/*
 * The Apache Software License, Version 1.1
 *
 *
 * Copyright (c) 1999-2003 The Apache Software Foundation.  All rights 
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer. 
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:  
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Xalan" and "Apache Software Foundation" must
 *    not be used to endorse or promote products derived from this
 *    software without prior written permission. For written 
 *    permission, please contact apache@apache.org.
 *
 * 5. Products derived from this software may not be called "Apache",
 *    nor may "Apache" appear in their name, without prior written
 *    permission of the Apache Software Foundation.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation and was
 * originally based on software copyright (c) 1999, Lotus
 * Development Corporation., http://www.lotus.com.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 */
package org.apache.xml.utils;

import java.util.*;

import org.apache.xml.res.XMLErrorResources;
import org.apache.xml.res.XMLMessages;


/**
 * <meta name="usage" content="internal"/>
 * Pool of object of a given type to pick from to help memory usage
 */
public class ObjectPool implements java.io.Serializable
{

  /** Type of objects in this pool.
   *  @serial          */
  private final Class objectType;

  /** Vector of given objects this points to.
   *  @serial          */
  private final Vector freeStack;

  /**
   * Constructor ObjectPool
   *
   * @param type Type of objects for this pool
   */
  public ObjectPool(Class type)
  {
    objectType = type;
    freeStack = new Vector();
  }
  
  /**
   * Constructor ObjectPool
   *
   * @param className Fully qualified name of the type of objects for this pool.
   */
  public ObjectPool(String className)
  {
    try
    {
      objectType = Class.forName(className);
    }
    catch(ClassNotFoundException cnfe)
    {
      throw new WrappedRuntimeException(cnfe);
    }
    freeStack = new Vector();
  }


  /**
   * Constructor ObjectPool
   *
   *
   * @param type Type of objects for this pool
   * @param size Size of vector to allocate
   */
  public ObjectPool(Class type, int size)
  {
    objectType = type;
    freeStack = new Vector(size);
  }

  /**
   * Constructor ObjectPool
   *
   */
  public ObjectPool()
  {
    objectType = null;
    freeStack = new Vector();
  }

  /**
   * Get an instance of the given object in this pool if available
   *
   *
   * @return an instance of the given object if available or null
   */
  public synchronized Object getInstanceIfFree()
  {

    // Check if the pool is empty.
    if (!freeStack.isEmpty())
    {

      // Remove object from end of free pool.
      Object result = freeStack.lastElement();

      freeStack.setSize(freeStack.size() - 1);

      return result;
    }

    return null;
  }

  /**
   * Get an instance of the given object in this pool 
   *
   *
   * @return An instance of the given object
   */
  public synchronized Object getInstance()
  {

    // Check if the pool is empty.
    if (freeStack.isEmpty())
    {

      // Create a new object if so.
      try
      {
        return objectType.newInstance();
      }
      catch (InstantiationException ex){}
      catch (IllegalAccessException ex){}

      // Throw unchecked exception for error in pool configuration.
      throw new RuntimeException(XMLMessages.createXMLMessage(XMLErrorResources.ER_EXCEPTION_CREATING_POOL, null)); //"exception creating new instance for pool");
    }
    else
    {

      // Remove object from end of free pool.
      Object result = freeStack.lastElement();

      freeStack.setSize(freeStack.size() - 1);

      return result;
    }
  }

  /**
   * Add an instance of the given object to the pool  
   *
   *
   * @param obj Object to add.
   */
  public synchronized void freeInstance(Object obj)
  {

    // Make sure the object is of the correct type.
    // Remove safety.  -sb
    // if (objectType.isInstance(obj))
    // {
    freeStack.addElement(obj);
    // }
    // else
    // {
    //  throw new IllegalArgumentException("argument type invalid for pool");
    // }
  }
}