In a multi-threaded environment, which stream class provides thread-safe read/write operations without external synchronization?

The correct answer is A: PrintStream. PrintStream (used by System.out) is internally synchronized for thread-safety, unlike other stream classes.

Which Collection method was introduced in Java 9 to create immutable collections?

The correct answer is B: List.of(). Java 9 introduced factory methods like List.of(), Set.of(), Map.of() for creating immutable collections.

Which of the following is true about try-with-resources (Java 7+)?

The correct answer is A: It automatically closes resources that implement Closeable or AutoCloseable. Try-with-resources automatically invokes close() on resources implementing AutoCloseable/Closeable. Syntax: try(Resource r = new Resource()) {...}

Which JDBC feature allows you to call stored procedures?

The correct answer is C: CallableStatement. CallableStatement is used to invoke stored procedures and functions. It extends PreparedStatement and supports IN, OUT, and INOUT parameters.

Which of the following classes is used to read primitive data types from an input stream in Java?

The correct answer is A: DataInputStream. DataInputStream is specifically designed to read primitive data types like int, double, boolean, etc. from an input stream. BufferedInputStream provides buffering, FileInputStream reads from files, and ObjectInputStream deserializes objects.

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Java Programming
Collections Framework

Java OOP, collections, multithreading

49 Q 10 Topics Take Mock Test

Difficulty: All Easy Medium Hard 1–10 of 49

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.1 Medium Collections Framework

What will be printed? Queue queue = new LinkedList(); queue.add(10); queue.add(20); queue.add(30); System.out.println(queue.poll()); System.out.println(queue.peek());

A 10 then 20

B 10 then 10

C 30 then 20

D 20 then 30

Correct Answer: A. 10 then 20

EXPLANATION

LinkedList implements Queue with FIFO behavior. poll() removes and returns 10. peek() returns 20 without removing it. Queue now contains [20, 30].

Test

Q.2 Medium Collections Framework

Which collection interface should be used if you need both key-value pairing and need to iterate in the order of keys' natural ordering?

A HashMap

B TreeMap

C Hashtable

D WeakHashMap

Correct Answer: B. TreeMap

EXPLANATION

TreeMap implements NavigableMap and SortedMap, storing key-value pairs in sorted order of keys using a Red-Black tree structure.

Test

Q.3 Medium Collections Framework

What is the time complexity of get() operation on a LinkedHashMap with n elements?

A O(1) average case

B O(n)

C O(log n)

D O(n log n)

Correct Answer: A. O(1) average case

EXPLANATION

LinkedHashMap extends HashMap and uses the same hash table for storage, maintaining O(1) average-case get operation. The doubly-linked list only maintains insertion order.

Test

Q.4 Medium Collections Framework

Which of the following statements is true about PriorityQueue?

A Elements are stored in insertion order

B It implements the sorted set interface

C Elements are ordered based on their natural ordering or a comparator

D It is thread-safe by default

Correct Answer: C. Elements are ordered based on their natural ordering or a comparator

EXPLANATION

PriorityQueue is a heap-based implementation where elements are ordered based on their priority determined by natural ordering or a custom comparator provided during initialization.

Test

Q.5 Medium Collections Framework

Which collection would you use if you need to maintain a sorted order of elements and also need O(log n) insertion/deletion time complexity?

A ArrayList

B LinkedList

C TreeSet

D Vector

Correct Answer: C. TreeSet

EXPLANATION

TreeSet maintains elements in sorted order using a Red-Black tree internally, providing O(log n) for add, remove, and contains operations.

Test

Q.6 Medium Collections Framework

Which collection interface guarantees that elements are stored in a sorted order with no duplicates?

A List

B Queue

C SortedSet

D Collection

Correct Answer: C. SortedSet

EXPLANATION

SortedSet interface guarantees sorted order and no duplicates. TreeSet is the primary implementation of SortedSet.

Test

Q.7 Medium Collections Framework

Consider a TreeMap with Integer keys. What will headMap(10) return?

A All entries with keys greater than 10

B All entries with keys less than 10

C All entries with keys less than or equal to 10

D All entries in reverse order

Correct Answer: B. All entries with keys less than 10

EXPLANATION

TreeMap.headMap(10) returns a view of all entries with keys strictly less than 10. It's exclusive of the provided key.

Test

Q.8 Medium Collections Framework

What is the purpose of the fail-fast iterator in Collections?

A To speed up iteration

B To detect concurrent modifications during iteration

C To remove elements faster

D To sort elements during iteration

Correct Answer: B. To detect concurrent modifications during iteration

EXPLANATION

Fail-fast iterators throw ConcurrentModificationException if the collection is modified during iteration (except via iterator.remove()).

Test

Q.9 Medium Collections Framework

Which collection implementation is best for frequent insertions and deletions at both ends?

A ArrayList

B LinkedList

C Vector

D Stack

Correct Answer: B. LinkedList

EXPLANATION

LinkedList provides O(1) operations for adding/removing at both ends via addFirst(), addLast(), removeFirst(), removeLast().

Test

Q.10 Medium Collections Framework

What happens when you add a null key to a HashMap?

A NullPointerException is thrown

B The null key is stored at index 0

C The null key is ignored

D The insertion fails silently

Correct Answer: B. The null key is stored at index 0

EXPLANATION

HashMap allows one null key which is handled specially and stored at index 0. TreeMap does not allow null keys.

Test

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