BagJava

Question

Please can who explain code?
Why output - 128 ?
byte by = 1
while(by>0)
by++;
System.out.println(by);

Answer 1

Imagine you have a computer which has numbers which can have at most three digits, and you start counting in a loop.
1, 2, 3, ..., 999
once you get to 999, something interesting happens: If you add 1, you get 1000. But since your computer can store only three digits, the 1 in front is discarded and you are back at 0. This is called overflow!

Something very similar is happening in your case - it's just that the digits are binary, not decimal (0 and 1 only), and the frontmost binary digit (bit) of the number is used to store if it's a positive or negative number; 0 is positive, 1 is negative. So just by counting you will count "into" the sign bit and the number flips into the negatives.

For example:
00000000 = 0
00000001 = 1
00000010 = 2
00000011 = 3
01111111 = 127
10000000 = -128 (the leftmost bit is flipped to negative)

Negative numbers are stored a bit differently in your computer, so you overflow to -128 instead of -0. (It's called two's complement if you want to look it up)

In hope that wasn't too complicated!