avg.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.aggregationfunctions;

/*
 * 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 java.math.*;
import org.mandarax.kernel.VariableTerm;
import org.mandarax.util.resultsetfilters.AggregationException;
import org.mandarax.util.resultsetfilters.AggregationFunction;
 
/**
 * AVG function.
 * @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 class AVG extends AbstractAggregationFunction {
	private static Class[] supportedTypes = {
		Integer.class,
		Double.class,
		Float.class,
		Long.class,
		Short.class,
		BigInteger.class,
		BigDecimal.class	
	};
	/**
	 * Constructor.
	 * @param var the variable
	 */
	public AVG(VariableTerm var) throws AggregationException {
		super(var);
	}
	/**
	 * Get the name of this function.
	 * @return a name
	 */
	public String getName() {
		return "AVG";
	}
	/**
	 * Get an array of supported types.
	 * @return an array of types
	 */
	protected Class[] getSupportedTypes() {
		return supportedTypes;
	}
	/**
	 * Compute the aggregated value.
	 * @return the computed object
	 */
	protected Object compute() throws AggregationException {
		try {
			if (type==Integer.class) {
				int sum = 0;
				for (int i=0;i<getNumberOfValues();i++) sum = sum+getValueAsInt(i);
				return new Integer(sum/getNumberOfValues());
			}
			if (type==Double.class) {
				double sum = 0;
				for (int i=0;i<getNumberOfValues();i++) sum = sum+getValueAsDouble(i);
				return new Double(sum/getNumberOfValues());
			}
			if (type==Float.class) {
				float sum = 0;
				for (int i=0;i<getNumberOfValues();i++) sum = sum+getValueAsFloat(i);
				return new Float(sum/getNumberOfValues());
			}
			if (type==Short.class) {
				int sum = 0;
				for (int i=0;i<getNumberOfValues();i++) sum = sum+this.getValueAsShort(i);
				return new Integer(sum/getNumberOfValues());
			}
			if (type==Long.class) {
				long sum = 0;
				for (int i=0;i<getNumberOfValues();i++) sum = sum+this.getValueAsLong(i);
				return new Long(sum/getNumberOfValues());
			}
			if (type==BigInteger.class) {
				BigInteger sum = BigInteger.ZERO;
				for (int i=0;i<getNumberOfValues();i++) sum = sum.add(getValueAsBigInteger(i));
				return sum.divide(BigInteger.valueOf(getNumberOfValues()));
			}
			if (type==BigDecimal.class) {
				BigDecimal sum = BigDecimal.valueOf(0);
				for (int i=0;i<getNumberOfValues();i++) sum = sum.add(getValueAsBigDecimal(i));
				return sum.divide(BigDecimal.valueOf(getNumberOfValues()),BigDecimal.ROUND_HALF_EVEN);
			}

		}
		catch (Throwable x) {
			throw new AggregationException("Error computing aggregated value",x);
		}
		throw new AggregationException("Cannot compute value - unsupported type");
	}
	/**
	 * Copy this function (get a newly initialized instance of this class).
	 * @return a function
	 */
	public AggregationFunction copy() throws AggregationException {
		return new AVG(var);
	}

}