Which of the following classes is used to read primitive data types from an input stream in Java?

The correct answer is A: DataInputStream. DataInputStream is specifically designed to read primitive data types like int, double, boolean, etc. from an input stream. BufferedInputStream provides buffering, FileInputStream reads from files, and ObjectInputStream deserializes objects.

In a high-concurrency scenario using Java 21, which approach is recommended for I/O-bound operations?

The correct answer is A: Virtual Threads with structured concurrency. Virtual Threads (Project Loom) are ideal for I/O-bound operations as they have minimal overhead and can number in millions, improving scalability significantly.

Consider the following code. What will be the likely behavior? java synchronized void method1() { method2(); } synchronized void method2() { }

The correct answer is C: Code will execute without issues due to reentrant locks. Java's intrinsic locks are reentrant, meaning the same thread can acquire the same lock multiple times. The thread can call method2() from method1() without deadlock.

What will happen if you try to access an index out of bounds in an array?

The correct answer is C: Throws ArrayIndexOutOfBoundsException. Accessing an array index that doesn't exist throws an ArrayIndexOutOfBoundsException at runtime. This is a checked exception that must be handled or declared.

What will be the output of the following code? Object lock = new Object(); synchronized(lock) { synchronized(lock) { System.out.println("Nested"); } }

The correct answer is A: Will compile and print 'Nested' successfully. Java supports reentrant locks on synchronized blocks. The same thread can acquire the same lock multiple times. The lock is released only when the outermost synchronized block exits.

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Java Programming

Java OOP, collections, multithreading

270 Q 10 Topics Take Mock Test

Difficulty: All Easy Medium Hard 261–270 of 270

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.261 Easy Basics & Syntax

What will be the output: String s = "Hello"; System.out.println(s.charAt(1));

A H

B e

C l

D o

Correct Answer: B. e

EXPLANATION

charAt() uses 0-based indexing. Index 1 refers to the second character, which is 'e' in "Hello".

Test

Q.262 Easy Basics & Syntax

Which of the following is the correct syntax for a multi-line comment in Java?

A // This is a comment

B /* This is a comment */

D # This is a comment

Correct Answer: B. /* This is a comment */

EXPLANATION

Multi-line comments in Java use /* */ syntax. Single-line comments use //. Other syntaxes are for different languages.

Test

Q.263 Easy Basics & Syntax

What will be printed? float f = 5.5f; System.out.println(f);

A 5.5

B 5.50

C Error

D 5

Correct Answer: A. 5.5

EXPLANATION

The 'f' suffix indicates a float literal. The output will be 5.5 (trailing zeros are not shown in standard printing).

Test

Q.264 Easy Basics & Syntax

Which of the following is a valid variable name in Java?

A 123abc

B _myVar

C my-Var

D class

Correct Answer: B. _myVar

EXPLANATION

Variable names must start with a letter, underscore (_), or dollar sign ($). They cannot start with digits, contain hyphens, or be reserved keywords.

Test

Q.265 Easy Basics & Syntax

Which keyword is used to prevent a class from being inherited?

A static

B abstract

C final

D private

Correct Answer: C. final

EXPLANATION

The 'final' keyword prevents a class from being extended/inherited. A final class cannot have subclasses.

Test

Q.266 Easy Basics & Syntax

What will be the output of: System.out.println(5 / 2);

A 2.5

B 2

C 2.0

D Error

Correct Answer: B. 2

EXPLANATION

Integer division in Java results in an integer. 5/2 = 2 (remainder is discarded). To get 2.5, at least one operand must be float/double.

Test

Q.267 Easy Basics & Syntax

What will be the output of: boolean flag = true; System.out.println(!flag);

A true

B false

C !true

D Compilation error

Correct Answer: B. false

EXPLANATION

The logical NOT operator (!) inverts the boolean value. !true becomes false.

Test

Q.268 Easy Basics & Syntax

What will be the output of the following code? int x = 5; x += 3; System.out.println(x);

A 3

B 5

C 8

D 53

Correct Answer: C. 8

EXPLANATION

The += operator adds the right operand to the left operand. x += 3 is equivalent to x = x + 3, so 5 + 3 = 8.

Test

Q.269 Easy Basics & Syntax

Which keyword is used to create a constant variable in Java?

A const

B constant

C final

D immutable

Correct Answer: C. final

EXPLANATION

The 'final' keyword is used to declare constants in Java. Once assigned, the value cannot be changed.

Test

Q.270 Easy Basics & Syntax

Which of the following is the correct syntax to declare a variable in Java?

A int x = 10;

B int x: 10;

C x int = 10;

D int: x = 10;

Correct Answer: A. int x = 10;

EXPLANATION

Java uses the syntax 'datatype variableName = value;' for variable declaration.

Test

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