Calculating price after sales commission and discount

Question

The code already works, but I just want tips for improving.

import javax.swing.JOptionPane;
import java.text.DecimalFormat;
public class Calculator
{
    public static void main(String[] args)
    {
        double initialPrice = 0.00;
        double commissionRate = 0;
        double discountRate = 0;
        initialPrice = Double.parseDouble(JOptionPane.showInputDialog(null, "What is the initial price total of the sale?"));
        commissionRate = Double.parseDouble(JOptionPane.showInputDialog(null, "What is the percentage amount of the sales commission? \nFor example for 20%, type 20."));
        discountRate = Double.parseDouble(JOptionPane.showInputDialog(null, "What is the customer's discount rate? \nFor example for a 15% discount, type 15."));
        JOptionPane.showMessageDialog(null, "The final cost to the customer is \n$" + computeFinalPrice(initialPrice, commissionRate, discountRate) + ".");
    }
    public static String computeFinalPrice (double initialPrice, double commissionRate, double discountRate)
    {
        double finalPrice;
        DecimalFormat d = new DecimalFormat("0.00");
        finalPrice = (initialPrice*(commissionRate+100)*.01)*((100-discountRate)*.01);      
        return (d.format(finalPrice));
    }

Answer 1

Interesting, consider the following:

• For extra DRYness, you could have created a helper function to get a double

  private double getDouble( String msg )
  

• computeFinalPrice should probably be private

• If you wanted computeFinalPrice to be re-usable, then it probably makes more sense to return a double and keep it public
• A company would probably rather compute commission after discount, otherwise sales people will get really excited about giving 99% discounts ;)
• Either you initialize doubles with zeroes like in main() or you don't like in computeFinalPrice.
• As mentioned by another reviewer, consider Long instead of Double, as Doubles can have rounding issues.

• I would write

  finalPrice = (initialPrice*(commissionRate+100)*.01)*((100-discountRate)*.01);  
  

  as

  `finalPrice = initialPrice*(commissionRate+100)*.01*(100-discountRate)*.01;`  
  

  if I felt like messing with the code reviewer I might even

  `finalPrice = initialPrice*(commissionRate+100)*(100-discountRate)*.0001;`  
  

Answer 2

Just a quick note: Don't use floating point variables where you may need exact results:

• Effective Java, 2nd Edition, Item 48: Avoid float and double if exact answers are required
• Why not use Double or Float to represent currency?

Fortunately Java has BigDecimal.