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/* ====================================================================
 * 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].
 *
 * 5. Products derived from this software may not be called "Apache"
 *    nor may "Apache" appear in their names without prior written
 *    permission of the Apache Software Foundation.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
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 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * 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;
    }
}




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