SAP interview question

1st Round : 1. '== 'vs equals() method in Java. 2. contract between equals() anf hashCode() 3. HashMap vs ConcurrentHashMap 4. Volatile keyword and atomic in multithreading 5. synchronize keyword and implementation 6. Exception vs Error in java 7. SQL: Find nth high salary from emp table 8. Find manager of an employee from employee table (self join using id) 9. like operator in SQL queries, indexing etc... Round 2: 1. java 7 vs 8 (Interfaces) 2. Why Functinal interface when abstract class is avail in java 8 3. default methods in java8 4. Lambda Expressions 5. Write code to find the given equation is balanced or not (hint : can solve using stack) 6. Find loop in a LinkedList if exists 7. Find the sub strings of length 'K' in a given String and arrange them in a lexical way. 8. Design Relational DB for Student, Course and Subject tables.