Java Interview @ CapGemini

Hi Friends,

I hope you have read my previous posts on Java interviews:

• Java Interview @ Dew Solutions
• Java/Android interview @ BirdEye
• Java Interview @ RBS
• Java Interview @ Virtusa Polaris
• Java/Android Interview @ Rocketalk
• Java Interview @ Aricent
• Java Interview @ WDTS

In this post, I'm sharing java questions asked in Aricent @ experience of 11 years.

Question 1:

How to handle transaction in Spring?

Answer:

In Spring, there are two ways of managing transactions:

• Programmatically manage by writing custom code
• Using Spring to manage transaction
• Programmatic Transaction management
• Declarative Transaction management

Programmatically manage by writing custom code:

EntityManagerFactory factory = Persistence.createEntityManagerFactory("persistance_unit_name");
EntityManager entityManager = factory.createEntityManager();
Transaction transaction = entityManager.getTransaction();

try{
    transaction.begin();
    //..........Business logic
    transaction.commit();
}
catch(Exception e){
    transaction.rollback();
    throw e;
}

Pros:

• The scope of the transaction is very clear in the code

Cons:

• It's repetitive and error prone
• Any error can have a very high impact
• A lot of boilerplate code needs to be written and if you want to call any another method from this method, then again you need to manage it in the code.

Using Spring to manage transaction:

1. Programmatic Transaction Management:

• Using the transaction template
• Using a PlatformTransactionManager implementation directly

2. Declarative Transaction

Question 2:

What is ORM and how to use it?

Answer:

ORM means Object Relational Mapping. It is a tool that helps in interacting with the database.

for example JPA is an ORM  which specifies some specifications which needs to be implemented.
In Spring, Hibernate is the implementation of JPA specifications.

So using ORM, Java object is mapped to relational table in database.




Question 3:

What is Heap dump?

Answer:

Heap Dump:  It is a snapshot of the memory of a java process.
This snapshot contains information about java objects and classes in the heap at the moment the snapshot is triggered.

Typically , a full GC is triggered before the heap dump is written, so the heap dump contains information about the remaining objects in the heap.

Typical information in a heap dump are:

• All objects: Class, fields, primitive values and references
• All Classes: Class Loader, name, super class and static fields
• Garbage collection roots: It is an object that is accessible from outside the heap.

Question 4:

Memory management in Java 8?

Answer:

Perm Gen in java 7 and earlier version has a default maximum size of 64 MB for 32-bit machine and 84 MB for 64-bit machine.

While default maximum size for metaspace is unlimited.

In java 8 ,we can set the initial and maximum size of metaspace using:

-XX:MetaspaceSize = N : Sets the initial and minimum size of metaspace

-XX:MaxMetaspaceSize=N : Sets the maximum size of the metaspace

Question 5:

Difference between Serial and Parallel streams.


Answer:

Parallel streams divide the task into many and run them in different threads, using multiple cores of the computer. It uses main thread along with ForkJoinPool.commonPool worker threads.

Sequential stream uses a single core. So it uses only 1 thread that is main thread.

Question 6:

How to find OutOfMemoryError in production app? And how to avoid this error immediately for long time?


Answer:

If we face OutOfMemoryError in production and we cannot really reason about it from stacktraces or logs, we need to analyze what was in there.

Get the VM Heap dump on OOM:

• -XX:+HeapDumpOnOutOfMemoryError
• -XX:HeapDumpPath="/tmp"

And use that for analysis. We can use memory analyzer tool for this.

How to avoid this error immediately for long time?

We can increase Heap space using -XX argument  for a while and it will work fine.


Question 7:

What is internal structure of heap memory?


Answer:

Question 8:

How to configure GC in Java application?

Answer:

GC tuning is only required when we have not set memory size in the application and too many Timeout logs are printed.

Question 9:

What are Serial and Parallel GC's?


Answer:

Serial Collector:

• Used for single threaded environments [32-bit Windows] and apps that use small heap
• It stops all threads when it is running. Means it is not suitable for server environment.
• We can use it by turning on the -XX:+UseSerialGC JVM argument.

Parallel Collector:

• This is JVM's default garbage collector
• It uses multiple threads to scan through and compact the heap and speeds up garbage collection.
• The downside is that it will stop application threads when performing either a minor GC or full GC.
• It is best suited for apps that can tolerate application pauses.
• Although it is default collector, but it can be configured using -XX:UseParallelGC JVM argument

Question 10:


What is Java Memory model?


Answer:

That's all for this interview.

Thanks for reading.