Java Programming Questions & Answers

Q.31 Medium Spring Framework Basics

A Spring application requires constructor-based dependency injection for a mandatory dependency. Which approach is best?

A @Autowired on setter method

B @Autowired on constructor

C @Resource annotation

D Manual object creation

Correct Answer: B. @Autowired on constructor

EXPLANATION

Constructor-based DI ensures mandatory dependencies are provided at object creation time and is considered a best practice for required dependencies.

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Q.32 Medium Lambda Expressions

Consider the following code:
List fruits = Arrays.asList("apple", "banana", "cherry");
fruits.removeIf(s -> s.length() > 5);

What will be the contents of 'fruits' list after execution?

A ["apple", "banana", "cherry"]

B ["apple"]

C ["apple", "cherry"]

D []

Correct Answer: B. ["apple"]

EXPLANATION

removeIf() removes all elements that satisfy the lambda predicate. Strings with length > 5 are "banana" (6 chars) and "cherry" (6 chars). Only "apple" (5 chars) remains as its length is not greater than 5.

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Q.33 Medium Lambda Expressions

A stream processes a list of strings and applies a lambda to convert them to uppercase. Which intermediate operation should be used?

A filter(s -> s.toUpperCase())

B map(s -> s.toUpperCase())

C peek(s -> s.toUpperCase())

D collect(s -> s.toUpperCase())

Correct Answer: B. map(s -> s.toUpperCase())

EXPLANATION

The map() intermediate operation transforms each element using the provided lambda function. filter() returns boolean, peek() doesn't transform, and collect() is a terminal operation. map() is the correct choice for transformation.

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Q.34 Medium Lambda Expressions

Which of the following lambda expressions is INVALID in Java?

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

B (int x) -> x * x

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

D (x, y) -> return x + y;

Correct Answer: D. (x, y) -> return x + y;

EXPLANATION

In a lambda expression, if the body uses curly braces, 'return' keyword is required. But without curly braces, 'return' keyword cannot be used. Option D is invalid because it has 'return' without curly braces.

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Q.35 Medium Lambda Expressions

Which stream operation uses a lambda expression to transform elements from one type to another?

A filter()

B map()

C forEach()

D reduce()

Correct Answer: B. map()

EXPLANATION

map() is used to transform elements. It takes a Function lambda that converts each element from one type/value to another.

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Q.36 Medium Lambda Expressions

Which of the following correctly uses a method reference as an alternative to a lambda expression?

A System.out::println instead of (x) -> System.out.println(x)

B String::length instead of (s) -> s.length()

C Integer::parseInt instead of (s) -> Integer.parseInt(s)

D All of the above

Correct Answer: D. All of the above

EXPLANATION

All three are valid method references that can replace their equivalent lambda expressions. Method references are a shorthand notation introduced in Java 8.

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Q.37 Medium Lambda Expressions

Consider: Comparator comp = (a, b) -> b - a; List list = Arrays.asList(3,1,2); Collections.sort(list, comp); What is the result?

A [1, 2, 3]

B [3, 2, 1]

C [2, 1, 3]

D [1, 3, 2]

Correct Answer: B. [3, 2, 1]

EXPLANATION

The comparator (a, b) -> b - a returns negative values when b < a, causing elements to be sorted in descending order. Result is [3, 2, 1].

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Q.38 Medium Lambda Expressions

Which lambda expression correctly implements a custom functional interface: public interface Math { int calculate(int a, int b); }

A (a, b) -> a + b

B () -> 0

C (int a, int b) -> a - b

D Both A and C

Correct Answer: D. Both A and C

EXPLANATION

Both expressions are valid. Option A uses type inference while Option C explicitly specifies types. Both can implement the calculate method.

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Q.39 Medium Lambda Expressions

What is the output of: List nums = Arrays.asList(1,2,3); nums.stream().filter(x -> x > 1).forEach(System.out::println);

A 1 2 3

B 2 3

C 1

D Nothing is printed

Correct Answer: B. 2 3

EXPLANATION

filter(x -> x > 1) keeps only elements greater than 1, which are 2 and 3. These are then printed on separate lines using forEach.

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Q.40 Medium Lambda Expressions

Consider the code: List names = Arrays.asList("Alice", "Bob"); names.forEach(name -> System.out.println(name)); What type of functional interface is used in forEach?

A Function

B Consumer

C Supplier

D Predicate

Correct Answer: B. Consumer

EXPLANATION

forEach accepts a Consumer functional interface. Consumer<T> takes an input and performs an action without returning anything, which matches the System.out.println action.

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