BigDecimal计算大数字

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();   
  }   
}