Java Programming Questions & Answers

Q.41 Medium Lambda Expressions

What will happen if you try to access a local variable from an enclosing scope that is not final or effectively final in a lambda expression?

A It will compile and run successfully

B Compilation error: variable must be final or effectively final

C Runtime exception will be thrown

D The variable value will be copied

Correct Answer: B. Compilation error: variable must be final or effectively final

EXPLANATION

Lambda expressions can only access local variables that are final or effectively final. This is because lambda expressions are translated to methods that need access to stable variable values.

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Q.42 Medium Lambda Expressions

Consider a lambda expression: (String s) -> s.length(). What is the correct functional interface for this?

A Function

B Supplier

C Consumer

D Predicate

Correct Answer: A. Function

EXPLANATION

Function<String, Integer> takes a String input and returns an Integer (the length). This matches the lambda that takes a String parameter and returns s.length().

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Q.43 Medium Lambda Expressions

What is the return type of a lambda expression (x, y) -> x + y where x and y are integers?

A void

B Integer

C Depends on the functional interface it's assigned to

D int

Correct Answer: C. Depends on the functional interface it's assigned to

EXPLANATION

The return type of a lambda expression is inferred from the functional interface it's assigned to. The same lambda can return Integer or int depending on the context.

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Q.44 Medium Lambda Expressions

Analyze: What is the output?
BiConsumer printer = (a, b) -> System.out.println(a + b);
printer.accept("Java", "8");

A Java8

B JavaCompilation error

C Java 8

D Compilation error

Correct Answer: A. Java8

EXPLANATION

BiConsumer accepts two parameters and performs the action. String concatenation of "Java" + "8" produces "Java8".

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Q.45 Medium Lambda Expressions

Which lambda expression is equivalent to the method reference Integer::parseInt?

A (s) -> Integer.parseInt(s)

B () -> Integer.parseInt()

C (Integer i) -> i.parseInt()

D (s) -> s.parseInt()

Correct Answer: A. (s) -> Integer.parseInt(s)

EXPLANATION

Method reference Integer::parseInt is equivalent to lambda (s) -> Integer.parseInt(s).

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Q.46 Medium Lambda Expressions

Consider: Comparator comp = (s1, s2) -> s2.compareTo(s1);
What does this lambda expression do?

A Sorts strings in ascending order

B Sorts strings in descending order

C Compares string lengths

D Checks string equality

Correct Answer: B. Sorts strings in descending order

EXPLANATION

By reversing the compareTo order (s2 compared to s1), it sorts in descending order.

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Q.47 Medium Lambda Expressions

Which of the following statements about variable scope in lambda expressions is TRUE?

A Lambda can access any local variable

B Lambda can only access effectively final local variables

C Lambda has its own scope separate from enclosing scope

D Lambda can modify local variables from enclosing scope

Correct Answer: B. Lambda can only access effectively final local variables

EXPLANATION

Lambda expressions can only access local variables that are effectively final (not modified after initialization).

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Q.48 Medium Lambda Expressions

In the lambda expression (x) -> x < 10 && x > 0, what is the parameter type?

A Explicitly specified as int

B Must be inferred from context

C Cannot be a numeric type

D Automatically defaults to Integer

Correct Answer: B. Must be inferred from context

EXPLANATION

Parameter type must be inferred from the functional interface it's assigned to, as it's not explicitly declared.

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Q.49 Medium Lambda Expressions

Which of the following lambda expressions will compile successfully?

A (int x) -> { int y = x * 2; return y; }

B (int x) -> { int x = 5; return x; }

C (int x) -> { var y = x; return y; }

D A and C

Correct Answer: D. A and C

EXPLANATION

Both A and C are valid. Option B fails because variable x is already declared as parameter. Option C uses var keyword (Java 10+).

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Q.50 Medium Lambda Expressions

Which of the following uses method reference correctly?

A list.forEach(System.out::println)

B list.forEach(System.out.println)

C list.forEach(x -> System.out.println(x))

D Both A and C

Correct Answer: D. Both A and C

EXPLANATION

Both method reference (::) and lambda expression are valid ways to print list elements. Option B has incorrect syntax.

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