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.xml.serializer;
  
  /**
   * This class is a stack frame that consists of 
   * information about the element currently being processed 
   * by a serializer. Consider this example:
   * <pre>
   *   <A>
   *     <B1>
   *     </B1>
   *     <B2>
   *     </B2>
   *   <A>
   * </pre> 
   * 
   * A stack frame will be pushed for "A" at depth 1, 
   * then another one for "B1" at depth 2.
   * Then "B1" stackframe is popped.  When the stack frame for "B2" is 
   * pushed, this implementation re-uses the old stack fram object used
   * by "B1" to be efficient at not creating too many of these object.
   * 
   * This is by no means a public class, and neither are its fields or methods,
   * they are all helper fields for a serializer.
   * 
   * The purpose of this class is to be more consistent with pushing information
   * when a new element is being serialized and more quickly restoring the old
   * information about the parent element with a simple pop() when the
   * child element is done.  Previously there was some redundant and error-prone
   * calculations going on to retore information.
   * 
   * @xsl.usage internal
   */
  final class ElemContext
  {
      // Fields that form the context of the element
  
      /**
       * The nesting depth of the element inside other elements.
       */
      final int m_currentElemDepth;
  
      /** HTML field, the element description of the HTML element */
      ElemDesc m_elementDesc = null;
  
      /**
       * The local name of the element.
       */
      String m_elementLocalName = null;
  
      /**
       * The fully qualified name of the element (with prefix, if any).
       */
      String m_elementName = null;
  
      /**
       * The URI of the element.
       * If this value is null it means that the URI is not yet determined
       * for the element. Valid values are the empty string "", meaning
       * that it is in no namespace, or a string of non-zero length.
       */
      String m_elementURI = null;
  
      /** If the element is in the cdata-section-names list
       * then the value is true. If it is true the text children of the element
       * should be output in CDATA section blocks. 
       */
      boolean m_isCdataSection;
  
      /** True if the current element has output escaping disabled.
       * This is true for SCRIPT and STYLE elements. 
       */
      boolean m_isRaw = false;
  
      /** The next element "stack frame". This value will only be
       * set once as deeper stack frames are not deleted when popped off,
       * but are rather re-used when a push is required.
       * 
       * This makes for very fast pushing and popping of stack frames 
       * because very few stack frame objects are ever created, they are
       * mostly re-used.  This re-use saves object creation but it also means
       * that connections between the frames via m_next and m_prev
       * never changes either. Just the contents of the frames change
       * as they are re-used. Only the reference to the current stack frame, which
       * is held by the serializer is changed via a quick pop() or push().
       */
      private ElemContext m_next;
  
      /** The previous element "stack frame". */
      final ElemContext m_prev;
  
      /**
       * Set to true when a start tag is started, or open, but not all the
       * attributes or namespace information is yet collected.
       */
      boolean m_startTagOpen = false;
  
      /**
       * Constructor to create the root of the element contexts. 
       *
       */
      ElemContext()
      {
          // this assignment means can never pop this context off
          m_prev = this;
          // depth 0 because it doesn't correspond to any element
          m_currentElemDepth = 0;
      }
  
      /**
       * Constructor to create the "stack frame" for a given element depth.
       * 
       * This implementation will re-use the context at each depth. If
       * a documents deepest element depth is N then there will be (N+1)
       * such objects created, no more than that.
       * 
       * @param previous The "stack frame" corresponding to the new
       * elements parent element.
       */
      private ElemContext(final ElemContext previous)
      {
          m_prev = previous;
          m_currentElemDepth = previous.m_currentElemDepth + 1;
      }
  
      /**
       * Pop the current "stack frame".
       * @return Returns the parent "stack frame" of the one popped.
       */
      final ElemContext pop()
      {
          /* a very simple pop.  No clean up is done of the deeper
           * stack frame.  All deeper stack frames are still attached
           * but dormant, just waiting to be re-used.
           */
          return this.m_prev;
      }
  
      /**
       * This method pushes an element "stack frame" 
       * but with no initialization of values in that frame.
       * This method is used for optimization purposes, like when pushing
       * a stack frame for an HTML "IMG" tag which has no children and
       * the stack frame will almost immediately be popped.
       */
      final ElemContext push()
      {
          ElemContext frame = this.m_next;
          if (frame == null)
          {
              /* We have never been at this depth yet, and there is no
               * stack frame to re-use, so we now make a new one.
               */
              frame = new ElemContext(this);
              this.m_next = frame;
          }
          /*
           * We shouldn't need to set this true because we should just
           * be pushing a dummy stack frame that will be instantly popped.
           * Yet we need to be ready in case this element does have
           * unexpected children.
           */
          frame.m_startTagOpen = true;
          return frame;
      }
      
      /**
       * Push an element context on the stack. This context keeps track of
       * information gathered about the element.
       * @param uri The URI for the namespace for the element name, 
       * can be null if it is not yet known.
       * @param localName The local name of the element (no prefix),  
       * can be null.
       * @param qName The qualified name (with prefix, if any) 
       * of the element, this parameter is required.
       */
      final ElemContext push(
          final String uri,
          final String localName,
          final String qName)
      {
          ElemContext frame = this.m_next;
          if (frame == null)
          {
              /* We have never been at this depth yet, and there is no
               * stack frame to re-use, so we now make a new one.
               */
              frame = new ElemContext(this);
              this.m_next = frame;
          }
  
          // Initialize, or reset values in the new or re-used stack frame.
          frame.m_elementName = qName;
          frame.m_elementLocalName = localName;
          frame.m_elementURI = uri;
          frame.m_isCdataSection = false;
          frame.m_startTagOpen = true;
  
          // is_Raw is already set in the HTML startElement() method
          // frame.m_isRaw = false; 
          return frame;
      }
  }
  