Top 10 Java 8 Coding and Programming Interview Questions and Answers

It has been 6 years since Java 8 was released. I have already shared the Java 8 Interview questions and answers. In this tutorial, I will be sharing the top 10 Java 8 coding and programming interview questions and answers. I have only used Stream API functions to solve the below questions. Please bookmark this page as I will keep adding more questions to it.

Read Also: Java 8 Interview Questions and Answers

Q1 Given a list of integers, find out all the even numbers exist in the list using Stream functions?

import java.util.*;
import java.util.stream.*;
public class JavaHungry {
    public static void main(String args[]) {
            List<Integer> myList = Arrays.asList(10,15,8,49,25,98,32);
            myList.stream()
                  .filter(n -> n%2 == 0)
                  .forEach(System.out::println);
    }
}

Output:
10, 8, 98, 32


Q2 Given a list of integers, find out all the numbers starting with 1 using Stream functions?

import java.util.*;
import java.util.stream.*;
public class JavaHungry {
    public static void main(String args[]) {
            List<Integer> myList = Arrays.asList(10,15,8,49,25,98,32);
            myList.stream()
                  .map(s -> s + "") // Convert integer to String
                  .filter(s -> s.startsWith("1"))
                  .forEach(System.out::println);
    }
}

Output:
10, 15



Q3 How to find duplicate elements in a given integers list in java using Stream functions?

import java.util.*;
import java.util.stream.*;
public class JavaHungry {
    public static void main(String args[]) {
            List<Integer> myList = Arrays.asList(10,15,8,49,25,98,98,32,15);
            Set<Integer> set = new HashSet();
            myList.stream()
                  .filter(n -> !set.add(n))
                  .forEach(System.out::println);
    }
}

Output:
98, 15

Q4 Given the list of integers, find the first element of the list using Stream functions?

import java.util.*;
import java.util.stream.*;
public class JavaHungry {
    public static void main(String args[]) {
            List<Integer> myList = Arrays.asList(10,15,8,49,25,98,98,32,15);
            myList.stream()
                  .findFirst()
                  .ifPresent(System.out::println);
    }
}

Output:
10

Q5 Given a list of integers, find the total number of elements present in the list using Stream functions?

import java.util.*;
import java.util.stream.*;
public class JavaHungry {
    public static void main(String args[]) {
            List<Integer> myList = Arrays.asList(10,15,8,49,25,98,98,32,15);
            long count =  myList.stream()
                                .count();
            System.out.println(count);                    
    }
}

Output:
9

Q6 Given a list of integers, find the maximum value element present in it using Stream functions?

import java.util.*;
import java.util.stream.*;
public class JavaHungry {
    public static void main(String args[]) {
            List<Integer> myList = Arrays.asList(10,15,8,49,25,98,98,32,15);
            int max =  myList.stream()
                             .max(Integer::compare)
                             .get();
            System.out.println(max);                    
    }
}

Output:
98

Q7 Given a String, find the first non-repeated character in it using Stream functions?

import java.util.*;
import java.util.stream.*;
import java.util.function.Function;

public class JavaHungry {
    public static void main(String args[]) {
            String input = "Java Hungry Blog Alive is Awesome";

            Character result = input.chars() // Stream of String       
                                    .mapToObj(s -> Character.toLowerCase(Character.valueOf((char) s))) // First convert to Character object and then to lowercase         
                                    .collect(Collectors.groupingBy(Function.identity(), LinkedHashMap::new, Collectors.counting())) //Store the chars in map with count 
                                    .entrySet()
                                    .stream()
                                    .filter(entry -> entry.getValue() == 1L)
                                    .map(entry -> entry.getKey())
                                    .findFirst()
                                    .get();
            System.out.println(result);                    
    }
}

Output:
j

Q8 Given a String, find the first repeated character in it using Stream functions?

import java.util.*;
import java.util.stream.*;
import java.util.function.Function;

public class JavaHungry {
    public static void main(String args[]) {
            String input = "Java Hungry Blog Alive is Awesome";

            Character result = input.chars() // Stream of String       
                                    .mapToObj(s -> Character.toLowerCase(Character.valueOf((char) s))) // First convert to Character object and then to lowercase         
                                    .collect(Collectors.groupingBy(Function.identity(), LinkedHashMap::new, Collectors.counting())) //Store the chars in map with count 
                                    .entrySet()
                                    .stream()
                                    .filter(entry -> entry.getValue() > 1L)
                                    .map(entry -> entry.getKey())
                                    .findFirst()
                                    .get();
            System.out.println(result);                    
    }
}

Output:
a

Q9 Given a list of integers, sort all the values present in it using Stream functions?

import java.util.*;
import java.util.stream.*;
import java.util.function.Function;

public class JavaHungry {
    public static void main(String args[]) {
            List<Integer> myList = Arrays.asList(10,15,8,49,25,98,98,32,15);

             myList.stream()
                   .sorted()
                   .forEach(System.out::println);
    }
}

Output:
 8
10
15
15
25
32
49
98
98

Q10 Given a list of integers, sort all the values present in it in descending order using Stream functions?

import java.util.*;
import java.util.stream.*;
import java.util.function.Function;

public class JavaHungry {
    public static void main(String args[]) {
            List<Integer> myList = Arrays.asList(10,15,8,49,25,98,98,32,15);

             myList.stream()
                   .sorted(Collections.reverseOrder())
                   .forEach(System.out::println);
    }
}

Output:
98
98
49
32
25
15
15
10
8

That's all for today regarding 10 java 8 coding and programming interview questions and answers. Please mention in the comments in case you know any other better approach to solving the above questions.