|关注一亩三分地公众号：In the interview I only mentioned that I know some API which to get the checksum of a file, with MD5 or SHA-1. I didn't walk into the details of how MD5 and SHA-1 works. Also in my coding, I was given the API, supposely getCheckSum(File a) to get the checksum. So how to get the checksum is not the major part of the questions. I don't think you will be asked to write your own method to get checksum. However, if you show your deep understanding of how checksum is calculated, it will be a huge bonus point, in my opinion.