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 * 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.
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/*
 * $Id: DTMIterator.java 468653 2006-10-28 07:07:05Z minchau $
 */
package org.apache.xml.dtm;

DTMIterators are used to step through a (possibly
filtered) set of nodes.  Their API is modeled largely after the DOM
NodeIterator.
A DTMIterator is a somewhat unusual type of iterator, in that it 
can serve both single node iteration and random access.
The DTMIterator's traversal semantics, i.e. how it walks the tree,
are specified when it is created, possibly and probably by an XPath
UnionExpr.
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.
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.
State: In progress!!
 /**

 * <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.
/**
   * 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).
/**
   * 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. 
/**
   * 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.
Params:
nodeHandle – the nodeHandle.
Returns:
a non-null DTM reference./**
   * 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.
Returns:
a non-null DTMManager reference./**
   * 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 DTMIterator, 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.
Returns:
nodeHandle int Handle of the context node./**
   * 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 DTMIterator, 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.
Params:
nodeHandle – int Handle of the context node.
environment – The environment object.  
The environment in which this iterator operates, which should provide:

a node (the context node... same value as "root" defined below) 
a pair of non-zero positive integers (the context position and the context size) 
a set of variable bindings 
a function library 
the set of namespace declarations in scope for the expression.

At this time the exact implementation of this environment is application 
dependent.  Probably a proper interface will be created fairly soon./**
   * 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.
/**
   * 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
whatToShow will be skipped, but their children may still
be considered.
Returns:
one of the SHOW_XXX constants, or several ORed together./**
   * 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();

  
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 whatToShow and the filter. 
 To produce a view of the document that has entity references
expanded and does not expose the entity reference node itself, use
the whatToShow flags to hide the entity reference node
and set expandEntityReferences to true when creating the
iterator. To produce a view of the document that has entity reference
nodes but no entity expansion, use the whatToShow flags
to show the entity reference node and set
expandEntityReferences to false.
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.
Returns:
true if entity references will be expanded./**
   * <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 DTMIterator has setRoot called,
the first call to nextNode() returns that root or (if it
is rejected by the filters) the first node within its subtree which is
not filtered out.
Returns:
The next node handle in the set being iterated over, or
 DTM.NULL if there are no more members in that set./**
   * 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
DTMIterator backwards in the set.
Returns:
The previous node handle in the set being iterated over,
  or DTM.NULL if there are no more members in that set./**
   * 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 DTMIterator from the set which it iterated
over, releasing any computational resources and placing the iterator
in the INVALID state. After detach has been invoked,
calls to nextNode or previousNode will
raise a runtime exception.
/**
   * 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.
Params:
allowRelease – true if it is OK for detach to release this iterator 
for pooling./**
   * 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).
Returns:
The current node handle, or -1./**
   * 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.
Returns:
true if the iteration of this list has not yet begun./**
   * 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?
Params:
b – true if the nodes should be cached./**
   * 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 setItem(int node, int index) method.
Returns:
True if the nodelist can be mutated./**
   * 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.
Returns:
The position of the iteration./** 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.
Params:
index – The index to run to, or -1 if the iterator should be run
             to the end./**
   * 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.
Params:
i – Must be a valid index./**
   * Set the current position in the node set.
   * 
   * @param i Must be a valid index.
   */
  public void setCurrentPos(int i);

  
Returns the node handle of an item in the collection. If
index is greater than or equal to the number of nodes in
the list, this returns null.
Params:
index – of the item.
Returns:
The node handle at the indexth position in the
  DTMIterator, or -1 if that is not a valid
  index./**
   * 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.
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.
Meant to be used for sorted iterators.
Params:
node – Node to set
index – Index of where to set the node/**
   * 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 length-1 inclusive. Note that this requires running
the iterator to completion, and presumably filling the cache.
Returns:
The number of nodes in the list./**
   * 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.
Throws:
CloneNotSupportedException – 
Returns:
A clone of this iteration that has been reset./**
   * 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.
Throws:
CloneNotSupportedException – 
Returns:
A clone of this object./**
   * 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.
Returns:
true if all the nodes in the iteration well be returned in document 
order./**
   * 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.
Returns:
Axis.CHILD, etc., or -1 if the axis is not known or is of multiple 
types./**
   * 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();

}