Fastenal interview questions

All the interview process had went well with interviewer being so polite and supportive throughout the interview. Firstly I was asked to introduce myself and go through the resume briefly and then I was asked to select my preferable language(JAVA, PYTHON etc.) then he started to ask me questions related to OOPS ,OS DBMS. He had asked me a lot questions from OOPS regarding the four pillars of OOPS, and coming to DSA he asked me what are the differences between ArrayList and LinkedList, HashMap and HashSet. Also he asked me about JAVA7 vs JAVA8, how do threads communicate with each other. From DBMS he asked me questions on ACID properties and DML,DDL,DCL. And from the OS he just asked me about Thrashing and diff between Thread and process. Then i was asked to write pseudo codes for implementation of enqueue and dequeue using arrays and an SQL query for finding second largest element in a table. Also he gave me a puzzle question which goes like you will be given 8 balls out of which 7 are alike with same size and one will be diff in min steps you have to find that ball using a weighing machine.