001/**
002 * This class is based on the Iterators.FilterIterator class from
003 * araSpect (araspect.sourceforge.net).  The original copyright follows ...
004 *
005 * =================================================================
006 * Copyright (c) 2001,2002 aragost ag, Z�rich, Switzerland.
007 * All rights reserved.
008 *
009 * This software is provided 'as-is', without any express or implied
010 * warranty. In no event will the authors be held liable for any
011 * damages arising from the use of this software.
012 *
013 * Permission is granted to anyone to use this software for any
014 * purpose, including commercial applications, and to alter it and
015 * redistribute it freely, subject to the following restrictions:
016 *
017 * 1. The origin of this software must not be misrepresented; you
018 *    must not claim that you wrote the original software. If you
019 *    use this software in a product, an acknowledgment in the
020 *    product documentation would be appreciated but is not required.
021 *
022 * 2. Altered source versions must be plainly marked as such, and
023 *    must not be misrepresented as being the original software.
024 *
025 * 3. This notice may not be removed or altered from any source
026 *    distribution.
027 *
028 * ==================================================================
029 *
030 * Changes (c) 2003 University Health Network include the following:
031 * - move to non-nested class
032 * - collapse inherited method remove()
033 * - accept iterator instead of object in constructor
034 * - moved to HAPI package
035 * - Predicate added as an inner class; also changed to an interface
036 *
037 * These changes are distributed under the same terms as the original (above). 
038 */
039package ca.uhn.hl7v2.util;
040
041import java.util.*;
042
043public class FilterIterator<T> implements Iterator<T> {
044    
045    private Predicate<T> predicate;
046    private Iterator<T> iter;
047    private T nextObject;
048    private boolean nextObjectSet = false;
049    
050    public FilterIterator(Iterator<T> iter, Predicate<T> predicate) {
051        this.iter = iter;
052        this.predicate = predicate;
053    }
054    
055    public boolean hasNext() {
056        if (nextObjectSet) {
057            return true;
058        } else {
059            return setNextObject();
060        }
061    }
062    
063    public T next() {
064        if (!nextObjectSet) {
065            if (!setNextObject()) {
066                throw new NoSuchElementException();
067            }
068        }
069        nextObjectSet = false;
070        return nextObject;
071    }
072    
073    /**
074     * Set nextObject to the next object. If there are no more
075     * objects then return false. Otherwise, return true.
076     */
077    private boolean setNextObject() {
078        while (iter.hasNext()) {
079            T object = iter.next();
080            if (predicate.evaluate(object)) {
081                nextObject = object;
082                nextObjectSet = true;
083                return true;
084            }
085        }
086        return false;
087    }
088    
089    /** Throws UnsupportedOperationException */
090    public void remove() {
091        throw new UnsupportedOperationException();
092    }
093    
094    /**
095     * Interface for evaluating whether an object should be returned by the iterator
096     */
097    public interface Predicate<T> {
098        public boolean evaluate(T obj);
099    }
100    
101}