Calculator (Brazil 2.3)

Calculator implements a simple arithmetic expression evaluator. It can evaluate typical expressions with the "normal" operators and precedence. Formally, the BNF for the supported grammar is:

 <stmt>    ::= <var> = <expr> | <expr>
 <expr>    ::= <rexpr> | <expr> <bool op> <rexpr>
 <bool op> ::= && | <or>
 <or>      ::= ||
 <rexpr>   ::= <aexpr> | <rexpr> <rel op> <aexpr>
 <rel op>  ::= < | <= | > | >= | == | !=
 <aexpr>   ::= <term> | <aexpr> <add op> <term>
 <add op>  ::= + | -
 <term>    ::= <factor> | <term> <mult op> <factor>
 <mult op> ::= * | / | %
 <factor>  ::= <var> | <num> | ! <factor> | ( <expr> )
 <var>     ::= <letter> | <var> <var2>
 <var2>    ::= <letterordigit> | . | _
 <num>     ::= <unum> | + <unum> | - <unum>
 <unum>    ::= <int> | <int> . | <int> . <int> | . <int>
 <int>     ::= <digit> | <int> <digit>

A <letter> is defined as a Java char for which Char.isLetter(char) is true. A <letterordigit> is defined as a Java char for which Char.isLetterOrDigit(char) is true. A digit is defined as a Java char for which Char.isDigit(char) is true.

Values for <var> are looked up in the supplied Dictionary. If <var> can not be found, it is assumed to have the value zero. If the value found is "true" or "yes" (case insensitive), it is assumed to be one. Similarly, if the value found is "false" or "no", it is assumed to be zero. Assignment to <var> stores the computed value in the same Dictionary.

The period in <unum>, if there is one, must be immediately adjacent to surrounding <int>s.

Version: 2.4

Author: Steve Drach <drach@sun.com>

Field Summary
boolean	debugging Set `true` for debug output.

Constructor Summary
	Calculator() The no argument constructor will create an internal `Hashtable` in which it looks up and stores values associated with variables.
	Calculator(Dictionary d) This constructor will use the `Dictionary` parameter to lookup and store values associated with variables.

Method Summary
String	getValue(String stmt) Computes the value of the statement passed in the parameter string and returns a string representation of the result.
String	getValue(String stmt, Dictionary d) Computes the value of the statement passed in the parameter string and returns a string representation of the result.
static void	main(String[] args) A test driver for the calculator.
void	stringsValid(boolean allStringsValid) Normally, variables whose values are "on", "yes", or "true" and converted to "1.0", while the values "off", "no", and "false" are converted to "0.0".

Parameters: stmt a string representation of an arithmetic expression or assignment

Returns: a string representation of the computed result or null

Throws: ArithmeticException occurs when a result is improper (e.g. infinity) or when the input statement can not be parsed

getValue

Computes the value of the statement passed in the parameter string and returns a string representation of the result. If the input statement consists only of a variable name and the result of the computation is zero, null is returned. The second parameter is used as a symbol table for the duration of this method call. Note this method is not thread safe!

Parameters: stmt a string representation of an arithmetic expression or assignment d the temporary symbol table

Returns: a string representation of the computed result or null

Throws: ArithmeticException occurs when a result is improper (e.g. infinity) or when the input statement can not be parsed

Class Calculator