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From Michael Stover <>
Subject [Collections] A new collection for consideration
Date Thu, 12 Aug 2004 19:09:49 GMT
You can view the code I'm talking about at:

Ignore  I'm primarily interested in

HashTree is essentially a Map of Maps.  I've looked through Collections
and not found such a thing (CompositeMap seems to be something else
entirely).  HashTree holds a tree of values and provides a lot of
methods for manipulating those values.  It's not unlike a DOM, except it
has nothing specific to XML or anything else - it works with objects
just like a Map does, and it provides better ways to access and store

For instance, to add a value(s) deep into the tree, I can do:


This will traverse the given path (a Collection or object[] or a single
object) and add the value as a leaf at the end, or add the entire list
of values at the end of the path.

I can get a list of values anywhere in the tree:

or	tree.getArray(path)

I can search a tree via search(object) and get back the Tree headed by
that element.

Perhaps best of all, there is a HashTreeTraverser interface that let's
one define more complex activities that can be done to a tree without
having to write any traversal code.  The tree will traverse itself
depth-first and execute callbacks to the HashTreeTraverser.  This is how
Search is implemented, and it's also how toString() is implemented (you
can see the inner classes in the code that implement HashTreeTraverser
to do this).

There is also a ListedHashTree implementation (ie an OrderedMap) and a
SortedHashTree, and a SearchByClass implementation of a
HashTreeTraverser.  I imagine people will want to change the names and
it would be nice to define an interface for it, which is all fine.  

Any interest?

Michael Stover <>
Apache Software Foundation

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