regarding negation operation

[betzi kuriakose]

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



}
}

The following code produces -4 .
I thought the answer was 0 as the result flows out of the range for byte primitive type.
Could anybody advise on this?

regards & thanks
betzi

[Jay Pawar]

The easiest way to calculate the result of negation operator :

Consider the code below;

int x = 6;
int y = ~x;

The result can be calculated using the formula y = (x+1) * (-1);
in this case it would y = (6+1) * (-1) which is -7.

Hope that helps...

[Joe Sondow]

And to understand why Jay's formula works, you can write out the bits.

byte x = 3;         // 00000011 which is 3
byte y = (byte) ~x; // 11111100 which is -4

Again, the formula is
~x = (x+1) * (-1)
or
~x = -(x+1)

You can see the formula in action from this chart of values. Remember that 11111111 is -1.

     x               ~x
00000000 = 0    11111111 = -1
00000001 = 1    11111110 = -2
00000010 = 2    11111101 = -3
00000011 = 3    11111100 = -4
00000100 = 4    11111011 = -5
00000101 = 5    11111010 = -6
00000110 = 6    11111001 = -7
00000111 = 7    11111000 = -8