Java J2EE Interview Questions and Answers

Practical Questions To be asked in Interviews

2010-05-18T03:38:00.000-07:00

Listed questions are for Interviewer. Its more of a discussion to analyze how a candidate approaches to resolve these practical problems, it also will give an idea of how much grasp technically the candidate has on web technologies - java, j2ee , application servers, databases ..

These questions dont have any particular answer. These are practical problems which I have faced in web projects executed by my team.

1. How would one analyze and find solutions to HIGH CPU usage by a web application? The CPU usage shoots close to 100% within 3 days of application server restart, and once the CPU reaches close to 100%, the web application hangs? What could be the probable causes? What would be line of approach to resolve this issue.?

Basically the candidate who answers this question, should try to reason out the issues which can shoot the CPU usage to 100%.

The Interviewer should bascially look the approach and discuss to find a solution.

I have asked this question very frequently and the answers give a very good feedback on the technology grasp of the candidate unlike theorotical questions which have one line answers.

2. How should a web application authenticate user id / passwords combinations?

a) should the password be sent in clear text to the server for authentication ?
b) should the password be hashed ?
c) if hashed, how wud one authenicate the password at server?
d) or any other mechanism?

3. Any approach to migrate passwords from an existing web application to migrated web application. ?

My Java Learnings

2009-12-15T23:13:00.000-08:00

Collection

set - no duplicate elements

list

HashSet

The iterators returned by this class's iterator method are fail-fast.

ListIterator can be used to add/modify elements in a list

Suppose you have a Collection, c, and you want to create another Collection containing the same elements,

but with all duplicates eliminated. The following one-liner does the trick

Collection noDups = new HashSet(c);

TreeSet , alphabetically stores the contents.

Vector is synchronized

ArrayList is not synchronized

Collections.synchronizedList (new ArrayList or any collection object for that case)

Map : No duplication

HashMap : no duplicates allowed

The HashMap class is roughly equivalent to Hashtable, except that it is unsynchronized and permits nulls

Collections.sort(list);

Actually String and Date both implement the Comparable

Comparator: method compare

Internationalization

MessageBundle.properties

MessageBundle_en_US.properties

ResourceBundle.getBundle("MessageBundle",locale)

error messages , GUI labels , date , currencies ,

ListResourceBundle

NumberFormat , to format numbers , currencies, date formats, time formats as per current locale

MessageFormat

MessageBundle , all messages specific to a locale can be placed here.

For Example : MessageBundle_en_US.properties

Some More Questions

How does java internally behave ?

System.out.println what is out ? PrintStream

new file(), Transient variables are not persisted.

Suppose If we have variable 'I' in run method,

If I can create one or more thread each thread will occupy a separate copy or same variable will be shared ?

Why there are some null interface in java ? What does it mean ? Give me some null interfaces in JAVA ?

When is the JVM invoked ?
JVM is involved when the "JAVA" command is executed by the application / java program

Why does EJB needs two interface( Home and Remote Interface) ?

Servlets

What do mean stateless protocol ? HTTP ? What do we do for maintaining the state

What is the difference in between doPost and doGet methods ?

Difference between rmi and ejbs ?

What is iiop ?

Why cant we invoke methods on ejbs directly ?

Why define Remote Interfaces ?

What is the functionality stubs and skeletons ?
JDBC insert call ..what is the default behaviour.

Servlet Interview Questions

2009-12-14T05:20:00.000-08:00

What's the difference between servlets and applets?
What are the purpose of having servlets in web application?
When parameters one will consider before deciding to have servlet or JSP in your web application?
What is the signifance of doGet() and doPost()?
Describe servlet life cycle?
Describe servlet API hirerachy?
Significance of servlet context ?
When to use Forward and sendRedirect?

Ask A Java Interview Question

2008-05-10T05:36:00.001-07:00

Based on the feedback received, I have decided to add a section which will enable to ask questions pertaining to java j2ee interviews and I would possibly try to answer these questions with some examples. You can also ask questions asked during HR rounds which at times I think are more difficult to answer then the technical questions !!

Java Architect Interview Questions

2007-06-26T02:00:00.000-07:00

Java Architect Interview Questions

1. What do you understand by UML. How to interpret UML diagrams?
2. State the effect of encapsulation, inheritance, and use of interfaces on architectural characteristics?
3. Differentiate between 2 tier, 3 tier and n-tier architectures.
4. How do the following characteristics scalability,performance, high availabilty behave based on the above architecture selected.
5. In what all ways (methods/concepts) can we achieve integration with legacy/n-n-legacy applications using JAVA technologies.
6. List the required classes/interfaces that must be provided for an EJB technology.
7. Distinguish stateful and stateless Session beans.
8. Distinguish Session and Entity beans.
9. Recognize appropriate uses for Entity, Stateful Session, and Stateless Session beans.
10. State the transactional behavior in a given scenario for an enterprise bean method with a specified transactional deployment descriptor.
11.Given a requirement specification detailing security and flexibility needs, identify architectures that would fulfill those requirements.
12. Identify costs and benefits of using an intermediate data-access object between an entity bean and the data resource.
13. State the benefits of bean pooling in an EJB container.
14. State the benefits of Passivation in an EJB container.
15. State the benefit of monitoring of resources in an EJB container.
16. Explain how the EJB container does lifecycle management and has the capability to increase scalability.
17. Given a scenario description, distinguish appropriate from inappropriate protocols to implement that scenario.
18. Identify a protocol, given a list of some of its features, where the protocol is one of the following: HTTP, HTTPS, IIOP, JRMP.
19. Select from a list, common firewall features that might interfere with the normal operation of a given protocol.
20. State the benefits of using design patterns.
21. State the name of a design pattern given the UML diagram and/or a brief description of the pattern's functionality.
22. Select from a list benefits of a specified design pattern.
23. Identify the design pattern associated with a specified J2EE feature.
24. Identify scenarios that are appropriate to implementation using messaging, EJB, or both.
25. List benefits of synchronous and asynchronous messaging.
26. Select scenarios from a list that are appropriate to implementation using synchronous and asynchronous messaging.
27. State three aspects of any application that might need to be varied or customized in different deployment locales.
28. Match the following features of the Java 2 platform with descriptions of their functionality, purpose or typical uses: Properties, Locale, ResourceBundle, Unicode, java.text package, 29. InputStreamReader and OutputStreamWriter.
30. Select from a list security restrictions that Java 2 environments normally impose on applets running in a browser.
31. Given an architectural system specification, identify appropriate locations for implementation of specified security features, and select suitable technologies for implementation of those features.

XML Interview Questions

2007-06-01T03:12:00.000-07:00

What is the difference between HTML and XML?
Was XML used in your project? If Yes, why it was decided to use XML ? In shortly, need to know the problem statement and why it was thought to use XML (Merits of XML)?
What XML parser was used in the project ?
Name the XML parser used in the project? and Why ?
Types of Parsers? DOM and SAX ?
When would you decide using a DOM parser or SAX parser?
Can you explain steps encountered in parsing an XML?
Can we validate an XML document?
Differentiate between a document, node and element?
What do you understand by DTD?
What do you understand by Schema?
Given an option how would you go about deciding whether to use DTD or Schema?
Advantages of Schema over DTD ?
What is SOAP?
Do you understand the concept of XSLT?
What is namespace?
What do you understand by JAXP?
What is JDOM?
What do you understand by XPATH?
How do convert an XML into PDF or Excel file?

Java J2EE Interview Questions and Answers

2007-05-17T04:37:00.000-07:00

Java Language Fundamentals Questions 1

2. Is Java a pure object oriented language ?

3. Explain encapsulation

4. Explain inheritance

5. Explain polymorphism

6. What are classes and objects? What is the relationship between them?

7. What do you understand by API

8. Name atleast 10 Java API class you have used while programming

9. What are reserved words in Java ?

10. What is size of int in Java?

11. What is the difference between Java Key words and reserved words?

12. What do you understand by private, protected and public?
A. private, protected and public are access modifiers.

13. Public is least restrictive while private is most restrictive.

14. How many static init can you have?
A. As many as you can

15. What is reference in Java?

16. Explain main() method modifiers?

17. In system.out.println what is out and println ? Can this be redirected to a file ? How ?

18. What is the difference between instanceof and isInstance?

19. What is an instance variable and instance method?

20. Explain terms subclass and superclass.

21. What is the difference between string and stringbuffer ?

22. What is the purpose of garbage collection?
A. The purpose of garbage collection is to identify and discard objects that are no longer needed by a program so that their resources may be reclaimed and reused.

23. What do you mean by Classpath and Classloader?
A. Classpath is the path where Compiller / JRE looks for dependent java sources

24. Classloader loads the classes into the Java virtual machine.

25. What package in java is implicitly imported
A. java.lang

26. What is the difference between a field variable and local variable?
A. A field variable is declared as a member of a class. A local variable is declared in a method (local to a method).

27. Significance of this and super() in constructors

28. What is a constructor?

29. What is reflection? What do you understand by Class.forName()

30. Does importing a package imports the subpackages as well?

31. What is the difference between declaring a variable and defining a variable?

32. What is the difference of signed and unsigned integer?

33. Significance of interface in java?

Java J2EE Interview Questions and Answers

2007-05-16T02:51:00.000-07:00

251 What is meant by event handling ?
252 What are all the listeners in java and explain ?
253 What is meant by an adapter class ?
254 What are the types of mouse event listeners ?
255 What are the types of methods in mouse listeners ?
256 What is the difference between panel and frame ?
257 What is the default layout of the panel and frame ?
258 What is meant by controls and types ?
259 What is the difference between a scroll bar and a scroll panel.
260 What is the difference between list and choice ?
261 How to place a component on Windows ?
262 What are the different types of Layouts ?
263 What is meant by CardLayout ?
264 What is the difference between GridLayout and GridBagLayout
265 What is the difference between menuitem and checkboxmenu item.
266 What is meant by vector class, dictionary class , hash table class,and
267 property class ?
268 Which class has no duplicate elements ?
269 What is resource bundle ?
270 What is an enumeration class ?
271 What is meant by Swing ?
272 What is the difference between AWT and Swing ?
273 What is the difference between an applet and a Japplet
274 What are all the components used in Swing ?
275 What is meant by tab pans ?
276 What is the use of JTree ?
277 How can you add and remove nodes in Jtree.
278 What is the method to expand and collapse nodes in a Jtree ?
279 What is the use of JTable ?
280 What is meant by JFC ?
281 What is the class in Swing to change the appearance of the Frame in
284 What is JDBC ?
285 How do you connect to the database ? What are the steps ?
286 What are the drivers available in JDBC ? Explain
287 How can you load the driver ?
288 What are the different types of statement s ?
289 How can you created JDBC statements ?
290 How will you perform transactions using JDBC ?
291 What are the two drivers for web apllication?
292 What are the different types of 2 tier and 3 tier architecture ?
293 How can you retrieve warning in JDBC ?
294 What is the exception thrown by JDBC ?
295 What is meant by PreparedStatement ?
296 What is difference between PreparedStatement and Statement ?
297 How can you call the stored procedures ?
298 What is meant by a ResultSet ?
299 What is the difference between ExecuteUpdate and ExecuteQuery ?
300 How do you know which driver is connected to a database ?

Java J2EE Interview Questions

2007-05-16T02:48:00.000-07:00

151 Checked & Unchecked exception
152 Use of throws exception
153 What is finally in exception handling
154 Vector class
155 What will happen to the Exception object after exception handling
156 Two types of multi-tasking
157 Two ways to create the thread
158 Synchronization
159 I/O Filter
160 How can you retrieve warnings in JDBC
161 Can applet in different page communicate with each other
162 Four driver Manager
163 Features of JDBC 2.0
164 Explain about stored procedures
165 Servlet Life cycle
166 Why do you go for servlet rather than CGI
167 How to generate skeleton & Stub classes
168 Explain lazy activation
169 What is meant by Java ?
170 What is meant by a class ?
171 What is meant by a method ?
172 What are the OOPS concepts in Java ?
173 What is meant by encapsulation ? Explain with an example
174 What is meant by inheritance ? Explain with an example
175 What is meant by polymorphism ? Explain with an example
176 Is multiple inheritance allowed in Java ? Why ?
177 What is meant by Java interpreter ?
178 What is meant by JVM ?
179 What is a compilation unit ?
180 What is meant by identifiers ?
181 What are the different types of modifiers ?
182 What are the access modifiers in Java ?
183 What are the primitive data types in Java ?
184 What is meant by a wrapper class ?
185 What is meant by static variable and static method ?
186 What is meant by Garbage collection ?
187 What is meant by abstract class
188 What is meant by final class, methods and variables ?
189 What is meant by interface ?
190 What is meant by a resource leak ?
191 What is the difference between interface and abstract class ?
192 What is the difference between public private, protected and static
193 What is meant by method overloading ?
194 What is meant by method overriding ?
195 What is singleton class ?
196 What is the difference between an array and a vector ?
197 What is meant by constructor ?
198 What is meant by casting ?
199 What is the difference between final, finally and finalize ?
200 What is meant by packages ?

Java J2EE Interview Questions

2007-05-16T02:45:00.000-07:00

51.What is serialization ?
Ans ) Process of persisting an object.

52.What is difference RMI registry and OSAgent ?

53.To a server method, the client wants to send a value 20,
with this value exceeds to 20, a message should be sent to the client ? What will you do for achieving for this ?

54 What are the benefits of Swing over AWT ?
55 Where the CardLayout is used ?
56 What is the Layout for ToolBar ?
57 What is the difference between Grid and GridbagLayout ?
58 How will you add panel to a Frame ?
59 What is the corresponding Layout for Card in Swing ?
60 What is light weight component ?
63 What is Servlet API used for conneting database ?
64 What is bean ? Where it can be used ?
65 What is difference in between Java Class and Bean ?
66 Can we send object using Sockets ?
67 What is the RMI and Socket ?
68 How to communicate 2 threads each other ?
72 What is the functionality stubs and skeletons ?
74 Diff between Application and Applet ?
75 What is serializable Interface ?
76 What is the difference between CGI and Servlet ?
77 What is the use of Interface ?
78 Why Java is not fully objective oriented ?
79 Why does not support multiple Inheritance ?
80 What it the root class for all Java classes ?
81 What is polymorphism ?
82 Suppose If we have variable 'I' in run method, If I can create one or more thread each thread will occupy a separate copy or same variable will be shared ?
83 In servlets, we are having a web page that is invoking servlets username and password ? which is cheks in the database ? Suppose the second page also If we want to
verify the same information whethe it will connect to the database or it will be used previous information?

90 What are session variable in Servlets ?
91 What is client server computing ?
93 Why we use OOPS concepts? What is its advantage ?
94 What is the middleware ? What is the functionality of Webserver ?
95 Why Java is not 100 % pure OOPS ?
96 When we will use an Interface and Abstract class ?
97 What is an RMI?
98 How will you pass parameters in RMI ? Why u serialize?
100 What is the main functionality of the Remote Reference Layer ?

Java J2EE Interview Questions

2007-05-16T02:42:00.000-07:00

371 managed persistent entity bean ?
372 What is J2EE ?
373 What is JTS ?
374 How many entity beans used and how many tables can u use in EJB project ?
375 What is scalable,portability in J2EE?
376 What is Connection pooling?Is it advantageous?
377 Method and class used for Connection pooling ?
378 How to deploy in J2EE(i.e Jar,War file) ?
379 How is entity bean created using Container managed entity bean ?
380 Sotware architechture of EJB ?
381 In Entity bean will the create method in EJB home and ejbCreate in Entity
382 bean have the same parameters ?
383 What methods do u use in Servlet - Applet communication ?
384 What are the types of Servlet ?
385 Difference between HttpServlet and Generic Servlets ?
386 Difference between doGet and doPost ?
387 What are the methods in HttpServlet?
388 What are the types of SessionTracking?
389 What is Cookie ? Why is Cookie used ?
390 If my browser does not support Cookie,and my server sends a cookie
instance What will happen ?
392 Why do u use Session Tracking in HttpServlet ?
393 Can u use javaScript in Servlets ?
394 What is the capacity the doGet can send to the server ?
395 What are the type of protocols used in HttpServlet ?
396 Difference between TCP/IP and IP protocol ?
397 Why do you use UniCastRemoteObject in RMI ?
398 How many interfaces are used in RMI?
399 Can Rmi registry be written in the code, without having to write it in the
command prompt and if yes where?
401 Why is Socket used ?
402 What are the types of JDBC drivers ?
403 Explain the third driver(Native protocol driver) ?
404 Which among the four driver is pure Java driver ?
405 What are the Isolation level in JDBC transaction ?
406 How do you connect with the database ?
407 How do you connect without the Class.forName (" ") ?
408 What does Class.forName return ?
409 What are the types of statement ?
410 Why is preparedStatement,CallableStatement used for?

412 Difference between AWT and Swing compenents ?

414 Can the Swing application if you upload in net, be compatible with your
browser?
416 What should you do get your browser compatible with swing components?
417 What are the methods in Applet ?
418 When is init(),start() called ?
419 When you navigate from one applet to another what are the methods called ?
420
421 What is the difference between Trusted and Untrusted Applet ?
422 What is Exception ?
423 What are the ways you can handle exception ?
424 When is try,catch block used ?
425 What is finally method in Exceptions ?
426 What are the types of access modifiers ?
427 What is protected and friendly ?
428 What are the other modifiers ?
429 Is synchronised modifier ?
430 What is meant by polymorphism ?
431 What is inheritance ?
432 What is method Overloading ? What is this in OOPS ?
433 What is method Overriding ? What is it in OOPS ?
434 Does java support multi dimensional arrays ?
435 Is multiple inheritance used in Java ?
436 How do you send a message to the browser in JavaScript ?
437 Does javascript support multidimensional arrays ?
438 Why is XML used mainly?
440 What is DTD ?
441 Is there any tool in java that can create reports ?
456 Describe an object.
457 What are sockets?
458 What are threads?
476 What's the difference between UDP and TCP?
478 What is the difference between a static and non-static field (Java)
479 What's the difference between a stack and a Queue?

Java J2EE Interview Questions and Answers

2007-05-09T04:24:00.000-07:00

302 What is meant by TCP, IP, UDP ?
303 What is the difference between TCP and UDP ?
304 What is a proxy server ?
305 What is meant by URL
306 What is a socket and server sockets ?
307 When MalformedURLException and UnknownHost Exception throws ?
308 What is InetAddress ?
309 What is datagram and datagram packets and datagram sockets ?
310 Write the range of multicast socket IP address ?
311 What is meant by a servlet ?
312 What are the types of servlets ? Explain
313 What is the different between a Servlet and a CGI.
314 What is the difference between 2 types of Servlets ?
315 What is the type of method for sending request from HTTP server ?
316 What are the exceptions thrown by Servlets ? Why ?
317 What is the life cycle of a servlet ?
318 What is meant by cookies ?
319 What is HTTP Session ?
320 What is the difference between GET and POST methods ?
321 How can you run a Servlet Program ?
322 How to commuincate between an applet and a servlet ?
323 What is a Servlet-to-Servlet communcation ?
324 What is Session Tracking ?
325 What are the security issues in Servlets ?
326 What is HTTP Tunneling
327 How do you load an image in a Servlet ?
328 What is Servlet Chaining ?
329 What is URL Rewriting ?
330 What is context switching ?
331 What is meant by RMI ?
332 Explain RMI Architecture ?
333 What is meant by a stub ?
334 What is meant by a skelotn ?
335 What is meant by serialisation and deserialisation ?
336 What is meant by RRL ?
337 What is the use of TL ?
338 What is RMI Registry ?
339 What is rmic ?
340 How will you pass parameter in RMI ?
341 What exceptions are thrown by RMI ?
342 What are the steps involved in RMI ?
343 What is meant by bind(), rebind(), unbind() and lookup() methods
344 What are the advanatages of RMI ?
345 What is JNI ?
346 What is Remote Interface ?
347 What class is used to create Server side object ?
348 What class is used to bind the server object with RMI Registry ?
349 What is the use of getWriter method ?
350 What is meant by Javabeans ?
351 What is JAR file ?
352 What is meant by manifest files ?
353 What is Introspection ?
354 What are the steps involved to create a bean ?
355 Say any two properties in Beans ?
356 What is persistence ?
357 What is the use of beaninfo ?
358 What are the interfaces you used in Beans ?
359 What are the classes you used in Beans ?
360 What is Entity Bean and Session Bean ?
361 What are the methods of Entity Bean?
362 How does Stateful Session bean store its state ?
363 Why does Stateless Session bean not store its state even though it has
364 ejbActivate and ejbPassivate ?
365 What are the services provided by the container ?
366 Types of transaction ?
367 What is bean managed transaction ?
368 Why does EJB needs two interface( Home and Remote Interface) ?
369 What are transaction attributes ?
370 What is the difference between Container managed persistent bean and Bean

Java J2EE Interview Questions and Answers

2007-05-09T04:21:00.000-07:00

201 Name 2 classes that can store arbitrary number of objects ?
202 What is the difference between java.applet.* and java.applet.Applet ?
203 What is a default package ?
204 What is meant by a super class and how can you call a super class ?
205 What is anonymous class ?
206 Name interfaces without a method ?
207 What is the use of an interface ?
208 What is a serializable interface ?
209 How to prevent field from serialization ?
210 What is meant by exception ?
211 How can you avoid the runtime exception ?
212 What is the difference between throw and throws ?
213 What is the use of finally ?
214 Can multiple catch statements be used in exceptions ?
215 Is it possible to write a try within a try statement ?
216 What is the method to find if the object exited or not ?
217 What is meant by a Thread ?
218 What is meant by multi-threading ?
219 What is the 2 way of creating a thread ? Which is the best way and why ?
220 What is the method to find if a thread is active or not ?
221 What are the thread-to-thread communcation ?
222 What is the difference between sleep and suspend ?
223 Can thread become a member of another thread ?
224 What is meant by deadlock ?
225 How can you avoid a deadlock ?
226 What are the three typs of priority ?
227 What is the use of synchronizations ?
228 Garbage collector thread belongs to which priority ?
229 What is meant by time-slicing ?
230 What is the use of ‘this’ ?
231 How can you find the length and capacity of a string buffer ?
232 How to compare two strings ?
233 What are the interfaces defined by Java.lang ?
234 What is the purpose of run-time class and system class
235 What is meant by Stream and Types ?
236 What is the method used to clear the buffer ?
237 What is meant by Stream Tokenizer ?
238 What is serialization and de-serialisation ?
239 What is meant by Applet ?
240 How to find the host from which the Applet has originated ?
241 What is the life cycle of an Applet ?
242 How do you load an HTML page from an Applet ?
243 What is meant by Applet Stub Interface ?
244 What is meant by getCodeBase and getDocumentBase method ?
245 How can you call an applet from a HTML file
246 What is meant by Applet Flickering ?
247 What is the use of parameter tag ?
248 What is audio clip Interface and what are all the methods in it ?
249 What is the difference between getAppletInfo and getParameterInfo ?
250 How to communicate between applet and an applet ?
251 What is meant by event handling ?
252 What are all the listeners in java and explain ?
253 What is meant by an adapter class ?
254 What are the types of mouse event listeners ?
255 What are the types of methods in mouse listeners ?
256 What is the difference between panel and frame ?
257 What is the default layout of the panel and frame ?
258 What is meant by controls and types ?
259 What is the difference between a scroll bar and a scroll panel.
260 What is the difference between list and choice ?
261 How to place a component on Windows ?
262 What are the different types of Layouts ?
263 What is meant by CardLayout ?
264 What is the difference between GridLayout and GridBagLayout
265 What is the difference between menuitem and checkboxmenu item.
266 What is meant by vector class, dictionary class , hash table class,and
267 property class ?
268 Which class has no duplicate elements ?
269 What is resource bundle ?
270 What is an enumeration class ?
271 What is meant by Swing ?
272 What is the difference between AWT and Swing ?
273 What is the difference between an applet and a Japplet
274 What are all the components used in Swing ?
275 What is meant by tab pans ?
276 What is the use of JTree ?
277 How can you add and remove nodes in Jtree.
278 What is the method to expand and collapse nodes in a Jtree ?
279 What is the use of JTable ?
280 What is meant by JFC ?
281 What is the class in Swing to change the appearance of the Frame in
284 What is JDBC ?
285 How do you connect to the database ? What are the steps ?
286 What are the drivers available in JDBC ? Explain
287 How can you load the driver ?
288 What are the different types of statement s ?
289 How can you created JDBC statements ?
290 How will you perform transactions using JDBC ?
291 What are the two drivers for web apllication?
292 What are the different types of 2 tier and 3 tier architecture ?
293 How can you retrieve warning in JDBC ?
294 What is the exception thrown by JDBC ?
295 What is meant by PreparedStatement ?
296 What is difference between PreparedStatement and Statement ?
297 How can you call the stored procedures ?
298 What is meant by a ResultSet ?
299 What is the difference between ExecuteUpdate and ExecuteQuery ?
300 How do you know which driver is connected to a database ?

Java J2EE Interview Questions and Answers

2007-05-09T04:17:00.000-07:00

101 How do you download stubs from a Remote place ?

104 What is the main functionality of the Prepared Statement ?
105 What is meant by static query and dynamic query ?

107 What is meant by Servlet? What are the parameters of the service method ?
108 What is meant by Session ? Tell me something about HTTPSession Class ? How do you invoke a Servelt? What is the difference in between doPost and doGet methods ?
109 What is the difference in between the HTTPServlet and Generic Servlet ? Expalin their methods ? Tell me their parameter names also ?
110 Have you used threads in Servelet ?
111 Write a program on RMI and JDBC using StoredProcedure ?

113 In a Container there are 5 components. I want to display all the components names, how will you do that one ?
114 Why there are some null interface in java ? What does it mean ? Give me some null interfaces in JAVA ?

116 What is meant by class loader ? How many types are there? When will we use them ?
117 How do you load an Image in a Servlet ?
118 What is meant by flickering ?
119 What is meant by distributed Application ? Why we are using that in our applications ?
120 What is the functionality of the stub ?

122 What is the latest version of JDBC ? What are the new features are added in that ?
123 Explain 2 tier and 3 -tier Architecture ?
124 What is the role of the webserver ?
127 What is meant by cookies ? Explain ?
132 Public static void main – Explain What are command line arguments
133 Difference between String & StringBuffer
134 Wrapper class. Is String a Wrapper Class
135 What are the restriction for static method
136 Purpose of the file class
137 Default modifier in Interface
138 Can abstract be declared as Final
139 Can we declare variables inside a method as Final Variables
140 What is the package concept and use of package
141 How can a dead thread be started
142 Difference between Applet & Application
143 Life cycle of the Applet
144 Can Applet have constructors
145 Differeence between canvas class & graphics class
146 Explain about Superclass & subclass
147 Difference between TCP & UDP

149 Explain Stream Tokenizer
150 What is the difference between two types of threads

J2EE Interview Questions

2007-03-08T02:08:00.000-08:00

J2EE Interview Questions

1. What do you understand by the term J2EE?
J2EE is a specification. provides middleware services.
EJB JDBC JNDI JMS JavaMail JTA Servlets JSPs Connectors JAAS

EJB : is Server Side component architecture for developing distributed applications.
Developers need to concentrate only on business logic.
The middleware services are provided by appserver.
(transaction management,persistence, threading,concurreny )

Session Beans : Model processes
Entity Beans : Model data
Message Driven beans : Similar to session beans. Invoked only by sending messages.

2. Diff between RMI and EJB

EJB uses RMI technology.
We have to declare the middleware services needed by the EJB in a descriptor.
The Appserver will generate stubs for the same.

RMI : one has to write the middleware services. (txn mgmt, persitence.)

EJB cannot be invoked directly by remote clients because there are not network enabled.
Location transparency.

3. How many tiers does an J2EE application have? Explain multi-tier applications?

4. What is a web component?
A web componenet is a software entity which runs on a web server, handles requests and generates dynamic web content.

5. What is a web container?
Runtime environment for servlets and jsp
Manages lifecycle of instances
Supports HTTP

6. Should web container always be a part of web server?
No.

7.What are servlets?
8. What are JSP’s?
9.What are web services?
10.Explain SOA?
11. Explain EJB containers?
12.What is the purpose of init() in servlet class?

13. Can servlets have constructors? Can they be used for initializing servlets instead of init()
Yes. But we shouldn’t. Reason being init has access to servlet config and servlet context object , constructors won’t.

14.Name JSP scripting elements?
declarations, scriptlets, expressions.

15.What is SingleThreadModel ?
16. How to implement a thread-safe JSP page? What directive should be added?

‹ %@ page isThreadSafe="false" %

17 .How can we include static files within a JSP page?
Answer: using the JSP include directive.

18.Distinguish between servletconfig and servlet context?
19.What is the difference in between doPost and doGet methods ?
20.Why does EJB needs two interface( Home and Remote Interface) ?
21.Explain deployment descriptors?
22.Why cant we invoke methods on ejbs directly ?
23.Explain clustering and fault tolerance
24.How would you go about analyzing performance of the application

Application performance testing

When performance testing a Web application, several requirements must be
determined either through interpretation of data from an existing application that
performs similar work. Those requirements are:

User base
What is the expected number of users that will access this application? This is
generally expressed in hits per month, day, hour, or minute depending on
volumes.

Total concurrent users

During a peak interval, what is the maximum possible number of users
accessing the application at the same time.

Peak request rate
How many pages will need to be served per second?

Core Java Interviews

2007-03-08T01:47:00.000-08:00

Listed here are areas from which one can possibly expect questions in Java Interviews.
Also I have mentioned some understanding on few important topics.

1. objects
a. polymorphism
b. inheritance
c. encapsulation
d. abstraction

equals() method performs deep checking.
Every class should override this method to perform object equality.

== performs shallow checking. It compares the references.

2. strings
a. string equality
b. immutable

a + b + c = new StringBuffer().append(a).append(b).append(c).toString();
StringBuffers

3. exception handling.
a. throwable
b. exceptions and errors
c. checked exceptions
d. overriding exceptions

4. threads
a. wait,notify,notifyall
b. Ready state
c. synchronization
d. sleep
e. interrupt exception

Collections

Collection
List or Sequence : one item following other
eSet : same value cannot be added twice
Map : Key value pair

Vector : ordered list

5. i/o.
System.out.println : OUT is printStream
System.setOut
System.setIn
System.setErr
new File() does not create a file in file system.

6. Serialization : Persisting an object to a file system.
Persist an object beyond the current application instance.
Marker interface.
ObjecOutputStream
Transient variables are not persisted.

7. garbage collection
Object is no longer being referenced in a program.
The heap used by the object can be recycled.
a. system.gc()
b. system.runFinalization()
c. finalize method is called before garbage collection. This method can be used for closing open connections,file i/o.

Algorithims : eg Mark and sweep
Define a set of roots and determining reachability from the roots.
Increasing heap size , less frequency of GB, more duration for GB.

8. jvm

loading : given the class name determine the binary form for the class
linking : verfication, Preparation and Resolution
verification : checks well formedness and semantic reqs of java language and jvm
Preparation : storage
intialization : execute the static intializers for the class and class variable initialization

JVM consists of
1. CLassLoader System
2. Execution Engine
3. Data Areas. : This has a Method Area and Heap. Common for all threads.
Stack is allocated for each thread (local variables are created on stack)

9. servlets
Define
Lifecycle of servlets
Session Tracking
1. URL Rewritting
2. Cookies
3. Hidden form fields
4. Session Mgmt

Single threading model.

Define all instance variable for a servlet in a factory class e.g instance data

Http Servlets
FTP Servlets
Telnet Servlets

10. jsp

11. rmi,ejb
EJB
session beans
entity beans
Lifecycle
Transaction Mgmt

12. websphere
AAT
Deployment
.ear , .war
web module
ejb module
virtual hosts
clones
server groups
Admin console
Application server
Class loading -- classes , /lib/ext/ , lib/app/ ,
Module visibilty
jvm properties
DataSources

13. xml
DOM
SAX
parsers
HTML/XML comparision

14. xsl
processing
commands

15. jdbc
16. jndi
17. jms
18. sql, pl/sql

Stack
Heap

Java Bytecodes : machine instructions for jvm. (.class file). Instructions specify operations and operands.
Architecture independent instructions.
These are interpreted by jvm and converted into native m/c code which is exceuted.

JIT compilers : Intrepret bytecodes and translate the same into m/c native code. These are stored on the m/c
It uses the same for execution.

Abstract classes cannot be Instantiated
Final classes cannot be extended

Signature of the method: Method Name and Aruguments
Overloaded Methods : Same Method Name ( Different arguments), different return type
OverRiding Methods : Same Name,arguments and Return Type. Their access cannot be narrowed.

Class : template for creating objects. Defines state and state
Object : Instance of a class

Objects are bound at Runtime (type of the object reference)
Varaibles are bound at compile time (class of the object reference)

ChecKed Exception : JVM does compile time checking. IO exception. Helps in improving Exception Handling of the program. Reducing the unchecked exception conditions in a program.

&& and : shortcircuit operators : Evaluates only one operand.
& and : boolean operators : Both operands. Also bitwise operators.

Constructors : Invoking default constructor when a constructor() is defined will result in compile time error.

Interview Questions on UML and Design Patterns

2006-07-06T23:17:00.000-07:00

Interview Questions on UML and Design Patterns

Why to use design patterns?
Give examples of design patterns?
What is UML?
What are advantages of using UML?
What is the need for modelling?
Is it requiste to use UML in software projects?
What are use cases? How did you capture use cases in your project?
Explain the different types of UML diagrams ? sequence diagram , colloboration diagram etc
What is the sequence of UML diagrams in project?
What tools did you use for UML in your project?
What is the difference between activity and sequence diagrams?
What are deployment diagrams?
What are the different object relationships ?
What is the difference between composition and aggregation?
Wheel acting as a part of car ? Is this composition or aggregation?

400+ Java Q's and A's : Core Java, Servlets, JSP ...and more

2006-04-24T04:16:00.000-07:00

1. What are the four corner stones of OOP ?
Abstraction, Encapsulation, Polymorphism and Inheritance.

2. What do you understand by private, protected and public ?
These are accessibility modifiers. Private is the most restrictive, while public is the least restrictive. There is no real difference between protected and the default type (also known as package protected) within the context of the same package, however the protected keyword allows visibility to a derived class in a different package.

3. Difference between a Class and an Object ?
A class is a definition or prototype whereas an object is an instance or living representation of the prototype.

4. What is Downcasting ?
Downcasting is the casting from a general to a more specific type, i.e. casting down the hierarchy.
5. What is Polymorphism ? What kinds ?

6. What is the difference between method overriding and overloading?
Overriding is a method with the same name and arguments as in a parent, whereas overloading is the same method name but different arguments.

7. What is the restriction on an Overridden methods’ accessibility ?
Overriding methods cannot reduce accessibility - they can either have same or greater accessibility.

8. What is the concept of a Virtual Function ?

9. What is the implication of a Virtual Destructor ? Virtual Constructor ?

10. Can a method be overloaded based on different return type but same argument type ?
No, because the methods can be called without using their return type in which case there is ambiquity for the compiler.

11. What is a "stateless" protocol ?
Without getting into lengthy debates, it is generally accepted that protocols like HTTP are stateless i.e. there is no retention of state between a transaction which is a
single request response combination.

12. What happens to a static var that is defined within a method of a class ?
Can't do it. You'll get a compilation error.

13. What is constructor chaining and how is it achieved in Java ?
A child object constructor always first needs to construct its parent (which in turn calls its parent constructor.). In Java it is done via an implicit call to the no-args
constructor as the first statement.

Link to Behavioural Interview Questions

14. How do you define a local inner class ?

15. How many static init can you have ?
As many as you want, but the static initializers and class variable initializers are executed in textual order and may not refer to class variables declared in the class whose
declarations appear textually after the use, even though these class variables are in scope.

16. What is passed by ref and what by value ?
All Java method arguments are passed by value. However, Java does manipulate objects by reference, and all object variables themselves are references.

17. How do you ensure size of a primitive data type ?
You can't.

18. Describe the Garbage Collection process in Java ?
The JVM spec mandates automatic garbage collection outside of the programmers control. The System.gc() or Runtime.gc() is merely a suggestion to the JVM to run the

GC process but is NOT guaranteed.

19. What is the difference amongst JVM Spec, JVM Implementation, JVM Runtime ?
The JVM spec is the blueprint for the JVM generated and owned by Sun. The JVM implementation is the actual implementation of the spec by a vendor and the JVM

runtime is the actual running instance of a JVM implementation.

20. Can RMI and Corba based applications interact ?
Yes they can. RMI is available with IIOP as the transport protocol instead of JRMP

21 .What is the diffrence between an Abstract class and Interface ?
Ans ) Interface defines the methods. There is no implementation.
Whereas Abstract class may have few implemented methods.If some common functionality needs to be shared.

22. What is user defined exception ?
Ans )

23. What do you know about the garbate collector ?
Ans ) Java has an inbuilt mechanisim for garbage collection.
All those objects not longer being referenced are garbage collected.i.e the memory used by these objects is released.

24.What is the difference between C++ & Java ?
25.Explain RMI Architecture?
26.How do you communicate in between Applets & Servlets ?

27.What is the use of Servlets ?
Ans ) To generate dynamic content based on the request.

28.What is JDBC? How do you connect to the Database ?
Ans ) Java Database connectivity.
Using jdbc drivers provided by db drivers.

29.In an HTML form I have a Button which makes us to open another page in 15 seconds. How will do you that ?

30.What is the difference between Process and Threads ?
Ans ) There could be no of processes(multi tasking) and every process could have no of threads(multi threading).

31. What is the difference between RMI & Corba ?
Ans ) Remote method invocation : java only. uses JRMP to communication between java objects
Common object request broker architecture : platform independent. Uses IIOP to communicate between objects.

32.What are the services in RMI ?
33.How will you initialize an Applet ?
34.What is the order of method invocation in an Applet?
35.When is update method called ?

36.How will you pass values from HTML page to the Servlet ?
Ans ) submitting the html form.

37.Have you ever used HashTable and Dictionary ?
Ans ) Dictionary is an abstract class. Hastable extends Dictionary.

38.How will you communicate between two Applets ?
39.What are statements in JAVA ?

40.What is JAR file ?
Ans ) Jar file is an archive of java classes.

41.What is JNI ?
Ans ) Java Native interfaces.

42.What is the base class for all swing components ?
43.What is JFC ?
Ans ) Java Foundation classes.

44.What is Difference between AWT and Swing ?

45.Considering notepad/IE or any other thing as process, What will happen if you start notepad or IE 3 times? Where 3 processes are started or 3 threads are started ?
Ans ) processes.

46.How does thread synchronization occurs inside a monitor ?
Ans ) A thread acquires the monitor.i.e it obtains a lock on the monitor.No other thread can acquire a lock on the same monitor until it is released by the previous thread.

47.What are 4 drivers available in JDBC ?
Ans ) jdbc-odbc bridge
Type 4 : pure java driver. no need to have db client installed on client mcs.

48.How you can know about drivers and database information ?
49.How will you perform transaction using JDBC ?
50.In RMI, server object first loaded into the memory and then the stub reference
is sent to the client ? or whether a stub reference is directly sent to the client ?
Suppose server object is not loaded into the memory, and the client request for it , what will happen?

51.What is serialization ?
Ans ) Process of persisting an object.

52.What is difference RMI registry and OSAgent ?

53.To a server method, the client wants to send a value 20,
with this value exceeds to 20, a message should be sent to the client ? What will you do for achieving for this ?

54 What are the benefits of Swing over AWT ?
55 Where the CardLayout is used ?
56 What is the Layout for ToolBar ?
57 What is the difference between Grid and GridbagLayout ?
58 How will you add panel to a Frame ?
59 What is the corresponding Layout for Card in Swing ?
60 What is light weight component ?
63 What is Servlet API used for conneting database ?
64 What is bean ? Where it can be used ?
65 What is difference in between Java Class and Bean ?
66 Can we send object using Sockets ?
67 What is the RMI and Socket ?
68 How to communicate 2 threads each other ?
72 What is the functionality stubs and skeletons ?
74 Diff between Application and Applet ?
75 What is serializable Interface ?
76 What is the difference between CGI and Servlet ?
77 What is the use of Interface ?
78 Why Java is not fully objective oriented ?
79 Why does not support multiple Inheritance ?
80 What it the root class for all Java classes ?
81 What is polymorphism ?
82 Suppose If we have variable 'I' in run method, If I can create one or more thread each thread will occupy a separate copy or same variable will be shared ?
83 In servlets, we are having a web page that is invoking servlets username and password ? which is cheks in the database ? Suppose the second page also If we want to
verify the same information whethe it will connect to the database or it will be used previous information?

90 What are session variable in Servlets ?
91 What is client server computing ?
93 Why we use OOPS concepts? What is its advantage ?
94 What is the middleware ? What is the functionality of Webserver ?
95 Why Java is not 100 % pure OOPS ?
96 When we will use an Interface and Abstract class ?
97 What is an RMI?
98 How will you pass parameters in RMI ? Why u serialize?
100 What is the main functionality of the Remote Reference Layer ?