Why is the output of this program -4? (Java - Datatypes Byte)

Question

I have a doubt in the following code:

public class test {
public static void main(String args[]) {
    byte x = 3;
        x = (byte)~x;
        System.out.println(x);

    }

}

The output is: -4

Do you understand what binary negation is? What did you expect the output to be? — RealSkeptic, Nov 25 '16 at 07:48
3 is 011 in binary world. Its negation is 100 which amount to 4 in base 10 and in Java it will be not(~) of a 32 bit long 011. — Vinay, Nov 25 '16 at 07:50
[How does the bitwise complement (~) operator work? Why is it that ~2 is -3?](http://stackoverflow.com/q/791328/995714) — phuclv, Nov 25 '16 at 08:13
Thanks, @LưuVĩnhPhúc, for the link. I understand the explanation given there much better than anything written in this thread (sorry, folks). — Ole V.V., Nov 25 '16 at 08:24

score 1 · Accepted Answer · answered Nov 25 '16 at 07:59

Binary negation of numver is the same as taking negative of number+1. Here's why:

Binary 3 is 0011 (leading bits skipped to make it more readable).

Binary negation ~3 is 1100.

Now, binary 4 is 0100

To determine -4, firstly write binary negation 1011.

and then add one (see wiki) 1100

1 Answers1