[jdom-interest] Jason's Node challenge

[Paul Philion]

I respectfully submit:

interface Element {
    Element getParent(); // returns null at root
    String getValue();
    Iterator children();
    boolean hasChildren();
    int numChildren();
    Element getChild(int i);
    String getName();
    Namespace getNamespace();
    String getAttribute(String attrName);
    Iterator getAttributeNames();
}

interface MutableElement extends Element {
    // setters for the above
    void addChild(Element elem);
    void insertChild(Element elem);
    String setAttribute(String name, String value);
    // etc...
}

I think the collection of really-strongly-typed stuff below goes far beyond
what JDOM needs.

- Paul Philion

> -----Original Message-----
> From: jdom-interest-admin at jdom.org
> [mailto:jdom-interest-admin at jdom.org]On Behalf Of Amy Lewis
> Sent: Tuesday, May 01, 2001 8:31 AM
> To: jdom-interest at jdom.org
> Subject: [jdom-interest] Jason's Node challenge
>
>
> Jason has suggested here that a reasonable Node implementation can't be
> developed.  I think, in the context of JDOM, that this is probably
> true.  Nonetheless, I present a Node-based interface specification
> here (without implementation).  It won't work with JDOM, because it
> lies at some conceptual distance from the underpinnings of JDOM.  Most
> notably, there is no way to extend final java.lang.String to StringNode
> extends String implements LeafNode.  Nevertheless, FWIW, YMMV, IANAL.
> Also, this definition is somewhat incomplete.  *shrug*
>
> This is somewhat lengthy, ignore, an it please you.
>
> interface Node
> {
>     BranchNode getParent();
>
>     String getValue();
>
>     RootNode getRoot();
>
>     // doesn't start you at the root, starts at this node
>     TreeIterator iterator();
>
>     NodeSet collectNodes(Axis axis, Namespace namespace, String name);
>
>     NodeSet collectNodes(Axis axis, Class nodeType);
>
>     NodeSet collectNodes(Axis axis, String value);
> }
>
> interface LeafNode extends Node
> {
>     // pure marker
> }
>
> interface BranchNode extends Node
> {
>     Node getFirstChild();
>
>     Node getNextChild(Node sibling);
>
>     NodeSet getChildren();
>
>     void addChild(Node child);
>
>     void removeChild(Node child);
>
>     String getName();
>
>     Namespace getNamespace();
>
>     NodeSet getAttributes();
>
>     void addAttribute(Attribute attrib);
>
>     void removeAttribute(Attribute attrib);
> }
>
> interface RootNode extends BranchNode
> {
> // note that it "extends" because in Java you can't say "restricts"
> // the contract is that getParent() returns a marker (null, perhaps),
> // and the attribute methods do nothing.  Otherwise, a marker.
> }
>
> interface NodeSet
> {
>     // set the context for collection, for a new set.
>     void setContext(Node context);
>
>     // these three add to the existing collection, using each current
>     // node in the set as a starting point.
>     NodeSet collectNodes(Axis axis, Namespace namespace, String name);
>
>     NodeSet collectNodes(Axis axis, Class nodeType);
>
>     NodeSet collectNodes(Axis axis, String value);
>
>     // these three operate to reduce the existing collection by
>     // filtering
>     NodeSet selectNodes(Axis axis, Namespace namespace, String name);
>
>     NodeSet selectNodes(Axis axis, Class nodeType);
>
>     NodeSet selectNodes(Axis axis, String value);
>
>     NodeSet union(NodeSet unionWith);
>
>     NodeSet intersection(NodeSet intersectWith);
>
>     void addNode(Node content, Node context);
>
>     void removeNode(Node content);
>
>     int size();
>
>     Node get(int);
>
>     // not a tree iterator.  It ought to be a NodeIterator, but WTF
>     // typical Collections semantics
>     Iterator iterator();
> }
>
> interface TreeIterator
> {
>     boolean hasNext();
>
>     Node next();
>
>     boolean hasPrevious();
>
>     Node previous();
>
>     boolean hasParent();
>
>     BranchNode parent();
>
>     boolean hasFirstChild();
>
>     Node firstChild();
>
>     boolean hasNextSibling();
>
>     nextSibling();
>
>     boolean hasPreviousSibling();
>
>     previousSibling();
> }
>
> Axis is an interface containing manifest constants appropriate to
> XPath; Attribute is a LeafNode; Namespace is a namespace.
>
> As noted, probably not suitable to Jason's challenge, because it would
> do violence to the JDOM model.  Nevertheless, in concept it's possible.
> The advantage of this model--if there really is one, which is of course
> unproven 'cause the implementation is still not finished and deadlines
> *always* seem to loom--is a high degree of navigability and mutability,
> starting from any position in the tree and moving relatively (this is
> mostly achieved by the existence of collectNodes() and iterator() in
> the Node interface).
>
> In case it isn't obvious, Element implements BranchNode, Document
> implements RootNode, everything else implements LeafNode (although the
> implementation that I've got treats DocType and the like as attributes
> of the root, not as nodes, for instance).  Most of the complexity (in
> the implementation) is in NodeSet and TreeIterator; it's hidden
> elsewhere.  The model is fairly easy to extend, as long as the
> subclasses hold to contract (Node isn't directly implemented, for
> instance).  The use of java.lang.Class in the signature for one of the
> collectNodes/selectNodes variants requires that the class supplied
> implement Node (it should IAE if it doesn't).  The implementation I've
> got also guarantees no nulls, using a static final Node (with suitable
> overrides) instead; this allows dotted-on methods:
> NodeSet set = node.collectNodes(this, that).selectNodes(theOther, blah);
> (and a NodeSet is always returned, even if empty, never null).
>
> It's possible, I suppose, that some of the ideas here might be portable
> to JDOM, so here it is.
>
> Amy!
> --
> Amelia A. Lewis          alicorn at mindspring.com
> amyzing at talsever.com
> Tongue-tied and twisted, just an earthbound misfit, I.
> -- Pink Floyd
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