sunlabs.brazil.util
Class Calculator

java.lang.Object
  sunlabs.brazil.util.Calculator (view source)

public class Calculator
extends Object

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.

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".

Methods inherited from class java.lang.Object

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

Field Detail

debugging

public boolean debugging

Set true for debug output. The output probably won't make sense to anyone other than the author.

Constructor Detail

Calculator

public Calculator()

The no argument constructor will create an internal Hashtable in which it looks up and stores values associated with variables.

See Also:

Hashtable

Calculator

public Calculator(Dictionary d)

This constructor will use the Dictionary parameter to lookup and store values associated with variables.

Parameters:

d - the Dictionary object that serves as a symbol table

See Also:

Dictionary

Method Detail

stringsValid

public 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". All other values are considered an error. By passing "true", all normally invalid strings are given a value of "1.0".

getValue

public String getValue(String stmt)
                throws ArithmeticException

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.

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

public String getValue(String stmt,
                       Dictionary d)
                throws ArithmeticException

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

main

public static void main(String[] args)

A test driver for the calculator. Type in arithmetic expressions or assignments and see the results. Use "dump" to see contents of all assigned variables.

Parameters:

args - required signature for main method, not used