src/org/apache/xml/dtm/DTMIterator.java

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 * originally based on software copyright (c) 1999, Lotus
 * Development Corporation., http://www.lotus.com.  For more
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package org.apache.xml.dtm;

/**

 * <code>DTMIterators</code> are used to step through a (possibly
 * filtered) set of nodes.  Their API is modeled largely after the DOM
 * NodeIterator.
 * 
 * <p>A DTMIterator is a somewhat unusual type of iterator, in that it 
 * can serve both single node iteration and random access.</p>
 * 
 * <p>The DTMIterator's traversal semantics, i.e. how it walks the tree,
 * are specified when it is created, possibly and probably by an XPath
 * <a href="http://www.w3.org/TR/xpath#NT-LocationPath>LocationPath</a> or 
 * a <a href="http://www.w3.org/TR/xpath#NT-UnionExpr">UnionExpr</a>.</p>
 * 
 * <p>A DTMIterator is meant to be created once as a master static object, and 
 * then cloned many times for runtime use.  Or the master object itself may 
 * be used for simpler use cases.</p>
 *
 * <p>At this time, we do not expect DTMIterator to emulate
 * NodeIterator's "maintain relative position" semantics under
 * document mutation.  It's likely to respond more like the
 * TreeWalker's "current node" semantics. However, since the base DTM
 * is immutable, this issue currently makes no practical
 * difference.</p>
 *
 * <p>State: In progress!!</p> */
public interface DTMIterator
{

  // Constants returned by acceptNode, borrowed from the DOM Traversal chapter
  // %REVIEW% Should we explicitly initialize them from, eg,
  // org.w3c.dom.traversal.NodeFilter.FILTER_ACCEPT?

  /**
   * Accept the node.
   */
  public static final short FILTER_ACCEPT = 1;

  /**
   * Reject the node. Same behavior as FILTER_SKIP. (In the DOM these
   * differ when applied to a TreeWalker but have the same result when
   * applied to a NodeIterator).
   */
  public static final short FILTER_REJECT = 2;

  /**
   * Skip this single node. 
   */
  public static final short FILTER_SKIP = 3;
    
  /**
   * Get an instance of a DTM that "owns" a node handle.  Since a node 
   * iterator may be passed without a DTMManager, this allows the 
   * caller to easily get the DTM using just the iterator.
   *
   * @param nodeHandle the nodeHandle.
   *
   * @return a non-null DTM reference.
   */
  public DTM getDTM(int nodeHandle);
  
  /**
   * Get an instance of the DTMManager.  Since a node 
   * iterator may be passed without a DTMManager, this allows the 
   * caller to easily get the DTMManager using just the iterator.
   *
   * @return a non-null DTMManager reference.
   */
  public DTMManager getDTMManager();

  /**
   * The root node of the <code>DTMIterator</code>, as specified when it
   * was created.  Note the root node is not the root node of the 
   * document tree, but the context node from where the iteration 
   * begins and ends.
   *
   * @return nodeHandle int Handle of the context node.
   */
  public int getRoot();

  /**
   * Reset the root node of the <code>DTMIterator</code>, overriding
   * the value specified when it was created.  Note the root node is
   * not the root node of the document tree, but the context node from
   * where the iteration begins.
   *
   * @param nodeHandle int Handle of the context node.
   * @param environment The environment object.  
   * The environment in which this iterator operates, which should provide:
   * <ul>
   * <li>a node (the context node... same value as "root" defined below) </li>
   * <li>a pair of non-zero positive integers (the context position and the context size) </li>
   * <li>a set of variable bindings </li>
   * <li>a function library </li>
   * <li>the set of namespace declarations in scope for the expression.</li>
   * <ul>
   * 
   * <p>At this time the exact implementation of this environment is application 
   * dependent.  Probably a proper interface will be created fairly soon.</p>
   * 
   */
  public void setRoot(int nodeHandle, Object environment);
  
  /**
   * Reset the iterator to the start. After resetting, the next node returned
   * will be the root node -- or, if that's filtered out, the first node
   * within the root's subtree which is _not_ skipped by the filters.
   */
  public void reset();

  /**
   * This attribute determines which node types are presented via the
   * iterator. The available set of constants is defined above.  
   * Nodes not accepted by
   * <code>whatToShow</code> will be skipped, but their children may still
   * be considered.
   *
   * @return one of the SHOW_XXX constants, or several ORed together.
   */
  public int getWhatToShow();

  /**
   * <p>The value of this flag determines whether the children of entity
   * reference nodes are visible to the iterator. If false, they  and
   * their descendants will be rejected. Note that this rejection takes
   * precedence over <code>whatToShow</code> and the filter. </p>
   * 
   * <p> To produce a view of the document that has entity references
   * expanded and does not expose the entity reference node itself, use
   * the <code>whatToShow</code> flags to hide the entity reference node
   * and set <code>expandEntityReferences</code> to true when creating the
   * iterator. To produce a view of the document that has entity reference
   * nodes but no entity expansion, use the <code>whatToShow</code> flags
   * to show the entity reference node and set
   * <code>expandEntityReferences</code> to false.</p>
   *
   * <p>NOTE: In Xalan's use of DTM we will generally have fully expanded
   * entity references when the document tree was built, and thus this
   * flag will have no effect.</p>
   *
   * @return true if entity references will be expanded.  */
  public boolean getExpandEntityReferences();

  /**
   * Returns the next node in the set and advances the position of the
   * iterator in the set. After a <code>DTMIterator</code> has setRoot called,
   * the first call to <code>nextNode()</code> returns that root or (if it
   * is rejected by the filters) the first node within its subtree which is
   * not filtered out.
   * @return The next node handle in the set being iterated over, or
   *  <code>DTM.NULL</code> if there are no more members in that set.
   */
  public int nextNode();

  /**
   * Returns the previous node in the set and moves the position of the
   * <code>DTMIterator</code> backwards in the set.
   * @return The previous node handle in the set being iterated over,
   *   or <code>DTM.NULL</code> if there are no more members in that set.
   */
  public int previousNode();

  /**
   * Detaches the <code>DTMIterator</code> from the set which it iterated
   * over, releasing any computational resources and placing the iterator
   * in the INVALID state. After <code>detach</code> has been invoked,
   * calls to <code>nextNode</code> or <code>previousNode</code> will
   * raise a runtime exception.
   */
  public void detach();
  
  /**
   * Specify if it's OK for detach to release the iterator for reuse.
   * 
   * @param allowRelease true if it is OK for detach to release this iterator 
   * for pooling.
   */
  public void allowDetachToRelease(boolean allowRelease);

  /**
   * Get the current node in the iterator. Note that this differs from
   * the DOM's NodeIterator, where the current position lies between two
   * nodes (as part of the maintain-relative-position semantic).
   *
   * @return The current node handle, or -1.
   */
  public int getCurrentNode();

  /**
   * Tells if this NodeSetDTM is "fresh", in other words, if
   * the first nextNode() that is called will return the
   * first node in the set.
   *
   * @return true if the iteration of this list has not yet begun.
   */
  public boolean isFresh();

  //========= Random Access ==========

  /**
   * If setShouldCacheNodes(true) is called, then nodes will
   * be cached, enabling random access, and giving the ability to do 
   * sorts and the like.  They are not cached by default.
   *
   * %REVIEW% Shouldn't the other random-access methods throw an exception
   * if they're called on a DTMIterator with this flag set false?
   *
   * @param b true if the nodes should be cached.
   */
  public void setShouldCacheNodes(boolean b);
  
  /**
   * Tells if this iterator can have nodes added to it or set via 
   * the <code>setItem(int node, int index)</code> method.
   * 
   * @return True if the nodelist can be mutated.
   */
  public boolean isMutable();

  /** Get the current position within the cached list, which is one
   * less than the next nextNode() call will retrieve.  i.e. if you
   * call getCurrentPos() and the return is 0, the next fetch will
   * take place at index 1.
   *
   * @return The position of the iteration.
   */
  public int getCurrentPos();

  /**
   * If an index is requested, NodeSetDTM will call this method
   * to run the iterator to the index.  By default this sets
   * m_next to the index.  If the index argument is -1, this
   * signals that the iterator should be run to the end and
   * completely fill the cache.
   *
   * @param index The index to run to, or -1 if the iterator should be run
   *              to the end.
   */
  public void runTo(int index);

  /**
   * Set the current position in the node set.
   * 
   * @param i Must be a valid index.
   */
  public void setCurrentPos(int i);

  /**
   * Returns the <code>node handle</code> of an item in the collection. If
   * <code>index</code> is greater than or equal to the number of nodes in
   * the list, this returns <code>null</code>.
   *
   * @param index of the item.
   * @return The node handle at the <code>index</code>th position in the
   *   <code>DTMIterator</code>, or <code>-1</code> if that is not a valid
   *   index.
   */
  public int item(int index);
  
  /**
   * Sets the node at the specified index of this vector to be the
   * specified node. The previous component at that position is discarded.
   *
   * <p>The index must be a value greater than or equal to 0 and less
   * than the current size of the vector.  
   * The iterator must be in cached mode.</p>
   * 
   * <p>Meant to be used for sorted iterators.</p>
   *
   * @param node Node to set
   * @param index Index of where to set the node
   */
  public void setItem(int node, int index);
  
  /**
   * The number of nodes in the list. The range of valid child node indices
   * is 0 to <code>length-1</code> inclusive. Note that this requires running
   * the iterator to completion, and presumably filling the cache.
   *
   * @return The number of nodes in the list.
   */
  public int getLength();
    
  //=========== Cloning operations. ============
  
  /**
   * Get a cloned Iterator that is reset to the start of the iteration.
   *
   * @return A clone of this iteration that has been reset.
   *
   * @throws CloneNotSupportedException
   */
  public DTMIterator cloneWithReset() throws CloneNotSupportedException;

  /**
   * Get a clone of this iterator, but don't reset the iteration in the 
   * process, so that it may be used from the current position.
   *
   * @return A clone of this object.
   *
   * @throws CloneNotSupportedException
   */
  public Object clone() throws CloneNotSupportedException;
  
  /**
   * Returns true if all the nodes in the iteration well be returned in document 
   * order.
   * 
   * @return true if all the nodes in the iteration well be returned in document 
   * order.
   */
  public boolean isDocOrdered();
  
  /**
   * Returns the axis being iterated, if it is known.
   * 
   * @return Axis.CHILD, etc., or -1 if the axis is not known or is of multiple 
   * types.
   */
  public int getAxis();

}