code: /*
   * 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.
   */
  /*
   * $Id$
   */
  package org.apache.xpath.axes;
  
  import java.util.ArrayList;
  
  import org.apache.xml.dtm.DTMIterator;
  import org.apache.xml.utils.WrappedRuntimeException;
  
  /**
   * Pool of object of a given type to pick from to help memory usage
   * @xsl.usage internal
   */
  public final class IteratorPool implements java.io.Serializable
  {
      static final long serialVersionUID = -460927331149566998L;
  
    /** 
     * Type of objects in this pool.
     */
    private final DTMIterator m_orig;
  
    /** 
     * Stack of given objects this points to.
     */
    private final ArrayList m_freeStack;
  
    /**
     * Constructor IteratorPool
     *
     * @param original The original iterator from which all others will be cloned.
     */
    public IteratorPool(DTMIterator original)
    {
      m_orig = original;
      m_freeStack = new ArrayList();
    }
    
    /**
     * Get an instance of the given object in this pool 
     *
     * @return An instance of the given object
     */
    public synchronized DTMIterator getInstanceOrThrow()
      throws CloneNotSupportedException
    {
      // Check if the pool is empty.
      if (m_freeStack.isEmpty())
      {
  
        // Create a new object if so.
        return (DTMIterator)m_orig.clone();
      }
      else
      {
        // Remove object from end of free pool.
        DTMIterator result = (DTMIterator)m_freeStack.remove(m_freeStack.size() - 1);
        return result;
      }
    }
    
    /**
     * Get an instance of the given object in this pool 
     *
     * @return An instance of the given object
     */
    public synchronized DTMIterator getInstance()
    {
      // Check if the pool is empty.
      if (m_freeStack.isEmpty())
      {
  
        // Create a new object if so.
        try
        {
          return (DTMIterator)m_orig.clone();
        }
        catch (Exception ex)
        {
          throw new WrappedRuntimeException(ex);
        }
      }
      else
      {
        // Remove object from end of free pool.
        DTMIterator result = (DTMIterator)m_freeStack.remove(m_freeStack.size() - 1);
        return result;
      }
    }
  
    /**
     * Add an instance of the given object to the pool  
     *
     *
     * @param obj Object to add.
     */
    public synchronized void freeInstance(DTMIterator obj)
    {
      m_freeStack.add(obj);
    }
  }
  