public byte byteValueExact ()

Converts this BigInteger to a byte, checking for lost information. If the value of this BigInteger is out of the range of the byte type, then an ArithmeticException is thrown.

Returns:  this BigInteger converted to a byte.

Exceptions:
ArithmeticException    if the value of this will not exactly fit in a byte.

See also:
BigInteger.byteValue

Since:  1.8