Java Programming - MCQ Practice Questions

Both Iterator and enhanced for loop use fail-fast mechanism and throw ConcurrentModificationException if collection is modified during iteration.

ArrayList starts with capacity 10. Growth factor is 50% + 1 in older versions, and 1.5x from Java 9 onwards.

In worst case with all collisions stored in linked list, get() becomes O(n). From Java 8, if collisions exceed threshold, linked list converts to balanced tree, making it O(log n).

LinkedHashMap with accessOrder=true maintains access-order. get() moves the element to the end (LRU cache behavior).

All three approaches work correctly for reverse sorting. Options A, B, and C are all valid Java code.

CopyOnWriteArrayList is optimal for read-heavy concurrent operations. It creates copy on write, allowing safe concurrent reads.

Records (Java 14+) provide compact syntax for data carriers used with collections, improving performance and readability.

ConcurrentHashMap uses segment-based locking allowing safe iteration during concurrent modifications. HashMap throws ConcurrentModificationException.

subList() returns a view (structural reference) to the original list in O(1) time, not a copy.

forEachOrdered() preserves encounter order even in parallel streams, while forEach() doesn't guarantee order.

Collections.sort() uses TimSort (hybrid of merge and insertion sort) with O(n log n) worst-case, but QuickSort's worst-case is O(n²).

LinkedHashMap can be extended and removeEldestEntry() overridden to implement LRU cache eviction policy.

Spliterator provides split() capability enabling efficient parallel stream processing with characteristics advertisement.

containsAll() returns true for empty collections because mathematically, all elements of an empty set are contained in any set (vacuous truth).

Java 8+ introduced tree nodes: when a bucket's linked list size exceeds TREEIFY_THRESHOLD (8), it converts to a Red-Black tree for better performance (O(log n) vs O(n)).

WeakHashMap uses weak references for keys. When a key is no longer strongly referenced elsewhere, it becomes eligible for garbage collection, and its entry is removed from the map.

putIfAbsent() is an atomic operation. Options A and C-D are compound operations that are not atomic and can have race conditions between checks and modifications.

Java 21+ enhanced sealed classes and pattern matching, allowing records to be used with pattern matching in collection operations and switch statements for type-safe data handling.

Collections.synchronizedMap() wraps a Map with synchronized access. However, iteration still requires external synchronization.

EnumSet is specialized for Enum constants and uses bit vectors internally, providing O(1) operations with minimal memory overhead.