Interview questions for Java developer, Struts, EJBs

[Gina vernon]

Here are a few questions I was asked at a recent interview. Hope somebody finds this helpful in preparing for an interview.

1. What is the difference between, FINAL, finally{} and finalize()?
2. What are weak and strong references?
3. What can an interface do that a 100% abstract class cannot?
3. Why use stateful beans for persistance instead of stateless beans?
4. How are singletons created in a cluster environment?
5. How are JSPs included within JSPs?
6. What does the ReflectionsAPI do?
7. What design patterns have you used?How?

[avi sinha]

thanks Gina for posting these questions. I didn't know about the weak references. Now got it.

Keep up the good work.

Avi Sinha

[Jeevan Reddy]

Thanks for posting them. It should be useful to us

[Tim McGuire]

These are great. It was good to review Strong References vs Weak References. I'll bet ignorance of these cause a lot of performance problems.

[Gina vernon]

Does anyone have an answer to the following question? I searched the internet but couldn't find anything that specifically addressed this question.

What can an interface do that a 100% abstract class cannot?

Basically, the question was if a developer can get all the functionality of an interface in a 100% abstract class, why even use an interface?

Thanks.

[Tim McGuire]

Gina vernon wrote:Does anyone have an answer to the following question? I searched the internet but couldn't find anything that specifically addressed this question.

What can an interface do that a 100% abstract class cannot?

Basically, the question was if a developer can get all the functionality of an interface in a 100% abstract class, why even use an interface?

Thanks.

I think they were looking for:
a class can only extend one abstract class while it can implement any number of interfaces.

[Gina vernon]

Tim McGuire wrote:
I think they were looking for:
a class can only extend one abstract class while it can implement any number of interfaces.

Yup, mentioned that. But the interviewer wasn't satisfied with the answer.

[Rohan kanade]

Gina vernon wrote:Does anyone have an answer to the following question? I searched the internet but couldn't find anything that specifically addressed this question.

What can an interface do that a 100% abstract class cannot?

Basically, the question was if a developer can get all the functionality of an interface in a 100% abstract class, why even use an interface?

Thanks.

if you use interfaces to define a contract, then if you change the interface in future, you have to implement the changes in all the classes which implement the interface.

but in a abstract class, you can add concrete methods without needing to make changes in classes which extend the abstract class, thus if your contract is gonna change too often , you should use a abstract class to have the base contract + any specialized additional contract features.

And about what a interface can do that a 100% abstract class cannot ? its easy, a interface can extend n numbers of other interfaces, which makes it easy to define a contract based on many other smaller contracts.