Java Lambda Expressions Coding Questions and Answers

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Welcome to the Java Lambda Expressions Coding Quiz. In this quiz, we present 10 coding MCQ questions to test your coding knowledge of the Java Lambda Expressions. Each question has a correct and brief explanation.

1. What is the output of the following Java code snippet?

Runnable r = () -> System.out.println("Hello Lambda!");
r.run();

a) Hello Lambda!

b) Compilation error

c) No output

d) Runtime error

Answer:

a) Hello Lambda!

Explanation:

This lambda expression implements the Runnable interface with a single method run that prints "Hello Lambda!".

2. What does this Java code snippet output?

Function<Integer, Integer> func = x -> x * x;
System.out.println(func.apply(5));

a) 10

b) 25

c) 30

d) 5

Answer:

b) 25

Explanation:

The lambda expression takes an integer x and returns x * x. func.apply(5) returns 5 squared, which is 25.

3. Identify the output of the following code:

Predicate<String> isLongerThan5 = s -> s.length() > 5;
System.out.println(isLongerThan5.test("Lambda"));

a) true

b) false

c) Compilation error

d) Runtime error

Answer:

a) true

Explanation:

The lambda expression checks if the string length is greater than 5. "Lambda" has 6 characters, so it returns true.

4. What will be printed by this Java code?

Consumer<String> printer = s -> System.out.println(s.toUpperCase());
printer.accept("lambda");

a) lambda

b) LAMBDA

c) Lambda

d) Compilation error

Answer:

b) LAMBDA

Explanation:

The lambda expression converts the input string to upper case and prints it. It prints "LAMBDA".

5. What does this code snippet output?

Supplier<String> stringSupplier = () -> "Java";
System.out.println(stringSupplier.get());

a) Java

b) ""

c) null

d) Compilation error

Answer:

a) Java

Explanation:

The Supplier lambda expression provides a string "Java". stringSupplier.get() returns this string.

6. What is the result of executing this code?

BiFunction<Integer, Integer, Integer> adder = (a, b) -> a + b;
System.out.println(adder.apply(10, 5));

a) 15

b) 10

c) 5

d) Compilation error

Answer:

a) 15

Explanation:

The lambda expression takes two integers a and b, and returns their sum. adder.apply(10, 5) returns 15.

7. What will the following Java code snippet output?

IntUnaryOperator doubleNumber = x -> x * 2;
System.out.println(doubleNumber.applyAsInt(4));

a) 2

b) 4

c) 8

d) 16

Answer:

c) 8

Explanation:

The lambda expression doubles the given number. doubleNumber.applyAsInt(4) returns 4 times 2, which is 8.

8. What does the following code snippet print?

BinaryOperator<Integer> multiplier = (a, b) -> a * b;
System.out.println(multiplier.apply(3, 7));

a) 10

b) 21

c) 24

d) 30

Answer:

b) 21

Explanation:

The lambda expression multiplies two integers. multiplier.apply(3, 7) returns 3 multiplied by 7, which is 21.

9. Determine the output of this Java code:

List<String> names = Arrays.asList("Alice", "Bob", "Charlie");
names.forEach(name -> System.out.println(name.toUpperCase()));

a) Alice Bob Charlie

b) alice bob charlie

c) ALICE BOB CHARLIE

d) Alice\nBob\nCharlie

Answer:

c) ALICE BOB CHARLIE

Explanation:

The lambda expression in forEach converts each name to upper case and prints it. The names are printed in upper case, each on a new line.

10. What is the result of the following code snippet?

UnaryOperator<String> exclaim = s -> s + "!";
String result = exclaim.apply("Hello");
System.out.println(result);

a) Hello

b) Hello!

c) Hello!!

d) Compilation error

Answer:

b) Hello!

Explanation:

The lambda expression appends an exclamation mark to the given string. exclaim.apply("Hello") returns "Hello!".