A multi-threaded application experiences poor performance despite having adequate CPU cores. Code inspection reveals frequent calls to synchronized blocks on shared objects. Which modern Java feature (2024-25) could optimize this without major refact

The correct answer is A: Virtual Threads with appropriate lock strategies. Virtual Threads (Project Loom, stable in Java 21+) allow massive parallelism with lightweight threads, reducing contention overhead. They enable better scaling than increasing pool size. volatile doesn't help with synchronized block contention, and static conversion is inappropriate.

What will be the output: int a = 10; int b = 20; System.out.println(a > b ? "A" : "B");

The correct answer is B: B. Ternary operator: condition ? trueValue : falseValue. Since 10 > 20 is false, "B" is printed.

In Java 16+, which sealed class feature allows you to restrict which classes can extend a class?

The correct answer is B: Using 'sealed' keyword with 'permits' clause. Java 17 introduced 'sealed' classes with the 'permits' clause to explicitly specify which classes can extend a sealed class, providing better control over inheritance.

What is the primary purpose of the synchronized keyword in Java?

The correct answer is B: To prevent race conditions by ensuring mutual exclusion. The synchronized keyword ensures that only one thread can execute a critical section at a time, preventing race conditions and data inconsistency.

What is a method reference (::) in Java?

The correct answer is A: A shorthand syntax for lambda expressions that call existing methods. Method references are compact lambda expressions that directly reference existing methods. They use :: syntax and are equivalent to lambdas that call those methods.

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Java Programming
Lambda Expressions

Java OOP, collections, multithreading

51 Q 10 Topics Take Mock Test

Difficulty: All Easy Medium Hard 11–20 of 51

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 Lambda Expressions

Consider a lambda expression: (String s) -> s.length(). What is the correct functional interface for this?

A Function

B Supplier

C Consumer

D Predicate

Correct Answer: A. Function

EXPLANATION

Function<String, Integer> takes a String input and returns an Integer (the length). This matches the lambda that takes a String parameter and returns s.length().

Test

Q.12 Medium Lambda Expressions

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

A void

B Integer

C Depends on the functional interface it's assigned to

D int

Correct Answer: C. Depends on the functional interface it's assigned to

EXPLANATION

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.

Test

Q.13 Medium Lambda Expressions

Analyze: What is the output?
BiConsumer printer = (a, b) -> System.out.println(a + b);
printer.accept("Java", "8");

A Java8

B JavaCompilation error

C Java 8

D Compilation error

Correct Answer: A. Java8

EXPLANATION

BiConsumer accepts two parameters and performs the action. String concatenation of "Java" + "8" produces "Java8".

Test

Q.14 Medium Lambda Expressions

Which lambda expression is equivalent to the method reference Integer::parseInt?

A (s) -> Integer.parseInt(s)

B () -> Integer.parseInt()

C (Integer i) -> i.parseInt()

D (s) -> s.parseInt()

Correct Answer: A. (s) -> Integer.parseInt(s)

EXPLANATION

Method reference Integer::parseInt is equivalent to lambda (s) -> Integer.parseInt(s).

Test

Q.15 Medium Lambda Expressions

Consider: Comparator comp = (s1, s2) -> s2.compareTo(s1);
What does this lambda expression do?

A Sorts strings in ascending order

B Sorts strings in descending order

C Compares string lengths

D Checks string equality

Correct Answer: B. Sorts strings in descending order

EXPLANATION

By reversing the compareTo order (s2 compared to s1), it sorts in descending order.

Test

Q.16 Medium Lambda Expressions

Which of the following statements about variable scope in lambda expressions is TRUE?

A Lambda can access any local variable

B Lambda can only access effectively final local variables

C Lambda has its own scope separate from enclosing scope

D Lambda can modify local variables from enclosing scope

Correct Answer: B. Lambda can only access effectively final local variables

EXPLANATION

Lambda expressions can only access local variables that are effectively final (not modified after initialization).

Test

Q.17 Medium Lambda Expressions

In the lambda expression (x) -> x < 10 && x > 0, what is the parameter type?

A Explicitly specified as int

B Must be inferred from context

C Cannot be a numeric type

D Automatically defaults to Integer

Correct Answer: B. Must be inferred from context

EXPLANATION

Parameter type must be inferred from the functional interface it's assigned to, as it's not explicitly declared.

Test

Q.18 Medium Lambda Expressions

Which of the following lambda expressions will compile successfully?

A (int x) -> { int y = x * 2; return y; }

B (int x) -> { int x = 5; return x; }

C (int x) -> { var y = x; return y; }

D A and C

Correct Answer: D. A and C

EXPLANATION

Both A and C are valid. Option B fails because variable x is already declared as parameter. Option C uses var keyword (Java 10+).

Test

Q.19 Medium Lambda Expressions

Which of the following uses method reference correctly?

A list.forEach(System.out::println)

B list.forEach(System.out.println)

C list.forEach(x -> System.out.println(x))

D Both A and C

Correct Answer: D. Both A and C

EXPLANATION

Both method reference (::) and lambda expression are valid ways to print list elements. Option B has incorrect syntax.

Test

Q.20 Medium Lambda Expressions

What is the difference between Consumer and Function functional interfaces?

A Consumer returns a value, Function doesn't

B Function returns a value, Consumer doesn't

C Both are identical

D Consumer can have multiple parameters, Function cannot

Correct Answer: B. Function returns a value, Consumer doesn't

EXPLANATION

Function<T, R> takes parameter T and returns R. Consumer<T> takes parameter T and returns void.

Test

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Lambda Expressions