Quiz: Java 8 Lambdas and Streams

5 questionsNo time limitPass: 60%+10 XP on first pass

Write modern Java: lambda expressions, functional interfaces, method references, the Stream API (filter, map, reduce, collect, groupingBy) and Optional.

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Question 1

What does this print?

import java.util.*;
public class Main {
    public static void main(String[] args) {
        List<Integer> l = List.of(1, 2, 3, 4, 5);
        System.out.println(l.stream().filter(x -> x % 2 == 1).map(x -> x * 10).toList());
    }
}

[10, 20, 30, 40, 50][10, 30, 50][20, 40][1, 3, 5]

Question 2
Which functional interface returns a boolean?
FunctionPredicateSupplierConsumer
Question 3
When does a stream pipeline actually run?
When stream() is calledAt each filter callWhen a terminal operation like collect or count is calledNever

Question 4

What does this print?

import java.util.*;
public class Main {
    public static void main(String[] args) {
        System.out.println(List.of(2, 3, 4).stream().reduce(0, Integer::sum));
    }
}

2490[2, 3, 4]

Question 5
Which is the method reference for s -> s.length()?
s::lengthString::lengthlength::StringString.length()