Interesting cast issue in Java

Some days ago I was convinced by my friend Fernando to start learning Java. I wondered, “Why not?”. While examining the first chapters of Java - A Beginner’s Guide, I stumbled upon this interesting “issue”.

Because of Java’s automatic type promotion in expressions, an aparently correct code can cause compilation errors. See…

byte b = 20;
b = b * 2;    // This will trigger a compilation error.  You can't assign an int to a byte.

To make this code work, you have to cast the expression to a byte. Something like this:

byte b = 20;
b = (byte) (b * 2);    // This will compile with no problems.

What I found really interesting is that I remembered, earlier in the book, the author saying that the += operator is slightly more performant than the standard sum and assignment combo.

int a = 10;
a = a + 5;    // This is slower.
a += 5;       // This is faster.

So I wondered, “Maybe this will work the same with a byte?”. And it turns out it worked.

byte b = 20;
b *= 2;    // Works like a charm.