In a complex Spring application, when would you prefer to use ObjectFactory over direct bean injection?

The correct answer is D: All of the above scenarios. ObjectFactory enables lazy initialization, provides new instances for prototype beans, and can help resolve circular dependencies through deferred access.

In a multi-threaded application, multiple threads are writing to the same file simultaneously using FileOutputStream. What is the primary issue and best solution?

The correct answer is B: Data corruption can occur; use synchronized blocks or PrintWriter with autoFlush enabled. FileOutputStream is NOT thread-safe. When multiple threads write simultaneously, race conditions can cause data corruption or interleaved writes. Solutions include: synchronizing access using synchronized blocks, using thread-safe wrapper classes, or employing a single-threaded writer pattern with a

In a high-traffic web application using Java 21 Virtual Threads, what is the main performance benefit?

The correct answer is B: Virtual Threads reduce memory overhead per thread, allowing millions of concurrent connections. Virtual Threads are lightweight (millions can run) with minimal memory overhead compared to platform threads (thousands). They automatically handle I/O blocking without thread creation, making them ideal for high-concurrency scenarios.

Consider a method signature: public void readFile() throws IOException. Which statement is correct?

The correct answer is B: This method may throw IOException that caller must handle. throws declaration indicates the method may throw IOException. The caller is responsible for handling it with try-catch or declaring throws. The method doesn't always throw it.

What will be the output? class Parent { void show() { System.out.println("Parent"); } } class Child extends Parent { void show() { System.out.println("Child"); } } parent obj = new Child(); obj.show();

The correct answer is B: Child. This demonstrates method overriding and polymorphism. The actual object type is Child, so Child's show() method is called.

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Java Programming
Collections Framework

Java OOP, collections, multithreading

49 Q 10 Topics Take Mock Test

Difficulty: All Easy Medium Hard 11–20 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.11 Medium Collections Framework

What is the initial capacity of a HashMap in Java?

A 8

B 16

C 32

D 64

Correct Answer: B. 16

EXPLANATION

HashMap has an initial capacity of 16 and doubles its capacity when load factor (0.75) is reached.

Test

Q.12 Medium Collections Framework

Which collection allows duplicate keys in Java?

A HashMap

B HashSet

C TreeSet

D None of these

Correct Answer: D. None of these

EXPLANATION

No collection allows duplicate keys. When a duplicate key is added to a Map, it overwrites the previous value. HashSet and TreeSet don't allow duplicates.

Test

Q.13 Medium Collections Framework

What does Collections.unmodifiableList() return?

A A list that cannot be modified

B An empty list

C A synchronized list

D A sorted list

Correct Answer: A. A list that cannot be modified

EXPLANATION

Collections.unmodifiableList() returns a read-only view of the list. Any modification attempts throw UnsupportedOperationException.

Test

Q.14 Medium Collections Framework

Which interface should be implemented to define custom sorting in Collections.sort()?

A Comparable

B Collection

C Iterator

D Serializable

Correct Answer: A. Comparable

EXPLANATION

The Comparable interface allows objects to define their natural ordering by implementing compareTo() method.

Test

Q.15 Medium Collections Framework

What is the key difference between TreeSet and HashSet?

A TreeSet allows null elements

B TreeSet maintains sorted order, HashSet does not

C HashSet is faster than TreeSet

D TreeSet is thread-safe

Correct Answer: B. TreeSet maintains sorted order, HashSet does not

EXPLANATION

TreeSet implements SortedSet and maintains elements in sorted order with O(log n) operations. HashSet has O(1) average operations but no order guarantee.

Test

Q.16 Medium Collections Framework

Which method is used to remove all elements from a Collection that satisfy a given predicate?

A remove(Object o)

B removeAll(Collection c)

C removeIf(Predicate filter)

D clear()

Correct Answer: C. removeIf(Predicate filter)

EXPLANATION

The removeIf() method was introduced in Java 8 to remove elements based on a given Predicate condition.

Test

Q.17 Medium Collections Framework

What is the advantage of using LinkedList over ArrayList for frequent insertions at the beginning?

A LinkedList has O(1) insertion at beginning, ArrayList has O(n)

B ArrayList is always faster

C LinkedList uses less memory

D LinkedList supports null values while ArrayList doesn't

Correct Answer: A. LinkedList has O(1) insertion at beginning, ArrayList has O(n)

EXPLANATION

LinkedList provides O(1) insertion at the beginning (head), while ArrayList requires O(n) time to shift elements. Both support nulls and LinkedList uses more memory due to node pointers.

Test

Q.18 Medium Collections Framework

Which method in NavigableMap returns a view of the map in descending order?

A descendingMap()

B reverseMap()

C inverseMap()

D sortedMap()

Correct Answer: A. descendingMap()

EXPLANATION

descendingMap() method of NavigableMap returns a reverse-ordered view. reverseMap() doesn't exist in Collections Framework.

Test

Q.19 Medium Collections Framework

Consider: Set set = new HashSet(Arrays.asList(1,2,3,2,1)); System.out.println(set.size()); What is the output?

A 5

B 3

C 2

D 1

Correct Answer: B. 3

EXPLANATION

HashSet removes duplicates. The list [1,2,3,2,1] is converted to a set containing only unique elements {1,2,3}, so size is 3.

Test

Q.20 Medium Collections Framework

In what scenario would you use a ConcurrentHashMap instead of HashMap?

A When you need faster performance

B When you need thread-safe operations without locking entire map

C When you need to store null values

D When you need to maintain insertion order

Correct Answer: B. When you need thread-safe operations without locking entire map

EXPLANATION

ConcurrentHashMap uses bucket-level locking (segment locking in Java 7, node-level in Java 8+) allowing concurrent reads/writes, making it thread-safe without synchronizing the entire map.

Test

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