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Floating Confusion  RSS feed

 
Greenhorn
Posts: 22
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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!
 
Ranch Hand
Posts: 2410
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Remember that an implict conversion to double is taking place.

Consider this code.



The output is

 
Talib Jockey
Greenhorn
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Thanks bro..but its kindda wierd!!
 
Ranch Hand
Posts: 1970
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(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 ]
     
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