This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
For LinkedList vs ArrayList, could you be more specific? Are you asking about performance differences between the two data structures?
For the HashMap, I'd suggest that you take a look at the API, try to apply what you find there in an example, and if you get stuck, show us what you've got, and we'll help you figure out what went wrong.