MCQs on Java Collections Framework | Java Data Structures
Java Collections Framework and Data Structures MCQs
Explore the essential concepts of Java Collections Framework and Data Structures with these 30 MCQs, designed to test your understanding of Lists, Sets, and Maps, along with ArrayList, LinkedList, HashMap, Iterators, and more. Whether you’re a beginner or experienced in Java, these questions will reinforce your knowledge of sorting, searching, and iterating over collections efficiently.
MCQs
1. Which interface in Java represents a collection that contains no duplicate elements?
- A. List
- B. Set
- C. Queue
- D. Map
2. The ArrayList class implements which Java interface?
- A. Set
- B. Queue
- C. List
- D. Map
3. Which class provides a dynamic array that can grow as needed?
- A. LinkedList
- B. ArrayList
- C. HashMap
- D. TreeMap
4. Which of the following methods is used to sort elements in a List?
- A. Collections.sort()
- B. Arrays.sort()
- C. List.sort()
- D. Map.sort()
5. The HashSet class in Java is part of which interface?
- A. Map
- B. Set
- C. List
- D. Queue
6. What is the time complexity of accessing an element by index in an ArrayList?
- A. O(1)
- B. O(n)
- C. O(log n)
- D. O(n log n)
7. Which of the following is NOT a valid method in the Map interface?
- A. put()
- B. get()
- C. add()
- D. containsKey()
8. Which List implementation is better suited for frequent insertions and deletions at the beginning of the list?
- A. ArrayList
- B. LinkedList
- C. Vector
- D. HashMap
9. The HashMap class stores key-value pairs and allows retrieval based on:
- A. Index
- B. Key
- C. Value
- D. Position
10. What is the purpose of the iterator() method in Java collections?
- A. To sort the collection
- B. To remove duplicates
- C. To traverse the collection
- D. To convert the collection to an array
11. Which Set implementation maintains the order of insertion?
- A. HashSet
- B. TreeSet
- C. LinkedHashSet
- D. EnumSet
12. What does the remove() method do when used with an Iterator?
- A. Removes the last accessed element
- B. Removes all elements in the collection
- C. Clears the collection
- D. Does nothing
13. Which of the following is true about HashMap keys?
- A. They must implement
Comparable - B. They must be unique
- C. They can be null
- D. Both B and C
14. In which collection can you access elements using a key-value pair?
- A. List
- B. Set
- C. Map
- D. Queue
15. Which interface should you use for a collection that doesn’t allow duplicate elements?
- A. List
- B. Set
- C. Map
- D. Queue
16. What does the ListIterator allow that the Iterator does not?
- A. Bidirectional traversal
- B. Sorting
- C. Duplicates
- D. Concurrent modifications
17. Which collection would you use to maintain a list of elements with fast access by index?
- A. HashMap
- B. LinkedList
- C. ArrayList
- D. TreeMap
18. The contains() method in Java collections is used to:
- A. Add an element
- B. Check for element existence
- C. Sort the collection
- D. Remove an element
19. Which of the following allows null values in Java Collections?
- A. HashMap keys
- B. TreeSet
- C. LinkedList
- D. None of these
20. How can you sort a list in natural order in Java?
- A. Using
sort() - B. Using
Collections.reverseOrder() - C. Using
Collections.sort() - D. Using
Arrays.sort()
21. In Java, the Comparator interface is used for:
- A. Defining natural ordering
- B. Comparing objects in custom order
- C. Sorting based on hash codes
- D. Iterating over collections
22. What is the best use case for LinkedList in Java?
- A. Random access
- B. Frequent insertions/deletions
- C. Thread safety
- D. None of these
23. Which Map implementation maintains a sorted order of keys?
- A. HashMap
- B. LinkedHashMap
- C. TreeMap
- D. EnumMap
24. The isEmpty() method returns true if:
- A. Collection is sorted
- B. Collection has no elements
- C. Collection has duplicates
- D. Collection has null values
25. The Collections.binarySearch() method requires:
- A. Unsorted list
- B. Sorted list
- C. Linked list
- D. Tree map
26. Which Set implementation uses a hashing mechanism?
- A. TreeSet
- B. HashSet
- C. LinkedList
- D. ArrayList
27. In Java, which of the following allows duplicate values?
- A. HashSet
- B. TreeSet
- C. LinkedList
- D. None of these
28. Which class would you choose for synchronized access to a List?
- A. ArrayList
- B. LinkedList
- C. Vector
- D. HashMap
29. What does the putIfAbsent method do in a Map?
- A. Replaces an existing value
- B. Adds only if the key is not present
- C. Sorts the map
- D. Removes null values
30. The addAll() method in Java collections is used to:
- A. Merge collections
- B. Remove duplicates
- C. Sort collections
- D. Clear collections
Answer Key
| QNo | Answer |
|---|---|
| 1 | B. Set |
| 2 | C. List |
| 3 | B. ArrayList |
| 4 | A. Collections.sort() |
| 5 | B. Set |
| 6 | A. O(1) |
| 7 | C. add() |
| 8 | B. LinkedList |
| 9 | B. Key |
| 10 | C. To traverse the collection |
| 11 | C. LinkedHashSet |
| 12 | A. Removes the last accessed element |
| 13 | D. Both B and C |
| 14 | C. Map |
| 15 | B. Set |
| 16 | A. Bidirectional traversal |
| 17 | C. ArrayList |
| 18 | B. Check for element existence |
| 19 | C. LinkedList |
| 20 | C. Using Collections.sort() |
| 21 | B. Comparing objects in custom order |
| 22 | B. Frequent insertions/deletions |
| 23 | C. TreeMap |
| 24 | B. Collection has no elements |
| 25 | B. Sorted list |
| 26 | B. HashSet |
| 27 | C. LinkedList |
| 28 | C. Vector |
| 29 | B. Adds only if the key is not present |
| 30 | A. Merge collections |