bitstreamdispatcher.java

dspace 用j2ee架构的一个数字图书馆.开源程序

/*
 * Copyright (c) 2004-2005, Hewlett-Packard Company and Massachusetts
 * Institute of Technology.  All rights reserved.
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 * Massachusetts Institute of Technology nor the names of their
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package org.dspace.checker;


/**
 * <p>
 * BitstreamDispatchers are strategy objects that hand bitstream ids out to
 * workers. Implementations must be threadsafe.
 * </p>
 * 
 * <p>
 * The rationale behind the use of the Sentinel pattern (rather than the more
 * traditional iterator pattern or a cursor c.f. java.sql.ResultSet): -
 * </p>
 * <ol>
 * <li>To make it easy to make implementations thread safe - multithreaded
 * invocation of the dispatchers is seen as a next step use case. In simple
 * terms, this requires that a single method does all the work.</li>
 * <li>Shouldn't an exception as the sentinel, as reaching the end of a loop is
 * not an exceptional condition.</li>
 * </ol>
 * 
 * 
 * @author Jim Downing
 * @author Grace Carpenter
 * @author Nathan Sarr
 * 
 */
public interface BitstreamDispatcher
{
    /**
     * This value should be returned by <code>next()</code> to indicate that
     * there are no more values.
     */
    public static int SENTINEL = -1;

    /**
     * Returns the next id for checking, or a sentinel value if there are no
     * more to check.
     * 
     * @return the next bitstream id, or BitstreamDispatcher.SENTINEL if there
     *         isn't another value
     * 
     */
    public int next();
}