Precision error with floats in Java

Question

I'm wondering what the best way to fix precision errors is in Java. As you can see in the following example, there are precision errors:

class FloatTest
{
  public static void main(String[] args)
  {
    Float number1 = 1.89f;
    
    for(int i = 11; i < 800; i*=2)
    {
      System.out.println("loop value: " + i);
      System.out.println(i*number1);
      System.out.println("");
    }
  }
}

The result displayed is:

loop value: 11

20.789999

loop value: 22

41.579998

loop value: 44

83.159996

loop value: 88

166.31999

loop value: 176

332.63998

loop value: 352

665.27997

loop value: 704

1330.5599

Also, if someone can explain why it only does it starting at 11 and doubling the value every time. I think all other values (or many of them at least) displayed the correct result.

Problems like this have caused me headache in the past and I usually use number formatters or put them into a String.

Edit: As people have mentioned, I could use a double, but after trying it, it seems that 1.89 as a double times 792 still outputs an error (the output is 1496.8799999999999).

I guess I'll try the other solutions such as BigDecimal

Answer 1

The problem is not with Java but with the good standard float's (http://en.wikipedia.org/wiki/IEEE_floating-point_standard).

You can either:

• use Double and have a bit more precision (but not perfect of course, it also has limited precision)

• use a arbitrary-precision-library

• use numerically stable algorithms and truncate/round digits of which you are not sure they are correct (you can calculate numeric precision of operations)

Answer 2

If you really care about precision, you should use BigDecimal

https://docs.oracle.com/javase/8/docs/api/java/math/BigDecimal.html

https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/math/BigDecimal.html