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Java Programming

Java OOP, collections, multithreading

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Difficulty: All Easy Medium Hard 211–220 of 476

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.211 Medium I/O Streams

What exception is thrown when trying to deserialize an object that was serialized with a different serialVersionUID?

A ClassCastException

B InvalidClassException

C StreamCorruptedException

D NotSerializableException

Correct Answer: B. InvalidClassException

EXPLANATION

InvalidClassException is thrown when a serialized object's serialVersionUID doesn't match the current class definition, indicating an incompatible class version.

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Q.212 Medium I/O Streams

A file contains 1000 lines. Using BufferedReader.readLine() repeatedly reads all lines. What is the time complexity?

A O(1)

B O(log n)

C O(n)

D O(n²)

Correct Answer: C. O(n)

EXPLANATION

Reading each line requires processing each character once, resulting in O(n) complexity where n is total characters.

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Q.213 Medium I/O Streams

Which scenario would require using a SequenceInputStream?

A Reading from multiple files sequentially as a single stream

B Reading very large files

C Parallel reading from multiple files

D Converting stream encoding

Correct Answer: A. Reading from multiple files sequentially as a single stream

EXPLANATION

SequenceInputStream concatenates multiple input streams, allowing them to be read as one continuous stream.

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Q.214 Medium I/O Streams

What happens when you write to a closed PrintWriter?

A The data is buffered and written on next open

B IOException is thrown

C Data is silently discarded

D The stream reopens automatically

Correct Answer: C. Data is silently discarded

EXPLANATION

PrintWriter suppresses IOException and continues silently, unlike other streams.

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Q.215 Medium I/O Streams

What is the serialVersionUID used for in Java serialization?

A To store the Java version number

B To identify the class version for deserialization compatibility

C To encrypt the serialized object

D To track the number of times an object was serialized

Correct Answer: B. To identify the class version for deserialization compatibility

EXPLANATION

serialVersionUID identifies class versions. Mismatched versions cause InvalidClassException during deserialization.

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Q.216 Medium I/O Streams

In a CSV file processing application, why is BufferedReader preferred over FileReader for reading large files?

A BufferedReader automatically parses CSV format

B BufferedReader reduces I/O operations by reading data in chunks

C FileReader cannot read text files

D BufferedReader is faster at character encoding

Correct Answer: B. BufferedReader reduces I/O operations by reading data in chunks

EXPLANATION

BufferedReader buffers input, reducing system calls and I/O overhead, improving performance significantly.

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Q.217 Medium I/O Streams

When implementing Externalizable interface, which method is mandatory?

A serialize()

B writeObject() and readObject()

C writeExternal() and readExternal()

D write() and read()

Correct Answer: C. writeExternal() and readExternal()

EXPLANATION

Externalizable requires implementation of writeExternal() and readExternal() for complete control over serialization.

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Q.218 Medium I/O Streams

Which statement about ObjectOutputStream.reset() is correct?

A It resets the file pointer to the beginning

B It clears the internal object graph cache to enable re-serialization of identical objects

C It closes the stream and reopens it

D It deletes the serialized file

Correct Answer: B. It clears the internal object graph cache to enable re-serialization of identical objects

EXPLANATION

reset() clears ObjectOutputStream's internal cache of serialized objects, allowing duplicate objects to be serialized again.

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Q.219 Medium I/O Streams

A serialized object contains a field marked as 'transient'. What happens to this field when the object is deserialized?

A It retains its original value from before serialization

B It is set to its default value (null for objects, 0 for primitives)

C An exception is thrown during deserialization

D It becomes immutable

Correct Answer: B. It is set to its default value (null for objects, 0 for primitives)

EXPLANATION

Transient fields are excluded from serialization and are initialized to default values upon deserialization.

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Q.220 Medium I/O Streams

A Java program needs to read a file containing 10 million integers. Which approach would be most memory-efficient?

A Use FileInputStream with a byte array buffer

B Load entire file into memory using Scanner

C Use DataInputStream with buffering for sequential reading

D Read all bytes at once using Files.readAllBytes()

Correct Answer: C. Use DataInputStream with buffering for sequential reading

EXPLANATION

DataInputStream with buffering allows sequential reading without loading the entire file into memory, making it ideal for large files.

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