Which of the following lambda expressions is invalid?
Answer: D
Lambda must have parameter list (even if empty with ()). Missing parameter list '() -> x + y' is invalid syntax.
Q.2Medium
What is the type of the following lambda expression: x -> x.length()?
Answer: A
Function<T,R> takes one argument of type T and returns R. Here String -> Integer (length), so Function<String, Integer>.
Q.3Medium
Which functional interface should be used for a lambda that filters elements?
Answer: A
Predicate<T> tests a condition and returns boolean. It's ideal for filtering. Function would return any type, Consumer doesn't return anything.
Q.4Medium
What will this code print?
List<Integer> list = Arrays.asList(1, 2, 3, 4, 5);
list.forEach(x -> System.out.print(x + " "));
Answer: B
forEach with Consumer lambda prints each element followed by space, resulting in '1 2 3 4 5 ' (with trailing space).
Q.5Medium
Can lambda expressions access local variables from their enclosing scope?
Answer: A
Lambda expressions can access local variables only if they are final or effectively final (not modified after initialization) due to closure requirements.
Advertisement
Q.6Medium
Which of the following correctly represents a BiFunction?
Answer: A
BiFunction takes 2 parameters and returns a result. (int a, int b) -> a + b fits this. Others are Function, Supplier, Consumer respectively.
Q.7Medium
What is the difference between a lambda expression and an anonymous inner class?
Answer: D
Lambdas provide concise syntax, are compiled directly without separate class files, and work only with functional interfaces (single abstract method).
Q.8Medium
Which of the following statements about @FunctionalInterface is true?
Answer: B
@FunctionalInterface is optional annotation that helps compiler verify interface has exactly one abstract method, catching errors early.
Q.9Medium
Can a lambda expression have multiple statements in its body?
Answer: B
Lambda can have multiple statements using braces: (x,y) -> { int z = x+y; return z; }. Single expression needs no braces or return.
Q.10Medium
Which functional interface is best suited for this scenario: method that takes no parameters and returns a random number?
Answer: A
Supplier<T> takes no parameters () and returns T. Perfect for generating/providing values like random numbers.
Q.11Medium
In Java streams, what does the filter() method use?
Answer: A
filter() method in streams takes Predicate which tests condition and returns boolean to determine if element should be included.
Q.12Medium
What will be the result of executing: List<Integer> nums = Arrays.asList(1, 2, 3, 4); nums.stream().map(x -> x * 2).collect(Collectors.toList());
Answer: A
The map() with lambda x -> x * 2 doubles each element: 1*2=2, 2*2=4, 3*2=6, 4*2=8, resulting in [2, 4, 6, 8].
Q.13Medium
Consider: Function<Integer, Integer> f = x -> x * x; What will f.apply(5) return?
Answer: A
Function<Integer, Integer> takes an Integer and returns an Integer. f.apply(5) computes 5 * 5 = 25.
Q.14Medium
What is the purpose of the Optional class when used with lambda expressions in Stream operations?
Answer: A
Optional is used to handle absence of values gracefully. Methods like ifPresent(lambda) and orElse() help prevent null pointer exceptions.
Q.15Medium
Which of the following lambda expressions is INCORRECT?
Answer: C
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.
Q.16Medium
Consider: Stream.of(1, 2, 3, 4, 5).filter(x -> x > 2).map(x -> x * x). What will the terminal operation need to be?
Answer: C
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.
Q.17Medium
What is method reference (::) in Java and how does it relate to lambda expressions?
Answer: A
Method reference (::) is syntactic sugar for lambda expressions. System.out::println is equivalent to x -> System.out.println(x).
Q.18Medium
What is the difference between peek() and forEach() when used with lambda expressions in Streams?
Answer: A
peek() is an intermediate operation used for debugging; it doesn't end the stream. forEach() is a terminal operation that consumes the stream.
Q.19Medium
In the lambda expression (a, b) -> a.compareTo(b), what is the implicit functional interface?
Answer: A
The Comparator<T> functional interface has the method compare(T a, T b) which returns an int, matching this lambda's behavior.
Q.20Medium
What will be the output of: IntStream.range(1, 4).map(x -> x * 2).sum();
Answer: A
range(1, 4) generates [1, 2, 3]. After map(x -> x * 2): [2, 4, 6]. Sum = 2 + 4 + 6 = 12.
