Top 10 Java Programs, Assignments, and Coding Interview Questions Answers

Java coding interview questions answers
Java coding interview questions are mostly some programming exercises which is asked to be solved in the java programming language in a limited time during any core Java or J2EE interview. No matter whether you have 2 years of experience or 4 years of experience, there is always some coding interview question in the Java programming job you are applying for. Actually, questions related to Java Coding are increasingly getting popular in Java interviews for two reasons, first its difficult to crack Java coding interview questions than answering fact-based questions like Why String is immutable in Java or Why main is static in Java etc.

Second reason of popularity of Coding question in Java interviews is read need of good developers who are required to do a lot of coding in projects rather than doing some maintenance works.

Since Java is front line language for any server-side application, and as the complexity of the business process and need of performance is increasing,  its obvious that the amount of coding skill required in Java programmers are getting increased with every passing day, which effectively means Java coding questions are top of any list of core Java interview question.

These Coding interview questions are collected from various Java programming interviews, from friends and colleagues, and can be a good starting point to refresh your coding skills before appearing on any Java interviews. These basics Java Programs and logical questions can also be a good resource for learning to program and improving your problem-solving skills in Java.

16 Programming Assignments, Homework, and Coding Interview questions answers in Java

Here are my list of 10 Java coding interview questions and answers, which is good to prepare before appearing on any Java interviews. As I said Java coding questions are mostly based on programming, logical analysis and problem-solving skill and are on top of any list of tough Java interview questions, so better to get it right in first place.

Anyway, you may be able to solve and find answers of these Java coding questions by yourself, but if you stuck do a google, and you can get many alternative ways to solve these problems. 

Sometimes knowing more than one way to solve any programming question or coding problem in Java also helps to impress the interviewer. This list mainly contains basic programs asked on Interviews.

1. Write a Java program to replace certain characters from String like 
public String replace(String str, char ch)
This is a tricky Java coding interview question and it was  asked in one of the written test my friend had appeared recently. 

This Java coding question can be solved in multiple way like by using charAt() or substring() method,  but any approach throws couple of follow-up question like you may be asked to write two version to solve this coding exercise, one by using recursion and other by using Iteration.

They may also ask you to write JUnit test for this function which means handling null, empty string etc. By the way this programming question is quite common on technical interviews not just Java but also C, C++ or Scala, but knowing API definitely helps to produce better solution quickly.

2. Write a Java program to print different kind of patterns like Triangular pattern, box pattern, Pyramid patter of stars, numbers or alphabets. 

This is one of the popular Java homework assignment as well as popular program to learn programming and coding. 

The trick to solve all pattern questions are using loops. You need to know how to nest loops into each other as well as how to use continue and break to come out from inner and outer loop.

You also need to understand how to use print() and println() methods to print characters in same line and different lines. In the past, I have showed you how to print left and right triangular pattern and pyramid pattern of stars as well as pyramid pattern of alphabets.

Here are a couple of patterns you can try printing to improve your coding skill in Java.  

3. Write a Java program to print Fibonacci series up to 100?
This is one of the most popular coding interview questions asked in Java programming language. Even though, a Writing program for Fibonacci series is one of the basic Java program, not every Java developer get it right in interview. 

Again interview can ask to solve this programming interview question, by using recursion or Iteration. This Java programming question also test your problem-solving skills and if you come up with an original solution, that may even help. See here for complete code example of Fibonacci series in Java



4. FizzBuzz problem : Write a Java program that prints the numbers from 1 to 50. But for multiples of three print "Fizz" instead of the number and for the multiples of five print "Buzz". For numbers which are multiples of both three and five print "FizzBuzz"

This is also one of the classical programming questions, which is asked on any Java programming or technical interviews. This question is very basic but can be very trick for programmers, who can't code, that's why it is used to differentiate programmers who can do coding and who can't.

Here is a sample Java program to solve the FizzBuzz problem :

public class FizzBuzzTest{
 
    public static void main(String args[]){
    
        for(int i = 1; i <= 50; i++) {
            if(i % (3*5) == 0) System.out.println("FizzBuzz");
            else if(i % 5 == 0) System.out.println("Buzz");
            else if(i % 3 == 0) System.out.println("Fizz");
            else System.out.println(i);
        } 
    } 

}

You can also see this post to solve FizzBuzz in Java 8 using functional programing, lambda and stream. 

5. Write a Comparator in Java to compare two employees based upon there name, departments, and age?
This is a pure Java based Coding exercise. In order to solve this Java coding or programming interview question, you need to know What is a Comparator in Java and how to use compare method in Java for sorting Object. Sorting is one of the most logical and practical question on technical interview and ability to sort Java object is must to code in Java.

This article helps you to solve this Java coding question by explaining how to sort object in Java using Comparable and Comparator. Just remember that Comparable has compareTo() method and use to sort object based upon there natural order e.g. numeric order for number, and alphabetic order for String, while Comparator can define any arbitrary sorting.

A good follow-up question can also be the difference between Comparator and Comparable in Java, so be ready for that. You can also see these Java Interview Courses for better preparation, it includes all important topics and questions to quickly prepare for your next Java interview. 


6. Design a vending machine in Java which vends Item based upon four denomination of coins and return coin if there is no Item. (solution)
This kind of Java coding interview question appears in written test and I believe if you get it right, you are almost through the Interview. These kinds of problem-solving questions in Java are not easy, you need to design, develop and write JUnit test within 2 to 3 hours and only good Java developers, with practical coding experience, can solve this kind of Java programming question. 

What helps you is to keep practicing your coding skill even before interview.

See this programming exercise in Java to get yourself going. I personally like to ask programming questions, which test your object oriented design skills like designing ATM machine, designing parking lot or implementing logic for Traffic Signal controller.

7. Write a Java program to check if a number is Armstrong or not ?
Another popular logical coding interview questions in Java, which is based on programming logic. In order to answer this programming question, you need to know what is Armstrong number, but that is not a problem because question may specify that and even provide sample input and output.

The key thing to demonstrate is logic to check if a number is Armstrong or not. In most cases, you can not use utility methods defined by logic and you need to produce logic by yourself by using basic operators and methods.

By the way, this is also one of the basic programming questions and I have already provided a solution for this. I suggest seeing this Java program to find Armstrong Number in Java   to answer this coding question


8. Write a Java program to prevent deadlock in Java?
Some of the programming or coding interview question is always based on a fundamental feature of Java programming language like multi-threading, synchronization, etc. 

Since writing deadlock proof code is important for a Java developer, programming questions which requires knowledge of concurrency constructs becomes popular coding question asked in Java Interviews.

The deadlock happens if four conditions is true like mutual exclusion, no waiting, circular wait and no preemption. If you can break any of this condition than you can create Java programs, which are deadlock-proof.

One easy way to avoid deadlock is by imposing an ordering on acquisition and release of locks. You can further check How to fix deadlock in Java  to answer this Java programming questions with coding in Java

9. Write Java program to reverse String in Java without using API functions?
Another classic Java programming or coding exercise mostly asked on 2 to 5 years experienced Java interviews. Despite being simple answering this coding question is not easy, specially if you are not coding frequently. Its best to prepare this programming question in advance to avoid any embarrassment during interviews. I suggest to see this post which shows How to reverse String using recursion in Java

10. Write a Java program to find if a number is a prime number or not? (solution)
One more basic Java program, which made it's way to Interviews. One of the simplest coding question and also a very popular Java programming exercise. The beauty of these kinds of logical questions is that, they can really test the basic programming skills or a coder, programmer or developer. 

Not just problem solving, you can also check there coding style and thought process. 

By the way. you can also check the Java Programming Interview Exposed for many of such Java coding interview questions. It also covers other important topics e.g. Spring, Hibernate, Java Fundamentals, Object-oriented programming etc.

11. How to Swap two numbers without using a third variable in Java?
This Java program might require just four lines to code, but it's worth preparing. Most of the programmers make the same kind of mistakes while writing solutions for this program like Integer overflow, they tend to forget that an integer can overflow if its limit is exceeded, which is not very big. Sure shot way to answer these programming questions is to use the XOR trick to swap numbers, as mentioned in that blog post.


12. Create a Java program to find the middle node of the linked list in Java in one pass?
Any list of programming questions is incomplete without any questions from a linked list, arrays, and string, these three forms bulk of coding questions asked on Java interviews. The trick to solving this problem is to remember that the last node of the linked list points to null and you can trade memory with speed.

Sometimes your approach to come to a two-pointer solution really matters, by taking rational steps as mentioned above, you can sound more intelligent, a problem solver, and genuine. A quick solution to this programming question can be found here.




13. How to find if a linked list contains a cycle or not in Java? (solution)
Another programming question is based on a linked list. By the way, this coding question is a bit tricky than the previous one, but this can also be solved using two pointer approach. If the linked list has a cycle, then the fast pointer will either catch the slow pointer or point to null.  

If you want to practice more such questions based upon the linked list, array, and String and asked in various companies before, then I suggest you check the Cracking the Coding Interview, it contains more than 190 questions from various tech companies, startups, and service-based companies like Infosys, TCS, and Wipro in India.

14. Implement Producer Consumer design Pattern in Java using wait, notify, and notifyAll method in Java?
Similar to deadlock-related programming interview questions, this is also used to test programmers' ability to write bug-free concurrent programs in Java. These coding questions can be difficult if you haven't used wait and notify before, you can confuse yourself as hell on different aspects like which condition to check, on which lock you should be synchronized, etc. I suggest following here to answer this multithreading-based programming interview question.


15. Write a Java program to calculate the Factorial of a number in Java?
This Java coding interview question is also based on a list of basic Java programs for beginners. As usual, you better remember how to calculate factorial and how to code solutions using loop and recursive method calls. For a complete code solution of this programming question, see the Java program to calculate factorial



16. How to design a Trade Position Aggregator or Portfolio Management Software in Java?

This is another interesting object oriented design problem which is asked to Java programs. In this program you need to create a core Java application which can calculate trade position in real time. 

Live trades will be fed to system, both buy and sell and it needs to update the position on real time. Position means how many shares of a particular company a particular account is holding. You need to support both multiple accounts and multiple trading symbol. 

You can try this problem yourself but if you stuck you can see my solution to create Trade aggregator in Java for a step by step guidance. 

These are some of the Java coding interview questions and answers, which appear frequently on Java Programming interviews. I have included links, with some of my blog posts, which discusses answers of these Java coding question, but you can also find answers by doing google yourself. Please share what kind of Programming, logical, Problem solving or coding-related questions, asked to you in Java interviews?


Other Java and Coding Interview questions from Java67 blog

• 10 tricky Java interview questions - Answered
• 189 Coding Interview Questions from Amazon, Google, and Microsoft
• 10 Linux and UNIX interview questions - Answered
• Best Java Collection interview questions answers for practice
• Top 40 Java Telephonic Interview Questions
• Top 20 Hibernate Interview Questions with Answers
• Top 21 Spring MVC Interview Questions
• Top 10 RESTful Web Services Interview Questions
• Top 30 Java OOP Interview Questions with Answers
• 10 Java Developer Interview Courses to Prepare Next Interview

Thanks for reading this article so far. If you like these Java Programming Coding Interview Questions then please share them with your friends and colleagues. If you have any questions or suggestions then please drop a note.