functionstatefulcounter.java

来自「High performance DB query」· Java 代码 · 共 74 行

/*
 * @(#)$Id: FunctionStatefulcounter.java,v 1.5 2004/07/02 23:59:21 huebsch Exp $
 *
 * Copyright (c) 2001-2004 Regents of the University of California.
 * All rights reserved.
 *
 * This file is distributed under the terms in the attached BERKELEY-LICENSE
 * file. If you do not find these files, copies can be found by writing to:
 * Computer Science Division, Database Group, Universite of California,
 * 617 Soda Hall #1776, Berkeley, CA 94720-1776. Attention: Berkeley License
 *
 * Copyright (c) 2003-2004 Intel Corporation. All rights reserved.
 *
 * This file is distributed under the terms in the attached INTEL-LICENSE file.
 * If you do not find these files, copies can be found by writing to:
 * Intel Research Berkeley, 2150 Shattuck Avenue, Suite 1300,
 * Berkeley, CA, 94704.  Attention:  Intel License Inquiry.
 */


package pier.helpers.functions;

/**
 * Class FunctionStatefulcounter
 *
 */
public class FunctionStatefulcounter implements Function {

    private long counter, delta;
    private boolean set = false;

    /**
     * Method evaluate
     *
     * @param parameters
     * @return
     */
    public Object evaluate(Object[] parameters) {
        int params = parameters.length;

        if ((params == 1) || (params == 2)) {

            // If the counter has not been setup yet, initialize values
            if ( !set) {
                counter = ((Long) parameters[0]).longValue();

                if (params == 2) {
                    delta = ((Long) parameters[1]).longValue();
                }

                set = true;
            }

            // Store current value
            Long result = new Long(counter);

            // Update counter
            counter += delta;

            return result;
        } else {
            return null;
        }
    }

    /**
     * Method cacheable
     * @return
     */
    public boolean cacheable() {
        return false;
    }
}