JDK 1.5 introduces some good concurrent collections which is highly efficient for high volume http://javarevisited.blogspot.com/2011/04/difference-between-concurren...
How HashMap works in Java or sometime how get method work in HashMap is common interview questions now days. Almost everybody who worked in Java knows http://javarevisited.blogspot.com/2011/02/how-hashmap-works-in-java.ht...
This question oftenly asked in interview to check whether candidate understand correct usage of collection classes and aware of alternative solutions http://javarevisited.blogspot.com/2010/10/difference-between-hashmap-a...
This question is from early ages of interview , I have not seen this question on recent interviews but it was common during 2006-2007 , now days quest http://javarevisited.blogspot.com/2010/10/what-is-difference-between-e...