Floating Confusion

[Talib Jockey]

Hi All,

I have a confusion...

The following code snippet prints "true"

float f = 1.0F/3.0F;
System.out.println( (f * 3.0F) == 1.0F );

whereas the following prints "false"

double d = 1.0F/3.0F;
System.out.println( (d * 3.0F) == 1.0F );


How is it possible, the value of 1/3 cannot be precisely stored by either variable type. Then why does double return false?

Am I missing something?

Thanks!

[Keith Lynn]

Remember that an implict conversion to double is taking place.

Consider this code.

class Test10 {
 
   public static void main(String[] args) {
      float f = 1.0F/3.0F;
 
      System.out.println(f);
 
      double d = 1.0F/3.0F;
 
      System.out.println(d);
   }
 
}

The output is

0.33333334
0.3333333432674408

[Talib Jockey]

Thanks bro..but its kindda wierd!!

[Peter Chase]

(Not an Advanced question at all)

Testing for equality, with floating point, is almost always wrong. It is an inexact data type, so exact equality test generally does not do what you want.

Therefore you have two mistakes: -

using float constants (F suffix) with double type

worrying about exact equality tests in floating-point

[ September 25, 2006: Message edited by: Peter Chase ]