Java Interview Questions

Middleware questions

2017-04-11T23:00:00.000-07:00

1. How is REST different from SOAP?
2. How can you map CRUD operations to REST operations?
3. How will you provide authentication and authorization in REST services?
4. Advantage of using API management tools such as API Connect?
5. How to use Swagger? Please explain how Swagger can be used for defining REST APIs?
6. What is MQTT? How is it different from JMS or AMQP?
7. What QoS of MQTT should we enable for our project?
8. How does Request/Response RPC work with AMQP?
9. What are web-sockets? How are they different from REST services?
10. How do you define API contracts? What are the standards?
11. What is Docker? What is Kubernetes?
12. What is ELK? How is it used for Logging along with Log4J?
13. What is Cloudant? How is data stored in Cloudant?
14. How can Kibana and ES be used for dashboards and other visualizations?
15. How to implement materialized views in DashDB?

Hibernate questions

2013-03-11T05:14:00.001-07:00

Can I pass Hibernate entities across the wire via web services?
What are hibernate proxies? How are they created?
What is lazy loading? Why do so many folks struggle with the LazyInitializationException error during lazy loading?
Do I need to learn Hyper SQL to use Hibernate? Can I use plain SQL?
What is the best approach - Data Model first and then Hibernate entities or vice versa. What are the pros and cons of each?
Are Hibernate annotations compile-time or run-time scope?
When we save/persist an object using Hibernate, how does Hibernate understand what fields/properties to save? Does it save all columns even if only one has changed? Hint: the _dirty flag :)
Should the Hibernate 'increment' id generator be used in production? What are the pitfalls?
How does Hibernate ENVERS work?
In Envers, the audit 'insert' is part of the same transaction, or async?
Can Hibernate supports Global Transactions ...i.e. two phase commit?
Can Hibernate be used in EJB 3.0 as JPA provider? What are the pros/cons? What would you recommend?
Can Hibernate prevent SQL Injection Attacks? How?

Security concepts

2012-11-05T05:43:00.000-08:00

What is the difference between pseudo-random numbers and real random numbers? PRNG and TRNG...
Is it even possible to create a true random number?
Why are random numbers important in cryptography?
What is the difference between hashing and encryption?
When would you use symmetric vs asymmetric encryption?
Does SSL / HTTPS use symmetric key or asymmetric key? What is session key?
What do you mean by 128-bit encryption? Is it the size of the symmetric key or asymmetric key?
What is the difference between digital signature and digital certificate?
What does a digital certificate contain? Also please explain how this all relates to the "Chain of Responsibility" design pattern?
What's the difference between a GUID generator and a random number generator?
When you install a digital certificate on the server, where is the private key stored?
What digital certs are installed on your brower? Who installs them and why are they required?

Sample scenarios: What to do? Whose public / private key to use?

You want to send a encrypted message to a person
You want to digitally sign a document/message

i18N concepts

2012-11-05T05:26:00.001-08:00

What is the difference between Unicode and UTF-16?
What is the significance of UTF-8? When to use it?
If Chinese characters are represented as 2 or 3 bytes, how will you find out the length of a string in Chinese? For e.g. for validating the length of a field on a form.
When do we need to use Base64 encoding?
If I need to make an application i18n enabled, besides label/message strings, what are the other areas (data-points) I need to take care of?
Can you open an unicode file (containing CJK chars) in notepad? If not, then why? What editors support unicode on your desktop?

BPMN questions

2012-10-15T09:49:00.000-07:00

What is the difference between a pool and a lane in a business process flow diagram?
What is the difference between a sequence flow and a message flow?
Can a sequence flow cross pools?
What are the different standards (diagrams) available for modelling business processes?
Why do we need BPEL? Is there a one-to-one mapping between BPMN and BPEL elements?

GC questions

2007-01-18T07:10:00.000-08:00

What is the default heap size allocated?

What should all threads stop when the GC runs ?

How does the low pause concurrent GC run?

What are the different generations/spaces in the heap? Diff between permanent generation, tenured generation and survivors?

What is the max heap size U can set on a 32-bit system?

JDBC questions

2006-06-18T00:20:00.000-07:00

-How would U insert a binary file contents into the database?
- What are batch statements in JDBC? Can U add a select sql in batch processing?
- How will U check that the JDBC driver supports batch processing/scrollable resultset etc?
- What are the different types of Rowsets? What is the advantage of a rowset?

On Logging

2006-05-03T13:00:00.000-07:00

What is the difference btw Log4J and java.util.logging?
Explain the concept of receivers and appenders in Log4J.
What is NDC, MDC in Log4J terminology?
I have 2 components - one written in C# and one in Java. How can I store the log of both of them in a single database table?
Can I make changes to the Log4J config file at runtime? (not requiring a server restart)

Messaging Questions

2006-01-26T22:19:00.000-08:00

How do I gaurantee once and only once delivery of a message in JMS ?
Can a message producer and message consumer be part of the same transaction?
How are message acknowledgements handled in JMS?

Scenario:
An application makes a remoting call and then puts a message on a queue and then makes one more database call. I want all of these 3 operations to be executed in a single transaction. How can U accomplish this ?

2006-01-03T00:57:00.000-08:00

How would U debug a multi-threaded application?. Say U have a Swing Application that creates 3 threads. Have U tried multi-threading debugging in Eclipse, Sun Studio ?

In a Swing Application, if the main thread dies, then what happens?

2005-11-23T04:30:00.000-08:00

When would U use thread pooling ?
How would U implement a thread pool ?
What are worker queues and worker threads ?
Have U explored the java.util.concurrent package in Java 5.0 ?
What is a deadlock and a race condition ?

2005-10-13T07:20:00.000-07:00

What's the advantage of adding a "serialVersionUID" to a Java source file?

2005-10-11T03:51:00.000-07:00

EJB Questions:
-----------------------
Give some examples of services offered by a EJB container?. What's the advantage of component model of software design?

How does the EJB container manage to intercept calls to a remote object and apply transactions, security?

Can an Entity EJB be dedicated to a single client?

What protocol is used when a EJB client communicates with a EJB server?

What's the difference btw EJB and CORBA models?

2005-10-05T04:41:00.000-07:00

What's the difference between JSP include directive and include element?

Struts Questions

2005-10-05T00:23:00.000-07:00

-- Explain the Struts architecture.
-- What are form-beans. Why are they required. Heard of DynaActionForm? Are form-beans required in Struts2?
-- How is form validation done in Struts?
-- Is validation done on server side of client side or both? Javascript vs Java?
-- Can there be more than one struts-config file?.
-- Can I change the name of the struts config file?
-- Can I use Tiles, Velocity template engine with struts?

-- What is the use of custom tags in JSP?
-- Would U use JSTL or Struts custom tags in Ur JSP pages?
-- What does the TLD file contain?
-- Difference between Struts 1.x and Struts 2.x?
-- How to use the MDC/NDC in Log4J with Struts? Where to put in the code? Which common place?
-- Can Struts2 be used with JSF?
-- How is AJAX handled in Struts 2?
-- Can we use JQuery instead of DWR?
-- Tiles vs IFrame? Pros and cons..
-- Can a single webapplication have some resources to be accessed thru HTTP and some by HTTPS?

2005-09-23T02:23:00.000-07:00

If I declare a class as 'protected', can other classes in the same package access the class?

2005-09-19T05:25:00.000-07:00

What is "inversion of control" design pattern? What is "dependency injection" ?

2005-09-08T03:03:00.000-07:00

Suppose U have a data collection (say a "arraylist"). U want to make sure that no one else can modify it. i.e. U want to make it immutable. How will U do it?

2005-09-08T02:49:00.000-07:00

What would U do if U need a "Multi-Map" collection? i.e. U have a collection where one key may map to many values.

2005-09-08T02:11:00.000-07:00

Can a Java class be private or protected?

2005-09-08T02:00:00.000-07:00

What is the advantage of Inner classes over encapsulation?
I can make a class as "package" access. Will this not suffice ? Why do I need Inner classes?

2005-09-06T03:27:00.000-07:00

How will U debug a Java program that has several threads running?
If U place a break-point somewhere, will all threads be suspended or only a single thread?

2005-08-16T04:12:00.000-07:00

What's the difference between the 'java.exe' and 'javaw.exe' processes?
When to use what?

2005-06-27T07:47:00.000-07:00

A circular project dependency occurs when two or more projects depend on each other. For example: FileOne in ProjectA depends on FileTwo in ProjectB, and FileThree in ProjectB depends on FileFour back in ProjectA.

How will U solve such dependencies in Java ?

2005-06-22T23:11:00.000-07:00

Suppose U have a file that needs to be shared between a Java application and a non-Java application for writing/reading. How will U do it ?