Collections

1. Which interface is the root interface in the Java Collection hierarchy?

• A. Collection

• B. Map

• C. Iterable

• D. List

2. What is the main difference between ArrayList and LinkedList?

• A. ArrayList is thread-safe, LinkedList is not

• B. LinkedList allows duplicate elements, ArrayList doesn't

• C. ArrayList uses a dynamic array, LinkedList uses nodes

• D. LinkedList is faster for indexing

3. Which of these classes implements the Set interface?

• A. HashMap

• B. ArrayList

• C. HashSet

• D. TreeMap

4. Which method is used to remove all elements from a Collection?

• A. clear()

• B. deleteAll()

• C. removeAll()

• D. erase()

5. What will the following code output?
Set<String> set = new HashSet<>();

set.add("Apple");

set.add("Banana");

set.add("Apple");

System.out.println(set.size());

• A. 1

• B. 2

• C. 3

• D. Compilation Error

6. Which class guarantees that the order of elements will remain the same as inserted?

• A. HashSet

• B. TreeSet

• C. LinkedHashSet

• D. PriorityQueue

7. What is the output of this code snippet?
Map<String, Integer> map = new HashMap<>();

map.put("A", 100);

map.put("B", 200);

map.put("A", 300);
System.out.println(map.get("A"));

• A. 100

• B. 200

• C. 300

• D. Null

8. Which of the following allows duplicate keys?

• A. HashMap

• B. Hashtable

• C. LinkedHashMap

• D. None of the above

9. What does the peek() method do in a Queue?

• A. Removes the head

• B. Adds a new element

• C. Returns the head without removing it

• D. Checks if the queue is empty

10. Which collection class stores elements in sorted (natural) order?

• A. HashSet

• B. ArrayList

• C. TreeSet

• D. Vector