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DeepNodeListImpl.javaAPI DocJava SE 5 API9690Fri Aug 26 14:55:42 BST 2005com.sun.org.apache.xerces.internal.dom

DeepNodeListImpl

public class DeepNodeListImpl extends 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.

version
$Id: DeepNodeListImpl.java,v 1.7 2002/01/29 01:15:07 lehors Exp $
since
PR-DOM-Level-1-19980818.

Fields Summary
protected NodeImpl
rootNode
protected String
tagName
protected int
changes
protected Vector
nodes
protected String
nsName
protected boolean
enableNS
Constructors Summary
public DeepNodeListImpl(NodeImpl rootNode, String tagName)
Constructor.


    //
    // Constructors
    //

      
         
        this.rootNode = rootNode;
        this.tagName  = tagName;
        nodes = new Vector();
public DeepNodeListImpl(NodeImpl rootNode, String nsName, String tagName)
Constructor for Namespace support.

        this(rootNode, tagName);
        this.nsName = (nsName != null && !nsName.equals("")) ? nsName : null;
        enableNS = true;
Methods Summary
public intgetLength()
Returns the length of the node list.

        // Preload all matching elements. (Stops when we run out of subtree!)
        item(java.lang.Integer.MAX_VALUE);
        return nodes.size();
public org.w3c.dom.Nodeitem(int index)
Returns the node at the specified index.

    	Node thisNode;

        // Tree changed. Do it all from scratch!
    	if(rootNode.changes() != changes) {
            nodes   = new Vector();     
            changes = rootNode.changes();
    	}
    
        // In the cache
    	if (index < nodes.size())      
    	    return (Node)nodes.elementAt(index);
    
        // Not yet seen
    	else {
    
            // Pick up where we left off (Which may be the beginning)
    		if (nodes.size() == 0)     
    		    thisNode = rootNode;
    		else
    		    thisNode=(NodeImpl)(nodes.lastElement());
    
    		// Add nodes up to the one we're looking for
    		while(thisNode != null && index >= nodes.size()) {
    			thisNode=nextMatchingElementAfter(thisNode);
    			if (thisNode != null)
    			    nodes.addElement(thisNode);
    		    }

            // Either what we want, or null (not avail.)
		    return thisNode;           
	    }
protected org.w3c.dom.NodenextMatchingElementAfter(org.w3c.dom.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().


	    Node next;
	    while (current != null) {
		    // Look down to first child.
		    if (current.hasChildNodes()) {
			    current = (current.getFirstChild());
		    }

		    // Look right to sibling (but not from root!)
		    else if (current != rootNode && null != (next = current.getNextSibling())) {
				current = next;
			}

			// Look up and right (but not past root!)
			else {
				next = null;
				for (; current != rootNode; // Stop when we return to starting point
					current = current.getParentNode()) {

					next = current.getNextSibling();
					if (next != null)
						break;
				}
				current = next;
			}

			// Have we found an Element with the right tagName?
			// ("*" matches anything.)
		    if (current != rootNode 
		        && current != null
		        && current.getNodeType() ==  Node.ELEMENT_NODE) {
			if (!enableNS) {
			    if (tagName.equals("*") ||
				((ElementImpl) current).getTagName().equals(tagName))
			    {
				return current;
			    }
			} else {
			    // DOM2: Namespace logic. 
			    if (tagName.equals("*")) {
				if (nsName != null && nsName.equals("*")) {
				    return current;
				} else {
				    ElementImpl el = (ElementImpl) current;
				    if ((nsName == null
					 && el.getNamespaceURI() == null)
					|| (nsName != null
					    && nsName.equals(el.getNamespaceURI())))
				    {
					return current;
				    }
				}
			    } else {
				ElementImpl el = (ElementImpl) current;
				if (el.getLocalName() != null
				    && el.getLocalName().equals(tagName)) {
				    if (nsName != null && nsName.equals("*")) {
					return current;
				    } else {
					if ((nsName == null
					     && el.getNamespaceURI() == null)
					    || (nsName != null &&
						nsName.equals(el.getNamespaceURI())))
					{
					    return current;
					}
				    }
				}
			    }
			}
		    }

		// Otherwise continue walking the tree
	    }

	    // Fell out of tree-walk; no more instances found
	    return null;