TotalMin.java from BIRT at Krugle

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/*
 *************************************************************************
 * Copyright (c) 2004 Actuate Corporation.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *  Actuate Corporation  - initial API and implementation
 *  
 *************************************************************************
 */
package org.eclipse.birt.data.engine.aggregation;

import org.eclipse.birt.data.engine.api.aggregation.Accumulator;
import org.eclipse.birt.data.engine.api.aggregation.IAggregation;

/**
 * 
 * Implements the built-in Total.min aggregation
 */
public class TotalMin implements IAggregation
{

    /*
     * (non-Javadoc)
     * 
     * @see org.eclipse.birt.data.engine.aggregation.Aggregation#getName()
     */
    public String getName()
    {
        return BuiltInAggregationFactory.TOTAL_MIN_FUNC;
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.eclipse.birt.data.engine.aggregation.Aggregation#getType()
     */
    public int getType()
    {
        return SUMMARY_AGGR;
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.eclipse.birt.data.engine.aggregation.Aggregation#getParameterDefn()
     */
    public boolean[] getParameterDefn()
    {
        return new boolean[] { true };
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.eclipse.birt.data.engine.aggregation.Aggregation#newAccumulator()
     */
    public Accumulator newAccumulator()
    {
        return new MyAccumulator();
    }

    private class MyAccumulator extends SummaryAccumulator
    {
        private Object min = null;

        public void start()
        {
            super.start();
            min = null;
        }

        /*
         * (non-Javadoc)
         * 
         * @see org.eclipse.birt.data.engine.aggregation.Accumulator#onRow(java.lang.Object[])
         */
        public void onRow(Object[] args)
        {
            assert (args.length > 0);
            if (args[0] != null)
            {
                if (min==null)
                {
                    min = args[0];
                }
                if (isLessThan(args[0],min))
                {
                    min = args[0];
                }
            }

        }
        
        private boolean isLessThan(Object origin, Object target)
        {
            if((origin instanceof Comparable)&&(target instanceof Comparable))
            {
                return ((Comparable)origin).compareTo(target)<0;
            }
            else
            {
                throw new RuntimeException("can't get max value!");
            }
        }

        /*
         * (non-Javadoc)
         * 
         * @see org.eclipse.birt.data.engine.aggregation.SummaryAccumulator#getSummaryValue()
         */
        public Object getSummaryValue()
        {
            return min;
        }

    }
}
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