Java Functional Interfaces Coding Questions and Answers

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

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

Function<Integer, String> converter = x -> Integer.toString(x);
System.out.println(converter.apply(10).getClass().getSimpleName());

a) String

b) Integer

c) Object

d) Function

Answer:

a) String

Explanation:

The Function<Integer, String> converts an Integer to String. converter.apply(10) returns a String object, so its class name is String.

2. What does this Java code snippet output?

Predicate<String> isEmpty = String::isEmpty;
System.out.println(isEmpty.test(""));

a) true

b) false

c) Compilation error

d) Runtime error

Answer:

a) true

Explanation:

The Predicate<String> checks if a string is empty. isEmpty.test("") returns true for the empty string.

3. Identify the output of the following code:

UnaryOperator<Integer> square = x -> x * x;
System.out.println(square.apply(5));

a) 10

b) 25

c) 30

d) 5

Answer:

b) 25

Explanation:

The UnaryOperator<Integer> takes one Integer and returns its square. square.apply(5) returns 25 (5 * 5).

4. What will be printed by this Java code?

BinaryOperator<Integer> sum = (a, b) -> a + b;
System.out.println(sum.apply(10, 20));

a) 10

b) 20

c) 30

d) 40

Answer:

c) 30

Explanation:

The BinaryOperator<Integer> takes two Integers and returns their sum. sum.apply(10, 20) returns 30.

5. What does this code snippet output?

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

a) Java

b) Supplier

c) "" (Empty String)

d) null

Answer:

a) Java

Explanation:

The Supplier<String> provides a string. supplier.get() returns the string "Java".

6. What is the result of executing this code?

Consumer<String> consumer = System.out::println;
consumer.accept("Hello, World!");

a) Hello, World!

b) Consumer

c) No output

d) Compilation error

Answer:

a) Hello, World!

Explanation:

The Consumer<String> takes a string and performs an action. Here, it prints "Hello, World!".

7. What will the following Java code snippet output?

BiFunction<Integer, Integer, String> biFunction = (a, b) -> "Result: " + (a + b);
System.out.println(biFunction.apply(5, 10));

a) Result: 5

b) Result: 10

c) Result: 15

d) Result: 20

Answer:

c) Result: 15

Explanation:

The BiFunction takes two Integer values, sums them up, and returns the result as a String.

8. What does the following code snippet print?

ToIntFunction<String> lengthFunction = String::length;
System.out.println(lengthFunction.applyAsInt("Hello"));

a) 5

b) Hello

c) 0

d) null

Answer:

a) 5

Explanation:

The ToIntFunction<String> converts a String into an int. Here, it returns the length of "Hello", which is 5.

9. Determine the output of this Java code:

BiConsumer<Integer, Integer> printer = (a, b) -> System.out.println(a + b);
printer.accept(3, 7);

a) 3 7

b) 10

c) 37

d) Compilation error

Answer:

b) 10

Explanation:

The BiConsumer takes two Integer values, adds them, and prints the result. It prints 10 (3 + 7).

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

IntPredicate isEven = x -> x % 2 == 0;
System.out.println(isEven.test(10));

a) true

b) false

c) Compilation error

d) Runtime error

Answer:

a) true

Explanation:

The IntPredicate checks if an int value is even. isEven.test(10) returns true as 10 is even.

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