Mostly core Java and SQL. Collections Hierarchy Collections.synchronizedCollection(Collection ) HashMap versus Hashtable Equals and hashCode ArrayList versus vector ArrayList verus LinkedList Treemap versus treeset Iterators Concurrent Hashmap Executor Pool Thread framework. Hashmap internals. Why doesn't hashtable allowe null key? BlockingQueue Reentrant lock Read write lock Deadlock program. How to avoid deadlock Wait, notify program Wait versus sleep,Wait versus yield InteruptedException Illegal monitor exception Exceptions thrown by threads. Why are strings immutable Abstract class versus interace OOPS Overriding versus overloading Exception hierarchy User defined exception Class.forname Reflection Garbage collection. When is it called. PermGen EdenSpace Static Final Comparator, comparable. Array.sort Colelctions.sort Joins SQL functions, like date, char String builder versus String buffer Singleton Factory Abstract factory Observer Composite JSP architecture