Java Programming Questions & Answers

Q.51 Medium Lambda Expressions

What is the difference between Consumer and Function functional interfaces?

A Consumer returns a value, Function doesn't

B Function returns a value, Consumer doesn't

C Both are identical

D Consumer can have multiple parameters, Function cannot

Correct Answer: B. Function returns a value, Consumer doesn't

EXPLANATION

Function<T, R> takes parameter T and returns R. Consumer<T> takes parameter T and returns void.

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Q.52 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).

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Q.53 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.

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Q.54 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.

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Q.55 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].

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Q.56 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.

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Q.57 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.

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Q.58 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.

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Q.59 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'.

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Q.60 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.

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