Page Comparison

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Once you create a TreeWizard, you can keep calling create as it will know what kind of nodes to make, how to hook them up, and what the token types are for the token names. The wizard really only has write-once data in it...just a convenience so you don't have to keep passing stuff to each of the methods.

Oh, if you want to set the text of a node, use the argument syntax with no quotes:

CommonTree t = (CommonTree)wiz.create("(A B[foo] C[bar])");

Note: no quotes for the arguments.

Tree Equality

If you want to compare to trees, you'd have to write your own method to do so right now. The equals() method in Java is not necessarily the right way to implement either because that is probably just matching to nodes not trees. The TreeWizard provides a method to check the equality two trees (one static and one instance method):

/** Compare t1 and t2; return true if token types/text, structure match exactly.
 *  The trees are examined in their entirety so that (A B) does not match
 *  (A B C) nor (A (B C)). 
public static boolean equals(Object t1, Object t2, TreeAdaptor adaptor);

/** Compare type, structure, and text of two trees, assuming adaptor
 *  in this instance of a TreeWizard.
 */
public boolean equals(Object t1, Object t2);

If you would only like to match the structure of a tree, but not the text associated with each node (so that, say, any ID node will match), use the parse method:

boolean matched = wiz.parse(t, "(A B C)");

Wildcards work too:

CommonTree t = (CommonTree)wiz.create("(A B C)");
boolean matched = wiz.parse(t, "(A . .)");

Sometimes you want some of the nodes to match the text exactly, but most of the time match just the structure. You can do that too:

CommonTree t = (CommonTree)wiz.create("(A B[foo] C)");
boolean matches = wiz.parse(t, "(A B[foo] C)");

Getting pointers to subtree nodes

Matching trees is great, but most of the time you want to get a pointer to some of the children not just determine if the tree structure matches. To accomplish this, label the elements in the tree pattern and pass in a hash table that the parse() method can fill in:

CommonTree t = (CommonTree)wiz.create("(A B C)");
Map labels = new HashMap();
boolean valid = wiz.parse(t, "(%a:A %b:B %c:C)", labels);

Then labels.get("a") points to the root etc... Cool, eh?

Indexing trees

Sometimes you want a list of all nodes with a certain type like VARDECL or METHOD:

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// from the unit tests
CommonTree t = (CommonTree)wiz.create("(A B (A C B) B D D)");
Map m = wiz.index(t);
String found = m.toString();
String expecting = "{8=[D, D], 6=[B, B, B], 7=[C], 5=[A, A]}";

Visitors

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In order to visit all nodes a particular type for all subtree that match a particular pattern, use the visit() method. For each node or subtree that matches, TreeWizard invokes the method and the following interface:

No Format
public interface ContextVisitor { public void visit(Object t, Object parent, int childIndex, Map labels); }

Notice that it passes you a lot of interesting contact information including "who's your daddy?" and "what child am I?" The labels printer is not set unless you're matching against a tree pattern (i.e., won't work for matching against a token type).

Here is some code that visits every B node and puts them into a list, which is of course how I implemented the find() that returns a list.

No Format
CommonTree t = (CommonTree)wiz.create("(A B (A C B) B D D)"); final List elements = new ArrayList(); wiz.visit(t, wiz.getTokenType("B"), new TreeWizard.Visitor() { public void visit(Object t) { elements.add(t); } });

where Visitor is just a convenience class that makes it easier for you to implement if all you want to do is visit without context information:

No Format
public static abstract class Visitor implements ContextVisitor { public void visit(Object t, Object parent, int childIndex, Map labels) { visit(t); } public abstract void visit(Object t); }

Now, let's say that you want to match a bunch of subtrees for declarations and pick out the identifier in each. No problem:

No Format
wiz.visit(t, "(VARDECL %type:. %id:ID)", new TreeWizard.ContextVisitor() { public void visit(Object t, Object parent, int childIndex, Map labels) { // labels.get("type") is first child // labels.get("id") is 2nd child } });