org.nfunk.jep
Class EvaluatorVisitor

java.lang.Object
  org.nfunk.jep.EvaluatorVisitor

All Implemented Interfaces:

ParserVisitor

Direct Known Subclasses:

XEvaluatorVisitor

public class EvaluatorVisitor

extends java.lang.Object

implements ParserVisitor

This class is used for the evaluation of an expression. It uses the Visitor design pattern to traverse the function tree and evaluate the expression using a stack.

Function nodes are evaluated by first evaluating all the children nodes, then applying the function class associated with the node. Variable and constant nodes are evaluated by pushing their value onto the stack.

Some changes implemented by rjm. Nov 03. Added hook to SpecialEvaluationI. Clears stack before evaluation. Simplifies error handeling by making visit methods throw ParseException. Changed visit(ASTVarNode node) so messages not calculated every time.

Field Summary

protected boolean	errorFlag Flag for errors during evaluation
protected java.util.Vector	errorList The current error list
protected java.util.Stack	stack Stack used for evaluating the expression
protected SymbolTable	symTab The symbol table for variable lookup

Constructor Summary

EvaluatorVisitor()
Constructor.

Method Summary

protected void	addToErrorList(java.lang.String errorStr) Adds an error message to the list of errors
java.lang.Object	getValue(Node topNode, java.util.Vector errorList_in, SymbolTable symTab_in) Returns the value of the expression as an object.
java.lang.Object	visit(ASTConstant node, java.lang.Object data) Visit a constant node.
java.lang.Object	visit(ASTFunNode node, java.lang.Object data) Visit a function node.
java.lang.Object	visit(ASTStart node, java.lang.Object data) This method should never be called when evaluating a normal expression.
java.lang.Object	visit(ASTVarNode node, java.lang.Object data) Visit a variable node.
java.lang.Object	visit(SimpleNode node, java.lang.Object data) This method should never be called when evaluation a normal expression.

Methods inherited from class java.lang.Object

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

Field Detail

stack

protected java.util.Stack stack

Stack used for evaluating the expression

errorList

protected java.util.Vector errorList

The current error list

symTab

protected SymbolTable symTab

The symbol table for variable lookup

errorFlag

protected boolean errorFlag

Flag for errors during evaluation

Constructor Detail

EvaluatorVisitor

public EvaluatorVisitor()

Constructor. Initialize the stack member

Method Detail

addToErrorList

protected void addToErrorList(java.lang.String errorStr)

Adds an error message to the list of errors

getValue

public java.lang.Object getValue(Node topNode,
                                 java.util.Vector errorList_in,
                                 SymbolTable symTab_in)
                          throws java.lang.Exception

Returns the value of the expression as an object. The expression tree is specified with its top node. The algorithm uses a stack for evaluation.

The errorList_in parameter is used to add error information that may occur during the evaluation. It is not required, and may be set to null if no error information is needed.

The symTab parameter can be null, if no variables are expected in the expression. If a variable is found, an error is added to the error list.

An exception is thrown, if an error occurs during evaluation.

Returns:

The value of the expression as an object.

Throws:

java.lang.Exception

visit

public java.lang.Object visit(SimpleNode node,
                              java.lang.Object data)
                       throws ParseException

This method should never be called when evaluation a normal expression.

Specified by:

visit in interface ParserVisitor

Throws:

ParseException

visit

public java.lang.Object visit(ASTStart node,
                              java.lang.Object data)
                       throws ParseException

This method should never be called when evaluating a normal expression.

Specified by:

visit in interface ParserVisitor

Throws:

ParseException

visit

public java.lang.Object visit(ASTFunNode node,
                              java.lang.Object data)
                       throws ParseException

Visit a function node. The values of the child nodes are first pushed onto the stack. Then the function class associated with the node is used to evaluate the function.

If a function implements SpecialEvaluationI then the evaluate method of PFMC is called.

Specified by:

visit in interface ParserVisitor

Throws:

ParseException

visit

public java.lang.Object visit(ASTVarNode node,
                              java.lang.Object data)
                       throws ParseException

Visit a variable node. The value of the variable is obtained from the symbol table (symTab) and pushed onto the stack.

Specified by:

visit in interface ParserVisitor

Throws:

ParseException

visit

public java.lang.Object visit(ASTConstant node,
                              java.lang.Object data)

Visit a constant node. The value of the constant is pushed onto the stack.

Specified by:

visit in interface ParserVisitor