Find best collection class for the scenarios given

Question

Hi Everyone,
Can u help me in answering this questions:
Indicate the most efficient / appropriate standard Java (JDK 1.4 or lower) collections class for each requirement. Do not use any classes that are not in the standard JDK (e.g. Apache commons-collections classes).
2.1. An un-ordered, unique collection
2.2. An insertion-ordered, non-unique collection
2.3. A sorted, unique collection
2.4. An insertion-ordered, unique collection
2.5. Random access to elements within a list
2.6. Insertion into random points within a list
2.7. A last-in-first-out queue
Please let me know what u think ?
IF possible please tell me the reason why u selected one over the other
Thanks in advance....

Answer 1

2.1. An un-ordered, unique collection
HashSet thereadOkay, why?
2.2. An insertion-ordered, non-unique collection
LinkedList thereadOkay, why?
2.3. A sorted, unique collection
TreeSet theread
TreeMap kv pair thereadOkay, but is collection with a small "c" or Collection with a captial "C"? Maps don't implement the Collection interface. In a general sense, you could consider them collections, but in Java land, usually that implies single-valued groupings--i.e., those that implement Collection.
>
2.4. An insertion-ordered, unique collection
LinkedHashSet theread
LinkedHashMap thereadSame comments as above.
2.5. Random access to elements within a list
LinkedList (In fact any class that implements List
Interface)No. Hint: Do you know what "random access" means, and why LinkedList is not a good choice?
2.6. Insertion into random points within a list
LinkedHashSet
LinkedHashMapNo. It doesn't say anything about uniqueness or k/v pairs.
2.7. A last-in-first-out queue
StackOkay.
2.8. List any of these classes which are not
thread-safe, if any. How
would you make these Collections thread-safe?
HashSet, LinkedList, TreeSet, TreeMap, LinkedHashSet,
LinkedHashMapI'm not going to match 'em all up one by one, but it seems about right.
This is typically accomplished by synchronizing on
some object that naturally encapsulates the collection
class. If no such object exists, the map should be
"wrapped" using the Collections.synchronizedMap
method. This is best done at creation time, to prevent
accidental unsynchronized access to the map:
Map m = Collections.synchronizedMap(new TreeMap(...));Sounds about right. Also sounds like it was copied and pasted. If so, do you understand it?