Explicit conversion from int to byte in Java

Question

I am trying to convert an int to byte.

int i = 128;
byte b = (byte) i;

I know the range of byte if -128 to 127 and the rule of storing an i

Answer 1

Logic is simple, Java numbers are always signed in two's complement.

Now a byte has 8 bits and 128 is 10000000. When you do

int i = 128

you end up with:

i == 00000000 00000000 00000000 10000000

When you cast it to a byte you the 24 most significative are truncated, so you end up with

b == 10000000

but a Java byte is signed, and 128 can't be represented, since it overflows and wraps around. So what happens is that the value ends up as 128 - 256 = -128 (that's because of two's complement).