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Java OOP, collections, multithreading

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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.431 Easy I/O Streams

A RandomAccessFile is opened with mode 'r'. Which operation will throw an exception?

A Reading bytes from the file

B Seeking to a specific position

C Writing bytes to the file

D Closing the file

Correct Answer: C. Writing bytes to the file

EXPLANATION

Mode 'r' allows read-only access. Write operations will throw IOException.

Test

Q.432 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.

Test

Q.433 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.

Test

Q.434 Hard I/O Streams

A developer uses PipedInputStream and PipedOutputStream in the same thread. What will happen?

A The program will execute successfully

B A deadlock will occur because both read and write happen in the same thread

C The pipe will be closed automatically

D An IOException will be thrown immediately

Correct Answer: B. A deadlock will occur because both read and write happen in the same thread

EXPLANATION

Pipes require separate threads for reading and writing. Using both in the same thread causes deadlock.

Test

Q.435 Easy I/O Streams

What will be the output of reading from a ByteArrayInputStream initialized with bytes [65, 66, 67] after calling read() three times?

A 65, 66, 67

B ABC

C A, B, C

D -1

Correct Answer: A. 65, 66, 67

EXPLANATION

read() returns integer values of bytes. [65, 66, 67] are ASCII values for 'A', 'B', 'C'. Multiple read() calls return these values sequentially.

Test

Q.436 Hard I/O Streams

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

A PrintStream

B FileOutputStream

C BufferedOutputStream

D PipedInputStream

Correct Answer: A. PrintStream

EXPLANATION

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

Test

Q.437 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.

Test

Q.438 Easy I/O Streams

Which of the following correctly demonstrates chaining multiple filters in Java I/O?

A new BufferedReader(new FileReader(file))

B new FileReader(new BufferedReader(file))

C new Reader(new BufferedReader(new FileReader(file)))

D new BufferedInputStream(new FileInputStream(new File(file)))

Correct Answer: A. new BufferedReader(new FileReader(file))

EXPLANATION

Filter streams are chained from inside-out. FileReader is wrapped with BufferedReader for better performance.

Test

Q.439 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.

Test

Q.440 Hard I/O Streams

Which of the following is true about serialization in Java?

A All classes are serializable by default

B A class must implement Serializable interface to be serialized

C Serialization is only for primitive types

D Static fields are always serialized

Correct Answer: B. A class must implement Serializable interface to be serialized

EXPLANATION

A class must explicitly implement the Serializable interface to be serialized. Static fields are not serialized, and not all classes are serializable by default.

Test

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