Java Programming Questions & Answers

Q.31 Easy Lambda Expressions

Which of the following is a valid lambda expression in Java?

A () -> System.out.println("Hello")

B (int x, int y) -> { return x + y; }

C (String s) -> s.length()

D All of the above

Correct Answer: D. All of the above

EXPLANATION

All three are valid lambda expression syntaxes with different parameter types and return statements.

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Q.32 Easy Lambda Expressions

Which stream operation would you use to transform elements from one type to another?

A filter()

B map()

C forEach()

D collect()

Correct Answer: B. map()

EXPLANATION

map() is the intermediate operation used to transform elements from one type/value to another. It applies a function to each element.

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Q.33 Easy Lambda Expressions

What is the purpose of the @FunctionalInterface annotation in Java?

A To indicate an interface can be used with lambda expressions

B To enforce that an interface has exactly one abstract method

C To improve performance of lambda expressions

D To allow multiple lambda expressions in one interface

Correct Answer: B. To enforce that an interface has exactly one abstract method

EXPLANATION

@FunctionalInterface is a compile-time check that ensures an interface has exactly one abstract method, making it safe for lambda implementation.

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Q.34 Easy Lambda Expressions

What is a method reference (::) in Java?

A A shorthand syntax for lambda expressions that call existing methods

B An operator for accessing private members

C A way to create anonymous classes

D A reference to a method's memory address

Correct Answer: A. A shorthand syntax for lambda expressions that call existing methods

EXPLANATION

Method references are compact lambda expressions that directly reference existing methods. They use :: syntax and are equivalent to lambdas that call those methods.

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Q.35 Easy Lambda Expressions

Which functional interface is used for operations that take two arguments and return a single value?

A Function

B BiFunction

C Consumer

D Supplier

Correct Answer: B. BiFunction

EXPLANATION

BiFunction<T, U, R> represents a function that accepts two arguments of types T and U, and returns a result of type R.

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Q.36 Easy Lambda Expressions

What will be the output of: List list = Arrays.asList("a", "bb", "ccc"); list.forEach(s -> System.out.print(s.length() + " "));

A 1 2 3

B a bb ccc

C 3 2 1

D 1 1 1

Correct Answer: A. 1 2 3

EXPLANATION

The lambda expression prints the length of each string. Lengths are 1, 2, and 3 respectively, with spaces between them.

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Q.37 Easy Lambda Expressions

What is the primary advantage of using lambda expressions in Java 8+?

A They reduce boilerplate code and enable functional programming style

B They increase execution speed significantly

C They eliminate the need for classes

D They are required for all stream operations

Correct Answer: A. They reduce boilerplate code and enable functional programming style

EXPLANATION

Lambda expressions reduce boilerplate code by allowing inline implementation of functional interfaces without creating anonymous inner classes, enabling a more functional programming style.

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Q.38 Easy Lambda Expressions

Which functional interface is used for operations that take no arguments and return a value?

A Supplier

B Function

C Predicate

D BiConsumer

Correct Answer: A. Supplier

EXPLANATION

Supplier<T> is a functional interface with method get() that takes no parameters and returns a value of type T.

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Q.39 Easy Lambda Expressions

Consider the code: List names = Arrays.asList("Raj", "Priya", "Amit"); names.forEach(n -> System.out.println(n)); What does this code do?

A Prints each name with a newline

B Creates a new list with uppercase names

C Filters names starting with 'A'

D Sorts the names alphabetically

Correct Answer: A. Prints each name with a newline

EXPLANATION

forEach with the lambda expression n -> System.out.println(n) iterates through each element and prints it with a newline.

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Q.40 Easy Lambda Expressions

What is the return type of the map() method when used with lambda expressions in Java Streams?

A Stream

B List

C Set

D Map

Correct Answer: A. Stream

EXPLANATION

The map() method in Stream API returns a new Stream with transformed elements of type R, maintaining the stream pipeline.

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