Java Streams API Interview Questions Mock Test

Question 1: JAVA - Streams Basics

What is the main advantage of using Streams in Java?

Question 2: JAVA - Stream Creation

Which of the following is a correct way to create a stream from a list?

Question 3: JAVA - Filter Operation

What will this code print?

import java.util.*;
public class Test {
    public static void main(String[] args) {
        List<Integer> nums = Arrays.asList(1, 2, 3, 4, 5);
        nums.stream().filter(n -> n % 2 == 0).forEach(System.out::print);
    }
}

Question 4: JAVA - Map Operation

What will this code print?

import java.util.*;
public class Test {
    public static void main(String[] args) {
        List<String> words = Arrays.asList("a", "bb", "ccc");
        words.stream().map(String::length).forEach(System.out::print);
    }
}

Question 5: JAVA - Reduce Operation

What will this code print?

import java.util.*;
public class Test {
    public static void main(String[] args) {
        List<Integer> nums = Arrays.asList(1, 2, 3, 4);
        int sum = nums.stream().reduce(0, (a, b) -> a + b);
        System.out.println(sum);
    }
}

Question 6: JAVA - Collectors

Which method collects stream results into a list?

Question 7: JAVA - Stream Count

What will this code print?

import java.util.*;
public class Test {
    public static void main(String[] args) {
        List<String> names = Arrays.asList("John", "Jane", "Jack");
        long count = names.stream().filter(s -> s.startsWith("J")).count();
        System.out.println(count);
    }
}

Question 8: JAVA - Parallel Stream

Which method is used to create a parallel stream from a list?

Question 9: JAVA - Distinct & Sorted

What will this code print?

import java.util.*;
public class Test {
    public static void main(String[] args) {
        List<Integer> nums = Arrays.asList(5, 1, 2, 2, 3);
        nums.stream().distinct().sorted().forEach(System.out::print);
    }
}

Question 10: JAVA - AnyMatch Example

What will this code return?

import java.util.*;
public class Test {
    public static void main(String[] args) {
        List<String> list = Arrays.asList("apple", "banana", "cherry");
        boolean result = list.stream().anyMatch(s -> s.contains("a"));
        System.out.println(result);
    }
}