| By Yakov Fain | Article Rating: |
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| June 17, 2007 06:00 AM EDT | Reads: |
1,086,899 |
JDJ's Enterprise Editor, Yakov Fain (pictured) writes: If you are planning to hit the job market, you may need to refresh some of the Java basic terms and techniques to prepare yourself for a technical interview. Let me offer you some of the core Java questions that you might expect during the interviews.
For most questions I’ve provided only short answers to encourage further research. I have included only questions for mid (*) and senior level (**) Java developers. These sample questions could also become handy for people who need to interview Java developers (see also the article "Interviewing Enterprise Java Developers").
Disclaimer. This article has been originally published three or four years ago, hundreds of thousands Java developers have read it, but I still use some of these questions while interviewing Java developers. Guess what? Every other Java developer doesn't now the answers to some of them.
30 Java Interview Questions
A. The class System has a variable out that represents the standard output, and the variable err that represents the standard error device. By default, they both point at the system console. This how the standard output could be re-directed:* Q2. What's the difference between an interface and an abstract class?
A. An abstract class may contain code in method bodies, which is not allowed in an interface. With abstract classes, you have to inherit your class from it and Java does not allow multiple inheritance. On the other hand, you can implement multiple interfaces in your class.
* Q3. Why would you use a synchronized block vs. synchronized method?
A. Synchronized blocks place locks for shorter periods than synchronized methods.
* Q4. Explain the usage of the keyword transient?
A. This keyword indicates that the value of this member variable does not have to be serialized with the object. When the class will be de-serialized, this variable will be initialized with a default value of its data type (i.e. zero for integers).
* Q5. How can you force garbage collection?
A. You can't force GC, but could request it by calling System.gc(). JVM does not guarantee that GC will be started immediately.
* Q6. How do you know if an explicit object casting is needed?
A. If you assign a superclass object to a variable of a subclass's data type, you need to do explicit casting. For example:
When you assign a subclass to a variable having a supeclass type, the casting is performed automatically.
* Q7. What's the difference between the methods sleep() and wait()
A. The code sleep(1000); puts thread aside for exactly one second. The code wait(1000), causes a wait of up to one second. A thread could stop waiting earlier if it receives the notify() or notifyAll() call. The method wait() is defined in the class Object and the method sleep() is defined in the class Thread.
* Q8. Can you write a Java class that could be used both as an applet as well as an application?
A. Yes. Add a main() method to the applet.
* Q9. What's the difference between constructors and other methods?
A. Constructors must have the same name as the class and can not return a value. They are only called once while regular methods could be called many times.
* Q10. Can you call one constructor from another if a class has multiple constructors
A. Yes. Use this() syntax.
* Q11. Explain the usage of Java packages.
A. This is a way to organize files when a project consists of multiple modules. It also helps resolve naming conflicts when different packages have classes with the same names. Packages access level also allows you to protect data from being used by the non-authorized classes.
* Q12. If a class is located in a package, what do you need to change in the OS environment to be able to use it?
A. You need to add a directory or a jar file that contains the package directories to the CLASSPATH environment variable. Let's say a class Employee belongs to a package com.xyz.hr; and is located in the file c:\dev\com\xyz\hr\Employee.java. In this case, you'd need to add c:\dev to the variable CLASSPATH. If this class contains the method main(), you could test it from a command prompt window as follows:
* Q13. What's the difference between J2SDK 1.5 and J2SDK 5.0?
A.There's no difference, Sun Microsystems just re-branded this version.
* Q14. What would you use to compare two String variables - the operator == or the method equals()?
A. I'd use the method equals() to compare the values of the Strings and the == to check if two variables point at the same instance of a String object.
* Q15. Does it matter in what order catch statements for FileNotFoundException and IOExceptipon are written?
A. Yes, it does. The FileNoFoundException is inherited from the IOException. Exception's subclasses have to be caught first.
* Q16. Can an inner class declared inside of a method access local variables of this method?
A. It's possible if these variables are final.
* Q17. What can go wrong if you replace && with & in the following code:
* Q18. What's the main difference between a Vector and an ArrayList
A. Java Vector class is internally synchronized and ArrayList is not.
* Q19. When should the method invokeLater()be used?
A. This method is used to ensure that Swing components are updated through the event-dispatching thread.
A. Use the following syntax: super.myMethod(); To call a constructor of the superclass, just write super(); in the first line of the subclass's constructor.
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Raghu 07/09/08 10:38:32 AM EDT | |||
A message to all,interview questions given here can be generic ONLY.Its not like for 2+ years,4+ years etc.It purely depends on the company and the role for which you are interviewed.Some of the interview questions i faced recently.I was able to clear all the theoretically related so they asked me by giving a scenario. 1. You need to read all the details from say.. www.yahoo.com/index.html, save it in a file in yor local PC. What API will you use in Java and what method?? If you need further information,drop a mail 2 [email protected] Cheers, |
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aruna 06/20/08 02:40:58 AM EDT | |||
Hi, Thanks you, |
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Ashvini 06/16/08 12:23:12 AM EDT | |||
Hi, Thanks you, |
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. 06/13/08 04:29:20 PM EDT | |||
these questions are stupid these are moronic questions that idiots that don't know how to interview asks lets get to some real world questions |
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deepa 06/11/08 07:48:12 AM EDT | |||
Please send me expert level questions on jdbc 4.0 |
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sandeep 06/06/08 04:55:35 AM EDT | |||
try http://www.java-interview.com for all the java related interview questions |
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shikha 05/30/08 04:05:33 AM EDT | |||
please send me the interview questions in java,jsp,jdbc,corejava for 1+ yers of experience as a software engineer. |
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sreekanth 05/28/08 04:29:58 PM EDT | |||
Thank you very much for such a good article.....as I'm in search of job this article would certainly be helpful for my preparation. |
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sandeep 04/20/08 04:13:09 AM EDT | |||
please send me the interview questions in java,jsp,jdbc,corejava for 1+ yers of experience as a software engineer. |
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siddharth 04/18/08 07:54:20 AM EDT | |||
I have 1+ yrs experience of working in java.. please help me by sending the interview questions.. |
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varun 04/05/08 06:38:16 AM EDT | |||
Data Migration/Conversion: It can be used to convert sql server tables into mysql tables |
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rajyalakshmi.M 03/26/08 12:53:10 AM EDT | |||
I need the type of questions asked in an interview for a job in java/j2ee foe 2+ years experience Thanks |
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Ranjani 03/12/08 09:39:19 AM EDT | |||
I need the type of questions asked in an interview for a job in java/j2ee with about 2 years experience. Thanks |
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archana 03/07/08 04:51:00 AM EST | |||
Hi, |
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sony 02/01/08 09:37:29 PM EST | |||
I have acquired abt 4-5yrs of Java/J2EE exp and will be attending an interview in the States...Could you pls let me know on what are the tips that I need and pls help me with some questions that they will ask me? |
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srinivas 01/20/08 07:28:34 AM EST | |||
plz send j2ee interview questions with 2+ exp |
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Mitesh 01/12/08 12:40:28 AM EST | |||
I need to Prepare for Internship as Java Programmer |
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VANI SARIN (Recruiter at GE Healthcare) 01/03/08 05:03:29 PM EST | |||
GE Healthcare is hiring Sr. J2EE Developer and Web Client Developers with Ajax and or googleweb toolkit. Please visit www.gecareers.com and enter job #s 756156 and 756161 |
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vani 01/03/08 12:58:02 PM EST | |||
can u plz send me 2+yrs core,jsp,servlet,jddbc questions |
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nirupama reddy 11/14/07 02:05:53 AM EST | |||
hi,plz send me 1+ yrs core,adv,servlets,jsps questions |
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Y.V.Rajesh 11/07/07 01:31:27 AM EST | |||
what is the need of constructors and what is the difference between class variables and instance variables? |
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sankari 11/02/07 04:56:36 AM EDT | |||
hi,plz send me the 2+yrs exp questions in java/j2ee |
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praveeb 10/16/07 11:15:51 AM EDT | |||
Hi,send me the 2+years interview questions please |
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prashant 09/19/07 08:19:58 AM EDT | |||
Hi, |
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Rahul 09/05/07 08:09:02 AM EDT | |||
Hi, Regards, |
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Rhea 08/14/07 01:07:54 PM EDT | |||
Hi, I have acquired abt 4-5yrs of Java/J2EE exp and will be attending an interview in the States...Could you pls let me know on what are the tips that I need and pls help me with some questions that they will ask me? |
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gayatri 08/14/07 03:30:11 AM EDT | |||
Hi, |
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Soumitra 08/01/07 10:32:55 AM EDT | |||
need some middle-level/expert-level core Java/EJB/JSP/Servlets Questions and answers |
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Srinivasarao Pentakota 07/28/07 07:40:00 AM EDT | |||
Hi, |
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surya 07/20/07 08:06:29 AM EDT | |||
some of the answers are wrong given by the other person so plz. beware of this.Go for RND and make it sure whether the answer is right or wrong |
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Svaba 07/20/07 06:09:40 AM EDT | |||
Questions are exilent. I wrote a technical test few days ago and I had few qestions from this list. |
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Infernoz 07/13/07 04:31:45 PM EDT | |||
Q2 Answer has confused grammar, so maybe part wrong. Q3 Answer is only half right. Q17 Answer is correct, for runtime Atul Gupta! Q19 Answer .. and (from recent Sun advice) for the creation of active Swing and AWT objects like JFrame, JWindow, Frame, Window etc. |
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Dave the Free Credit Report Guy 07/12/07 08:54:50 AM EDT | |||
Oh yes, it would be totally helpful to master these important Java basics before getting out there for those job interviews...Good job! |
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Atul Gupta 07/12/07 03:29:45 AM EDT | |||
Hi, The answer to Question 17 is wrong, it wont give in any compilation errors. |
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Durga Prasad 07/04/07 02:39:07 AM EDT | |||
Hi, |
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Rajalakshmi K 06/25/07 12:51:56 AM EDT | |||
I need some middle-level/expert-level core Java/EJB/JSP/Servlets Questions and answers |
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Govindaraj.S. 06/18/07 11:08:27 PM EDT | |||
Hai, |
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Govindaraj.S. 06/18/07 11:06:11 PM EDT | |||
Please send me java and j2ee question papers for 1.5+ years of experience |
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N.V.Balasubramaniam 05/24/07 04:14:18 AM EDT | |||
Hi, Thanks in Advance for your Help. |
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Amit 02/22/07 02:22:48 AM EST | |||
Hi, |
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Anand 12/27/06 01:13:11 PM EST | |||
All the interview questions are answered here, I just love this site |
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akumaran 11/02/06 02:15:07 AM EST | |||
Very good questions and answers. Also would be nice to add a "How would you go about..." section. Sometimes the candidate does not have to know the exact answer (e.g. performance, memory profiling etc) but should know how to go about solving a given problem or a task. Some other useful Q&A covering wide range of topics relating to Java/J2EE can be found at http://www.lulu.com/java-success and also google for "Java Job interview questions" or "J2EE Job interview questions" |
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himanshu 09/19/06 05:35:55 AM EDT | |||
Hi, |
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sachin 09/17/06 02:36:59 AM EDT | |||
Hi, |
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madhavi 09/16/06 01:37:04 AM EDT | |||
Hi, |
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prajjal nag 09/15/06 03:19:48 AM EDT | |||
Please send some interview question for Core Java for 2+ yrs experience, preferably java 1.4 and java 1.5 |
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ABDULLAHI ABUBAKAR 09/14/06 08:30:00 AM EDT | |||
I want you to send me the questions because i will start to study, Certified Enterprise Developer and Solution Architect on Sun Java Platform in this year. |
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Peter 09/14/06 05:59:12 AM EDT | |||
Hi, I need some interview questions for a Java/J2EE Developer role, it's a phone interview taking place within the next 2 hours. any immediate help will be deeply appreciated. |
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surya 09/09/06 12:01:25 PM EDT | |||
Hi, |
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imran 09/07/06 09:56:10 AM EDT | |||
asdgsda |
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