/*
***************************************************************************************
* Copyright (C) 2006 EsperTech, Inc. All rights reserved. *
* http://www.espertech.com/esper *
* 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;
/**
* Maintains aggregation state applying values as entering and leaving the state.
* <P>Implementations must also act as a factory for further independent copies of aggregation states such that
* new aggregation state holders and be created from a prototype.
*/
public interface AggregationMethod {
/**
* Apply the value as entering aggregation (entering window).
* <p>The value can be null since 'null' values may be counted as unique separate values.
*
* @param value to add to aggregate
*/
public void enter(Object value);
/**
* Apply the value as leaving aggregation (leaving window).
* <p>The value can be null since 'null' values may be counted as unique separate values.
*
* @param value to remove from aggregate
*/
public void leave(Object value);
/**
* Returns the current value held.
*
* @return current value
*/
public Object getValue();
/**
* Clear out the collection.
*/
public void clear();
}