What is the difference between a lambda expression and an anonymous inner class in Java?

The correct answer is D: Both A and B. Lambda expressions can only be used with functional interfaces (single abstract method), whereas anonymous classes can implement any interface. Lambda expressions are also more concise.

What is the output of the following code? FileReader fr = new FileReader("test.txt"); int data = fr.read(); System.out.println(data);

The correct answer is B: ASCII value of the character. FileReader.read() returns the ASCII/Unicode value of the character as an integer, not the character itself. It returns -1 when EOF is reached.

What is the size of 'char' data type in Java?

The correct answer is B: 2 bytes. The 'char' data type in Java is 2 bytes (16 bits) because it uses Unicode character encoding.

Consider a scenario where a developer uses getConnection() without closing it. What is the potential impact?

The correct answer is B: Connection leak occurs, exhausting available database connections. Unclosed connections remain allocated and unavailable for other operations, eventually exhausting the connection pool and causing connection exhaustion errors.

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

The correct answer is D: All of the above. All three are valid lambda expression syntaxes with different parameter types and return statements.

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Java Programming

Java OOP, collections, multithreading

476 Q 10 Topics Take Mock Test

Difficulty: All Easy Medium Hard 61–70 of 476

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.61 Medium Lambda Expressions

What is the difference between peek() and forEach() in streams?

A peek() is terminal, forEach() is intermediate

B peek() is intermediate and returns a stream, forEach() is terminal and returns void

C There is no difference, they are aliases

D peek() modifies elements, forEach() doesn't

Correct Answer: B. peek() is intermediate and returns a stream, forEach() is terminal and returns void

EXPLANATION

peek() is an intermediate operation that returns a stream for chaining, useful for debugging. forEach() is terminal and returns void, ending the stream chain.

Test

Q.62 Medium Lambda Expressions

Consider: Stream.of(1, 2, 3, 4, 5).filter(x -> x > 2).map(x -> x * 2).forEach(System.out::println); What will be the output?

A 6 8 10

B 2 4 6 8 10

C 3 4 5

D 1 2 3 4 5

Correct Answer: A. 6 8 10

EXPLANATION

filter(x -> x > 2) keeps 3, 4, 5. map(x -> x * 2) transforms them to 6, 8, 10. forEach prints each value.

Test

Q.63 Medium Lambda Expressions

What will be the output of: IntStream.range(1, 4).map(x -> x * 2).sum();

A 12

B 9

C 6

D 24

Correct Answer: A. 12

EXPLANATION

range(1, 4) generates [1, 2, 3]. After map(x -> x * 2): [2, 4, 6]. Sum = 2 + 4 + 6 = 12.

Test

Q.64 Medium Lambda Expressions

In the lambda expression (a, b) -> a.compareTo(b), what is the implicit functional interface?

A Comparator

B BiFunction

C BiPredicate

D BinaryOperator

Correct Answer: A. Comparator

EXPLANATION

The Comparator<T> functional interface has the method compare(T a, T b) which returns an int, matching this lambda's behavior.

Test

Q.65 Medium Lambda Expressions

What is the difference between peek() and forEach() when used with lambda expressions in Streams?

A peek() is intermediate and doesn't consume the stream, forEach() is terminal and consumes it

B forEach() is faster than peek()

C peek() can only be used with Collectors

D forEach() returns a value while peek() returns void

Correct Answer: A. peek() is intermediate and doesn't consume the stream, forEach() is terminal and consumes it

EXPLANATION

peek() is an intermediate operation used for debugging; it doesn't end the stream. forEach() is a terminal operation that consumes the stream.

Test

Q.66 Medium Lambda Expressions

What is method reference (::) in Java and how does it relate to lambda expressions?

A Method reference is a shorthand for lambda expressions that call a single method

B Method reference is used for declaring new methods

C Method reference is faster than lambda but less readable

D Method reference can only be used with static methods

Correct Answer: A. Method reference is a shorthand for lambda expressions that call a single method

EXPLANATION

Method reference (::) is syntactic sugar for lambda expressions. System.out::println is equivalent to x -> System.out.println(x).

Test

Q.67 Medium Lambda Expressions

Consider: Stream.of(1, 2, 3, 4, 5).filter(x -> x > 2).map(x -> x * x). What will the terminal operation need to be?

A collect(Collectors.toList())

B forEach(System.out::println)

C Either a or b

D reduce(0, Integer::sum)

Correct Answer: C. Either a or b

EXPLANATION

Both collect() and forEach() are valid terminal operations. collect() returns a list, forEach() performs an action. reduce() is also valid but would sum the squares.

Test

Q.68 Medium Lambda Expressions

Which of the following lambda expressions is INCORRECT?

A () -> 42

B x -> x + 1

C (int x, int y) -> x + y

D (x, y) -> (x > y) ? x : y

Correct Answer: C. (int x, int y) -> x + y

EXPLANATION

In option C, you cannot specify types in lambda parameters when using implicit typing. It should be either (x, y) or explicitly define all parameters.

Test

Q.69 Medium Lambda Expressions

What is the purpose of the Optional class when used with lambda expressions in Stream operations?

A To handle null values and avoid NullPointerException

B To increase stream processing speed

C To convert streams to lists automatically

D To sort elements in reverse order

Correct Answer: A. To handle null values and avoid NullPointerException

EXPLANATION

Optional is used to handle absence of values gracefully. Methods like ifPresent(lambda) and orElse() help prevent null pointer exceptions.

Test

Q.70 Medium Lambda Expressions

Consider: Function f = x -> x * x; What will f.apply(5) return?

A 25

B 10

C 5

D 30

Correct Answer: A. 25

EXPLANATION

Function<Integer, Integer> takes an Integer and returns an Integer. f.apply(5) computes 5 * 5 = 25.

Test

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