This interface is used by implementors classes that builds some kind of object from a query tree.
This class should be used when there is a builder for each type of node.
The package org.apache.lucene.queryParser.builders contains the interface that
builders must implement, it also contain a utility
QueryTreeBuilder, which walks the tree
and call the Builder for each node in the tree.
Builder normally convert QueryNode Object into a Lucene Query Object,
and normally it's a one-to-one mapping class.
But other builders implementations can by written to convert QueryNode objects to other non lucene objects.