hashnodelist.java

derby database source code.good for you.

/*

   Derby - Class org.apache.derby.impl.sql.compile.HashNodeList

   Copyright 1997, 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.compile;

import org.apache.derby.iapi.error.StandardException;

import org.apache.derby.iapi.services.sanity.SanityManager;

import java.util.Hashtable;
import java.util.Enumeration;


/**
 * HashNodeList is the root class for all hashlists of query tree nodes.
 * It implements the QueryTree interface that is part of the Language
 * protocols
 *
 * @author Rick Hillegas
 */


public abstract class HashNodeList extends QueryTreeNode
{
	private	Hashtable		hashtable = new Hashtable();

	/////////////////////////////////////////////////////////////////
	//
	//	HASHTABLE FORWARDS
	//
	/////////////////////////////////////////////////////////////////

	/**
	  *	Add an element to this hash list.
	  *
	  *	@param	key		hash key for new value
	  *	@param	value	new item to add to list
	  *
	  */
	public	void	add( Object key, Object value )
	{
		hashtable.put( key, value );
	}


    /**
	  *	Returns the size of the list.
	  *
	  *	@return	size of the list
	  */
    public	int	size() { return hashtable.size(); }

	/**
	  *	Get an iterator to walk this hash list
	  *
	  *	@return	an Enumeration for walking this hash list
	  */
	public	Enumeration	elements()
	{
		return	hashtable.elements();
	}


	/**
	  *	Gets an element by key
	  *
	  *	@param	key		hash key to lookup
	  *
	  *	@return	the element associated with the hash key
	  *			null if no element with that key exists
	  *
	  */
	public	Object	get( Object key )
	{
		return	hashtable.get( key );
	}


	/////////////////////////////////////////////////////////////////
	//
	//	OBJECT SUPPORT
	//
	/////////////////////////////////////////////////////////////////

	/**
	 * Convert this object to a String.  See comments in QueryTreeNode.java
	 * for how this should be done for tree printing.
	 *
	 * @return	This object as a String
	 */

	public String toString()
	{
		if (SanityManager.DEBUG)
		{
			Enumeration		iterator;
			StringBuffer	buffer = new StringBuffer("");
			Object			item;

			for (iterator = elements(); iterator.hasMoreElements() == true; )
			{
				item = iterator.nextElement();
				buffer.append(item.toString());
				buffer.append("\n");
			}

			return buffer.toString();
		}
		else
		{
			return "";
		}
	}

	/////////////////////////////////////////////////////////////////
	//
	//	QUERY TREE NODE METHODS
	//
	/////////////////////////////////////////////////////////////////

	/**
	 * Get the optimizer's cost estimate for an optimized QueryTree.
	 * For non-optimizable statements (for example, CREATE TABLE),
	 * return null.  For optimizable statements, this method will be
	 * over-ridden in the statement's root node (DMLStatementNode in
	 * all cases we know about so far).
	 *
	 * @return	null
	 */
	// public CostEstimate	getCostEstimate()
	// {
		// return null;
	// }

	/**
	 * Returns whether or not this Statement requires a set/clear savepoint
	 * around its execution.  The following statement "types" do not require them:
	 *		Cursor	- unnecessary and won't work in a read only environment
	 *		Xact	- savepoint will get blown away underneath us during commit/rollback
	 *
	 * @return boolean	Whether or not this Statement requires a set/clear savepoint
	 */
	public boolean needsSavepoint()
	{
		if (SanityManager.DEBUG)
		{
			SanityManager.ASSERT(false,
				"needsSavepoint() not expected to be called.");
		}
		return false;
	}
}