net.jxta.impl.util.SequenceIterator Maven / Gradle / Ivy

/*
 * Copyright (c) 2002-2007 Sun Microsystems, Inc.  All rights reserved.
 *  
 *  The Sun Project JXTA(TM) Software License
 *  
 *  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 acknowledgment: "This product includes software 
 *     developed by Sun Microsystems, Inc. for JXTA(TM) technology." 
 *     Alternately, this acknowledgment may appear in the software itself, if 
 *     and wherever such third-party acknowledgments normally appear.
 *  
 *  4. The names "Sun", "Sun Microsystems, Inc.", "JXTA" and "Project JXTA" must 
 *     not be used to endorse or promote products derived from this software 
 *     without prior written permission. For written permission, please contact 
 *     Project JXTA at http://www.jxta.org.
 *  
 *  5. Products derived from this software may not be called "JXTA", nor may 
 *     "JXTA" appear in their name, without prior written permission of Sun.
 *  
 *  THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES,
 *  INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND 
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 *  
 *  JXTA is a registered trademark of Sun Microsystems, Inc. in the United 
 *  States and other countries.
 *  
 *  Please see the license information page at :
 *   for instructions on use of 
 *  the license in source files.
 *  
 *  ====================================================================
 *  
 *  This software consists of voluntary contributions made by many individuals 
 *  on behalf of Project JXTA. For more information on Project JXTA, please see 
 *  http://www.jxta.org.
 *  
 *  This license is based on the BSD license adopted by the Apache Foundation. 
 */

package net.jxta.impl.util;


import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

import java.util.NoSuchElementException;


/**
 *  This class lets you combine a number of iterators.
 */
public class SequenceIterator implements Iterator {
    
    private Iterator iterators;
    
    private Iterator current = null;
    
    private Iterator previous = null;
    
    /**
     * Creates a new instance of SequenceIterator
     *
     * @param iterators An iterator containing instances of Iterator. This
     * iterator will iterate over all of the item in these iterators.
     **/
    public SequenceIterator(Iterator iterators) {
        this.iterators = iterators;
    }
    
    /**
     * Creates a new instance of SequenceIterator
     **/
    public SequenceIterator(Iterator first, Iterator second) {
        List iterators = new ArrayList(2);
        
        iterators.add(first);
        iterators.add(second);
        
        this.iterators = iterators.iterator();
    }
    
    /**
     *  {@inheritDoc}
     **/
    public boolean hasNext() {
        
        if ((null == current) || (!current.hasNext())) {
            do {
                if (!iterators.hasNext()) {
                    return false;
                }
                
                current = (Iterator) iterators.next();
            } while (!current.hasNext());
        }
        
        return true;
    }
    
    /**
     *  {@inheritDoc}
     **/
    public Object next() {
        if (!hasNext()) {
            throw new NoSuchElementException("no next element");
        }

        previous = current;
        return current.next();
    }
    
    /**
     *  {@inheritDoc}
     **/
    public void remove() {
        if (null == previous) {
            throw new IllegalStateException("next() has not been called");
        }
        
        previous.remove();
        previous = null;
    }
}