How does this work

[sun par]

  
byte b1 = -5;
int i = 0xff;
byte b2 = (byte) (b1 ^ 1);
b2++;
System.out.println(b2)

The Ouptput is 5. Can someone explain
Thanks

[Jose Botella]

byte b1 = -5;
int i = 0xff;
byte b2 = (byte) (b1 ^ 1);
f 1011
f 1111
_______^
0 0100
b2++;
4 + 1
^ is or-exclusive. Only yields true if its two entries are distinct. That is 1^1 or 0^0 yield 0, but 1^0 or 0^1 yields 1
Read Cat and Mouse Games with bits for more.

[Todd Killingsworth]

Jose, where did this come from? Operand was 1, not -1.
f 1011
f 1111 <---- ???
_______^
0 0100
I'm getting an answer of -5.

Taking this from the top:

  
public class BitTest
{
    
    /** Creates a new instance of BitTest */
    public BitTest()
    {
    }
 
    public static void main (String argv [])
    {
        byte b1 = -5;
        int i = 0xff;               // red herring - not used.
        byte b2 = (byte) (b1 ^ 1);  // b2 = -5 ^ 1 = -6
        b2++;                       // b2 = -6 + 1 = -5
        System.out.println(b2);
    }
}

f 1011 -5
f 0001 1
_______^
0 1010 -6
f 0001 1
_______+
0 1011 -5

Please let me know if I'm missing something - my 2's compliment isn't very sturdy yet
Todd Killingsworth

[sun par]

I also get -5 and I am confused

[John Paverd]

Originally posted by sun par:
I also get -5 and I am confused

Sunita
If you replace byte b2 = (byte) (b1 ^ 1);
with byte b2 = (byte) (b1 ^ i);
the result will be 5. Perhaps there was a typo in the test question?
[ January 10, 2003: Message edited by: John Paverd ]

[Bert Bates]

I agree with John, not only do you get 5, but you actually use i - which otherwise you don't use.