org.josef.util.rpn

Class RpnCalc

java.lang.Object

org.josef.util.rpn.RpnCalc

public final class RpnCalc
extends Object

Basic RPN (Reverse Polish Notation) calculator.
For an explanation of RPN, check out the article at WikiPedia here.
An RPN calculator is stack based. Lets examine the evaluation of the * expression: "3 4 - 5 + sqrt". The following steps are performed in order:

1. 3 is pushed on the stack
2. 4 is pushed on the stack
3. The "-" operator is encountered
4. pop the right operand (4) from the stack
5. pop the left operand (3) from the stack
6. push the result of "3 - 4" on the stack
7. 5 is pushed on the stack
8. The "+" operator is encountered
9. pop the right operand (5) from the stack
10. pop the left operand (-1) from the stack
11. push the result of "-1 + 5" on the stack
12. The "sqrt" operator is encountered
13. pop the operand (4) from the stack
14. push the result of sqrt(4) on the stack

The stack should now contain the single value "2.0".
Note: Besides the basic operators +, - , *, /, this class supports most methods of Math as operators. So exp is a method on class Math and hence "exp" is also the name of a supported operator.

Version:

2.0 $Revision: 3753 $

Author:

Kees Schotanus

Constructor Summary

Constructors

Constructor and Description
RpnCalc() Creates a new RPN calculator with an empty stack.

Method Summary

Modifier and Type	Method and Description
double	evaluate(String expression) Evaluates the supplied expression which should be written in RPN notation.
static void	main(String[] args) Command line version of this calculator.

Methods inherited from class java.lang.Object

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

Constructor Detail

RpnCalc

public RpnCalc()

Creates a new RPN calculator with an empty stack.

Method Detail

evaluate

public double evaluate(String expression)

Evaluates the supplied expression which should be written in RPN notation.
A valid expression would be: "3 4 - 5 + sqrt". The result is: sqrt((3 - 4) + 5) = 2.

Parameters:

expression - The expression to evaluate.
Operands and operators should be separated by spaces or tabs.

Returns:

The result of evaluating the expression.

main

public static void main(String[] args)

Command line version of this calculator.
Simply enter an RPN expression and press enter to evaluate it. Expressions can be entered using multiple arguments like this:
3 4 - 5 + sqrt
Or as a single argument using quotes, like this: "3 4 - 5 + sqrt".

Parameters:

args - Optional RPN expression
When present the command line arguments will be evaluated and no further user input is asked.