Which of these declarations would NOT cause a compilation warning or error?

The correct answer is A: List list = new ArrayList();. Option A uses proper diamond syntax with matching type parameters on both sides. Options B, C produce unchecked warnings, and Option D is invalid due to invariance.

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?

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

Which of the following is a feature of Java 8 that allows functional programming?

The correct answer is A: Lambda expressions. Lambda expressions were introduced in Java 8, enabling functional programming. Syntax: (parameters) -> expression or statement

Which lambda expression is equivalent to the method reference Integer::parseInt?

The correct answer is A: (s) -> Integer.parseInt(s). Method reference Integer::parseInt is equivalent to lambda (s) -> Integer.parseInt(s).

In JDBC, what is the purpose of using a SavePoint in a transaction?

The correct answer is B: To create a checkpoint within a transaction that can be rolled back to independently. A SavePoint allows you to roll back part of a transaction without rolling back the entire transaction. You can create nested transactions by setting multiple savepoints and rolling back to specific ones.

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Java Programming
I/O Streams

Java OOP, collections, multithreading

20 Q 10 Topics Take Mock Test

Difficulty: All Easy Medium Hard 1–10 of 20

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 Hard I/O Streams

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

A FileOutputStream is thread-safe by default, no issues will occur

B Data corruption can occur; use synchronized blocks or PrintWriter with autoFlush enabled

C Only the last thread's data will be written; use multiple FileOutputStreams

D FileOutputStream will throw ConcurrentModificationException automatically

Correct Answer: B. Data corruption can occur; use synchronized blocks or PrintWriter with autoFlush enabled

EXPLANATION

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 queue. PrintWriter with autoFlush provides some buffering protection.

Test

Q.2 Hard I/O Streams

What is the primary advantage of PushbackInputStream?

A It reads data faster than regular InputStream

B It allows pushing back bytes to be read again

C It automatically compresses data

D It provides thread-safe reading

Correct Answer: B. It allows pushing back bytes to be read again

EXPLANATION

PushbackInputStream allows you to 'unread' bytes using the unread() method. This is useful for parsers that need to look ahead without consuming the data.

Test

Q.3 Hard I/O Streams

Consider a scenario where you need to read a large binary file efficiently without loading it entirely into memory. Which approach combines best practices?

A FileInputStream with small fixed-size buffer array

B BufferedInputStream with DataInputStream for typed data

C FileInputStream with manual buffering

D ByteArrayInputStream after reading entire file

Correct Answer: B. BufferedInputStream with DataInputStream for typed data

EXPLANATION

BufferedInputStream provides automatic buffering (8KB default), and DataInputStream allows reading typed data. Together they enable efficient reading of large binary files without loading everything into memory.

Test

Q.4 Hard I/O Streams

When deserializing an object, which methods are called in order?

A Constructor, then readObject()

B readObject() only, constructor is not called

C readObject(), then constructor

D Depends on the class implementation

Correct Answer: B. readObject() only, constructor is not called

EXPLANATION

During deserialization, the constructor is NOT called. readObject() restores the object state directly from the serialized data. This is why transient fields need special handling.

Test

Q.5 Hard I/O Streams

What is the main advantage of using RandomAccessFile over sequential streams?

A Faster reading speed

B Ability to seek to any position in the file

C Smaller memory footprint

D Better thread safety

Correct Answer: B. Ability to seek to any position in the file

EXPLANATION

RandomAccessFile allows you to read/write at any position in a file using seek() method. Sequential streams can only read/write sequentially from current position.

Test

Q.6 Hard I/O Streams

In a log aggregation system, what is the primary advantage of using RandomAccessFile over sequential streams?

A It's always faster

B It allows seeking to specific positions without reading all data sequentially

C It supports threading automatically

D It automatically compresses data

Correct Answer: B. It allows seeking to specific positions without reading all data sequentially

EXPLANATION

RandomAccessFile supports seek() operation to jump to specific file positions, useful for reading log tail or accessing specific records directly.

Test

Q.7 Hard I/O Streams

Which approach would you use to read and write objects to a file efficiently in a production application?

A Manually serialize each field with DataOutputStream

B Use ObjectInputStream/ObjectOutputStream with proper version control

C Convert objects to JSON and use FileWriter

D Create custom byte arrays for each object

Correct Answer: B. Use ObjectInputStream/ObjectOutputStream with proper version control

EXPLANATION

ObjectInputStream/ObjectOutputStream with serialVersionUID ensures compatibility, versioning, and is the standard approach for object persistence in Java.

Test

Q.8 Hard I/O Streams

Given the code: PrintWriter pw = new PrintWriter(new FileWriter("file.txt")); What issue might occur?

A FileWriter is not suitable for text files

B Data might not be written to disk if flush() is not called before closing

C PrintWriter cannot wrap FileWriter

D Encoding issues will definitely occur

Correct Answer: B. Data might not be written to disk if flush() is not called before closing

EXPLANATION

PrintWriter uses buffering by default. If flush() or close() is not called, buffered data may not be written to disk.

Test

Q.9 Hard I/O Streams

For developing a high-performance file copying utility handling files up to 10GB, which approach is optimal?

A Use FileInputStream/FileOutputStream with 1KB buffer

B Use BufferedInputStream/BufferedOutputStream with large buffer size

C Use FileChannel.transferTo() or NIO channels with direct buffers

D Use ObjectInputStream for binary data

Correct Answer: C. Use FileChannel.transferTo() or NIO channels with direct buffers

EXPLANATION

FileChannel.transferTo() uses OS-level optimizations for file copying, and NIO channels with direct buffers are most efficient for large file transfers.

Test

Q.10 Hard I/O Streams

Which serialization approach maintains backward compatibility better?

A Updating serialVersionUID each time the class changes

B Never using serialVersionUID

C Keeping serialVersionUID constant and managing version compatibility in readObject()

D Using random serialVersionUID values

Correct Answer: C. Keeping serialVersionUID constant and managing version compatibility in readObject()

EXPLANATION

Maintaining a constant serialVersionUID and implementing version-aware readObject() methods allows deserializing objects from different class versions.

Test

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