/*
* Copyright 1999-2004,2006 The Apache Software Foundation
*
* Licensed 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.collections.iterators;
import java.util.Iterator;
import java.util.NoSuchElementException;
import org.apache.commons.collections.Predicate;
/**
* Decorates another {@link Iterator} using a predicate to filter elements.
* <p>
* This iterator decorates the underlying iterator, only allowing through
* those elements that match the specified {@link Predicate Predicate}.
*
* @since Commons Collections 1.0
* @version $Revision: 366576 $ $Date: 2006-01-06 22:07:07 +0000 (Fri, 06 Jan 2006) $
*
* @author James Strachan
* @author Jan Sorensen
* @author Ralph Wagner
* @author Stephen Colebourne
*/
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 Object nextObject;
/** Whether the next object has been calculated yet */
private boolean nextObjectSet = false;
//-----------------------------------------------------------------------
/**
* Constructs a new <code>FilterIterator</code> that will not function
* until {@link #setIterator(Iterator) setIterator} is invoked.
*/
public FilterIterator() {
super();
}
/**
* Constructs a new <code>FilterIterator</code> that will not function
* until {@link #setPredicate(Predicate) setPredicate} is invoked.
*
* @param iterator the iterator to use
*/
public FilterIterator(Iterator iterator) {
super();
this.iterator = iterator;
}
/**
* Constructs a new <code>FilterIterator</code> that will use the
* given iterator and predicate.
*
* @param iterator the iterator to use
* @param predicate the predicate to use
*/
public FilterIterator(Iterator iterator, 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
*/
public boolean hasNext() {
if (nextObjectSet) {
return true;
} else {
return 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
*/
public Object next() {
if (!nextObjectSet) {
if (!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 <code>next()</code> was called, but not after
* <code>hasNext()</code>, because the <code>hasNext()</code> call
* changes the base iterator.
*
* @throws IllegalStateException if <code>hasNext()</code> has already
* been called.
*/
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(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(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()) {
Object object = iterator.next();
if (predicate.evaluate(object)) {
nextObject = object;
nextObjectSet = true;
return true;
}
}
return false;
}
}