Which Collection method was introduced in Java 9 to create immutable collections?

The correct answer is B: List.of(). Java 9 introduced factory methods like List.of(), Set.of(), Map.of() for creating immutable collections.

What does the Comparable interface do in Collections Framework?

The correct answer is A: It defines comparison logic for sorting. Comparable interface provides compareTo() method to define natural ordering for objects. Used by TreeSet and TreeMap for sorting.

In a producer-consumer scenario using BlockingQueue, what happens when a consumer thread calls take() on an empty queue?

The correct answer is B: It blocks until a producer adds an element. BlockingQueue's take() method blocks the calling thread until an element becomes available. This is safer and more efficient than busy-waiting. NoSuchElementException is thrown by non-blocking operations like remove().

What is the difference between 'this' and 'super' keywords in Java?

The correct answer is B: 'this' refers to current class object and 'super' refers to parent class. 'this' is a reference to the current object instance, while 'super' is a reference to the parent class object. They are used to access members of current and parent classes respectively.

Which JDBC API is used to execute parameterized queries safely?

The correct answer is B: PreparedStatement. PreparedStatement allows parameterized queries using placeholders (?) and prevents SQL injection attacks.

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Java Programming
Lambda Expressions

Java OOP, collections, multithreading

17 Q 10 Topics Take Mock Test

Difficulty: All Easy Medium Hard 11–17 of 17

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 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.

Test

Q.12 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>.

Test

Q.13 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.

Test

Q.14 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.

Test

Q.15 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 -> ...).

Test

Q.16 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.

Test

Q.17 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.

Test

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Lambda Expressions