Java Interview @ Aricent

Hi Friends,

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

Also read my other interviews:

• Interview @ CapGemini
• Java Interview @ SAP
• Java Interview @ GalaxE
• Java Interview @ OrangeMantra
• Java Interview @ Concirrus
• Interview @ Dew Solutions
• Interview @ BirdEye
• Interview @ RBS
• Interview @ WDTS
• Interview @ Rocketalk

Question 1:

When does deadlock occur?

Answer:

• Due to nested synchronized block
• Due to calling of synchronized method from another synchronized method
• Trying to get lock on two different objects

Code that causes Deadlock:

public class DeadlockDemo{

    public void method1(){

        synchronized(String.class){

            synchronized(Integer.class){

            }

       }

    }

    public void method2(){

        synchronized(Integer.class){

            synchronized(String.class){

            }

        }

    }

}

Question 2:

What is LiveLock?

Answer:

When all the threads are blocked or unable to proceed due to unavailability of required resources, then it is known as LiveLock.

1. It occurs when all threads call Object.wait(0) on an object with 0 as parameter. The program is live-locked and cannot proceed until one or more threads call Object.notify() or Object.notifyAll() on the relevant objects.
2. When all the threads are stuck in infinite loops.

Question 3:

Is there any way to find a deadlock has occured in java?


Answer:

Yes. There is a way to find it.
From JDK 1.5, we have java.lang.management package to diagnose and detect deadlocks.
java.lang.management.ThreadBean interface is management interface for the thread system of JVM.

It has methods like findMonitorDeadlockedThreads() and findDeadlockedThreads().


Question 4:

Sort list of Employee objects using Designation, then age and then salary [nth level sorting]

Answer:

public class ComparatorChain implements Comparator<Employee>{

    private List<Comparator<Employee>> listComparators;

    public ComparatorChain(Comparator<Employee>... comparators){
        this.listComparators = Arrays.asList(comparators);
    }

    @Override
    public int compare(Employee emp1, Employee emp2){
 
        for(Comparator<Employee> comparator : listComparators){
             int finalResult = comparator.compare(emp1, emp2);
             if(finalResult !=0){

                 return finalResult;
             }

        }
        return 0;
    }

}

DesignationComparator.java:

public class DesginationComparator implements Comparator<Employee>{

    @Override
     public int compare(Employee emp1, Employee emp2){

         return emp1.getDesignation().compareTo(emp2.getDesignation());
    }

}

AgeComparator.java

public class AgeComparator implements Comparator<Employee>{

    @Override
     public int compare(Employee emp1, Employee emp2){

        return emp1.getAge() - emp2.getAge();
    }

}


SalaryComparator.java:

public class SalaryComparator implements Comparator<Employee>{

    @Override
    public int compare(Employee emp1, Employee emp2){

        returm emp1.getSalary() - emp2.getSalary();
    }
}


public class ListObjectsComparisonAndSortingExample{

    public static void main(String[] args){

        List<Employee> employees = new ArrayList<Employee>();

       employees.add(new Employee("Mittal", "Developer", 35, 100000));
       // Add more Employee objects

      Collections.sort(employees, new ComparatorChain(
          new DesignationComparator(),
          new AgeComparator(),
          new SalaryComparator())
       );

    }

}

Question 5:

How to change logs from Info to Debug using log4j?

Answer:

In Log4j, we have multiple methods like debug(), info() , error() which can be called based on some condition and after that this Log API will print only that types of logs.

So, whenever we need to change logs from Info level to Debug level, we can easily do that by switching the call from info() to debug() as shown in example below:

static Logger logger = Logger.getLogger(MyClass.class.getName()); // Creating logger instance

logger.info("info"); // Suppose , initially it was printing info logs

logger.setLevel(Level.DEBUG); From now on, only debug, info, warn, error and fatal logs will be printed. But trace logs will not get printed.
logger.debug("debug"); 

logger.error("error");

logger.trace("trace");//it will not get printed.

Question 6:

What is the Log4j log level hierarchy order?

Answer:

From above diagram, we can see that for WARN, FATAL, ERROR and WARN are visible.

And for OFF, nothing will be visible.

Question 7:

What is a Daemon thread? How it works?

Answer:

Daemon thread acts like service providers for other threads running in the same process.
Daemon threads will be terminated by JVM when there are no other threads running, it includes main thread of execution as well.

To specify that a thread is a Daemon thread, call the setDaemon() method with the argument true.

To determine if a thread is a daemon thread, use the accessor method isDaemon().
Daemon threads are used to provide background support to the user threads.

Example of a daemon thread is Garbage Collection thread. gc() method is defined in System class that is used to send request to JVM to perform garbage collection.

public class DaemonThread extends Thread{

    public DaemonThread(){
        setDaemon(true);
    }

    public void run(){

        System.out.println("Is this thread Daemon? - "+isDaemon());
    }

    public static void main(String[] args){

        DaemonThread dt = new DaemonThread();
        dt.start();
    }
}




Question 8:

Describe two code cases where Race condition occur in java?

Answer:

Two code scenarios where race condition occur are:

• Check and Act race condition
• Read. Modify, Update race condition

Check and Act race condition: 

In this, we take example of creating Singleton instance.

if(instance == null){

    return class.getInstance();

}

Here, in this code, Suppose we have two threads T1 and T2. When T1 crosses if check, then it goes inside and CPU switches to T2. Now, it T1 is taking more time to create instance, then T2 also checks if statement and find instance as null. It also goes inside if() check and creates another instance.

So 2 instances will be created for Singleton instance.


Question 9:

How does Time complexity for get() and put() methods in HashMap is O(1)?

Answer:

Whenever we search for a key in HashMap or HashSet, it follows these steps:

• Calculate hashcode for the key using their own hash() method.
• This key acts as a m/m address and it is used to find array index/bucket location.
• Then entries in LinkedList are compared.

As, m/m address from array can be get in one step, that's why it is O(1).

But in case, there are 1000 entries in LinkedList in a bucket, then it is not O(1). Then it is based on number of entries in LinkedList. So, in worse case, it is O(n).


Hope these interview questions help everybody.

Thanks for reading.