Top 50 Java Programming Interview Questions: A Comprehensive Guide

JavaScript is one of the widely used programming languages and used to create engaging and dynamic websites. Due to its vast scope, JavaScript interviews can be challenging. However, thorough preparation can help overcome these challenges. An interviewee should familiarize themselves with the most basic concepts to the most complex libraries and frameworks.

These top 50 JavaScript interview questions and answers will help people who are being interviewed practice a lot and get ready for their meeting.

public static String reverse(String in) {    if (in == null)        throw new IllegalArgumentException("Null is not valid input");    StringBuilder out = new StringBuilder();    char[] chars = in.toCharArray();    for (int i = chars.length - 1; i >= 0; i--)        out.append(chars[i]);    return out.toString();}

b = b + a; // now b is sum of both the numbersa = b - a; // b - a = (b + a) - a = b (a is swapped)b = b - a; // (b + a) - b = a (b is swapped)

public static boolean stringContainsVowels(String input) {    return input.toLowerCase().matches(".*[aeiou].*");}

public static boolean isPrime(int n) {    if (n == 0 || n == 1) {        return false;    }    if (n == 2) {        return true;    }    for (int i = 2; i <= n / 2; i++) {        if (n % i == 0) {            return false;        }    }    return true;}

public static void printFibonacciSequence(int count) {    int a = 0;    int b = 1;    int c = 1;    for (int i = 1; i <= count; i++) {        System.out.print(a + ", ");        a = b;        b = c;        c = a + b;    }}

public static boolean onlyOddNumbers(List<Integer> list) {    for (int i : list) {        if (i % 2 == 0)            return false;    }    return true;}

boolean checkPalindromeString(String input) {    boolean result = true;    int length = input.length();    for (int i = 0; i < length/2; i++) {        if (input.charAt(i) != input.charAt(length - i - 1)) {            result = false;            break;        }    }    return result;}

String removeWhiteSpaces(String input) {    StringBuilder output = new StringBuilder();        char[] charArray = input.toCharArray();        for (char c : charArray) {        if (!Character.isWhitespace(c))            output.append(c);    }        return output.toString();}

String s = "  abc  deft";s = s.strip();System.out.println(s);

int[] array = {1, 2, 3, -1, -2, 4};Arrays.sort(array);System.out.println(Arrays.toString(array));

public class ThreadDeadlock {    public static void main(String[] args) throws InterruptedException {        Object obj1 = new Object();        Object obj2 = new Object();        Object obj3 = new Object();            Thread t1 = new Thread(new SyncThread(obj1, obj2), "t1");        Thread t2 = new Thread(new SyncThread(obj2, obj3), "t2");        Thread t3 = new Thread(new SyncThread(obj3, obj1), "t3");                t1.start();        Thread.sleep(5000);        t2.start();        Thread.sleep(5000);        t3.start();            }}class SyncThread implements Runnable {    private Object obj1;    private Object obj2;    public SyncThread(Object o1, Object o2) {        this.obj1 = o1;        this.obj2 = o2;    }    @Override    public void run() {        String name = Thread.currentThread().getName();        System.out.println(name + " acquiring lock on " + obj1);        synchronized (obj1) {            System.out.println(name + " acquired lock on " + obj1);            work();            System.out.println(name + " acquiring lock on " + obj2);            synchronized (obj2) {                System.out.println(name + " acquired lock on " + obj2);                work();            }            System.out.println(name + " released lock on " + obj2);        }        System.out.println(name + " released lock on " + obj1);        System.out.println(name + " finished execution.");    }    private void work() {        try {            Thread.sleep(30000);        } catch (InterruptedException e) {            e.printStackTrace();        }    }}

public static long factorial(long n) {    if (n == 1)        return 1;    else        return (n * factorial(n - 1));}

LinkedList<Integer> ll = new LinkedList<>();ll.add(1);ll.add(2);ll.add(3);System.out.println(ll);LinkedList<Integer> ll1 = new LinkedList<>();ll.descendingIterator().forEachRemaining(ll1::add);System.out.println(ll1);

Advanced JavaScript coding interview questions

Advanced JavaScript coding includes various complex concepts and techniques. Such key concepts are often tested in JavaScript interviews. Functional programming, design patterns, memory management, ES6 features, closure and scope are just a few of the ideas that are covered.

1. Create a debounce function in JavaScript that limits how often a function runs when it is called more than once within a certain amount of time.

Interviewers want candidates who can clearly explain what the debounce function does and how to use it in situations where function calls need to be controlled. They are looking for the person’s ability to articulate technical concepts clearly.

Sample answer: The frequency can be limited by waiting for the debounce function to run until the time frame has elapsed.

function debounce(func, delay) {

timer = setTimeout(func, delay);

2. Give a function an array of objects and a key. The function should return a new array that is sorted by the values of the key in ascending order.

When hiring managers ask this question, they test how well the candidate can talk about the sorting algorithm and how long it takes. It’s also crucial for candidates to demonstrate their code’s robustness.

To sort an array of objects in ascending order, use the following function, which takes an array of objects and a key.

function sortByKey(arr, key) {

return arr.sort((a, b) => a[key] – b[key]);

3. Create a JavaScript deep clone function that makes a copy of an object or array that is nested inside another object or array. This copy will not be linked to the original.

The person being interviewed is being looked at by hiring managers to see how well they can handle difficult coding tasks and understand how to avoid reference problems while cloning.

I can serialize the object to a JSON string by using two methods together and making a deep clone. I would then parse it back into a new object, thereby removing any reference to the original object.

4. Write a recursive function to calculate the factorial of a given number.

Interviewers expect the candidate to write a concise recursive function that handles edge cases. Candidates must show their understanding of how recursion works to avoid infinite loops or stack overflow errors.

Sample answer:

if (num <= 1) return 1;

return num * factorial(num – 1);

5. Come up with a way to merge two sorted arrays into a single sorted array that doesn’t use any built-in sorting functions.

When interviewers ask this question, they want to see how well the person knows algorithms and how quickly they can sort data. They also look for the ability to think of and execute a correct solution.

Sample answer: I can implement a function that can efficiently merge two sorted arrays.

function mergeSortedArrays(arr1, arr2) {

return […arr1, …arr2].sort((a, b) => a – b);

6. Write a function that takes a string as input and checks to see if it is a palindrome by only looking at the letters and numbers and not the case.

Interviewers look at how the person answers questions about how to run code and show that they know how to deal with case-sensitive and alphanumeric checks, regular expressions, and JavaScript string methods.

Sample answer:

const cleanStr = str.replace(/[^a-zA-Z0-9]/g, ”).toLowerCase();

const reversedStr = cleanStr.split(”).reverse().join(”);

return cleanStr === reversedStr;

7. Make a JavaScript class for a linked list that has methods to add a node at the beginning, end, or a certain spot and remove a node from a certain spot.

Interviewers can see how well a candidate can design and implement a class for a linked list as well as how well they can solve problems by asking this question.

Example answer: I would make a linked list with ways to add a node at the beginning, end, and certain points in the list. Then, I would delete a node from a given position.

8. Implement a function that flattens a nested array in JavaScript, converting it into a single-level array.

Managers can gauge the candidate’s logical thinking skills and capability to handle complex data structures. Interviewees should demonstrate their knowledge of loops, recursion, and arrays.

Sample answer:

const flattenArray = (nestedArray) => {

9. Write a function that determines if two strings are anagrams of each other

When interviewers ask this question, they want to see how well the candidate can use the right string-related techniques and correctly find anagrams.

Sample answer:

function areAnagrams(str1, str2) {

return str1.split(“”).sort().join(“”) === str2.split(“”).sort().join(“”);

10. Use memoization to speed up the performance of your JavaScript function that returns the Fibonacci sequence up to a certain number.

Interviewees are expected to show their proficiency in OOP and familiarity with recursion and memoization. They can also determine the candidate’s attention to detail in class design and organizing code.

An example answer: A Fibonacci sequence can be made by making a function that stores the calculated values in an array.

let memo = [0, 1];

for (let i = 2; i <= n; i++) {

memo[i] = memo[i – 1] + memo[i – 2];

Tricky JavaScript coding questions

By asking tricky JavaScript coding questions, managers can assess problem—solving skills, JavaScript concepts, and critical thinking. These go beyond syntax knowledge and require the candidate to think creatively and logically to solve problems.

1. Write a function that reverses the order of words in a sentence without using the built-in reverse() method.

This question not only tests how creative the candidates are, but it also shows hiring managers how well they can design a solution that is clear and easy to understand.

Sample answer:

const words = sentence.split(‘ ‘);

const reversedWords = words.reverse();

2. Make a function that checks a string to see if it is a palindrome (reads the same forwards and backwards) and doesn’t care about spaces or punctuation.

Interviewers can gauge the interviewee’s capability to handle whitespace and punctuation gracefully while also maintaining the palindrome-checking logic. Candidates must express their knowledge of regular expressions or any other efficient approach.

Sample answer:

const cleanedStr = str.replace(/[^w]/g, ”).toLowerCase();

const reversedStr = cleanedStr.split(”).reverse().join(”);

return cleanedStr === reversedStr;

3. Give an array of integers to the function, and it should return the largest difference between any two numbers in the array.

To deal with edge cases and invalid input, candidates should show how they find the largest difference between the elements of an array.

Sample answer:

let min = arr[0];

let maxDiff = 0;

for (let i = 1; i < arr.length; i++) {

if (arr[i] < min) {

const diff = arr[i] – min;

if (diff > maxDiff) {

4. Implement a function that removes duplicates from an array, keeping only the unique elements.

Interviewers can analyze how well a candidate can effectively communicate code explanations and their familiarity with algorithmic efficiency.

Sample answer:

return arr.filter((item, index) => arr.indexOf(item) === index);

5. Write a function that accepts a number and returns its factorial (e. g. , factorial of 5 is 5 x 4 x 3 x 2 x 1).

By asking this question during the interview, hiring managers can see how well the candidate can manipulate numbers. They can also determine how well the interviewee can pay attention to handling edge cases, if applicable.

Sample answer:

if (num === 0 || num === 1) {

return num * factorial(num – 1);

6. Implement a function that flattens a nested array into a single-dimensional array.

During interviews, candidates are expected to show that they can work with complex data structures and complete tasks using the right methods.

Sample answer:

7. You need to write a function that checks if two strings are anagrams (have the same characters but in a different order).

Candidates should showcase how well they can handle complex algorithms and logic. Interviewers are specifically looking for knowledge in string methods, data structures, and loop constructs.

Sample answer:

function isAnagram(str1, str2) {

const sortedStr1 = str1.split(”).sort().join(”);

const sortedStr2 = str2.split(”).sort().join(”);

return sortedStr1 === sortedStr2;

8. Implement a function that finds the second smallest element in an array of integers.

Interviewers can measure the candidate’s problem-solving skills and their understanding of conditional statements, loops, and arrays.

Sample answer:

const sortedArr = arr.sort((a, b) => a – b);

9. Write a function that generates a random alphanumeric string of a given length.

Interviewers can find out how well a candidate can make sure the function produces a reliable and consistent random output by asking this question.

Sample answer:

const characters = ‘ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789’;

let result = ”;

for (let i = 0; i < length; i++) {

const randomIndex = Math.floor(Math.random() * characters.length);

10. Implement a function that converts a number to its Roman numeral representation.

Hiring managers can gauge a candidate’s capability to implement coding solutions and create an efficient algorithm.

Sample answers:

// Implement your code here

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