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/*
Derby - Class org.apache.derbyTesting.functionTests.tests.lang.ModeAggregate
Licensed to the Apache Software Foundation (ASF) under one or more
contributor license agreements. See the NOTICE file distributed with
this work for additional information regarding copyright ownership.
The ASF licenses this file to you under the Apache License, Version 2.0
(the "License"); you may not use this file except in compliance with
the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
package org.apache.derbyTesting.functionTests.tests.lang;
import java.io.Serializable;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import org.apache.derby.agg.Aggregator;
/**
* <p>
* This is a mode aggregator for ints.
* </p>
*/
public class ModeAggregate implements Aggregator<Integer,Integer,ModeAggregate>
{
///////////////////////////////////////////////////////////////////////////////////
//
// STATE
//
///////////////////////////////////////////////////////////////////////////////////
private HashMap<Integer,Accumulator> _accumulators;
///////////////////////////////////////////////////////////////////////////////////
//
// CONSTRUCTOR
//
///////////////////////////////////////////////////////////////////////////////////
public ModeAggregate() {}
public void init()
{
_accumulators = new HashMap<Integer,Accumulator>();
}
public void accumulate( Integer value )
{
getAccumulator( value ).add( 1 );
}
public void merge( ModeAggregate otherAggregator )
{
HashMap<Integer,Accumulator> otherAccumulators = otherAggregator._accumulators;
for ( Integer value : otherAccumulators.keySet() )
{
getAccumulator( value ).add( otherAccumulators.get( value ).getCount() );
}
}
public Integer terminate()
{
return _accumulators.isEmpty() ? null : Collections.max( _accumulators.values() ).getValue();
}
private Accumulator getAccumulator( Integer value )
{
Accumulator retval = _accumulators.get( value );
if ( retval == null )
{
retval = new Accumulator( value );
_accumulators.put( value, retval );
}
return retval;
}
///////////////////////////////////////////////////////////////////////////////////
//
// NESTED CLASSES
//
///////////////////////////////////////////////////////////////////////////////////
public static final class Accumulator implements Comparable<Accumulator>, Serializable
{
private Integer _value;
private int _count;
public Accumulator( Integer value )
{
_value = value;
_count = 0;
}
public void add( int increment ) { _count += increment; }
public Integer getValue() { return _value; }
public int getCount() { return _count; }
// Comparable behavior
public int compareTo( Accumulator that )
{
int retval = this._count - that._count;
if ( retval != 0 ) { return retval; }
else { return this._value.intValue() - that._value.intValue(); }
}
}
}
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