quick java question
Author
my book on the subject mentions nothing about it, so i wonder, can i make an unsigned variable in java like in c++, and if so, how?
thanks
Author
hmm, so would an int would take less space in memory if i masked it off like that? could you explain what happens here a bit further?
No, an int will use the same amount of memory regardless of the operation you are doing on it.
Author
but then, aint there little point in doing this? i might as well use the whole integer then, instead of masking it off to simulate an unsigned 8-bit, if theres no gain in memory use, right?
In some cases it will be possible to keep the value stored in a normal-sized variable (as signed; so a value in the top half of the range will instead be stored as a negative value) and just do the masking when you need to do a calculation - then store the result back if needed. Example:
Of course, optimization (according to the specific way in which you are using the variables) is left as an exercise ;)
byte numberOfEggs = (byte)144; // actually -112// ...// Tell the user how many dozens of eggs there are.System.out.println("You have " + (numberOfEggs & 255) / 12 + "dozen eggs.");// ...// Oh noes! Teh haxorz haev st0len half the eggs!!!11numberOfEggs = (byte)((numberOfEggs & 255) / 2);// The byte cast is necessary even though the value is < 128,// because Java promotes everything to an int when evaluating// the arithmetic expression.Of course, optimization (according to the specific way in which you are using the variables) is left as an exercise ;)
Author
zahlman: thanks that cool. could you explain how it works though?
to me it feels like (byte & 255) would just stay the same as it is...
say we take the number -236 (or whatever):
so why does makes java decide its positive? is it the typecast to integer or what is it?
to me it feels like (byte & 255) would just stay the same as it is...
say we take the number -236 (or whatever):
10010100 & 11111111------------- 10010100so why does makes java decide its positive? is it the typecast to integer or what is it?
As I alluded to, all the intermediate calculations are done in integers. So if you need to use unsigned ints, you'll have to add some (long) casts; and if you need to use unsigned longs, you're SOL :)
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