My worst interview experience.For an experienced Java developer with 9 years of experience , he is asking difference between HashMap , HashTable ConcurrentHashMap.Internal implementation of HashMap? So far so good, then he asked my Substring implementation, whether source string contains pattern string? When I gave the answer of Rabin-Karp algorithm, using rolling hash function? He said what meight the problem with it and will it work in all scenario.Since I knew this algorithm, I told so. Then he said you can leave for the day. I said ok. As I was leaving , I asked in which scenario(or input) do you think it will fail, he said you can go read at home without bothering to explain the failure scenario he thinks it has.