In the first case, when adding two byte variables, internally they are being promoted to int and so the result is an int, which you must cast back to a byte - because in Java for an arithmetic operation to be performed, the operands must be atleast an int.
In the second case, since you are adding two final byte variables, Java compiler knows that you cannot change them in future and so it performs addition at the compile time itself and assigns it to b7. Here the promoting to int & casting to byte - all are done internally at the compiling stage itself.
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