I have some data in field type Byte ( I save eight inputs in Byte, every bit is one input ). How to change just one input in that field ( Byte) but not to lose information about
You really owe it to yourself to look into masking functions for and, or, and xor -- they allow you to simultaneously verify, validate, or change... one, some, or all of the bits in a byte structure in a single statement.
I'm not a java programmer by trade, but it's derived from C and a quick search online seemed to reveal support for those bitwise operations.
See this Wikipedia article for more information about this technique.