What is the benefit of using PreparedStatement over Statement for repeated queries?

The correct answer is D: Both A and B. PreparedStatement offers both pre-compilation for performance and SQL injection prevention through parameterized queries.

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.

What is the output of the following code? int x = 10; try { x = x / 0; } catch (ArithmeticException e) { x = 20; } finally { x = 30; } System.out.println(x);

The correct answer is C: 30. The finally block always executes last and sets x to 30. The output will be 30 because finally block assignments override catch block assignments.

Which class in Java is used to read primitive data types from a binary stream?

The correct answer is A: DataInputStream. DataInputStream is specifically designed to read primitive data types (int, float, double, etc.) from a binary stream using methods like readInt(), readFloat(), etc.

Which of the following correctly represents the hierarchy of Collection framework?

The correct answer is B: Iterable -> Collection -> List/Set/Queue. The correct hierarchy is Iterable (interface) -> Collection -> List/Set/Queue/Deque interfaces.

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Java Programming
I/O Streams

Java OOP, collections, multithreading

100 Q 10 Topics Take Mock Test

Difficulty: All Easy Medium Hard 1–10 of 100

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 Easy I/O Streams

Which interface must a class implement to be eligible for serialization in Java, and what is the significance of implementing it with no abstract methods?

A Cloneable interface; it marks the class as eligible for deep copying

B Serializable interface; it's a marker interface with no abstract methods that indicates serialization capability

C Externalizable interface; it provides default serialization behavior

D Comparable interface; it enables object comparison during serialization

Correct Answer: B. Serializable interface; it's a marker interface with no abstract methods that indicates serialization capability

EXPLANATION

Serializable is a marker interface (contains no methods) that signals to the JVM that objects of that class can be serialized. The absence of abstract methods means implementing classes don't need to override any methods; they just need to implement the interface to indicate serialization support.

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Q.3 Medium I/O Streams

Consider a scenario where you're processing a 5GB log file and need to count specific error messages. Which I/O strategy would be most memory-efficient?

A Load the entire file into a byte array and process it

B Use BufferedReader with readLine() in a loop to process line-by-line

C Use FileInputStream to read all bytes at once

D Convert the entire file to a String and use split() method

Correct Answer: B. Use BufferedReader with readLine() in a loop to process line-by-line

EXPLANATION

BufferedReader with readLine() processes the file line-by-line, maintaining a constant memory footprint regardless of file size. Options A, C, and D would attempt to load the entire 5GB file into memory, causing OutOfMemoryError. This is the standard approach for large file processing.

Test

Q.4 Medium I/O Streams

What will happen if you attempt to serialize a class that contains a non-serializable instance variable without declaring it as transient?

A The program will compile successfully but throw NotSerializableException at runtime

B The compiler will generate a compile-time error

C Only the serializable fields will be written to the stream

D The non-serializable field will be automatically converted to String

Correct Answer: A. The program will compile successfully but throw NotSerializableException at runtime

EXPLANATION

Java serialization requires all instance variables to be serializable or marked as transient. If a non-serializable object is encountered during serialization, NotSerializableException is thrown at runtime, not compile-time. There's no automatic conversion.

Test

Q.5 Medium I/O Streams

In a file I/O operation, you need to write objects to a file and later retrieve them. Which approach is most appropriate?

A Use FileOutputStream with DataOutputStream for object serialization

B Use ObjectOutputStream for serialization and ObjectInputStream for deserialization

C Use PrintWriter to write object toString() values

D Use ByteArrayOutputStream to store objects in memory

Correct Answer: B. Use ObjectOutputStream for serialization and ObjectInputStream for deserialization

EXPLANATION

ObjectOutputStream and ObjectInputStream are specifically designed for object serialization and deserialization. They handle the complete object state preservation. Other options are either inefficient or unsuitable for preserving object state.

Test

Q.6 Easy I/O Streams

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

A DataInputStream

B BufferedInputStream

C FileInputStream

D ObjectInputStream

Correct Answer: A. DataInputStream

EXPLANATION

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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Q.7 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.

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Q.8 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.9 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.10 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.

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