What is the difference between @Component and @Service annotations in Spring?

The correct answer is A: @Component is generic, while @Service is semantically used for business logic classes. @Component is a generic stereotype, while @Service is a specialized annotation indicating the class contains business logic, improving code readability.

Which statement about interface implementation in Java is true?

The correct answer is D: Both B and C are correct. Java 8 introduced default and static methods in interfaces. Any class implementing an interface must provide implementations for all its abstract methods (unless the implementing class is abstract).

What is the output? public class Test { public static void main(String[] args) { int x = 0; try { x = 5; System.out.println(x / 0); x = 10; } catch (ArithmeticException e) { x = 15; } finally { System.out.println(x); } } }

The correct answer is C: 15. x becomes 5, then ArithmeticException occurs. x becomes 15 in catch block. Finally block prints 15.

What will happen if a finally block contains a return statement?

The correct answer is A: It will override any return from try or catch block. Return in finally block overrides returns in try or catch blocks. The finally return value is what gets returned.

Which interface must be implemented to make an object serializable in Java?

The correct answer is B: Serializable. The Serializable interface must be implemented to serialize objects. It is a marker interface with no methods. Classes implementing it can be serialized using ObjectOutputStream.

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Java Programming
Collections Framework

Java OOP, collections, multithreading

22 Q 10 Topics Take Mock Test

Difficulty: All Easy Medium Hard 11–20 of 22

Topics in Java Programming

All Basics & Syntax 100 OOP in Java 100 Collections Framework 100 Multithreading 100 Exception Handling 100 I/O Streams 100 JDBC 100 Generics 100 Lambda Expressions 100 Spring Framework Basics 58

Q.11 Hard Collections Framework

In a scenario where you need to maintain a mapping with LRU (Least Recently Used) eviction policy, which class should be extended?

A LinkedHashMap with override of removeEldestEntry()

B TreeMap

C WeakHashMap

D ConcurrentHashMap

Correct Answer: A. LinkedHashMap with override of removeEldestEntry()

EXPLANATION

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

Test

Q.12 Hard Collections Framework

What is the worst-case time complexity of QuickSort when used with Collections.sort()?

A O(n log n)

B O(n²)

C O(n)

D O(log n)

Correct Answer: B. O(n²)

EXPLANATION

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).

Test

Q.13 Hard Collections Framework

Which stream terminal operation preserves encounter order in parallel streams for Collections?

A collect() with unordered Collector

B collect() with CONCURRENT and UNORDERED characteristics

C forEach() directly

D forEachOrdered()

Correct Answer: D. forEachOrdered()

EXPLANATION

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

Test

Q.14 Hard Collections Framework

What is the time complexity of subList() operation in ArrayList?

A O(1) - returns a view

B O(n) - creates a copy

C O(log n)

D O(n log n)

Correct Answer: A. O(1) - returns a view

EXPLANATION

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

Test

Q.15 Hard Collections Framework

What is the behavior when concurrent modification occurs during iteration in ConcurrentHashMap vs HashMap?

A Both throw ConcurrentModificationException

B ConcurrentHashMap allows safe iteration, HashMap throws exception

C Neither throws exception

D HashMap allows safe iteration, ConcurrentHashMap throws exception

Correct Answer: B. ConcurrentHashMap allows safe iteration, HashMap throws exception

EXPLANATION

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

Test

Q.16 Hard Collections Framework

In Java 16+, what feature improved collection performance by allowing value-based classes?

A Records with Collections

B Sealed classes restriction

C Pattern matching in iteration

D Stream API enhancements

Correct Answer: A. Records with Collections

EXPLANATION

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

Test

Q.17 Hard Collections Framework

In a multi-threaded environment, if you need a thread-safe list that allows concurrent reads, which is optimal?

A Collections.synchronizedList(new ArrayList())

B new CopyOnWriteArrayList()

C new Vector()

D new LinkedList()

Correct Answer: B. new CopyOnWriteArrayList()

EXPLANATION

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

Test

Q.18 Hard Collections Framework

Consider implementing a Comparator for custom sorting in reverse order. Which approach is correct?
List list = Arrays.asList(5, 2, 8, 1);

A Collections.sort(list, Collections.reverseOrder());

B Collections.sort(list, (a,b) -> b.compareTo(a));

C Collections.sort(list, (a,b) -> a.compareTo(b) * -1);

D All of above

Correct Answer: D. All of above

EXPLANATION

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

Test

Q.19 Hard Collections Framework

What is the behavior of get() method in LinkedHashMap with accessOrder=true?

A Returns element without affecting order

B Moves accessed element to end (updates access order)

C Throws exception

D Returns null for accessed elements

Correct Answer: B. Moves accessed element to end (updates access order)

EXPLANATION

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

Test

Q.20 Hard Collections Framework

What is the worst-case time complexity of HashMap.get() when hash collisions occur?

A O(1)

B O(log n)

C O(n)

D O(n log n)

Correct Answer: C. O(n)

EXPLANATION

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).

Test

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