com.singularsys.jep.walkers
Class PostfixTreeWalker

java.lang.Object
  com.singularsys.jep.walkers.PostfixTreeWalker

Direct Known Subclasses:

PostfixEvaluator, SerializableExpression, TreeAnalyzer

public abstract class PostfixTreeWalker
extends java.lang.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 transverse the various nodes. In general these methods should not recursively walk the child nodes. This class uses a postfix transversal 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

PostfixTreeWalker()

Method Summary

protected boolean	supressExaminingChildren(Node child) Whether to examine the children of this nodes.
protected abstract void	visit(ASTConstant node, int nchildren, int depth) Visit a constant node
protected abstract void	visit(ASTFunNode node, int nchildren, int depth) Visit a function node
protected abstract void	visit(ASTOpNode node, int nchildren, int depth) Visit an operator node
protected abstract void	visit(ASTVarNode node, int nchildren, int depth) Visit a variable node
protected void	walk(Node top) Start transversal of the expression.
protected void	walkSubEquations(Node top) If a supressExaminingChildren() 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 Detail

PostfixTreeWalker

public PostfixTreeWalker()

Method Detail

walk

protected final void walk(Node top)
                   throws JepException

Start transversal of the expression.

Parameters:

top - top node for the expression

Throws:

JepException

supressExaminingChildren

protected boolean supressExaminingChildren(Node child)

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

Parameters:

child -

Returns:

false unless overridden by sub-class

walkSubEquations

protected final void walkSubEquations(Node top)
                               throws JepException

If a supressExaminingChildren() returns true, then the children of the node will not be visited by default. This method allows a sub-class to visit the children of such a node if needed.

Parameters:

top -

Throws:

JepException

visit

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

Visit a function node

Parameters:

node - the current node being visited

nchildren - number of children of the node

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

Throws:

JepException

visit

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

Visit an operator node

Parameters:

node - the current node being visited

nchildren - number of children of the node

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

Throws:

JepException

visit

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

Visit a variable node

Parameters:

node - the current node being visited

nchildren - number of children of the node

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

Throws:

JepException

visit

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

Visit a constant node

Parameters:

node - the current node being visited

nchildren - number of children of the node

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

Throws:

JepException