Package com.singularsys.jep.walkers

Class PostfixTreeWalker

java.lang.Object

com.singularsys.jep.walkers.PostfixTreeWalker

Direct Known Subclasses:

HookRemover, PostfixEvaluator, TreeAnalyzer

public abstract class PostfixTreeWalker
extends Object

Base class for routines which use a non-recursive tree walker strategy. The typical recursive strategy can use a lot of stack frames for very large expressions these can cause a stack overflow exception. Subclasses should implement the visit methods. to traverse the various nodes. In general these methods should not recursively walk the child nodes. This class uses a postfix traversal scheme hence the nodes of '1+2' will be visited in the order 1,2,+.

Since:

3.2 depth of root node is now 1 not 0

Author:

Richard Morris

See Also:

• PrefixTreeWalker

Constructor Summary

Constructors

Constructor	Description
PostfixTreeWalker()

Method Summary

Modifier and Type	Method	Description
protected boolean	suppressExaminingChildren(Node node)	Whether to examine the children of this nodes.
protected abstract void	visit(ASTConstant node, int nchildren, int depth1)	Visit a constant node
protected abstract void	visit(ASTFunNode node, int nchildren, int depth1)	Visit a function node
protected abstract void	visit(ASTOpNode node, int nchildren, int depth1)	Visit an operator node
protected abstract void	visit(ASTVarNode node, int nchildren, int depth1)	Visit a variable node
protected final void	walk(Node top)	Start transversal of the expression.
protected final void	walkSubEquations(Node child)	If a suppressExaminingChildren(Node) returns true, then the children of the node will not be visited by default.

Methods inherited from class java.lang.Object

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

Constructor Details

PostfixTreeWalker

public PostfixTreeWalker()

Method Details

walk

protected final void walk(Node top)
                   throws JepException

Start transversal of the expression.

Parameters:

top - top node for the expression

Throws:

JepException

suppressExaminingChildren

protected boolean suppressExaminingChildren(Node node)

Whether to examine the children of this nodes. In some cases it is necessary to jump out of traversal strategy to process a node.

Parameters:

node -

Returns:

false unless overridden by sub-class

walkSubEquations

protected final void walkSubEquations(Node child)
                               throws JepException

If a suppressExaminingChildren(Node) returns true, then the children of the node will not be visited by default. This method allows a subclass to visit the children of such a node if needed.

For example an evaluator which wants to implement lazy evaluation for the logical AND operator the subclass will call this method when needed from its implementation of visit(ASTOpNode, int, int).

Parameters:

child - child of a node to start traversing from

Throws:

JepException

visit

protected abstract void visit(ASTFunNode node,
 int nchildren,
 int depth1)
                       throws JepException

Visit a function node

Parameters:

node - the current node being visited

nchildren - number of children of the node

depth1 - depth of tree, root node is depth 1.

Throws:

JepException

visit

protected abstract void visit(ASTOpNode node,
 int nchildren,
 int depth1)
                       throws JepException

Visit an operator node

Parameters:

node - the current node being visited

nchildren - number of children of the node

depth1 - depth of tree, root node is depth 1.

Throws:

JepException

visit

protected abstract void visit(ASTVarNode node,
 int nchildren,
 int depth1)
                       throws JepException

Visit a variable node

Parameters:

node - the current node being visited

nchildren - number of children of the node

depth1 - depth of tree, root node is depth 1.

Throws:

JepException

visit

protected abstract void visit(ASTConstant node,
 int nchildren,
 int depth1)
                       throws JepException

Visit a constant node

Parameters:

node - the current node being visited

nchildren - number of children of the node

depth1 - depth of tree, root node is depth 1.

Throws:

JepException