Java Programming — MCQ Practice Questions & Answers

Question 1

What will be the output of this nested lambda? Function > add = x -> y -> x + y; System.out.println(add.apply(3).apply(5));

Accepted Answer

Correct answer: A. 8 — Curried function: add.apply(3) returns a Function that adds 3. .apply(5) on that adds 5 to 3, returning 8.

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B. 3

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C. 5

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D. Compilation error

Question 2

What will happen if you try to compile this code? BiFunction concat = (a, b) -> a + b; concat.apply("Java", "8", "Features");

Accepted Answer

Correct answer: C. Compilation error - too many arguments — BiFunction takes exactly 2 parameters. Passing 3 arguments is compilation error. apply() only accepts 2 arguments.

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A. It will compile and run successfully

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B. Runtime error - extra argument

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D. No output produced

Question 3

What is the type inference mechanism in lambda expressions?

Accepted Answer

Correct answer: A. Compiler infers parameter types from functional interface and context — Compiler uses target type (functional interface) to infer parameter types. If context is clear, explicit types not needed: list.forEach(x -> ...).

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B. Parameters must always have explicit types

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C. Type inference only works with single parameter

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D. Lambda expressions don't support type inference

Question 4

Consider a lambda that needs to throw a checked exception. Which approach is correct?

Accepted Answer

Correct answer: A. Wrap the checked exception in a try-catch block within the lambda — Lambda expressions don't propagate checked exceptions. They must be caught within the lambda body using try-catch.

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B. Create a custom functional interface with throws clause

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C. Use @FunctionalInterface with throws declaration

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D. Lambda expressions cannot throw checked exceptions

Question 5

What is the time complexity of reducing a stream with a lambda expression using reduce()?

Accepted Answer

Correct answer: A. O(n) in sequential, potentially O(log n) in parallel with proper associative operation — Sequential reduce is O(n). Parallel reduction can be O(log n) with a properly associative and commutative operation, enabling divide-and-conquer approach.

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B. Always O(1)

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C. O(n²) regardless of parallelism

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D. O(n log n) always

Question 6

Consider: List list = Arrays.asList("a", "b", "c"); list.stream().collect(Collectors.toMap(s -> s, s -> s.length())). What type is returned?

Accepted Answer

Correct answer: A. Map — Collectors.toMap with key mapper (s -> s) produces String keys and value mapper (s -> s.length()) produces Integer values, resulting in Map .

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B. Map

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C. List

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D. Set

Question 7

What issue can arise when using lambda expressions with flatMap() in nested streams?

Accepted Answer

Correct answer: A. Excessive memory consumption from creating multiple intermediate streams — Each flatMap creates intermediate streams. Deeply nested flatMap with lambdas can consume significant memory, especially with large datasets.

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B. flatMap() cannot accept lambda expressions

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C. Type erasure causes ClassCastException

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D. Lambda expressions become unreadable

Question 8

Consider: Function > curry = x -> y -> x + y; What does curry.apply(5).apply(3) return?

Accepted Answer

Correct answer: A. 8 — This is a curried function. curry.apply(5) returns a function that adds 5. Applying that with 3 gives 5 + 3 = 8.

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B. 15

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C. 5

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D. 3

Java Programming - MCQ Practice Questions