What will happen when you compile and run this code? java List strings = Arrays.asList("a", "b", "c"); List raw = strings; raw.add(123); String s = strings.get(3);

The correct answer is C: Compiles with warning, throws ClassCastException at runtime. Assigning generic type to raw type suppresses type checking. The Integer added bypasses the type system, causing ClassCastException when retrieved as String.

Consider a scenario where class B extends class A. If class A has a constructor with parameters, what must class B do?

The correct answer is B: Must explicitly call parent constructor using super(). If a parent class has a parameterized constructor and no default constructor, the child class must explicitly call it using super() to initialize parent class members.

Consider: Stream.of(1, 2, 3).map(x -> { System.out.println(x); return x * 2; }).collect(Collectors.toList()); What will print?

The correct answer is A: 1 2 3. map() is an intermediate operation. The println executes because collect() is a terminal operation that triggers evaluation. It prints 1, 2, 3 (the original values).

What is the return type of a lambda expression (x, y) -> x + y where x and y are integers?

The correct answer is C: Depends on the functional interface it's assigned to. The return type of a lambda expression is inferred from the functional interface it's assigned to. The same lambda can return Integer or int depending on the context.

Which generic wildcard usage is INCORRECT?

The correct answer is D: List. Nested wildcards like '? extends ? super T' are not allowed. Wildcards cannot be combined or nested.

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Java Programming
I/O Streams

Java OOP, collections, multithreading

53 Q 10 Topics Take Mock Test

Difficulty: All Easy Medium Hard 11–20 of 53

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.11 Medium I/O Streams

In a scenario where you need to write formatted output (like printf), which class should be used?

A BufferedWriter

B FileWriter

C PrintWriter

D OutputStreamWriter

Correct Answer: C. PrintWriter

EXPLANATION

PrintWriter provides print() and printf() methods for formatted output. It is the best choice for formatted writing to files or streams.

Test

Q.12 Medium I/O Streams

Which of the following best describes the relationship between InputStream and Reader classes?

A Reader extends InputStream

B InputStream extends Reader

C Both extend a common abstract class

D They are independent, parallel hierarchies for byte and character streams

Correct Answer: D. They are independent, parallel hierarchies for byte and character streams

EXPLANATION

InputStream and Reader are independent class hierarchies. InputStream is for byte streams and Reader is for character streams. They do not extend each other.

Test

Q.13 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.

Test

Q.14 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).

Test

Q.15 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.

Test

Q.16 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.

Test

Q.17 Medium I/O Streams

In Java NIO, which class is used for channel-based I/O?

A FileInputStream

B FileChannel

C BufferedInputStream

D DataInputStream

Correct Answer: B. FileChannel

EXPLANATION

FileChannel provides non-blocking and efficient I/O operations, memory-mapped file access, and file locking capabilities compared to traditional streams.

Test

Q.18 Medium I/O Streams

What does the available() method in InputStream return?

A Number of bytes that can be read without blocking

B Total bytes in the stream

C Remaining bytes in the file

D Whether the stream is open

Correct Answer: A. Number of bytes that can be read without blocking

EXPLANATION

available() returns an estimate of bytes that can be read without blocking. It doesn't return total file size.

Test

Q.19 Medium I/O Streams

Consider processing a 1GB file. Which approach would be most memory-efficient?

A Read entire file into a byte array

B Use BufferedInputStream with small buffer size

C Use BufferedInputStream with appropriate buffer size and process in chunks

D Use ObjectInputStream to load the whole file

Correct Answer: C. Use BufferedInputStream with appropriate buffer size and process in chunks

EXPLANATION

Processing large files in chunks using BufferedInputStream with an appropriate buffer size (like 8KB-64KB) balances memory usage and I/O efficiency.

Test

Q.20 Medium I/O Streams

What is the difference between InputStreamReader and FileReader?

A InputStreamReader accepts any InputStream; FileReader is specifically for files

B FileReader is faster than InputStreamReader

C InputStreamReader supports custom character encoding; FileReader doesn't

D Both A and C

Correct Answer: D. Both A and C

EXPLANATION

InputStreamReader is a bridge from byte streams to character streams and accepts any InputStream with optional charset. FileReader is specifically for file input with default charset.

Test

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