Class Parser

java.lang.Object
  Parser

public class Parser
extends java.lang.Object

A parser for simple arithmetic expressions with the operators +, -, *, / and ( ) It was written as a demonstration of a recursive descent parser, therefore the emphasis is on simplicity.

Version:

16. Dec. 2007

Author:

P. Tellenbach

Field Summary

protected int	position Current position in the string
protected java.lang.String	str String to be parsed

Constructor Summary

Parser()

Method Summary

Node	parse(java.lang.String expr) Sets up the members, starts the parser and checks if the whole string was parsed correctly.
protected Node	parseExpression() Parses an "expression", which is a production with the operators + and -
protected Node	parseFactor() Parses a "factor", which is either an expression enclosed by "(" and ")" or a simple number.
protected Node	parseNumber() Returns an integer number from the string
protected Node	parseTerm() Parses a "term", which is a production with the operators "*" or "/"

Methods inherited from class java.lang.Object

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

Field Detail

str

protected java.lang.String str

String to be parsed

position

protected int position

Current position in the string

Constructor Detail

Parser

public Parser()

Method Detail

parseTerm

protected Node parseTerm()
                  throws ParseException

Parses a "term", which is a production with the operators "*" or "/"

Throws:

ParseException - thrown by parseFactor

parseFactor

protected Node parseFactor()
                    throws ParseException

Parses a "factor", which is either an expression enclosed by "(" and ")" or a simple number. Note the recursion via parseExpression.

Throws:

ParseException - if the expression is not terminated by ")"

parseExpression

protected Node parseExpression()
                        throws ParseException

Parses an "expression", which is a production with the operators + and -

Throws:

ParseException - thrown by parseTerm

parseNumber

protected Node parseNumber()
                    throws ParseException

Returns an integer number from the string

Throws:

ParseException - if the number is not valid

parse

public Node parse(java.lang.String expr)
           throws ParseException

Sets up the members, starts the parser and checks if the whole string was parsed correctly. Note that the string to be parsed may not contain whitespace.

Throws:

ParseException - if there are any unparsed characters