Java Interview Questions

Java Queries:

• What is your understanding with serialization? Where you have use that?
• What is a difference between Abstract class and interface? Give example where you will you.
• Abstract class and where you will use interface.
• What is a difference between HashMap and Properties Class.
• Where instance variable are stored and where local variable are stored.
• Have you ever overridden equal method?
• What new features added to JDK 1.5? Explain few out of those?
• Which driver type you have use in JDBC connection and Why?
• What is the difference between Check and Uncheck exception? How exceptions are handled in your project.
• What is difference between Applet and servlet?
• What will be returned from this block.

try{
.
.
.
return 3;

}catch(Exception e){
.
.
.
return -1;

}finally{
.
.
.
return 0;
}

• Difference between Set & Arraylist.
• Is Set a class or an interface?
• Can a private class be executed? How do we access public method of private class?
• If public static void main(String args[]) is changed to protected static void main(String args[]), will the class compile? Will the class be executed using java command?
• If public static void main(String args[]) is changed to public static void main(String name[]), will the class compile? Can the class be executed using java command?
• Is finally block manadatory in try/catch block?
• Can runtimeexception be extended?
• While overriding methods, what are rules applicable for Exception?
• While overriding methods, what are rules applicable for access modifiers?
• Can a class have a private constructors?
• What isi serialization?
• What is the difference between abstraction and encapsulation?
• What is the difference between abstract class and interface?
• What are the access specifiers and why interface has to be declared Public?
• What is the difference between Checked exceptions and unchecked exception?
• What are the rules for method overloading?
• What do you mean by threadsafe?
• Which collection is thread-safe? What will happen when 2 or more threads will try to insert data in an arraylist in a method which is not synchronized?
• When a method is thread safe, the thread will apply a lock on method level or Object level?
  The example of try catch and finally block with return statement?
• Collections – Equals method vs Hashcode, use of Hashcode, best hashcode implementations, Vector vs Array list, Hashtable vs Hashmap, Generics.
• Threads – Join(), Wait() – study all the overloaded methods of wait, Notify() and NotyfyAll(), Sleep(),synchronization.
• String – String constant pool, Heap vs stack, Diff bet string vs string buffer
• General – Abstract class vs Interface( which one u will choose for which scenario), Access modifiers(Public,Protected,private and default), Overriding(Including static method override).
• Exception handling –
• Memory – Study about JVM and Garbage collections, Memory leak, Local vs class variable
  core java design patterns(Singleton with thread safe, Factory pattern etc).
  JSP/servlets – Session handling, security, JSP implicit objects, tags.

UML:

• What is diff between aggregation and composition? Give example
• What is encapsulation and abstraction?
• What is multiplicity?
• What is polymorphism and types of polymorphism?

J2EE:

• What is post difference between Post and Get request? When you use what?
• What is difference between <@ include> and <jsp:include>
• What is request forward and request redirect
• What is difference between stateful and stateless session beans?
• Why you have use EJBs?
•  What is JNDI? Where you have used it? Can two connection pools have same JNDI?
• Give 5 ANT utilities you have worked on?
• What is M in Structs MVC? How it is implemented in struts?
• How action servlet works ?

Hibernate:

• What is difference between SessionFactory and Session in Hibernate?
• What is lazy loading in hibernate? Which design pattern it follows?
• What is meaning of cascading=alldeleteorphan in hibernate mapping file?
• What is difference between L1 Cache and L2 Cache and how it is implemented in hibernate?
• How you have managed DB transaction in you project? How concurrency is controlled?
• ORM advantages & disadvantages.
• Configuring hibernate application(sessionfactory, entity generation, entity mapping, defining named queries)
• Criteria API.
• Cache mechanism(first level/second level)
• Transaction management. 

Struts:

• Overview of MVC
• Role of ActionServlet/Request Processor
• The J2EE design patterns implemented by action servlet/Request processor
• Request flow in struts
• Different action types.

Design Pattern:

• What is Singleton pattern? How you have implemented it? Why you use singleton pattern
• What is Factory Pattern and why it is used?
•  What is your understanding with connection pooling
• Other queries based on resources skill set?

Problem Solving Approach:

• If there is a ticket raised by the client, the page that was opening in 5 seconds yesterday, is taking 4-5 mins today. What will be your approach to resolve this issue?
• Logic to remove duplicate character from a string and “how you will unit test your code”?

Sample questions asked by the client:

• Difference between checked vs. unchecked, and how to create unchecked exception.
• Hash code versus equal code.
• Queue/topic difference.
• What is  transactionality   when reading from JMS queues.
• How to write a template class.
• How to get ID’s out of a hibernate mappings.