Java Programming — I/O Streams Questions & Answers

Q.21 Medium I/O Streams

Which class is used to read primitive data types and strings from a binary stream?

A BufferedInputStream

B DataInputStream

C ObjectInputStream

D SequenceInputStream

Correct Answer: B. DataInputStream

EXPLANATION

DataInputStream provides methods like readInt(), readDouble(), readUTF() to read primitive data types and strings from binary streams.

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Q.22 Easy I/O Streams

In Java, what is the primary purpose of the flush() method in output streams?

A To close the stream permanently

B To clear the internal buffer and write pending data

C To reset the stream position to the beginning

D To increase the buffer size

Correct Answer: B. To clear the internal buffer and write pending data

EXPLANATION

The flush() method forces any buffered output bytes to be written out. It does not close the stream, allowing further writes after flushing.

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Q.23 Easy I/O Streams

Which interface must be implemented to make an object serializable in Java?

A Cloneable

B Serializable

C Comparable

D Iterable

Correct Answer: B. Serializable

EXPLANATION

The Serializable interface must be implemented to serialize objects. It is a marker interface with no methods. Classes implementing it can be serialized using ObjectOutputStream.

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Q.24 Medium I/O Streams

What is the default buffer size used by BufferedInputStream?

A 512 bytes

B 1024 bytes

C 8192 bytes

D 4096 bytes

Correct Answer: C. 8192 bytes

EXPLANATION

The default buffer size for BufferedInputStream is 8192 bytes (8 KB). This can be overridden by using the constructor BufferedInputStream(InputStream, int size).

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Q.25 Easy I/O Streams

Which of the following is NOT a character stream class in Java?

A FileReader

B BufferedWriter

C FileInputStream

D PrintWriter

Correct Answer: C. FileInputStream

EXPLANATION

FileInputStream is a byte stream class, not a character stream. FileReader, BufferedWriter, and PrintWriter are all character stream classes.

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Q.26 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.

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Q.27 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.

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Q.28 Medium I/O Streams

What happens when you create a FileOutputStream with an existing file?

A Throws FileAlreadyExistsException

B Appends to the existing file

C Overwrites the existing file contents

D Merges with existing content

Correct Answer: C. Overwrites the existing file contents

EXPLANATION

FileOutputStream(String filename) by default overwrites existing file. Use FileOutputStream(File, boolean append) with true to append.

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Q.29 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.

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Q.30 Medium I/O Streams

What is the correct way to ensure resources are properly closed in Java 7+?

A Call close() in finally block

B Use try-with-resources statement

C Rely on garbage collector

D Call flush() before closing

Correct Answer: B. Use try-with-resources statement

EXPLANATION

Try-with-resources (try-with-resources statement) automatically closes AutoCloseable resources, ensuring proper cleanup even if exceptions occur.

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