Which class in Java is used to read primitive data types from a binary stream?

The correct answer is A: DataInputStream. DataInputStream is specifically designed to read primitive data types (int, float, double, etc.) from a binary stream using methods like readInt(), readFloat(), etc.

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

The correct answer is C: Either a or b. 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.

Which method in Set collection prevents duplicate insertion by returning false?

The correct answer is A: add(). The add() method in Set returns boolean - true if element is added, false if duplicate exists.

In Spring Framework 6.0, what is the role of the @EnableAutoConfiguration annotation in Spring Boot?

The correct answer is D: Both A and C are correct. @EnableAutoConfiguration (or @SpringBootApplication which includes it) auto-configures Spring beans based on jar dependencies on the classpath.

Which of the following about static variables is incorrect?

The correct answer is C: Each object has its own copy of static variables. Static variables are shared among ALL instances of a class, not individual copies per object.

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Java Programming
Lambda Expressions

Java OOP, collections, multithreading

51 Q 10 Topics Take Mock Test

Difficulty: All Easy Medium Hard 21–30 of 51

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.21 Medium Lambda Expressions

Which functional interface should be used for a lambda with no parameters and no return value?

A Supplier

B Consumer

C Runnable

D Function

Correct Answer: C. Runnable

EXPLANATION

Runnable is the functional interface for operations with no parameters and no return value (void).

Test

Q.22 Medium Lambda Expressions

What will be the type of the lambda expression (x) -> x.toString()?

A Function

B Function

C Cannot be determined without context

D Consumer

Correct Answer: C. Cannot be determined without context

EXPLANATION

Without context, the parameter type cannot be inferred. The functional interface type determines the parameter type.

Test

Q.23 Medium Lambda Expressions

Which of the following lambda expressions has incorrect syntax?

A (int x) -> x * 2

B x -> x * 2

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

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

Correct Answer: D. (int x, int y) -> x > y ? x : y

EXPLANATION

Ternary operator inside lambda requires braces and explicit return statement for type inference.

Test

Q.24 Medium Lambda Expressions

What will be the output of: List list = Arrays.asList(1, 2, 3); list.replaceAll(x -> x * 2); System.out.println(list);

A [1, 2, 3]

B [2, 4, 6]

C [] (empty list)

D [2, 2, 2]

Correct Answer: B. [2, 4, 6]

EXPLANATION

replaceAll() with a lambda expression modifies the list in-place, multiplying each element by 2. Result is [2, 4, 6].

Test

Q.25 Medium Lambda Expressions

What happens when a lambda expression references a local variable from its enclosing scope?

A The variable must be explicitly final or effectively final

B The variable is automatically copied into the lambda's scope

C Any variable can be accessed without restrictions

D The variable must be static

Correct Answer: A. The variable must be explicitly final or effectively final

EXPLANATION

Lambda expressions can only access local variables that are final or effectively final (not reassigned). This ensures thread-safety and consistency.

Test

Q.26 Medium Lambda Expressions

Which of the following correctly uses method reference with constructor?

A String::new

B new String::

C String->new

D new::String

Correct Answer: A. String::new

EXPLANATION

Constructor method references use ClassName::new syntax. String::new refers to the String constructor and can be used wherever a Supplier<String> is expected.

Test

Q.27 Medium Lambda Expressions

In the lambda expression (a, b) -> a.compareTo(b), what can we infer about the parameters?

A Both a and b are integers

B Both a and b are Comparable objects

C a is a String and b is a number

D Types cannot be determined without context

Correct Answer: D. Types cannot be determined without context

EXPLANATION

Without explicit type declarations or context, the compiler must infer types from usage. We can only determine they have a compareTo() method, likely Comparable types.

Test

Q.28 Medium Lambda Expressions

What will be the output of: IntStream.range(1, 4).map(x -> x * x).forEach(System.out::print);

A 149

B 123

C 111

D 000

Correct Answer: A. 149

EXPLANATION

range(1, 4) generates 1, 2, 3. map(x -> x * x) produces 1, 4, 9. Printed without spaces gives '149'.

Test

Q.29 Medium Lambda Expressions

What issue can arise when using lambda expressions with checked exceptions?

A Checked exceptions cannot be thrown directly in lambda expressions

B They must be wrapped in try-catch or a custom functional interface must be created

C Checked exceptions automatically become unchecked in lambdas

D Lambda expressions cannot handle any exceptions

Correct Answer: B. They must be wrapped in try-catch or a custom functional interface must be created

EXPLANATION

Since standard functional interfaces don't declare checked exceptions, you must either wrap in try-catch or create a custom functional interface that throws the checked exception.

Test

Q.30 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

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Lambda Expressions