Class DeepNodeListImpl

All Implemented Interfaces:
Direct Known Subclasses:

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.


Field Summary
protected  int changes
protected  boolean enableNS
protected  java.util.Vector nodes
protected  java.lang.String nsName
protected  NodeImpl rootNode
protected  java.lang.String tagName
Constructor Summary
DeepNodeListImpl(NodeImpl rootNode, java.lang.String tagName)
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.
protected  Node nextMatchingElementAfter(Node current)
          Iterative tree-walker.
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail


protected NodeImpl rootNode


protected java.lang.String tagName


protected int changes


protected java.util.Vector nodes


protected java.lang.String nsName


protected boolean enableNS
Constructor Detail


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


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


public int getLength()
Returns the length of the node list.
Specified by:
getLength in interface NodeList


public Node item(int index)
Returns the node at the specified index.
Specified by:
item in interface NodeList
Following copied from interface: org.w3c.dom.NodeList
indexIndex - into the collection.
The node at the indexth position in the NodeList, or null if that is not a valid index.


protected Node nextMatchingElementAfter(Node current)
Iterative tree-walker. When you have a Parent link, there's often no need to resort to recursion. NOTE THAT only Element nodes are matched since we're specifically supporting getElementsByTagName().

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