Rounding off numbers?

[m brown]

okay, i know this is easy, but ive been up all night and my brain just froze.
its for the following problem


" The rounding rules for
tax are that for a tax rate of n%, a shelf price of p contains
(np/100 rounded up to the nearest 0.05) amount of sales tax."

basically i just need to round the tax off to the nearest 0.5

i looked in my books and searched google they were no help.


so lets say i have

double tax;

and the tax value is 1.499.

how do i round that off to point 1.5?

[Mark Van Tuyl]

To display the rounded value, you can use something like this:

DecimalFormat format = new DecimalFormat("#.00");
 
System.out.println(format.format(1.499));

[marc weber]

Careful... DecimalFormat uses a ROUND_HALF_EVEN mode, which rounds "towards the 'nearest neighbor' unless both neighbors are equidistant, in which case, round towards the even neighbor."

This is probably not what you expect. For example, 0.15 would round to 0.2, but 0.25 would also round to 0.2 (because 2 is even). Similarly, 0.35 and 0.45 would both round to 0.4.



Run the code below to verify.

import java.text.*;
 
class DecimalRounding {
  public static void main(String[] args) {
    DecimalFormat df = new DecimalFormat("0.0");
    double d15 = 0.15;
    double d25 = 0.25;
    double d35 = 0.35;
    double d45 = 0.45;
    System.out.println(d15 + " rounds to " + df.format(d15));
    System.out.println(d25 + " rounds to " + df.format(d25));
    System.out.println(d35 + " rounds to " + df.format(d35));
    System.out.println(d45 + " rounds to " + df.format(d45));
  }
}

I suggest using instances of BigDecimal rather than doubles. This provides the precision lacking from floating-point primitives, and also offers 8 different rounding modes.