primacyconflictresolver.java

rule engine drools-2.0-beta-18

package org.drools.conflict;

/*
 * $Id: PrimacyConflictResolver.java,v 1.4 2004/11/28 05:02:38 simon Exp $
 *
 * Copyright 2001-2003 (C) The Werken Company. All Rights Reserved.
 *
 * Redistribution and use of this software and associated documentation
 * ("Software"), with or without modification, are permitted provided that the
 * following conditions are met:
 *
 * 1. Redistributions of source code must retain copyright statements and
 * notices. Redistributions must also contain a copy of this document.
 *
 * 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 name "drools" must not be used to endorse or promote products derived
 * from this Software without prior written permission of The Werken Company.
 * For written permission, please contact [e-mail].
 *
 * 4. Products derived from this Software may not be called "drools" nor may
 * "drools" appear in their names without prior written permission of The Werken
 * Company. "drools" is a trademark of The Werken Company.
 *
 * 5. Due credit should be given to The Werken Company. (http://werken.com/)
 *
 * THIS SOFTWARE IS PROVIDED BY THE WERKEN COMPANY AND CONTRIBUTORS ``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 THE WERKEN COMPANY 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
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 */

import org.drools.spi.Activation;
import org.drools.spi.ConflictResolver;
import org.drools.spi.Tuple;

/**
 * <code>ConflictResolver</code> that uses the leastRecentFactTimeStamp of
 * tuples to resolve conflict.
 *
 * @see #getInstance
 * @see Tuple#getLeastRecentFactTimeStamp
 *
 * @author <a href="mailto:[e-mail]">bob mcwhirter </a>
 * @author <a href="mailto:[e-mail]">Simon Harris </a>
 */
public class PrimacyConflictResolver extends AbstractConflictResolver
{
    // ----------------------------------------------------------------------
    // Class members
    // ----------------------------------------------------------------------

    /** Singleton instance. */
    private static final PrimacyConflictResolver INSTANCE = new PrimacyConflictResolver( );

    // ----------------------------------------------------------------------
    // Class methods
    // ----------------------------------------------------------------------

    /**
     * Retrieve the singleton instance.
     *
     * @return The singleton instance.
     */
    public static ConflictResolver getInstance()
    {
        return INSTANCE;
    }

    // ----------------------------------------------------------------------
    // Constructors
    // ----------------------------------------------------------------------

    /**
     * Construct.
     */
    public PrimacyConflictResolver()
    {
        // intentionally left blank
    }

    // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

    /**
     * @see ConflictResolver
     */
    public int compare(Activation lhs,
                       Activation rhs)
    {
        return (int) ( lhs.getTuple( ).getLeastRecentFactTimeStamp( ) - rhs.getTuple( ).getLeastRecentFactTimeStamp( ) );
    }
}