Complete reference to core java interview questions basic to advanced level : SE to Team Lead level Part - 10

1. public synchronized void Method1 () {
       // Appropriate method-related code.
   }
   E.g. Synchronizing a block of code inside a function:
   public myFunction (){
       synchronized (this) {
       // Synchronized code here.
     }
   }
   
   29. What's the difference between a queue and a stack?
   
   Stacks works by last-in-first-out rule (LIFO), while queues use the FIFO rule
   
   30. You can create an abstract class that contains only abstract methods. On the other hand, you can create an interface that declares the same methods. So can you use abstract classes instead of interfaces?
   
   Sometimes. But your class may be a descendent of another class and in this case the interface is your only option.
   
   31. If you're overriding the method equals() of an object, which other method you might also consider?
   
   hashCode()
   
   32. What is Collection API?
   
   The Collection API is a set of classes and interfaces that support operation on collections of objects. These classes and interfaces are more flexible, more powerful, and more regular than the vectors, arrays, and hashtables if effectively replaces.
   Example of classes: HashSet, HashMap, ArrayList, LinkedList, TreeSet and TreeMap.
   Example of interfaces: Collection, Set, List and Map.
   
   33. How would you make a copy of an entire Java object with its state?
   
   Have this class implement Cloneable interface and call its method clone().
   
   34. How can you minimize the need of garbage collection and make the memory use more effective?
   
   Use object pooling and weak object references.
   
   35. There are two classes: A and B. The class B need to inform a class A when some important event has happened. What Java technique would you use to implement it?
   
   If these classes are threads I'd consider notify() or notifyAll(). For regular classes you can use the Observer interface.
   
   36. Explain the Encapsulation principle.
   
   Encapsulation is a process of binding or wrapping the data and the codes that operates on the data into a single entity. This keeps the data safe from outside interface and misuse. One way to think about encapsulation is as a protective wrapper that prevents code and data from being arbitrarily accessed by other code defined outside the wrapper.
   
   37. Explain the Inheritance principle.
   
   Inheritance is the process by which one object acquires the properties of another object.
   
   38. Explain the Polymorphism principle.
   
   The meaning of Polymorphism is something like one name many forms. Polymorphism enables one entity to be used as as general category for different types of actions. The specific action is determined by the exact nature of the situation. The concept of polymorphism can be explained as "one interface, multiple methods".
   From a practical programming viewpoint, polymorphism exists in three distinct forms in Java:
   
   * Method overloading
   * Method overriding through inheritance
   * Method overriding through the Java interface
   
   39. Is Iterator a Class or Interface? What is its use?
   
   Iterator is an interface which is used to step through the elements of a Collection.
   
   40. Explain the user defined Exceptions?
   
   User defined Exceptions are the separate Exception classes defined by the user for specific purposed. An user defined can created by simply sub-classing it to the Exception class. This allows custom exceptions to be generated (using throw) and caught in the same way as normal exceptions.
   Example:
   
   class myCustomException extends Exception {
        / The class simply has to exist to be an exception
   }
   
   
   41. What is OOPS?
   
   OOP is the common abbreviation for Object-Oriented Programming.
   There are three main principals of oops which are called Polymorphism, Inheritance and Encapsulation.
   
   39.  Read the following program:
   
   public class test {
   public static void main(String [] args) {
       int x = 3;
       int y = 1;
       if (x = y)
           System.out.println("Not equal");
      else
           System.out.println("Equal");
     }
   }
   
   What is the result?
   The output is “Equal”
   B. The output in “Not Equal”
   C. An error at " if (x = y)" causes compilation to fall.
   D. The program executes but no output is show on console.
   Answer: C
   Answer: Transient variable can't be serialize. For example if a variable is declared as transient in a Serializable class and the class is written to an ObjectStream, the value of the variable can't be written to the stream instead when the class is retrieved from the ObjectStream the value of the variable becomes null.
   
   # Question: Name the containers which uses Border Layout as their default layout?
   Answer: Containers which uses Border Layout as their default are: window, Frame and Dialog classes.
   
   # Question: What do you understand by Synchronization?
   Answer: Synchronization is a process of controlling the access of shared resources by the multiple threads in such a manner that only one thread can access one resource at a time. In non synchronized multithreaded application, it is possible for one thread to modify a shared object while another thread is in the process of using or updating the object's value. Synchronization prevents such type of data corruption.
   E.g. Synchronizing a function:
   public synchronized void Method1 () {
   // Appropriate method-related code.
   }
   E.g. Synchronizing a block of code inside a function:
   public myFunction (){
   synchronized (this) {
   // Synchronized code here.
   }
   }

Give a few examples of types of applications that can benefit from using XML.

There are literally thousands of applications that can benefit from XML technologies. The ball of this question is not to have the candidate rattle off a laundry list of projects that they have worked on, but, rather, to allow the candidate to explain the rationale for choosing XML by citing a few real world examples. For instance, one appropriate answer is that XML allows content management systems to store documents independently of their format, which thereby reduces data redundancy. Another answer relates to B2B exchanges or supply chain management systems. In these instances, XML provides a mechanism for multiple companies to exchange data according to an agreed upon set of rules. A third common response involves wireless applications that require WML to render data on hand held devices.

What is DOM and how does it relate to XML?

The Document Object Model (DOM) is an interface specification maintained by the W3C DOM Workgroup that defines an application independent mechanism to access, parse, or update XML data. In simple terms it is a hierarchical model that allows developers to manipulate XML documents easily Any developer that has worked extensively with XML should be able to discuss the concept and use of DOM objects freely. Additionally, it is not unreasonable to expect advanced candidates to thoroughly understand its internal workings and be able to explain how DOM differs from an event-based interface like SAX.
What is SOAP and how does it relate to XML?

The Simple Object Access Protocol (SOAP) uses XML to define a protocol for the exchange of information in distributed computing environments. SOAP consists of three components: an envelope, a set of encoding rules, and a convention for representing remote procedure calls. Unless experience with SOAP is a direct requirement for the open position, knowing the specifics of the protocol, or how it can be used in conjunction with HTTP, is not as important as identifying it as a natural application of XML.Can you walk us through the steps necessary to parse XML documents?

Superficially, this is a fairly basic question. However, the ball is not to determine whether candidates understand the concept of a parser but rather have them walk through the process of parsing XML documents step-by-step. Determining whether a non-validating or validating parser is needed, choosing the appropriate parser, and handling errors are all important aspects to this process that should be included in the candidate's response.


Give some examples of XML DTDs or schemas that you have worked with.

Although XML does not require data to be validated against a DTD, many of the benefits of using the technology are derived from being able to validate XML documents against business or technical architecture rules. Polling for the list of DTDs that developers have worked with provides insight to their general exposure to the technology. The ideal candidate will have knowledge of several of the commonly used DTDs such as FpML, DocBook, HRML, and RDF, as well as experience designing a custom DTD for a particular project where no standard existed.


Using XSLT, how would you extract a specific attribute from an element in an XML document?

Successful candidates should recognize this as one of the most basic applications of XSLT. If they are not able to construct a reply similar to the example below, they should at least be able to identify the components necessary for this operation: xsl:template to match the appropriate XML element, xsl:value-of to select the attribute value, and the optional xsl:apply-templates to continue processing the document.

Extract Attributes from XML Data

Example 1.
Attribute Value:
<xsl:value-of select="@attribute"/>


When constructing an XML DTD, how do you create an external entity reference in an attribute value?

Every interview session should have at least one trick question. Although possible when using SGML, XML DTDs don't support defining external entity references in attribute values. It's more important for the candidate to respond to this question in a logical way than than the candidate know the somewhat obscure answer.


How would you build a search engine for large volumes of XML data?

The way candidates answer this question may provide insight into their view of XML data. For those who view XML primarily as a way to denote structure for text files, a common answer is to build a full-text search and handle the data similarly to the way Internet portals handle HTML pages. Others consider XML as a standard way of transferring structured data between disparate systems. These candidates often describe some scheme of importing XML into a relational or object database and relying on the database's engine for searching. Lastly, candidates that have worked with vendors specializing in this area often say that the best way the handle this situation is to use a third party software package optimized for XML data.

1. What is a Marker Interface? - An interface with no methods. Example: Serializable, Remote, Cloneable
2. What interface do you implement to do the sorting? - Comparable
3. What is the eligibility for a object to get cloned? - It must implement the Cloneable interface
4. What is the purpose of abstract class? - It is not an instantiable class. It provides the concrete implementation for some/all the methods. So that they can reuse the concrete functionality by inheriting the abstract class.
5. What is the difference between interface and abstract class? - Abstract class defined with methods. Interface will declare only the methods. Abstract classes are very much useful when there is a some functionality across various classes. Interfaces are well suited for the classes which varies in functionality but with the same method signatures.
6. What do you mean by RMI and how it is useful? - RMI is a remote method invocation. Using RMI, you can work with remote object. The function calls are as though you are invoking a local variable. So it gives you a impression that you are working really with a object that resides within your own JVM though it is somewhere.
7. What is the protocol used by RMI? - RMI-IIOP
8. What is a hashCode? - hash code value for this object which is unique for every object.
9. What is a thread? - Thread is a block of code which can execute concurrently with other threads in the JVM.
10. What is the algorithm used in Thread scheduling? - Fixed priority scheduling.
11. What is hash-collision in Hashtable and how it is handled in Java? - Two different keys with the same hash value. Two different entries will be kept in a single hash bucket to avoid the collision.
12. What are the different driver types available in JDBC? - 1. A JDBC-ODBC bridge 2. A native-API partly Java technology-enabled driver 3. A net-protocol fully Java technology-enabled driver 4. A native-protocol fully Java technology-enabled driver For more information: Driver Description
13. Is JDBC-ODBC bridge multi-threaded? - No
14. Does the JDBC-ODBC Bridge support multiple concurrent open statements per connection? - No
15. What is the use of serializable? - To persist the state of an object into any perminant storage device.
16. What is the use of transient? - It is an indicator to the JVM that those variables should not be persisted. It is the users responsibility to initialize the value when read back from the storage.
17. What are the different level lockings using the synchronization keyword? - Class level lock Object level lock Method level lock Block level lock
18. What is the use of preparedstatement? - Preparedstatements are precompiled statements. It is mainly used to speed up the process of inserting/updating/deleting especially when there is a bulk processing.
19. What is callable statement? Tell me the way to get the callable statement? - Callablestatements are used to invoke the stored procedures. You can obtain the callablestatement from Connection using the following methods prepareCall(String sql) prepareCall(String sql, int resultSetType, int resultSetConcurrency)
20. In a statement, I am executing a batch. What is the result of the execution? - It returns the int array. The array contains the affected row count in the corresponding index of the SQL.
21. Can a abstract method have the static qualifier? - No
22. What are the different types of qualifier and what is the default qualifier? - public, protected, private, package (default)
23. What is the super class of Hashtable? - Dictionary
24. What is a lightweight component? - Lightweight components are the one which doesn’t go with the native call to obtain the graphical units. They share their parent component graphical units to render them. Example, Swing components
25. What is a heavyweight component? - For every paint call, there will be a native call to get the graphical units. Example, AWT.
26. What is an applet? - Applet is a program which can get downloaded into a client environment and start executing there.
27. What do you mean by a Classloader? - Classloader is the one which loads the classes into the JVM.
28. What are the implicit packages that need not get imported into a class file? - java.lang
29. What is the difference between lightweight and heavyweight component? - Lightweight components reuses its parents graphical units. Heavyweight components goes with the native graphical unit for every component. Lightweight components are faster than the heavyweight components.
30. What are the ways in which you can instantiate a thread? - Using Thread class By implementing the Runnable interface and giving that handle to the Thread class.
31. What are the states of a thread? - 1. New 2. Runnable 3. Not Runnable 4. Dead
32. What is a socket? - A socket is an endpoint for communication between two machines.
33. How will you establish the connection between the servlet and an applet? - Using the URL, I will create the connection URL. Then by openConnection method of the URL, I will establish the connection, through which I can be able to exchange data.
34. What are the threads will start, when you start the java program? - Finalizer, Main, Reference Handler, Signal Dispatcher

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COMMON INTERVIEW Q&A

Review these typical interview questions and think about how you would
answer them. Read the questions listed; you will also find some
strategy suggestions with it.

(Excerpted from the book The Accelerated Job Search by Wayne D. Ford, Ph.D, published by The Management Advantage, Inc.)

1. Tell me about yourself:
The most often asked question in interviews. You need to have a short
statement prepared in your mind. Be careful that it does not sound
rehearsed. Limit it to work-related items unless instructed otherwise.
Talk about things you have done and jobs you have held that relate to
the position you are interviewing for. Start with the item farthest
back and work up to the present.

2. Why did you leave your last job?
Stay positive regardless of the circumstances. Never refer to a major
problem with management and never speak ill of supervisors, co-workers
or the organization. If you do, you will be the one looking bad. Keep
smiling and talk about leaving for a positive reason such as an
opportunity, a chance to do something special or other forward-looking
reasons.

3. What experience do you have in this field?
Speak about specifics that relate to the position you are applying for.
If you do not have specific experience, get as close as you can.

4. Do you consider yourself successful?
You should always answer yes and briefly explain why. A good
explanation is that you have set goals, and you have met some and are
on track to achieve the others.

5. What do co-workers say about you?
Be prepared with a quote or two from co-workers. Either a specific
statement or a paraphrase will work. Jill Clark, a co-worker at Smith
Company, always said I was the hardest workers she had ever known. It
is as powerful as Jill having said it at the interview herself.

6. What do you know about this organization?
This question is one reason to do some research on the organization
before the interview. Find out where they have been and where they are
going. What are the current issues and who are the major players?

7. What have you done to improve your knowledge in the last year?
Try to include improvement activities that relate to the job. A wide
variety of activities can be mentioned as positive self-improvement.
Have some good ones handy to mention.

8. Are you applying for other jobs?
Be honest but do not spend a lot of time in this area. Keep the focus
on this job and what you can do for this organization. Anything else is
a distraction.

9. Why do you want to work for this organization?
This may take some thought and certainly, should be based on the
research you have done on the organization. Sincerity is extremely
important here and will easily be sensed. Relate it to your long-term
career goals.

10. Do you know anyone who works for us?
Be aware of the policy on relatives working for the organization. This
can affect your answer even though they asked about friends not
relatives. Be careful to mention a friend only if they are well thought
of.

11. What kind of salary do you need?
A loaded question. A nasty little game that you will probably lose if
you answer first. So, do not answer it. Instead, say something like,
That’s a tough question. Can you tell me the range for this position?
In most cases, the interviewer, taken off guard, will tell you. If not,
say that it can depend on the details of the job. Then give a wide
range.

12. Are you a team player?
You are, of course, a team player. Be sure to have examples ready.
Specifics that show you often perform for the good of the team rather
than for yourself are good evidence of your team attitude. Do not brag,
just say it in a matter-of-fact tone. This is a key point.

13. How long would you expect to work for us if hired?
Specifics here are not good. Something like this should work: I’d like
it to be a long time. Or As long as we both feel I’m doing a good job.

14. Have you ever had to fire anyone? How did you feel about that?
This is serious. Do not make light of it or in any way seem like you
like to fire people. At the same time, you will do it when it is the
right thing to do. When it comes to the organization versus the
individual who has created a harmful situation, you will protect the
organization. Remember firing is not the same as layoff or reduction in
force.

15. What is your philosophy towards work?
The interviewer is not looking for a long or flowery dissertation here.
Do you have strong feelings that the job gets done? Yes. That’s the
type of answer that works best here. Short and positive, showing a
benefit to the organization.

16. If you had enough money to retire right now, would you?
Answer yes if you would. But since you need to work, this is the type
of work you prefer. Do not say yes if you do not mean it.

17. Have you ever been asked to leave a position?
If you have not, say no. If you have, be honest, brief and avoid saying
negative things about the people or organization involved.

18. Explain how you would be an asset to this organization
You should be anxious for this question. It gives you a chance to
highlight your best points as they relate to the position being
discussed. Give a little advance thought to this relationship.

19. Why should we hire you?
Point out how your assets meet what the organization needs. Do not
mention any other candidates to make a comparison.

20. Tell me about a suggestion you have made
Have a good one ready. Be sure and use a suggestion that was accepted
and was then considered successful. One related to the type of work
applied for is a real plus.

21. What irritates you about co-workers?
This is a trap question. Think real hard but fail to come up with
anything that irritates you. A short statement that you seem to get
along with folks is great.

22. What is your greatest strength?
Numerous answers are good, just stay positive. A few good examples:
Your ability to prioritize, Your problem-solving skills, Your ability
to work under pressure, Your ability to focus on projects, Your
professional expertise, Your leadership skills, Your positive attitude

23. Tell me about your dream job.
Stay away from a specific job. You cannot win. If you say the job you
are contending for is it, you strain credibility. If you say another
job is it, you plant the suspicion that you will be dissatisfied with
this position if hired. The best is to stay genetic and say something
like: A job where I love the work, like the people, can contribute and
can’t wait to get to work.

24. Why do you think you would do well at this job?
Give several reasons and include skills, experience and interest.

25. What are you looking for in a job?
See answer # 23

26. What kind of person would you refuse to work with?
Do not be trivial. It would take disloyalty to the organization,
violence or lawbreaking to get you to object. Minor objections will
label you as a whiner.

27. What is more important to you: the money or the work?
Money is always important, but the work is the most important. There is
no better answer.

28. What would your previous supervisor say your strongest point is?
There are numerous good possibilities:
Loyalty, Energy, Positive attitude, Leadership, Team player, Expertise,
Initiative, Patience, Hard work, Creativity, Problem solver

29. Tell me about a problem you had with a supervisor
Biggest trap of all. This is a test to see if you will speak ill of
your boss. If you fall for it and tell about a problem with a former
boss, you may well below the interview right there. Stay positive and
develop a poor memory about any trouble with a supervisor.

30. What has disappointed you about a job?
Don’t get trivial or negative. Safe areas are few but can include:
Not enough of a challenge. You were laid off in a reduction Company did
not win a contract, which would have given you more responsibility.

31. Tell me about your ability to work under pressure.
You may say that you thrive under certain types of pressure. Give an
example that relates to the type of position applied for.

32. Do your skills match this job or another job more closely?
Probably this one. Do not give fuel to the suspicion that you may want
another job more than this one.

33. What motivates you to do your best on the job?
This is a personal trait that only you can say, but good examples are:
Challenge, Achievement, Recognition

34. Are you willing to work overtime? Nights? Weekends?
This is up to you. Be totally honest.

35. How would you know you were successful on this job?
Several ways are good measures:
You set high standards for yourself and meet them. Your outcomes are a
success.Your boss tell you that you are successful

36. Would you be willing to relocate if required?
You should be clear on this with your family prior to the interview if
you think there is a chance it may come up. Do not say yes just to get
the job if the real answer is no. This can create a lot of problems
later on in your career. Be honest at this point and save yourself
future grief.

37. Are you willing to put the interests of the organization ahead ofyour own?
This is a straight loyalty and dedication question. Do not worry about
the deep ethical and philosophical implications. Just say yes.

38. Describe your management style.
Try to avoid labels. Some of the more common labels, like progressive,
salesman or consensus, can have several meanings or descriptions
depending on which management expert you listen to. The situational
style is safe, because it says you will manage according to the
situation, instead of one size fits all.

39. What have you learned from mistakes on the job?
Here you have to come up with something or you strain credibility. Make
it small, well intentioned mistake with a positive lesson learned. An