jltools.ast
Class NodeVisitor

java.lang.Object
  |
  +--jltools.ast.NodeVisitor

Direct Known Subclasses:

BaseVisitor, ClassSerializer, DumpAst, ExceptionChecker, FlattenVisitor, FlowChecker, NodeScrambler, NodeScrambler.FirstPass

public abstract class NodeVisitor

extends java.lang.Object

The NodeVisitor represents an implementation of the "Visitor" style of tree traversal. There is a convention among jltools visitors which states that traversals will lazily reconstruct the tree. That is, the AST is functionally "modified" by creating new nodes on each traversal, but only when necessary-- only when nodes (or their children) are actually changed. Up to three seperate calls into the visitor may be invoked for each AST node. override allows the visitor to redefine the entire traversal for a particular subtree. enter notifies the visitor that traversal of a particular subtree has begun. leave informs the visitor that traversal is finishing a particular subtree.

See Also:

Node.visit(jltools.ast.NodeVisitor), Node

Constructor Summary

NodeVisitor()

Method Summary

NodeVisitor	enter(Node n) Begin normal traversal of a subtree rooted at n.
void	finish() The finish method is called after the entire tree has been visited.
Node	leave(Node old, Node n, NodeVisitor v) This method is called after all of the children of n have been visited.
Node	override(Node n) Given a tree rooted at n, the visitor has the option of overriding all traversal of the children of n.
java.lang.String	toString()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

NodeVisitor

public NodeVisitor()

Method Detail

override

public Node override(Node n)

Given a tree rooted at n, the visitor has the option of overriding all traversal of the children of n. If no changes were made to n and the visitor wishes to prevent further traversal of the tree, then it should return n. If changes were made to the subtree, then the visitor should return a copy of n with appropriate changes. Finally, if the visitor does not wish to override traversal of the subtree rooted at n, then it should return null.

Parameters:

n - The root of the subtree to be traversed.

Returns:

A node if normal traversal is to stop, null if it is to continue.

enter

public NodeVisitor enter(Node n)

Begin normal traversal of a subtree rooted at n. This gives the visitor the option of changing internal state or returning a new visitor which will be used to visit the children of n.

Parameters:

n - The root of the subtree to be traversed.

Returns:

The NodeVisitor which should be used to visit the children of n.

leave

public Node leave(Node old,
                  Node n,
                  NodeVisitor v)

This method is called after all of the children of n have been visited. In this case, these children were visited by the visitor v. This is the last chance for the visitor to modify the tree rooted at n. This method will be called exactly the same number of times as entry is called. That is, for each node that is not overriden, enter and leave are each called exactly once.

Note that if old == n then the vistior should make a copy of n before modifying it. It should then return the modified copy.

Parameters:

old - The original state of root of the current subtree.

n - The current state of the root of the current subtree.

v - The NodeVisitor object used to visit the children.

Returns:

The final result of the traversal of the tree rooted at n.

finish

public void finish()

The finish method is called after the entire tree has been visited. This method allows the visitor to perform any last minute cleanup, including flushing buffers and I/O connections.

toString

public java.lang.String toString()

Overrides:

toString in class java.lang.Object