MIN_VALUE of Float & Double class

[shweta mathur]

Is there any specific reason why the MIN_VALUE of Float & Double class are constants holding the smallest positive nonzero value of type float/double and not the negative number.
I would always expect that MIN_VALUE of a class means you cannot have a object having a value less than MIN_VALUE. But was amazed to see the output of the following Code.

 
class CheckMinFloat{
public static void main(String args[]){
Float fl1 = new Float("-1.23454");
float f1 = fl1.floatValue();
float f2 = Float.MIN_VALUE;
Float fl2 = new Float(Float.MIN_VALUE);
System.out.println("fl1 = "+fl1);
System.out.println("fl2 = "+fl2);
if (f1 < f2 )
System.out.println("fl is less than MIN_VALUE");
if (fl1.compareTo(fl2) < 0)
System.out.println("fll is less than MIN_VALUE");
}
}

o/p
fl1 = -1.23454
fl2 = 1.4E-45
fl is less than MIN_VALUE
fll is less than MIN_VALUE

[Ben Ritchie]

It is due to the way in which floating point numbers are stored. Unlike integers, floats and doubles are stored in binary as an exponent and a mantissa (a Google search will show how these work). Simplified a bit, if you think of the number 2x10^3 (==2000), the 2 is the mantissa and the 3 is the exponent.
Both the exponent and the mantissa have a sign bit. For MAX_VALUE neither will be set, and the value is the largest that can be stored given the width of the type. The most negative number that can be stored in a Float or Double is simply equal to MAX_VALUE with the mantissa sign bit set, or in other words "-MAX_VALUE". As this is easy to work out there is not much point in storing it.
It is more useful to know the smallest number that can be stored - this will have the exponent sign bit set (so it will be very small - given the example above, 2x10^-3 == 0.002) but not the mantissa sign bit. That is what is stored in MIN_VALUE.
Hope that is clear - or at least clearer
Ben.

[shweta mathur]

Thanks Ben,
That was really nice & interesting to know..!!