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The CORRECT ANSWER is (b) REMOVE()

Easy explanation: None.

Correct ANSWER is (B) HashMap

The EXPLANATION: AbstractMap, WEAKHASHMAP, HashMap and TreeMap provide implementation of MAP interface.

The CORRECT answer is (b) set()

EASY explanation: An ELEMENT in a LinkedList object can be changed by first using GET() to obtain the index or location of that object and the PASSING that location to method set() along with its new value.

The CORRECT OPTION is (a) ADD()

For EXPLANATION: NONE.

Correct option is (b) HashSet

The EXPLANATION: HashSet and TreeSet IMPLEMENTS Set INTERFACE where as LinkedList and ARRAYLIST implements List interface.

The CORRECT CHOICE is (d) addFirst()

To ELABORATE: NONE.

The correct answer is (d) SortedSet is an INTERFACE; TREESET is a concrete class

Explanation: SortedSet is an interface. It maintains an ORDERED set of ELEMENTS. TreeSet is an implementation of SortedSet.

Correct choice is (a) ConcurrentModificationException is thrown

Best explanation: TreeSet PROVIDES fail-fast ITERATOR. Hence when concurrently MODIFYING TreeSet it throws ConcurrentModificationException.

Correct choice is (a) True

Easy explanation: SET has CONTAINS(OBJECT o) METHOD instead of get(Object o) method as get is needed for comparing object and GETTING corresponding value.

Right answer is (C) 16, 0.75

For EXPLANATION I would SAY: We should not set the initial CAPACITY too high and load factor too LOW if iteration performance is needed.

Correct option is (a) Immutable Set

To EXPLAIN I WOULD say: Immutable Set is USEFUL in multithreaded environment. One does not need to DECLARE generic type collection. It is inferred by the context of METHOD call.

Correct CHOICE is (b) False

To explain: get(Object o) METHOD is useful when we want to compare objects based on the comparison of values. HASHSET does not provide any way to compare objects. It just guarantees UNIQUE objects STORED in the collection.

The CORRECT OPTION is (b) Shallow clone

Explanation: Default clone() METHOD uses shallow copy. The INTERNAL elements are not cloned. A shallow copy only copies the reference object.

The correct answer is (d) SESSIONLIST

To explain I WOULD say: SessionList is not an IMPLEMENTATION of LIST interface. The OTHERS are concrete classes of List.

Correct CHOICE is (b) COPYONWRITEARRAYLIST

The explanation: CopyOnWriteArrayList is a concurrent collection class. Its very efficient if ARRAYLIST is mostly used for reading purpose because it allows multiple threads to read data without LOCKING, which was not POSSIBLE with synchronized ArrayList.

Correct answer is (d) length() returns the capacity of ArrayList and size() returns the actual NUMBER of elements stored in the LIST

Explanation: length() returns the capacity of ArrayList and size() returns the actual number of elements stored in the list which is ALWAYS less than or EQUAL to capacity.

Right choice is (B) ConcurrentModificationException is thrown

To explain I WOULD say: ArrayList is not SYNCHRONIZED. Vector is the synchronized DATA structure.

The correct answer is (C) Arrays.asList() returns a FIXED length list and doesn’t allow to add or remove elements

Easiest explanation: List returned by Arrays.asList() is a fixed length list which doesn’t allow us to add or remove ELEMENT from it.add() and remove() METHOD will throw UNSUPPORTEDOPERATIONEXCEPTION if used.

Right choice is (b) COLLECTIONS.sort(listObj);

To explain: Collections provides a METHOD to sort the LIST. The order of sorting can be DEFINED USING Comparator.

Correct OPTION is (a) HASHSET listToSet = NEW HashSet(duplicateList);

Explanation: Duplicate elements are ALLOWED in List. Set contains UNIQUE objects.

The CORRECT option is (c) remove() method and using Iterator

The BEST explanation: There are 2 ways to remove an object from ARRAYLIST. We can use overloaded method remove(int INDEX) or remove(Object obj). We can also use an Iterator to remove the object.

Right OPTION is (a) ConcurrentModificationException

The best I can explain: The code will THROW ConcurrentModificationException if two THREADS ACCESS the same hashmap at the same TIME.

Right choice is (b) False

Easy explanation: Hashmap outputs in the order of HASHCODE of the keys. So it is UNORDERED but will ALWAYS have same result for same set of keys.

The CORRECT choice is (B) 2

Explanation: The key is hashed twice; FIRST by hashCode() of Object CLASS and then by internal hashing method of HASHMAP class.

Correct answer is (a) The new object replaces the older object

To explain I would SAY: HASHMAP always CONTAINS unique keys. If same KEY is inserted again, the new object replaces the PREVIOUS object.

Right option is (a) Reference equality

The explanation is: IdentityHashMap is RARELY used as it violates the BASIC CONTRACT of implementing equals() and HASHCODE() METHOD.

Right answer is (d) VECTOR

Easy explanation: Vector implements ABSTRACTLIST which internally implements Collection. OTHERS COME from implementing the MAP interface.

Correct answer is (C) toArray()

The EXPLANATION is: NONE.

The correct answer is (B) False

Easiest explanation: COLLECTION INTERFACE provides add, remove, search or ITERATE while map has clear, get, put, remove, etc.

Right option is (d) ensureCapacity()

To elaborate: When we add an element, the capacity of ArrayList OBJECT increases automatically, but we can INCREASE it manually to SPECIFIED length X by using FUNCTION ensureCapacity(x);

The CORRECT CHOICE is (a) ARRAYLIST()

For EXPLANATION: NONE.