Consider a ThreadLocal variable initialized in a thread pool executor with 10 threads. If the same thread is reused from the pool for a different task, what is the state of its ThreadLocal variable?

The correct answer is B: It retains the value from the previous task execution. ThreadLocal values persist across task executions in the same thread. ThreadPools reuse threads, so previous ThreadLocal values remain unless explicitly removed. This can cause data leakage. Developers must call remove() to clean up.

Which of the following lambda expressions will compile successfully?

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

What will be the result of executing this code? PriorityQueue pq = new PriorityQueue(); pq.add(5); pq.add(3); pq.add(7); System.out.println(pq.peek());

The correct answer is B: 3. PriorityQueue orders elements based on their natural ordering (min-heap by default). peek() returns 3, the minimum element.

Which method of PriorityQueue returns the element without removing it?

The correct answer is C: peek(). peek() returns the head element without removing it. poll() removes and returns, remove() throws exception if empty, and pop() is not a PriorityQueue method.

Consider the declaration: List

The correct answer is B: List of Integer and its superclasses. '? super Integer' is a lower bounded wildcard that accepts Integer and all its superclasses like Number, Object. This allows write operations with Integer values.

Home

Home › Subjects › Java Programming › Lambda Expressions

Java Programming
Lambda Expressions

Java OOP, collections, multithreading

32 Q 10 Topics Take Mock Test

Difficulty: All Easy Medium Hard 11–20 of 32

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 Easy Lambda Expressions

Which of the following best describes a functional interface?

A An interface that can only have lambda expressions

B An interface with exactly one abstract method

C An interface with all methods as default

D An interface with multiple abstract methods that are related

Correct Answer: B. An interface with exactly one abstract method

EXPLANATION

A functional interface must have exactly one abstract method, which can be implemented using lambda expressions.

Test

Q.12 Easy Lambda Expressions

What is the result of this code?
UnaryOperator square = x -> x * x;
System.out.println(square.apply(5));

A 25

B 10

C 5

D Compilation error

Correct Answer: A. 25

EXPLANATION

UnaryOperator applies the operation x * x where x = 5, resulting in 25.

Test

Q.13 Easy Lambda Expressions

What is the output of:
BiFunction add = (a, b) -> a + b;
System.out.println(add.apply(5, 3));

A 8

B 53

C Compilation error

D Runtime exception

Correct Answer: A. 8

EXPLANATION

BiFunction takes two Integer parameters and returns their sum. apply(5, 3) returns 5 + 3 = 8.

Test

Q.14 Easy Lambda Expressions

What is the return type of the lambda expression: (a, b) -> a > b?

A int

B boolean

C void

D Cannot be determined

Correct Answer: B. boolean

EXPLANATION

The expression uses comparison operator (>), which returns a boolean value.

Test

Q.15 Easy Lambda Expressions

A lambda expression can only be used with which type of interface?

A Regular interface

B Functional interface with single abstract method

C Interface with multiple abstract methods

D Interface with default methods only

Correct Answer: B. Functional interface with single abstract method

EXPLANATION

Lambda expressions can only be assigned to functional interfaces that have exactly one abstract method.

Test

Q.16 Easy Lambda Expressions

Which of the following is a valid lambda expression in Java?

A () -> System.out.println("Hello")

B (int x, int y) -> { return x + y; }

C (String s) -> s.length()

D All of the above

Correct Answer: D. All of the above

EXPLANATION

All three are valid lambda expression syntaxes with different parameter types and return statements.

Test

Q.17 Easy Lambda Expressions

Which stream operation would you use to transform elements from one type to another?

A filter()

B map()

C forEach()

D collect()

Correct Answer: B. map()

EXPLANATION

map() is the intermediate operation used to transform elements from one type/value to another. It applies a function to each element.

Test

Q.18 Easy Lambda Expressions

What is the purpose of the @FunctionalInterface annotation in Java?

A To indicate an interface can be used with lambda expressions

B To enforce that an interface has exactly one abstract method

C To improve performance of lambda expressions

D To allow multiple lambda expressions in one interface

Correct Answer: B. To enforce that an interface has exactly one abstract method

EXPLANATION

@FunctionalInterface is a compile-time check that ensures an interface has exactly one abstract method, making it safe for lambda implementation.

Test

Q.19 Easy Lambda Expressions

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

A A shorthand syntax for lambda expressions that call existing methods

B An operator for accessing private members

C A way to create anonymous classes

D A reference to a method's memory address

Correct Answer: A. A shorthand syntax for lambda expressions that call existing methods

EXPLANATION

Method references are compact lambda expressions that directly reference existing methods. They use :: syntax and are equivalent to lambdas that call those methods.

Test

Q.20 Easy Lambda Expressions

Which functional interface is used for operations that take two arguments and return a single value?

A Function

B BiFunction

C Consumer

D Supplier

Correct Answer: B. BiFunction

EXPLANATION

BiFunction<T, U, R> represents a function that accepts two arguments of types T and U, and returns a result of type R.

Test

1 2 3 4

All Subjects & Topics

Govt. Exams

Entrance Exams

Teacher Exams

Subjects

Quick Links

Java Programming Lambda Expressions

Java Programming
Lambda Expressions