VM memory usage with DOM objects

Hi - I have a general question regarding VM memory use (and garbage collection) when using instances of XMLDocument (we're using the Java version of the parser, v2.0.2.6).
Say we have an existing instance of XMLDocument containing a valid xml document. What happens when:
a) XMLDocument is set to null? When will all the previous xml Node/Element instances that were referenced in the document structure be garbage collected? My understanding is that objects will only be garbage collected when there are no remaining references to them. How does this apply to the tree structure of references between Node instances in the XML document? I am guessing that by setting XMLDocument to null, this change will eventually cascade through all the other nodes, so eventually they are released?
b) Secondly, what happens to the existing Node/Element instances referenced in an instance of XMLDocument if I assign it new document contents from getDocument() on an instance of DOMParser? Does this create a new document tree structure from scratch and create new instances of Nodes to represent the new document, or are the previous instances of Node etc from the previous document reused somehow?
c) Following on from above, if the previous instances of Node from the previous document are not reused, when are these garbage collected?
Thanks in advance,
Kevin Hooke

The XMLdocument object, although representing the entire document, is referenced solely to the root of the DOM tree. To clean up the DOM Tree, one should set all the references to the tree (doc, node, elements, ...) to null.
Here are the specic answers to your questions:
a) Setting XMLDocument to null will NOT have the cascading effect on the other Nodes/Elements.
b) Yes, the previous DOM Tree still exists if there are any Node/Elements pointing to it even if you get a new document. When you get a new document, you get a new DOM Tree representation.
c) Unfortunately, there is no way to guarantee when the garbage collection takes place in the JVM. Check out the method System.gc() to "suggest" to the JVM the invocation of the gabage collector.
Oracle XML Team

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