unsigned bytes in Java byte array

I thought that the 0xff made it unsigned.

Well, it does, sort of - it promotes it to an int, and keeps just the last 8 bits.

However, you're then casting the result of that back to a byte, and a byte in Java is always signed. (It's annoying, but it's the way it is.) So you might as well just have written:

byte[] bArray = { (byte) 0x80 };

The result would be exactly the same.

You're storing the bit pattern you want to store (10000000) so if you're transmitting this elsewhere, you don't need to worry... it's just when you're viewing it as a byte in Java that it's annoying.