AggregatorDistinctValue.java

/**************************************************************************************
 * Copyright (C) 2008 EsperTech, Inc. All rights reserved.                            *
 * http://esper.codehaus.org                                                          *
 * http://www.espertech.com                                                           *
 * ---------------------------------------------------------------------------------- *
 * The software in this package is published under the terms of the GPL license       *
 * a copy of which has been included with this distribution in the license.txt file.  *
 **************************************************************************************/
package com.espertech.esper.epl.agg.aggregator;

import com.espertech.esper.collection.RefCountedSet;

/**
 * AggregationMethod for use on top of another aggregator that handles unique value aggregation (versus all-value aggregation)
 * for the underlying aggregator.
 */
public class AggregatorDistinctValue implements AggregationMethod
{
    protected final AggregationMethod inner;
    protected final RefCountedSet<Object> valueSet;

    /**
     * Ctor.
     * @param inner is the aggregator function computing aggregation values
     */
    public AggregatorDistinctValue(AggregationMethod inner)
    {
        this.inner = inner;
        this.valueSet = new RefCountedSet<Object>();
    }

    public void clear()
    {
        valueSet.clear();
        inner.clear();
    }

    public void enter(Object value)
    {
        // if value not already encountered, enter into aggregate
        if (valueSet.add(value))
        {
            inner.enter(value);
        }
    }

    public void leave(Object value)
    {
        // if last reference to the value is removed, remove from aggregate
        if (valueSet.remove(value))
        {
            inner.leave(value);
        }
    }

    public Object getValue()
    {
        return inner.getValue();
    }

    public Class getValueType()
    {
        return inner.getValueType();
    }
}