Wrapper-Q

Vishnu Prakash
Ranch Hand
Posts: 1026

Q: Why Integer.MAX_VALUE is not returning equal.

Mike Gershman
Ranch Hand
Posts: 1272
Integer.MAX_VALUE has 31 bits of precision plus a sign.

A 32 bit float has 8 bits for the exponent, 23 bits for the fraction, and a sign bit. So a float loses precision (not magnitude) in the conversion from a 31 bit value.

A 64 bit double has 11 bits for the exponent, 52 bits for the fraction, and a sign bit. So double can hold a 31 bit value with no loss of precision.

Comparing an approximate number to an exact number, we get an unequal result.

Rituparno Pal
Greenhorn
Posts: 12
Dear Mike
If your Logic is fitting in this case tehn, why do the same thing is not happening for Long.MAX_VALUE

Mike Gershman
Ranch Hand
Posts: 1272
Dear Rituparno:

Thanks for your excellent question. And I thought young'uns today didn't care about bits and bytes.

Please first run the following enhancement to Vishnu's program and examine the results:

Integer.MAX_VALUE comes out differently when it is first converted to a float and then to a double than when it is converted directly to a double. This is because it must be rounded from 2147483647 to 2147483648 to fit in a float and the rounded value is then converted exactly to a double. However, any int can be exactly converted into a double without rounding. So we are comparing 2147483648 to 2147483647.

Long.MAX_VALUE is rounded from 9223372036854775807 to 9223372036854775808 when converted to either a float or a double. The rounded value converts exactly from a float to a double, without further rounding. So Long.MAX_VALUE comes out the same, whether converted directly to a double or converted to a float and then to a double.

Please feel free to study the bit representations and compare them to whichever write-up on IEEE 754 floating point format you prefer. Or ask another question - someone is always in the Big Moose Saloon.

Mike

Rituparno Pal
Greenhorn
Posts: 12
Dear Mike
Thanks very much for you reply. That was real beauty to discover the bit n byte stuffs.
Rituparno

ankur rathi
Ranch Hand
Posts: 3830
Mike the first post is clear but second one ( long one ) is not clear .
can you put some more light on this .

thanks .

Mike Gershman
Ranch Hand
Posts: 1272
Please run the code I provided, examine the output, then ask me a question and I'll do my best to explain.

Mohammed Al-Qaimari
Greenhorn
Posts: 7
I beleive you know that it's better to take 311-055 exam if you have 6-12 months of experience in Tiger.

I've been working with tiger since it's first beta release and I find the exam objectives challanging.
[ January 05, 2005: Message edited by: Mohammed Al-Qaimari ]