confusion of negation output of an int in java

Question

I have a int a=255=>1111 1111 after negating i.e ~a=10000 0000=>-64
isnt it suposed to be 0000 0000=>0
basically want to ~255 to 0 like in 8 bit binary format i.e
1111 1111 to 0000 0000 with out making it negative.

answer is here http://stackoverflow.com/questions/15575520/bitwise-negation-gives-unexpected-result — Fedor Skrynnikov, Feb 25 '14 at 12:53
You use `-` to negate (swap positive number for the same negative), and `~` to invert (flip all the bits). They are very similar, but not the same. — Peter Lawrey, Feb 25 '14 at 13:01

score 5 · Accepted Answer · answered Feb 25 '14 at 12:54

5

The problem is that a is probably of type int, which in Java takes up 4 bytes. So what you're getting is:

1111 1111 1111 1111 1111 1111 0000 0000

You should just mask the result, if you know that you're always going to work with 8 bits:

int b = ~a ^ 0xFF;

answered Feb 25 '14 at 12:54

PaF

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thanks i hadnt known aboout masking int objects. – Dhroiden Feb 26 '14 at 07:18

confusion of negation output of an int in java

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