Question

The question is:

Why in this case i get compilation error in Java?

byte x = 0;
x = 128;

But this is legal:

x+= 999l;

I use eclipse, jdk 7.

Thank You

Answer 1

In your first one:

byte x = 0;
x = 128;

A byte is a signed integral type, 8-bits wide, and can express the range of -128 to +127.

x = 128 means “assign x to 128“, and by default, 128 is of type int, so you’re trying to assign an int to byte which would cause Possible loss of precision errors, because int is wider than byte. To get this to work, you would have to explicitly cast the value of 128.

byte x = 0;
x = (byte)128; // x is now -128.

For your second example, adding values to x is fine, but you just overflow the values.

byte x = 0;
x += 999L; // don't really need the long qualifier here
// x is now -25.