Module: | Arrays, Strings & Exception Handling
Q60: Consider the following statements regarding HashSet and TreeSet:
1. HashSet internally instantiates and utilizes a HashMap to store its elements, explicitly inserting the Set elements as keys and a static dummy object as the values.
2. TreeSet guarantees an ultra-fast O(1) constant time complexity for fundamental operations such as add, remove, and contains.
3. TreeSet automatically sorts its elements into a naturally ascending sequence by physically implementing a self-balancing Red-Black Tree data structure.
Which of the above statements is/are correct?
2. TreeSet guarantees an ultra-fast O(1) constant time complexity for fundamental operations such as add, remove, and contains.
3. TreeSet automatically sorts its elements into a naturally ascending sequence by physically implementing a self-balancing Red-Black Tree data structure.
Which of the above statements is/are correct?
✅ Correct Answer: B
🎯 Quick Answer:
The correct combination is 1 and 3. Statement 2 is incorrect because the Red-Black Tree architecture of TreeSet dictates an O(log n) time complexity for basic operations, not O(1).HashSet relies on hashing for maximum speed, whereas TreeSet relies on binary trees for guaranteed sorting.
Structural Breakdown: HashSet = Unordered, accepts one null, O(1) time complexity.
TreeSet = Sorted (natural or custom comparator), rejects nulls, O(log n) time complexity.
Historical/Related Context: The architectural reuse of HashMap to build HashSet (Statement 1) was a brilliant engineering shortcut by Java's creators.
Because HashMap already possessed a perfectly optimized algorithm for preventing duplicate keys, the creators simply wrapped a HashMap inside the HashSet class and fed all added elements directly into the key parameter.
Causal Reasoning: TreeSet rejects null elements because it must continuously compare every new element against existing elements using the compareTo() method to determine left/right tree placement.
Attempting to invoke compareTo() on a null reference instantly triggers a fatal NullPointerException, breaking the tree's balancing algorithm.