I was going through Questions every good .Net developer should be able to answer and was highly impressed with the content and approach of this question, and so in the same spirit, I am asking this question for Java/Java EE Developer.
What questions do you think should a good Java/Java EE programmer be able to answer?
I am marking this question as community wiki as it is not user specific and it aims to serve programming community at large.
Looking forward for some amazing responses.
EDIT: Please answer questions too, as suggested in the comments, so that people could learn something new regarding the language, too.
This question is related to
java
jakarta-ee
Write a program to accept two integers and output the largest of two numbers to a file at a location of your choice. Now describe what each statement does.
It's possible to drill down pretty deep starting from the significance of the import statement, right down to abnormal termination
Many questions and interviews are available at http://www.techinterviews.com/interview-questions/java and I don't really see value in copy / pasting a selection of them.
No, it's up to you to create your own compilation of things you think are important. Personally, I proceed always in two steps: first a few questions to get a basic idea of the experience and skills, then a problem solving situation. I'm indeed not convinced that being able to answer any known questions makes you a good or bad unknown problems solver. So, I prefer to ask people to solve a given problem, to give them some requirements, and ask them to write code (but not on paper). I give them some time to come back to me and check how they did it, their coding style, how they used the suggested APIs, etc.
That all being said, my favorite question is "what don't you like about Java?" (in the spirit of this one). It is really a excellent question, it gives you an immediate feedback on how much a candidate has used Java and explored its API and if he just religious about it or not (as the OP wrote).
Update: As suggested by CPerkins, a better wording for the question suggested above might be "What would you most like to see changed in Java?". And indeed, I prefer this way.
The list of J2EE/JEE middleware questions I have faced is exceptionally long, but here are the top 5 that I have been asked, and have lead to good discussions:
javax.naming.Context questions.Another tricky question I find troubling, but have faced many times is,
How are dependent libraries packaged into an archive?
or Visibility of various classes in a bundled archive.
If the discussion does not lead to class loader hierarchy of different application servers, resource archives, etc., it is best to resign and move on.
Set, List, Map, and the importance of Object.equals() and Object.hashCode() in every implementation of these interfaces.Simple questions such as,
Though these are very basic, many developers do not know the answers. I suggest these be asked before the code-related queries.
Q. Give a real world example scenario where you will use GenericServlet not HttpServlet ?
This is the question I faced in my interview.
Why is main method in Java called as public static void main(String[] args) ?
Answer:
1.main() must be declared public because it is invoked by JVM whenever the program execution starts.JVM doesnot belong to our program package.
Inorder to access main outside the package we have to declare it as public.If we declare it as anything other than public it shows a Runtime Error but not Compilation time error
2.main() must be declared as static because if a method is declared as static then we can call that method outside the class using ClassName.methodName();
class Sample
{
static void fun()
{
System.out.println("Hello");
}
}
class Test
{
public static void main(String[] args)
{
Sample.fun();
}
}
The JVM will first Load the Test class,and will check for the Commandline arguments and calls the main method as Test.main();
3.main() must be declared as void main() because JVM is not expecting any value from main().So,it must be declared as void.
If other return type is provided,the it is a RunTimeError i.e;NoSuchMethodFoundError.
4.main() must have String arguements as arrays because JVM calls main method by passing command line arguement.As they are stored in string array object it is passed as an argument to main().
What do you like most / least about Java and why?
When would you use Session Beans or Message Driven Beans ?
How are transactions handled in session beans ?
What is the difference between local and remote session beans ? This question is more about knowing that RPCs are in the picture or not, since a method that is exposed as both Local or Remote might still work differently (side-effects on parameters are possible with Locals, while not possible with Remotes).
A good test is: never ask the questions in the same order. We had the experience with offshoring that sometimes they were actually giving the response in the wrong order :-). As a result you should make sure that you can actually see the person you are interrogating.
Core: 1. What are checked and unchecked exceptions ? 2. While adding new exception in code what type (Checked/Unchecked) to use when ?
Servlet: 1. What is the difference between response.sendRedirect() and request.forward() ?
How about what is a session bean and describe some differences between stateless and stateful session beans.
How do threads work? What is synchronized? If there are two synchronized methods in a class can they be simultaneously executed by two threads. You will be surprised to hear many people answer yes. Then all thread related question, e.g. deadlock, starvation etc.
One thing many Java programmers don't know is that Strings are immutable, so use StringBuilder or StringBuffer!
String s = "";
for(int i = 0; i < 100; i++) {
s += "Strings " + "are " + "immutable, " + " so use StringBuilder/StringBuffer to reduce memory footprint";
}
You said "Good","Developer". Here are my 2 cents too.. :)
For J2EE:
I can think many, many, many more of 'em but this'll do for now :)
What is the difference between J2SE and J2EE (or JSE and JEE)?
A developer should be able to point out that the enterprise edition is basically an interface definition (i.e. a specification) which can be implemented by vendors. Whereas the standard edition is an implementation in its own right
What is 'System', 'out', 'println' in System.out.println ? What happens when you call 'put' on HashMap ?
"What's a deployment descriptor?"
If the candidate shudders involountarily, he has experience working with pre-3.0 EJBs.
What is the difference between an abstract class and an interface? When would you use each of them?
Lots of Java developers don't know this, I asked most people on my computer science course at university and the vast majority could not answer it.
What will be printed?
public void testFinally(){
System.out.println(setOne().toString());
}
protected StringBuilder setOne(){
StringBuilder builder=new StringBuilder();
try{
builder.append("Cool");
return builder.append("Return");
}finally{
builder.append("+1");
}
}
Answer: CoolReturn+1
A bit more difficult:
public void testFinally(){
System.out.println(setOne().toString());
}
protected StringBuilder setOne(){
StringBuilder builder=new StringBuilder();
try{
builder.append("Cool");
return builder.append("Return");
}finally{
builder=null; /* ;) */
}
}
Answer: CoolReturn
One sure is comparison of string. Difference between
String helloWorld = "Hello World";
helloWorld == "Hello World";
"Hello World".equals(helloWorld);
Great questions and great answers by all.It is nice to see such type of questions. I would like to add some more which can make this answer repository more rich.
For Core Java Is main is keyword in java ? More info
Java is plat form independent what about JVM?
Can we have private constructor in class, If yes what the usage of it.
Why we need to have constructors in abstract class though we cant instantiate it? More Info
Instead of above all there are many more question related to core java. More Info
A more pure Java question:
What is the difference between sleep and wait ? Not many people actually understand how wait is working.
How do you need to handle InterruptedExceptions ?
Trick question: What kinds of parameters are passed by reference in Java?
It's amazing how many people still parrot the "primitives are passed by value, objects are passed by reference" mantra.
Usage of final keyword in method calls.
For example why does the method test in below code does not give any compile error despite using final qualifier for the method parameter.
class Name {
private String name;
public Name (String s) {
this.name = s;
}
public void setName(String s) {
this.name = s;
}
}
private void test (final Name n) {
n.setName("test");
}
If you are hiring graduates with Java "experience" a simple question like Write some code that will cause a NullPointerException to be thrown can distinguish which candidates have used Java recently, and didn't just stop when they finished their unit/course.
Difference between and web server and a web container
Advantages and disadvantages of thread-safe classes and explicitly synchronized code and examples of good applications of both. It is often not correct to trust on thread-safe classes as guarantees for data consistency in multi-threaded applications.
What is difference between String, StringBuffer and StringBuilder?
Describe the differences between the "four" (not three ;)) types of inner class..
why would you override the toString() method?
Can an interface extend multiple interfaces?
Most people answer "no", because they know java doesn't have multiple inheritance. But an interface can still extend multiple interfaces (but a class can't extend multiple classes). This doesn't lead to the diamond problem.
If the answer is "no", the interviewer should ask "why would it be forbidden?". Then you start thinking about it and you should realize that there is not problem with it.
So you learned something (by yourself) in the interview and you showed the interviewer that you are able to reason about classes, objects, inheritance, polymorphism, etc. It's actually much better than a candidate who knows the answer by heart but doesn't understand why
How does volatile affect code optimization by compiler?
What is the difference between Set, Map and List?
I'm still amazed how many people don't know this one in a telephone interview.
Source: Stackoverflow.com