final byte variable

Question

byte a = 1;
byte b = 2;
byte c = a + b; //error: incompatible types: possible lossy conversion from int to byte
System.out.println(c);

//add final
final byte d = 1;
final byte e = 2;
byte f = d + e;
System.out.println(f);
//Output: 3

Why the code compile success when I mark byte variable as final ?

Answer 1

I believe it is giving that error because of a unary numeric promotion (using the + operator).
When I ran your code and declared your first set of data types (a, b ,c) as an integer while keeping the rest of your code as is (I added 'final' as you had commented), it compiled and ran successfully for me.

Check out the link I have posted below the comment. You may have to dig a bit to understand, but I am sure it will be worth the reference.

https://docs.oracle.com/javase/specs/jls/se7/html/jls-5.html

Answer 2

Thanks Apocryphon and Ipang.

I find some description about this issue.

https://stackoverflow.com/questions/32005417/why-does-adding-final-bytes-result-in-a-byte-but-adding-non-final-bytes-results

https://stackoverflow.com/questions/15655012/how-final-keyword-works

Actually, I still can't understand.

Answer 3

@Kuanlin Chen,

I tried this and it worked on Code Playground:

byte c = (byte)(a + b);

But honestly, I don't have any idea why or how, the a, b, c are all byte but requires casting.

Answer 4

Mb 'cause type byte is too short?

Answer 5

What??????!!!!!!!