/**************************************************************************************
* 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;
import com.espertech.esper.collection.RefCountedSet;
import com.espertech.esper.epl.agg.AggregationMethod;
import com.espertech.esper.epl.core.MethodResolutionService;
/**
* AggregationMethod for use on top of another aggregator that handles unique value aggregation (versus all-value aggregation)
* for the underlying aggregator.
*/
public class DistinctValueAggregator implements AggregationMethod
{
private final AggregationMethod inner;
private final Class childType;
private final RefCountedSet<Object> valueSet;
/**
* Ctor.
* @param inner is the aggregator function computing aggregation values
* @param childType is the return type of the inner expression to aggregate, if any
*/
public DistinctValueAggregator(AggregationMethod inner, Class childType)
{
this.inner = inner;
this.childType = childType;
this.valueSet = new RefCountedSet<Object>();
}
public void clear()
{
valueSet.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();
}
public AggregationMethod newAggregator(MethodResolutionService methodResolutionService)
{
AggregationMethod innerCopy = inner.newAggregator(methodResolutionService);
return methodResolutionService.makeDistinctAggregator(innerCopy, childType, false);
}
}