peerviewsequentialstrategy.java

JXTA&#8482 is a set of open, generalized peer-to-peer (P2P) protocols that allow any networked devi

/*
 * Copyright (c) 2002-2004 Sun Microsystems, Inc.  All rights reserved.
 *  
 *  The Sun Project JXTA(TM) Software License
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 *  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.
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 *  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.
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 *  
 *  Please see the license information page at :
 *  <http://www.jxta.org/project/www/license.html> 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.rendezvous.rpv;

import java.util.SortedSet;
import java.util.Iterator;

/**
 * Sequential
 */
class PeerViewSequentialStrategy implements PeerViewStrategy {

    private final SortedSet<PeerViewDestination> set;
    private PeerViewElement current;

    PeerViewSequentialStrategy(SortedSet<PeerViewDestination> aset) {
        set = aset;
        reset();
    }

    /**
     * {@inheritDoc}
     */
    public void reset() {
        current = null;
    }

    /**
     * {@inheritDoc}
     */
    public PeerViewElement next() {

        synchronized (set) {
            do {
                if (null == current) {
                    if (!set.isEmpty()) {
                        // no current, take the first
                        current = (PeerViewElement) set.first();
                        break;
                    } else {
                        // no first, return null
                        break;
                    }
                } else {
                    SortedSet<PeerViewDestination> tail = set.tailSet(current);

                    Iterator<PeerViewDestination> fromTail = tail.iterator();

                    if (fromTail.hasNext()) {
                        PeerViewDestination tailFirst = fromTail.next();

                        if (0 == current.compareTo(tailFirst)) {
                            if (fromTail.hasNext()) {
                                // first in tail is current so the new current
                                // is second in tail.
                                current = (PeerViewElement) fromTail.next();
                                break;
                            } else {
                                // none left in tail after current, start over.
                                current = null;
                            }
                        } else {
                            // current is not in the tail set, so first in tail
                            // is new current
                            current = (PeerViewElement) tailFirst;
                            break;
                        }
                    } else {
                        // none in tail, start over.
                        current = null;
                    }
                }
                //FIXME by hamada this does not loop, current is always null, is the intended behavior?
            } while (null == current);
        }

        return current;
    }
}