The ChecksumAccumulator class has a single private field value sum, which is initialized to 0. It further has two methods, namely add, which is adding the bytes of a string, and checksum which is calculating the final checksum. checksum first uses the bitwise operator & with the final sum and the hexadecimal 0xFF. It then takes the result of the & operator and applies another bitwise operator to it ~. Finally, it adds a 1 to the result of the ~ operator, resulting in the final checksum value.