Package com.singularsys.jep.walkers

Class PostfixEvaluator

java.lang.Object

com.singularsys.jep.walkers.PostfixTreeWalker

com.singularsys.jep.walkers.PostfixEvaluator

All Implemented Interfaces:

Evaluator, JepComponent, Serializable

public class PostfixEvaluator
extends PostfixTreeWalker
implements Evaluator

Evaluation component that avoids excessive use of the stack for large expressions. Instead of using recursion to traverse the expression tree, traversal is based on the PostfixTreeWalker.

Author:

Richard Morris

See Also:

• Serialized Form

Field Summary

Fields

Modifier and Type	Field	Description
protected Stack<Object>	stack

Constructor Summary

Constructors

Constructor	Description
PostfixEvaluator()

Method Summary

Modifier and Type	Method	Description
Object	eval(Node node)	Evaluates a sub expression.
Object	evaluate(Node node)	Main entry point, evaluates a node and returns and object with the value of the node.
JepComponent	getLightWeightInstance()	Return new PostfixEvaluator
void	init(Jep jep)	Initialize the component.
protected boolean	suppressExaminingChildren(Node child)	Whether to examine the children of this nodes.
protected void	visit(ASTConstant node, int nchildren, int depth)	Visit a constant node
protected void	visit(ASTFunNode node, int nchildren, int depth)	Visit a function node
protected void	visit(ASTOpNode node, int nchildren, int depth)	Visit an operator node
protected void	visit(ASTVarNode node, int nchildren, int depth)	Visit a variable node

Methods inherited from class com.singularsys.jep.walkers.PostfixTreeWalker

walk, walkSubEquations

Methods inherited from class java.lang.Object

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

Field Details

stack

protected transient Stack<Object> stack

Constructor Details

PostfixEvaluator

public PostfixEvaluator()

Method Details

evaluate

public Object evaluate(Node node)
                throws EvaluationException

Description copied from interface: Evaluator

Main entry point, evaluates a node and returns and object with the value of the node.

Specified by:

evaluate in interface Evaluator

Parameters:

node - node to evaluate

Returns:

value after evaluation

Throws:

EvaluationException - if errors occur during evaluation;

visit

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

Description copied from class: PostfixTreeWalker

Visit a function node

Specified by:

visit in class PostfixTreeWalker

Parameters:

node - the current node being visited

nchildren - number of children of the node

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

Throws:

EvaluationException

visit

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

Description copied from class: PostfixTreeWalker

Visit an operator node

Specified by:

visit in class PostfixTreeWalker

Parameters:

node - the current node being visited

nchildren - number of children of the node

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

Throws:

EvaluationException

visit

protected void visit(ASTVarNode node,
 int nchildren,
 int depth)

Description copied from class: PostfixTreeWalker

Visit a variable node

Specified by:

visit in class PostfixTreeWalker

Parameters:

node - the current node being visited

nchildren - number of children of the node

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

visit

protected void visit(ASTConstant node,
 int nchildren,
 int depth)

Description copied from class: PostfixTreeWalker

Visit a constant node

Specified by:

visit in class PostfixTreeWalker

Parameters:

node - the current node being visited

nchildren - number of children of the node

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

suppressExaminingChildren

protected boolean suppressExaminingChildren(Node child)

Description copied from class: PostfixTreeWalker

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

Overrides:

suppressExaminingChildren in class PostfixTreeWalker

Returns:

false unless overridden by sub-class

eval

public Object eval(Node node)
            throws EvaluationException

Description copied from interface: Evaluator

Evaluates a sub expression. This method can be called by PostfixMathCommands which implement CallbackEvaluationI

Specified by:

eval in interface Evaluator

Parameters:

node - node to evaluate

Returns:

The value after evaluating the sub expression.

Throws:

EvaluationException - if errors occur during evaluation;

init

public void init(Jep jep)

Description copied from interface: JepComponent

Initialize the component. This method is called whenever a component is added to Jep. Hence, it allows components to keep track of the other components they may rely on.

Specified by:

init in interface JepComponent

Parameters:

jep - the current Jep instance

getLightWeightInstance

public JepComponent getLightWeightInstance()

Return new PostfixEvaluator

Specified by:

getLightWeightInstance in interface JepComponent

Returns:

either a new instance, null or 'this'.