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Types that extend and augment the Java Collections Framework.
/* ====================================================================
* The Apache Software License, Version 1.1
*
* Copyright (c) 1999-2004 The Apache Software Foundation. All rights
* reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* 3. The end-user documentation included with the redistribution, if
* any, must include the following acknowledgement:
* "This product includes software developed by the
* Apache Software Foundation (http://www.apache.org/)."
* Alternately, this acknowledgement may appear in the software itself,
* if and wherever such third-party acknowledgements normally appear.
*
* 4. The names "The Jakarta Project", "Commons", and "Apache Software
* Foundation" must not be used to endorse or promote products derived
* from this software without prior written permission. For written
* permission, please contact [email protected].
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* SUCH DAMAGE.
* ====================================================================
*
* This software consists of voluntary contributions made by many
* individuals on behalf of the Apache Software Foundation. For more
* information on the Apache Software Foundation, please see
* .
*/
package org.apache.commons.collections.iterators;
import java.util.Iterator;
import java.util.NoSuchElementException;
import org.apache.commons.collections.Predicate;
/**
* Decorates an iterator such that only elements matching a predicate filter
* are returned.
*
* @since Commons Collections 1.0
* @version $Revision: 1.7 $ $Date: 2004/01/14 21:43:15 $
*
* @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 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(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(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
*/
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 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 next()
was called, but not after
* hasNext()
, because the hasNext()
call
* changes the base iterator.
*
* @throws IllegalStateException if hasNext()
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;
}
//-----------------------------------------------------------------------
/**
* 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(Predicate predicate) {
this.predicate = predicate;
}
//-----------------------------------------------------------------------
/**
* 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;
}
}