Java Programming Questions & Answers

Q.21 Hard Lambda Expressions

What is the time complexity of reducing a stream with a stateful lambda operation?

A O(n) for sequential, O(log n) for parallel

B O(n) for both sequential and parallel streams

C O(1) regardless of stream size

D Depends on the operation and stream characteristics

Correct Answer: D. Depends on the operation and stream characteristics

EXPLANATION

Time complexity depends on the specific reduction operation, whether the lambda is stateless, and stream characteristics. Generally O(n), but parallelization overhead affects actual performance.

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Q.22 Hard Lambda Expressions

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

A 8

B 15

C 5

D 3

Correct Answer: A. 8

EXPLANATION

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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Q.23 Hard Lambda Expressions

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

A Excessive memory consumption from creating multiple intermediate streams

B flatMap() cannot accept lambda expressions

C Type erasure causes ClassCastException

D Lambda expressions become unreadable

Correct Answer: A. Excessive memory consumption from creating multiple intermediate streams

EXPLANATION

Each flatMap creates intermediate streams. Deeply nested flatMap with lambdas can consume significant memory, especially with large datasets.

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Q.24 Hard Lambda Expressions

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

A Map

B Map

C List

D Set

Correct Answer: A. Map

EXPLANATION

Collectors.toMap with key mapper (s -> s) produces String keys and value mapper (s -> s.length()) produces Integer values, resulting in Map<String, Integer>.

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Q.25 Hard Lambda Expressions

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

A O(n) in sequential, potentially O(log n) in parallel with proper associative operation

B Always O(1)

C O(n²) regardless of parallelism

D O(n log n) always

Correct Answer: A. O(n) in sequential, potentially O(log n) in parallel with proper associative operation

EXPLANATION

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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Q.26 Hard Lambda Expressions

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

A Wrap the checked exception in a try-catch block within the lambda

B Create a custom functional interface with throws clause

C Use @FunctionalInterface with throws declaration

D Lambda expressions cannot throw checked exceptions

Correct Answer: A. Wrap the checked exception in a try-catch block within the lambda

EXPLANATION

Lambda expressions don't propagate checked exceptions. They must be caught within the lambda body using try-catch.

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Q.27 Hard Lambda Expressions

What is the type inference mechanism in lambda expressions?

A Compiler infers parameter types from functional interface and context

B Parameters must always have explicit types

C Type inference only works with single parameter

D Lambda expressions don't support type inference

Correct Answer: A. Compiler infers parameter types from functional interface and context

EXPLANATION

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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Q.28 Hard Lambda Expressions

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

A It will compile and run successfully

B Runtime error - extra argument

C Compilation error - too many arguments

D No output produced

Correct Answer: C. Compilation error - too many arguments

EXPLANATION

BiFunction takes exactly 2 parameters. Passing 3 arguments is compilation error. apply() only accepts 2 arguments.

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Q.29 Hard Lambda Expressions

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

A 8

B 3

C 5

D Compilation error

Correct Answer: A. 8

EXPLANATION

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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Q.30 Hard Generics

A method processes collections where items need to be added back to the same collection type. Which wildcard approach ensures type safety for write operations?

A public static void addElements(List

B public static void addElements(List destination, List source)

C public static void addElements(List destination, List source)

D public static void addElements(List destination, List source)

Correct Answer: A. public static void addElements(List

EXPLANATION

'? super T' allows writing T instances (contravariant), while '? extends T' allows safe reading (covariant). This combination enables flexible yet type-safe collection manipulation.

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