Which of the following statements about abstract classes is TRUE?

The correct answer is C: Abstract classes can have abstract methods and concrete methods. Abstract classes can contain both abstract methods (without implementation) and concrete methods (with implementation). They cannot be instantiated directly.

In Java, a class can implement multiple interfaces but can extend only one class. This design choice primarily supports which principle?

The correct answer is C: Avoiding diamond problem in single inheritance. Multiple inheritance of implementation can cause the diamond problem. Java avoids this by allowing single class inheritance but multiple interface implementation.

What is the correct order of execution when you create an object in a multi-level inheritance hierarchy?

The correct answer is B: Grandparent constructor -> Parent constructor -> Child constructor. Constructor execution follows the inheritance chain from top to bottom. super() is implicitly called, executing parent constructors first.

What will happen if you try to compile this code? BiFunction concat = (a, b) -> a + b; concat.apply("Java", "8", "Features");

The correct answer is C: Compilation error - too many arguments. BiFunction takes exactly 2 parameters. Passing 3 arguments is compilation error. apply() only accepts 2 arguments.

What is the time complexity of get() method in HashMap?

The correct answer is C: O(1) average case. HashMap provides O(1) average time complexity for get() operation. In worst case with hash collisions, it can be O(n).

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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 1–10 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.1 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.2 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.3 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.4 Medium I/O Streams

In the try-with-resources statement, what happens to resources automatically?

A They are flushed but not closed

B They are closed in reverse order of opening

C They are closed in the order they were opened

D They must be manually closed in finally block

Correct Answer: B. They are closed in reverse order of opening

EXPLANATION

Try-with-resources automatically closes resources in reverse order (LIFO). All resources must implement AutoCloseable. This ensures proper resource cleanup even if exceptions occur.

Test

Q.5 Medium I/O Streams

Which class wraps a byte stream to handle character encoding/decoding?

A InputStreamReader

B BufferedReader

C FileReader

D CharArrayReader

Correct Answer: A. InputStreamReader

EXPLANATION

InputStreamReader is a bridge between byte streams and character streams. It converts bytes to characters using specified character encoding (UTF-8, ISO-8859-1, etc.).

Test

Q.6 Medium I/O Streams

What happens if you try to read from a closed stream?

A It returns -1

B It returns null

C It throws IOException

D It silently fails

Correct Answer: C. It throws IOException

EXPLANATION

Attempting to read from a closed stream throws IOException. The stream should be checked and reopened if needed, or proper resource management (try-with-resources) should be used.

Test

Q.7 Medium I/O Streams

You need to read a file line by line efficiently. Which approach is best?

A FileInputStream with byte-by-byte reading

B BufferedReader with readLine()

C FileReader with manual character buffering

D Scanner with default buffer

Correct Answer: B. BufferedReader with readLine()

EXPLANATION

BufferedReader with readLine() is the most efficient and convenient way to read files line by line. It provides buffering and a dedicated method for reading lines.

Test

Q.8 Medium I/O Streams

What is the purpose of the serialVersionUID field in a serializable class?

A To identify the version of the JVM

B To ensure version compatibility during deserialization

C To encrypt the serialized data

D To improve serialization speed

Correct Answer: B. To ensure version compatibility during deserialization

EXPLANATION

serialVersionUID is used to verify that sender and receiver have compatible versions of a Serializable class. If serialVersionUID doesn't match during deserialization, InvalidClassException is thrown.

Test

Q.9 Medium I/O Streams

Which exception is thrown when you try to serialize an object that contains non-serializable fields?

A IOException

B NotSerializableException

C SerializationException

D InvalidObjectException

Correct Answer: B. NotSerializableException

EXPLANATION

NotSerializableException is thrown when attempting to serialize an object whose class does not implement Serializable or contains non-serializable fields.

Test

Q.10 Medium I/O Streams

What is the difference between read() and read(byte[] b) methods in InputStream?

A read() returns a byte, read(byte[] b) returns multiple bytes in an array

B read(byte[] b) is faster than read()

C read() is for text files, read(byte[] b) is for binary files

D There is no practical difference

Correct Answer: A. read() returns a byte, read(byte[] b) returns multiple bytes in an array

EXPLANATION

read() reads and returns a single byte as an int (0-255 or -1 for EOF). read(byte[] b) reads bytes into an array and returns the number of bytes read.

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