Java Interview in Concirrus

Hi Friends,

In this post, I'm sharing interview questions asked in Concirrus.

You can read Questions-Answers asked in other interviews as well here:

• Java Interview @ NexGen
• Java Interview @ SAP
• Java Interview @ GalaxE
• Java Interview @ OrangeMantra
• Java Interview @ CapGemini
• Java Interview @ RBS
• Java Interview @ Handygo
• Java Interview @ Virtusa Polaris

Here are the list of questions asked in Concirrus:

Question 1:

How Singleton is handled in Deserialization? What, if we use clone() in singleton?

Answer:

When we serialize Singleton instance and try to deserialize it, then if we call deserialization multiple times, then it can result in more than one instance of singleton class.

To avoid this problem, we can implement readResolve() method. This readResolve() method is called immediately after an object of this class is deserialized, Means when ObjectInputStream has read an object from input stream and is preparing to return it to the caller, then it checks whether the readResolve() method is implemented or not.

Note: Both objects [Read by ObjectInputStream and returned by readResolve() method] should be compatible [Identical] else ClassCastException is thrown.


Implementation of readResolve() method:

protected void readResolve(){
    // Instead of the object we are on, return the class variable singleton.
    return singletonInstance;
}


What if we use clone() method in Singleton?

Answer:

 If we override clone() method in singleton class, then we must throw CloneNotSupportedException from this method.


Question 2:

How HashMap works?

Answer:

HashMap in java contains key-value pairs. It doesn't maintain the insertion order of key-value pairs.

Whenever a key-value pair is required to be stored in HashMap, The overridden hashcode() method [if there is one] is used to calculate the hashcode and then Object's class hash() method is called on that value which provides the index in underlying bucket of HashMap.

HashMap uses array based structure to store each key-value entry. That array is called bucket and each location in bucket maintains a simple optimized LinkedList.

So, after the index in the bucket is found, then if there is no entry matching the key in that bucket indexed LinkedList, then that key-value pair is stored. Else , if there is some key-value pairs already there in the LinkedList, then key is compared to every key in LinkedList using equals() method and if a match found, then the value for that key is replaced with new value.

If there is no match found, then that new key-value pair is stored as a new entry in HashMap.



Question 3:

Create Immutable class?

Answer:

There are 2 ways to create immutable class in java:

• Make the class final and all it's instance variable as final. So they can be initialized in constructor only. 
• Make all the instance variables private and don't change them except constructor. Don't provide any setter methods for them. Make the getter methods final so that subclasses don't override these getter methods and return other values.

Question 4:

Detect loop in LinkedList


Answer:

I wrote the entire code for this problem.
It took almost 25-30 minutes.

I'm sharing the source code here :

class LinkedList{

    static Node head;

    static class Node{
        int data;
        Node next;

        Node(int d){
            data = d;
            next = null;
        }
    }

    int detectLoop(Node node){

        Node slow = node, fast = node;
   
        while(slow != null && fast != null && fast.next != null){

            slow = slow.next;
            fast = fast.next.next;

            // If fast node reaches slow node, means there is a loop.
            if(slow == fast){

                return 1;
            }
       }
       return 0;
}


}

Question 5:

Dynamically confiuring a new microservice. Does it require deploying all microservices, if we use static way?

Answer:

No. We can just deploy our microservice to some host and it will register itself with Service Registry. From there it can be discovered by other microservices and also it can discover other required microservices.

And this way, communication can be established among various microservices without any external configuration.


Question 6:

Is there any loophole in using Git-> Jenkins CI/CD way?

Answer:

There is no loophole in Git-> Jenkins CI/CD way. The problems/loopholes  occur in the way these tools are configured by Software Delivery teams [DevOps].

There are multiple things that can cause problems in using Jenkins as CI/CD tool:

• Jenkins has too many plugins
• Jenkins was not designed for the Docker age
• Jenkins doesn't support microservices well

Jenkins has too many plugins:

Plugins are good when they are used properly and efficiently. Plugins give users the choice to add various features  to the tools they use.

But in Jenkins, for achieving every single basic task, you need a separate plugin. 

e.g.: for creating a build for Docker environment, you need a plugin.

To pull code from Github, you need a plugin.

Jenkins was not designed for the Docker age:

CI servers don't match with Docker container infrastructure easily. They require multiple plugins to integrate with Docker. There are more than 14 plugins with Docker in their names. And almost 6 of them are for core Docker platform.


Question 7:

Design TinyURL algorithm.


Answer:

I designed it as per my knowledge.



Question 8:

Which Docker command is used to know the list of running containers?

Answer:

docker ps


Question 9:

Difference between GitHub and GitLab?

Answer:

That's all for this post of interview questions.

Hope this post helps everybody in clearing java interviews.

Thanks for reading!!