointerException if either the iterator or predicate are null
*/
@Override
public boolean hasNext() {
return nextObjectSet || setNextObject();
}
/**
* Returns the next object that matches the predicate.
*
* @return the next object which matches the given predicate
* @throws NullPointerException if either the iterator or predicate are null
* @throws NoSuchElementException if there are no more elements that
* match the predicate
*/
@Override
public E next() {
if (!nextObjectSet && !setNextObject()) {
throw new NoSuchElementException();
}
nextObjectSet = false;
return nextObject;
}
/**
* Removes from the underlying collection of the base iterator the last
* element returned by this iterator.
* This method can only be called
* if next() was called, but not after
* hasNext(), because the hasNext() call
* changes the base iterator.
*
* @throws IllegalStateException if hasNext() has already
* been called.
*/
@Override
public void remove() {
if (nextObjectSet) {
throw new IllegalStateException("remove() cannot be called");
}
iterator.remove();
}
//-----------------------------------------------------------------------
/**
* Gets the iterator this iterator is using.
*
* @return the iterator
*/
public Iterator getIterator() {
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 setIterator(final Iterator iterator) {
this.iterator = iterator;
nextObject = null;
nextObjectSet = false;
}
//-----------------------------------------------------------------------
/**
* 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 predicate to use
*/
public void setPredicate(final Predicate predicate) {
this.predicate = predicate;
nextObject = null;
nextObjectSet = false;
}
//-----------------------------------------------------------------------
/**
* Set nextObject to the next object. If there are no more
* objects then return false. Otherwise, return true.
*/
private boolean setNextObject() {
while (iterator.hasNext()) {
final E object = iterator.next();
if (predicate.evaluate(object)) {
nextObject = object;
nextObjectSet = true;
return true;
}
}
return false;
}
}