maxminaggregator.java

derby database source code.good for you.

/*

   Derby - Class org.apache.derby.impl.sql.execute.MaxMinAggregator

   Copyright 2001, 2004 The Apache Software Foundation or its licensors, as applicable.

   Licensed 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.derby.impl.sql.execute;

import org.apache.derby.iapi.services.sanity.SanityManager;
import org.apache.derby.iapi.types.DataValueDescriptor;
import org.apache.derby.iapi.error.StandardException;

import org.apache.derby.iapi.sql.execute.ExecAggregator;
import org.apache.derby.iapi.services.io.StoredFormatIds;
import java.io.ObjectOutput;
import java.io.ObjectInput;
import java.io.IOException;

/**
 * Aggregator for MAX()/MIN().  Defers most of its work
 * to OrderableAggregator.
 *
 * @see OrderableAggregator
 *
 * @author jamie
 */
public final class MaxMinAggregator 
	extends OrderableAggregator
{

	private boolean isMax; // true for max, false for min

	/**
	 */
	public void setup(String aggregateName)
	{
		super.setup(aggregateName);
		isMax = aggregateName.equals("MAX");
	}
	/**
	 * Accumulate
 	 *
	 * @param addend	value to be added in
	 *
	 * @exception StandardException on error
	 *
	 */
	protected void accumulate(DataValueDescriptor addend) 
		throws StandardException
	{
		if ( (value == null) ||
			      (isMax && (value.compare(addend) < 0)) ||
				  (!isMax && (value.compare(addend) > 0))
				  )
		{
			/* NOTE: We need to call getClone() since value gets
			 * reused underneath us
			 */
			value = addend.getClone();
		}
	}

	/**
	 * @return ExecAggregator the new aggregator
	 */
	public ExecAggregator newAggregator()
	{
		MaxMinAggregator ma = new MaxMinAggregator();
		ma.isMax = isMax;
		return ma;
	}

	/////////////////////////////////////////////////////////////
	// 
	// FORMATABLE INTERFACE
	// 
	/////////////////////////////////////////////////////////////
	public void writeExternal(ObjectOutput out) throws IOException
	{
		super.writeExternal(out);
		out.writeBoolean(isMax);
	}

	/** 
	 * @see java.io.Externalizable#readExternal 
	 *
	 * @exception IOException on error
	 * @exception ClassNotFoundException on error
	 */
	public void readExternal(ObjectInput in) 
		throws IOException, ClassNotFoundException {
		super.readExternal(in);
		isMax = in.readBoolean();
	}
	/**
	 * Get the formatID which corresponds to this class.
	 *
	 *	@return	the formatID of this class
	 */
	public	int	getTypeFormatId()	{ return StoredFormatIds.AGG_MAX_MIN_V01_ID; }
}