1) Data structure used in java like ArrayLIst,LinkedList,Set,Map 2) internal working of hashmap-> interviewer is not aware hashmap improvements, he is like why hashmap is converting in Tree, this is not possible. 3) Diff between ArrayList and LinkedList 4) Diff between Controller and RestController 6) If You are not aware of completablefuture that means you are week in threading. according to interviewer. 7) Interview Asked if sudden in your microservice load is increase how you handle it 8) scenario based Question from project.