question from dan's exam:On operators

[Chiran Mathur]

class D {
public static void main (String args[]) {
int i1 = ~1;
int i2 = -1;
int i3 = -2;
System.out.print(Integer.toHexString(i1) + ",");
System.out.print(Integer.toHexString(i2) + ",");
System.out.print(Integer.toHexString(i3));
}
}

What is the result of attempting to compile and run the above program?
a. Prints: ffffffff,ffffffff,ffffffff
b. Prints: ffffffff,ffffffff,fffffffe
c. Prints: ffffffff,fffffffe,ffffffff
d. Prints: ffffffff,fffffffe,fffffffe
e. Prints: fffffffe,ffffffff,ffffffff
f. Prints: fffffffe,ffffffff,fffffffe
g. Prints: fffffffe,fffffffe,ffffffff
h. Prints: fffffffe,fffffffe,fffffffe
i. Runtime error
j. Compiler error
k. None of the above
I am somehow just not getting any of the above values. The answer is:f

[Ambapali Pal]

You should get it.
What is your answer ?

[Barry Gaunt]

Running the program gives the answer of f.
What does your program give?

[Dan Chisholm]

Chiran,
This is really just a question about the two's complement representation of integral values. A good tutorial on the subject is the Cat and Mouse Games with Bits.
If you need to review hexadecimal then the following base conversions tutorial might be helpful.

[Dan Chisholm]

Originally posted by Barry Gaunt:
Running the program gives the answer of f.
What does your program give?

Barry,
I'm sure that Chiran obtains the results specified by answer f. Furthermore, I suspect that Chiran is either American or lives here in the United States and sometimes uses the statement "I don't get it" in place of the statement "This appears to be nonsense."

[Barry Gaunt]

Hi Dan. I know, I'm an absolute beast sometimes
I actually did paste the program into BlueJ (plug) to test it, just in case, and it gave answer f. I was just trying to get Chiran to elaborate on his misunderstanding...
Cheers ,
-Barry

[Chiran Mathur]

Dan,
Thanks a lot for the great tutorials. I am confused about -2 though. Wouldn't -2 be
1111 1101
and therfore the answer will be fffffffd
instead of fffffffe
Please clarify.
Thanks,

[Barry Gaunt]

Chiran, the trick to remember is "flip the bits and add one". So, using 8 bits, 2 is 0000 0010.
"Flipping" the bits gives: 1111 1101
Adding one: 1111 1110, in hexadecimal that is FE.
So, in terms of an int: -2 is 0xfffffffe.
Cheers , Barry