What is the difference between 'this' and 'super' keywords in Java?

The correct answer is B: 'this' refers to current class object and 'super' refers to parent class. 'this' is a reference to the current object instance, while 'super' is a reference to the parent class object. They are used to access members of current and parent classes respectively.

Which method is used to read a single byte from a FileInputStream?

The correct answer is A: read(). The read() method reads a single byte and returns it as an integer. Returns -1 if end of stream is reached.

What is the purpose of ForkJoinPool in Java?

The correct answer is B: To divide work recursively using divide-and-conquer approach. ForkJoinPool is designed for divide-and-conquer tasks where large problems are split (fork) into smaller subtasks and results are combined (join). It's optimized for recursive parallel algorithms.

When using ObjectInputStream, what exception is thrown if the serialVersionUID doesn't match?

The correct answer is B: InvalidClassException. InvalidClassException is thrown when deserialized class's serialVersionUID doesn't match the serialized object.

Which of the following correctly demonstrates method overloading?

The correct answer is B: Two methods with same name but different number or type of parameters in the same class. Method overloading allows multiple methods with the same name but different parameters (number, type, or order) in the same class. This is a way to implement compile-time (static) polymorphism.

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Java Programming

Java OOP, collections, multithreading

212 Q 10 Topics Take Mock Test

Difficulty: All Easy Medium Hard 161–170 of 212

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.161 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.162 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.163 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.164 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.165 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.166 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.167 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

Q.168 Hard Collections Framework

What is the initial capacity and growth strategy of ArrayList?

A Initial capacity 10, grows by 50%

B Initial capacity 16, grows by 100%

C Initial capacity 10, grows by 100% (1.5x from Java 9)

D Initial capacity 5, grows by 25%

Correct Answer: C. Initial capacity 10, grows by 100% (1.5x from Java 9)

EXPLANATION

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

Test

Q.169 Hard Collections Framework

Which method throws ConcurrentModificationException when collection is modified during iteration?

A Iterator.next()

B Enhanced for loop only

C Both Iterator and enhanced for loop

D Collection.remove()

Correct Answer: C. Both Iterator and enhanced for loop

EXPLANATION

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

Test

Q.170 Hard OOP in Java

In a banking system, Account is a parent class with method withdraw(). SavingsAccount and CurrentAccount both override it. A programmer writes: List accounts = new ArrayList(); accounts.add(new SavingsAccount()); accounts.add(new CurrentAccount()); for(Account a : accounts) a.withdraw(1000); Which concept is primarily demonstrated here?

A Encapsulation

B Abstraction only

C Polymorphism and Runtime Binding

D Inheritance only

Correct Answer: C. Polymorphism and Runtime Binding

EXPLANATION

The same withdraw() call behaves differently for SavingsAccount and CurrentAccount based on the actual object type at runtime. This is polymorphism with runtime (dynamic) binding.

Test

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