Package sunlabs.brazil.util
Class Calculator
java.lang.Object
sunlabs.brazil.util.Calculator
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
Fields -
Constructor Summary
ConstructorsConstructorDescriptionThe no argument constructor will create an internalHashtable
in which it looks up and stores values associated with variables.This constructor will use theDictionary
parameter to lookup and store values associated with variables. -
Method Summary
Modifier and TypeMethodDescriptionComputes the value of the statement passed in the parameter string and returns a string representation of the result.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
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".
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Field Details
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debugging
public boolean debuggingSettrue
for debug output. The output probably won't make sense to anyone other than the author.
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Constructor Details
-
Calculator
public Calculator()The no argument constructor will create an internalHashtable
in which it looks up and stores values associated with variables.- See Also:
-
Calculator
This constructor will use theDictionary
parameter to lookup and store values associated with variables.- Parameters:
d
- theDictionary
object that serves as a symbol table- See Also:
-
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Method Details
-
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
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
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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 assignmentd
- 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
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main
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 formain
method, not used
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