Crack Interview: Java 8 Coding Questions

In your interview preparation journey, we are here to help you as much we can so that you can crack the interview. Java 8 was officially released in March 18, 2014. It has introduces several new features and improvements to the Java programming language.

These updates have made Java more efficient, concise, and functional. And this updates is now adopting by IT industries. As a result, Java 8 coding questions are commonly asked in job interviews and programming competitions. This article aims to provide you with a list of coding questions for better practice of your java 8 concepts.

Java 8, with its introduction of lambdas, streams, and functional interfaces has now changed the coding approach of developers. Whether you’re fresher or experiences and preparing for a job interview or just willing to enhance your problem-solving skills, the below list of problem will really help you in your journey to begins.

Welcome to a comprehensive exploration of “Java 8 Coding Questions” – a series designed to unravel the intricacies of Java 8 through hands-on coding exercises. Let’s dive into the world of functional programming, lambda expressions, and stream processing as we sharpen our Java 8 skills one coding question at a time.

Focused Code

👉 Convert Array into List In Java 8.

1. Number-Based Functional & Stream API Programs

✔️ Basic Operations on Numbers

Program	YouTube Link
1. Find the sum, average, maximum and minimum of numbers in a list using Streams.
2. Find the sum, average, maximum and minimum of all elements in an array using Streams.

✔️ Sorting & Searching

Program	YouTube Link
1. Sort numbers in ascending and descending order using Streams.
2. Find the second highest and lowest number in a list using Streams.
3. Find the second highest and lowest number in an array using Streams.
4. Find the first non-repeating number in a list and array using Streams.

✔️ Filtering & Grouping

Program	YouTube Link
1. Group even and odd numbers in a list and print using Stream.
2. Find duplicate elements in a list and array using Streams.
3. Remove duplicate elements from an array using Streams.
4. Filter numbers greater than a given value from a list using Streams.
5. Find all prime numbers in a list using Streams.

✔️ Array & List Operations

Program	YouTube Link
1. Find common elements in two arrays using filter().
2. Merge two arrays into a single sorted array using Stream.concat().
3. Reverse an array using Streams.
4. Reverse a list using Streams.
5. Find the most frequently occurring element in a list using groupingBy().
6. Calculate the product of all numbers in a list using reduce().
7. Find the count of even and odd numbers in a list using partitioningBy().
8. Filter out numbers greater than a given value from a list using filter().
9. Remove duplicate elements from a list using distinct().
10. Find the intersection of two lists using filter().
11. Find the union of two lists using distinct().
12. Check if all elements in a list are unique using Set.
13. Sort a list in ascending and descending order using Streams.

2. String-Based Functional & Stream API Programs

✔️ Basic String Operations

Program	YouTube Link
1. Convert a list of strings to uppercase using Streams.
2. Convert a list of Integers to a list of Strings using map().
3. Reverse a string using reduce().
4. Remove duplicate characters from a string using Streams.

✔️ Filtering & Grouping

Program	YouTube Link
1. Find the most frequently occurring character in a string using Streams.
2. Find duplicate words in a sentence using Streams.
3. Count the number of vowels in a string using Streams.
4. Find the longest word in a list of strings using reduce().
5. Group words by their first character using Collectors.groupingBy().

✔️ Sorting & Comparisons

Program	YouTube Link
1. Sort a list of strings by length using Streams.
2. Check if two strings are anagrams using Streams.

3. Collection-Based Functional & Stream API Programs

✔️ Collection Conversions

Program	YouTube Link
1. Convert a list to a set using Streams.
2. Convert a set to a list using Streams.
3. Convert a Map to a List of keys and values using Streams.

✔️ Filtering & Grouping

Program	YouTube Link
1. Find the frequency of each element in a collection using Collectors.groupingBy().
2. Remove null values from a list using Streams.
3. Group elements by their occurrence count using Collectors.groupingBy().
4. Partition a collection into two groups based on a condition using partitioningBy().

✔️ Sorting & Merging

Program	YouTube Link
1. Sort a Map by values in ascending and descending order using Streams.
2. Merge two maps into a single map using Streams.
3. Find the sum of values in a Map using Streams.
4. Filter a Map based on a condition using Streams.
5. Find the top N elements from a collection using limit().
6. Find common elements between two sets using Streams.
7. Find unique elements from two sets (union – intersection) using Streams.

4. Employee/Custom Object Functional & Stream API Programs

✔️ Filtering & Grouping

Program	YouTube Link
1. Find employees with a salary greater than 50,000 using Streams.
2. Find the highest-paid employee in a list using max().
3. Find the youngest employee in a department using min().
4. Group employees by department using Collectors.groupingBy().
5. Find the average salary of employees using Collectors.averagingDouble().
6. Partition employees based on experience (>5 years, <5 years) using partitioningBy().

✔️ Sorting & Mapping

Program	YouTube Link
1. Sort employees by name using sorted().
2. Convert a List of Employees to a Map using Collectors.toMap().

5. Some Advanced Program

Practicing these will enhance your proficiency and confidence:

✔️ Lambda Expressions and Functional Interfaces

Program	YouTube Video Link
1. Implement a comparator using a lambda expression to sort a list of strings by their length.
2. Define a custom functional interface and use it with a lambda expression.

✔️ Stream API

Program	YouTube Link
1. Given a list of integers, filter out the even numbers and compute their sum using Streams.
2. Convert a list of strings to uppercase and remove duplicates using Streams.
3. Find the first non-repeated character in a string using Streams.
4. Group a list of strings by their length using the Collectors.groupingBy method.

✔️ Optional Class

Program	YouTube Link
1. Write a method that returns an Optional object. If a string is non-empty, return it; otherwise, return an empty Optional.
2. Use Optional to handle the possibility of a null value when retrieving a value from a map.

✔️ Date and Time API (java.time)

Program	YouTube Link
1. Calculate the difference in days between two dates using the java.time API.
2. Display the current time in a specific time zone.
3. Format a LocalDate to a string with the pattern “dd-MM-yyyy”.

✔️ Default and Static Methods in Interfaces

Program	YouTube Link
1. Create an interface with a default method and demonstrate its usage in a class.
2. Define a static method in an interface and explain how it can be invoked.

✔️ Miscellaneous

Program	YouTube Link
1. Demonstrate the use of the map, flatMap, filter, and reduce operations in Streams with examples.
2. Explain the concept of effectively final variables in the context of lambda expressions.
3. Discuss the improvements in memory management with the introduction of the Metaspace in Java 8.