peerviewsequentialstrategy.java

jxta_src_2.41b jxta 2.41b 最新版源码 from www.jxta.org

/*
 * Copyright (c) 2002-2004 Sun Microsystems, Inc.  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 acknowledgment:
 *       "This product includes software developed by the
 *       Sun Microsystems, Inc. for Project JXTA."
 *    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 FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL SUN MICROSYSTEMS OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * 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 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.
 *
 * $Id: PeerViewSequentialStrategy.java,v 1.5 2004/05/18 19:22:11 bondolo Exp $
 */
package net.jxta.impl.rendezvous.rpv;


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


/**
 * Sequential
 */
class PeerViewSequentialStrategy implements PeerViewStrategy {
    
    private SortedSet set;
    private PeerViewElement current;
    
    PeerViewSequentialStrategy(SortedSet aset) {
        set = aset;
        reset();
    }
    
    /**
     *  {@inheritDoc}
     **/
    public void reset() {
        current = null;
    }
    
    /**
     *  {@inheritDoc}
     **/
    public PeerViewElement next() {
                    
        synchronized (set) {
            do {
                if (null == current) {
                    if (set.size() > 0) {
                        // no current, take the first
                        current = (PeerViewElement) set.first();
                        break;
                    } else {
                        // no first, return null
                        break;
                    }
                } else {
                    SortedSet tail = set.tailSet(current);

                    Iterator fromTail = tail.iterator();
                    
                    if (fromTail.hasNext()) {
                        Comparable tailFirst = (Comparable) 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;
                                continue;
                            }
                        } 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;
                        continue;
                    }
                }
            } while (null == current);
        }
        
        return current;
    }
}