BigNumCalc.java Source code

Introduction

Here is the source code for BigNumCalc.java

Source

import java.math.BigDecimal;
import java.util.Stack;

/** A trivial reverse-polish stack-based calculator for big numbers */
public class BigNumCalc {

    /** an array of Objects, simulating user input */
    public static Object[] testInput = { new BigDecimal("3419229223372036854775807.23343"), new BigDecimal("2.0"),
            "*", };

    public static void main(String[] args) {
        BigNumCalc calc = new BigNumCalc();
        System.out.println(calc.calculate(testInput));
    }

    Stack s = new Stack();

    public BigDecimal calculate(Object[] input) {
        BigDecimal tmp;
        for (int i = 0; i < input.length; i++) {
            Object o = input[i];
            if (o instanceof BigDecimal) {
                s.push(o);
            } else if (o instanceof String) {
                switch (((String) o).charAt(0)) {
                // + and * are commutative, order doesn't matter
                case '+':
                    s.push(((BigDecimal) s.pop()).add((BigDecimal) s.pop()));
                    break;
                case '*':
                    s.push(((BigDecimal) s.pop()).multiply((BigDecimal) s.pop()));
                    break;
                // - and /, order *does* matter
                case '-':
                    tmp = (BigDecimal) s.pop();
                    s.push(((BigDecimal) s.pop()).subtract(tmp));
                    break;
                case '/':
                    tmp = (BigDecimal) s.pop();
                    s.push(((BigDecimal) s.pop()).divide(tmp, BigDecimal.ROUND_UP));
                    break;
                default:
                    throw new IllegalStateException("Unknown OPERATOR popped");
                }
            } else {
                throw new IllegalArgumentException("Syntax error in input");
            }
        }
        return (BigDecimal) s.pop();
    }
}