org.apache.xerces.dom
Class DeepNodeListImpl

java.lang.Object
  org.apache.xerces.dom.DeepNodeListImpl

All Implemented Interfaces:

NodeList

Direct Known Subclasses:

NameNodeListImpl

public class DeepNodeListImpl
extends java.lang.Object
implements NodeList

This class implements the DOM's NodeList behavior for Element.getElementsByTagName()

The DOM describes NodeList as follows:

1) It may represent EITHER nodes scattered through a subtree (when returned by Element.getElementsByTagName), or just the immediate children (when returned by Node.getChildNodes). The latter is easy, but the former (which this class addresses) is more challenging.

2) Its behavior is "live" -- that is, it always reflects the current state of the document tree. To put it another way, the NodeLists obtained before and after a series of insertions and deletions are effectively identical (as far as the user is concerned, the former has been dynamically updated as the changes have been made).

3) Its API accesses individual nodes via an integer index, with the listed nodes numbered sequentially in the order that they were found during a preorder depth-first left-to-right search of the tree. (Of course in the case of getChildNodes, depth is not involved.) As nodes are inserted or deleted in the tree, and hence the NodeList, the numbering of nodes that follow them in the NodeList will change.

It is rather painful to support the latter two in the getElementsByTagName case. The current solution is for Nodes to maintain a change count (eventually that may be a Digest instead), which the NodeList tracks and uses to invalidate itself.

Unfortunately, this does _not_ respond efficiently in the case that the dynamic behavior was supposed to address: scanning a tree while it is being extended. That requires knowing which subtrees have changed, which can become an arbitrarily complex problem.

We save some work by filling the vector only as we access the item()s... but I suspect the same users who demanded index-based access will also start by doing a getLength() to control their loop, blowing this optimization out of the water.

NOTE: Level 2 of the DOM will probably _not_ use NodeList for its extended search mechanisms, partly for the reasons just discussed.

Since:

PR-DOM-Level-1-19980818.

Version:

$Id: DeepNodeListImpl.java 447266 2006-09-18 05:57:49Z mrglavas $

Constructor Summary

DeepNodeListImpl(NodeImpl rootNode, java.lang.String tagName)
Constructor.

DeepNodeListImpl(NodeImpl rootNode, java.lang.String nsName, java.lang.String tagName)
Constructor for Namespace support.

Method Summary

int	getLength() Returns the length of the node list.
Node	item(int index) Returns the node at the specified index.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

DeepNodeListImpl

public DeepNodeListImpl(NodeImpl rootNode,
                        java.lang.String tagName)

Constructor.

DeepNodeListImpl

public DeepNodeListImpl(NodeImpl rootNode,
                        java.lang.String nsName,
                        java.lang.String tagName)

Constructor for Namespace support.

Method Detail

getLength

public int getLength()

Returns the length of the node list.

Specified by:

getLength in interface NodeList

item

public Node item(int index)

Returns the node at the specified index.

Specified by:

item in interface NodeList

Parameters:

index - Index into the collection.

Returns:

The node at the indexth position in the NodeList, or null if that is not a valid index.