1) Why main method is void in JAVA? 2) Are string parameters mandatory in main method? At what time are the parameters read? 3)Difference between sleep and wait 4)Difference between yield vs join 5)Checked and unchecked exceptions. 6) Concurrent hash map. 7)Difference between isInstance and Instance of 8)When to use reflection and name few methods? 9)Fail fast vs fail safe iterator 10) JVM JRE and JDK.What does rt.jar contain? 11 )When to use LinkedHash Map and Tree map? Which is better for insertion,deletion and search? 12) What is static method?Where are static variable stored in memory? 13) JAVA memory model. 14)JAVA garbage collection process.What is survivor space? 15)When to override toString() method? 16)