aggregationfunction.java

Mandarax是一个规则引擎的纯Java实现。它支持多类型的事实和基于反映的规则

package org.mandarax.util.resultsetfilters;

/*
 * Copyright (C) 1999-2004 <A href="http://www-ist.massey.ac.nz/JBDietrich" target="_top">Jens Dietrich</a>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

import org.mandarax.kernel.ResultSet;
import org.mandarax.kernel.VariableTerm;
 
/**
 * Interface for aggregation functions that can be used by the GROUP BY filter.
 * @author <A href="http://www-ist.massey.ac.nz/JBDietrich" target="_top">Jens Dietrich</A>
 * @version 3.4 <7 March 05>
 * @since 3.0
 */
public interface AggregationFunction {
	/**
	 * Add a value.
	 * @param rs a result set
	 */
	public void add(ResultSet rs) throws AggregationException;
	/**
	 * Set the type. This should be done before values are added.
	 * May throw an AggregationException indicating that values of this type 
	 * cannot be aggregated. 
	 * @param type a type
	 */
	public void setType(Class type) throws AggregationException ;
	/**
	 * Get the aggregated value.
	 * @return a value
	 */
	public Object getAggregatedValue() throws AggregationException;
	/**
	 * Get the name of this function.
	 * @return a name
	 */
	public String getName();
	/**
	 * Copy this function (get a newly initialized instance of this class).
	 * @return a function
	 */
	public AggregationFunction copy() throws AggregationException ;
	/**
	 * Get the result type. This type might differ from the input type (e.g. when counting records).
	 * @return the result type
	 */
	public Class getResultType();
	/**
	 * Get the variable that can be used to retrieve the value from
	 * the filtered result set.
	 * @return a variable name
	 */
	public VariableTerm getVariableInResult();


}