Server : Core Java, Algorithm, Data structure(Linked list, Stack, Binary tree, Graph, Searching, sorting, Complexity, Traversal from top to bottom). Analyze thread dump, memory dump , AWR, JFR, Profiling Java, Kafka, Elastic search, Kubernetes, Spark, Hadoop, Tuning, Garbage collection algorithm, XML, JSON, Docker, Micro services, No SQL, distributed application, Multi threading , concurrency, Collections, Concurrent