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Agenda For Today
Basic Java Questions
OOPS Questions
Servlets
JDBC
Spring
Hibernate

Basic
Questions
OOPS
Servlets
JDBC Hibernate
Spring

Q1. What is difference between JDK,JRE and JVM?
Java Interview Questions

Q1. What is difference between JDK,JRE and JVM?
JDK
JRE
JVM
JVM (Java Virtual Machine) is an abstract machine. It is a
specification that provides runtime environment in which java
bytecode can be executed.
JRE (Java Runtime Environment) is a runtime environment
which implements JVM and provides all class libraries and
other files that JVM uses at runtime.
JDK(Java Development Kit) is the tool necessary to compile,
document and package Java programs. The JDK completely
includes JRE.

Q2. What is synchronization?

Q2. What is synchronization?
➢ Synchronization is a process which keeps all
concurrent threads in execution to be in sync.
➢ Synchronization avoids memory consistency
errors caused due to inconsistent view of shared
memory.

Q3. What are the differences between processes and threads?

Q3. What are the differences between processes and threads?
Process Thread
Definition
An executing instance of a program is called a
process.
A thread is a subset of the process.
Communication
Processes must use inter-process communication
to communicate with sibling processes.
Threads can directly communicate with other
threads of its process.
Control
Processes can only exercise control over child
processes.
Threads can exercise considerable control over
threads of the same process.
Changes
Any change in the parent process does not affect
child processes.
Any change in the main thread may affect the
behavior of the other threads of the process.
Memory Run in separate memory spaces. Run in shared memory spaces.
Controlled by Process is controlled by the operating system.
Threads are controlled by programmer in a
program.
Dependence Processes are independent. Threads are dependent.

Q4. What are Wrapper classes?

Q4. What are Wrapper classes?
Primitive Wrapper Class Constructor Argument
boolean Boolean boolean or String
byte Byte byte or String
char Character char
int Integer int or String
float Float float, double or String
double Double double or String
long Long long or String
short Short short or String
Each of Java's eight primitive data types has a class dedicated to it. These are known as wrapper classes
because they "wrap" the primitive data type into an object of that class

Q5. What purpose does the keywords final, finally, and finalize fulfill?

Q5. What purpose does the keywords final, finally, and finalize fulfill?
final finally
➢ Final is used to apply restrictions
on class, method and variable.
➢ Final class can't be inherited, final
method can't be overridden and
final variable value can't be
changed.
➢ Finally is used to place important
code, it will be executed whether
exception is handled or not.
➢ Finalize is used to perform clean
up processing just before object
is garbage collected.
finalize

Q6. What is the difference between StringBuffer and StringBuilder?

➢ StringBuffer operations are thread-safe and
synchronized where StringBuilder operations are not
thread-safe.
➢ StringBuffer is to be used when multiple threads are
working on same String and StringBuilder in the single
threaded environment.
➢ StringBuilder performance is faster when compared to
StringBuffer because of no overhead of synchronized
Q6. What is the difference between StringBuffer and StringBuilder?

Q7. What are the differences between Heap and Stack Memory?

Q7. What are the differences between Heap and Stack Memory?
Stack Heap
Memory
Stack memory is used only by one thread
of execution.
Heap memory is used by all the parts of
the application.
Access
Objects stored in the heap are globally
accessible
Stack memory can’t be accessed by other
threads.
Memory
Management
Follows LIFO manner to free memory.
Memory management is based on
generation associated to each object.
Lifetime
Exists until the end of execution of the
tread.
Heap memory lives from the start till the
end of application execution.
Usage
Stack memory only contains local
primitive variables and reference
variables to objects in heap space.
Whenever an object is created, it’s always
stored in the Heap space

Q8. What is the difference between Arrylist and Vector?

Array List Vector
Array List is not synchronized. Vector is synchronized.
Array List is fast as it’s non-synchronized Vector is slow as it is thread safe.
If an element is inserted into the Array List, it
increases its Array size by 50%.
Vector defaults to doubling size of its array.
Array List does not define the increment size. Vector defines the increment size.
Array List can only use Iterator for traversing an
Array List.
Except Hashtable, Vector is the only other class
which uses both Enumeration and Iterator.
Q8. What is the difference between Arrylist and Vector?

Q9. What is the difference between HashMap and HashTable

Q9. What is the difference between HashMap and HashTable
HashMap HashTable
HashMap is non synchronized and are not-
thread safe.
Hashtable is synchronized. It is thread-safe
and can be shared with many threads.
HashMap allows one null key and multiple null
values.
Hashtable doesn't allow any null key or value.
HashMap is fast compared to HashTable Hashtable is slow compared to HashMap
We can make the HashMap as synchronized by
calling Collections.synchronizedMap(hashMap)
Hashtable is internally synchronized and can't
be unsynchronized.
HashMap is traversed by Iterator. Hashtable is traversed by Enumerator and
Iterator.
HashMap inherits AbstractMap class. Hashtable inherits Dictionary class.

Q10. What is the difference between equals() and == operator ?

Q10. What is the difference between equals() and == operator ?
➢ Equals() method is defined in Object class in Java and
used for checking equality of two objects defined by
business logic.
➢ "==" or equality operator in Java is a binary operator
provided by Java programming language and used to
compare primitives and objects.

Q11. What will be the output of this program?

Output:
11

Basic Questions
OOPS
Questions
Servlets
JDBC Hibernate
Spring

Q12. What is the difference between Abstract classes and Interfaces?

Abstract Class Interfaces
An abstract class can provide complete,
default code and/or just the details that have
to be overridden.
An interface cannot provide any code at
all,just the signature.
In case of abstract class, a class may extend
only one abstract class.
A Class may implement several interfaces.
An abstract class can have non-abstract
methods.
All methods of an Interface are abstract.
An abstract class can have instance variables. An Interface cannot have instance variables.
An abstract class can have any visibility: public,
private, protected.
An Interface visibility must be public (or) none.
An abstract class can contain constructors . An Interface cannot contain constructors .
Abstract classes are fast.
Interfaces are slow as it requires extra
indirection to find corresponding method in
the actual class.
Q12. What is the difference between Abstract classes and Interfaces?

Q13. What is Polymorphism?

Q13. What is Polymorphism?
Mobile
Camera Remote MP3 Player
➢ Polymorphism is briefly described as “one
interface, many implementations”.
➢ It is a characteristic of being able to assign
a different meaning or usage to something
in different contexts.

Q14. What is runtime polymorphism or dynamic method dispatch?

Q14. What is runtime polymorphism or dynamic method dispatch?
➢ It is a process in which a call to an overridden method is
resolved at runtime rather than at compile-time.
➢ In this process, an overridden method is called through
the reference variable of a superclass.
➢ The determination of the method to be called is based
on the object being referred to by the reference variable.

Q15. What is the difference between method overloading and method overriding?

Q15. What is the difference between method overloading and method overriding?
Overloaded Method Overridden Method
Definition
In Method Overloading, Methods of the same
class shares the same name but each method
must have different number of parameters or
parameters having different types and order.
In Method Overriding, sub class have the same
method with same name and exactly the same
number and type of parameters and same return
type as a super class.
Behavior
Method Overloading is to “add” or “extend” more
to method’s behavior.
Method Overriding is to “Change” existing
behavior of method.
Polymorphism It is a compile time polymorphism. It is a run time polymorphism.
Signature The methods must have different signature. The methods must have same signature.
Inheritance
It may or may not need inheritance in Method
Overloading.
It always requires inheritance in Method
Overriding.

Q15. What is the difference between Method overloading and Method overriding?
Method overloading Method overriding

Q16. Can you override a private or static method in Java?

Q16. Can you override a private or static method in Java?
➢ A private method cannot be overridden since it
is not visible from any other class.
➢ If you create a similar method with same return
type and same method arguments in child class
then it will hide the super class method; this is
known as method hiding.

Q17. What is multiple inheritance and does java support?

Q17. What is multiple inheritance and does java support?
➢ If a child class inherits the property from multiple
classes is known as multiple inheritance.
➢ The problem with multiple inheritance is that if
multiple parent classes have a same method
name, then at runtime it becomes difficult for the
compiler to decide which method to execute from
the child class
Class A
Class A Class A
Class A

Output:
I am foo in Super
I am foo in Child
I am bar in Child
I am bar in Child

Output:
How are you?
Hello
Hi

Output:
First 2
Third 0
Second 2
Fourth 6
6

Basic Questions
OOPS Questions
Servlets
JDBC Hibernate
Spring

Q21. What is a Servlet?

Q21. What is a Servlet?
➢ Java Servlet is server side technologies to extend the capability
of web servers by providing support for dynamic response and
data persistence.
➢ The javax.servlet and javax.servlet.http packages provide
interfaces and classes for writing our own servlets.
➢ All servlets must implement the javax.servlet.Servlet interface,
which defines servlet lifecycle methods.
➢ As most web applications are accessed using HTTP protocol ,we
mostly extend HttpServlet class. Servlet API hierarchy. Servlet
Browser
Internet
Java Web
Server

Q22. What is difference between Get and Post method?

Q22. What is difference between Get and Post method?
Get Post
Limited amount of data can be sent
because data is sent in header.
Large amount of data can be sent
because data is sent in body.
Not Secured because data is exposed
in URL bar.
Secured because data is not
exposed in URL bar.
Can be bookmarked Cannot be bookmarked
Idempotent Non-Idempotent
It is more efficient and used than Post It is less efficient and used

Q23. What are different methods of session management in servlets?

Q23. What are different methods of session management in servlets?
➢ Session is a conversational state between client and server and it can consists of multiple request and response
between client and server.
➢ Since HTTP and Web Server both are stateless, the only way to maintain a session is when some unique
information about the session (session id) is passed between server and client in every request and response.
Session Management
User
Authentication
HTML Hidden Field Cookies URL Rewriting
Session
Management API

Q24. What is the .Difference between ServletContext vs ServletConfig?

Q24. What is the .Difference between ServletContext vs ServletConfig?
ServletConfig ServletContext
Servlet config object represent single servlet
It represent whole web application running on particular
JVM and common for all the servlet
Its like local parameter associated with particular servlet
Its like global parameter associated with whole
application
It’s a name value pair defined inside the servlet section
of web.xml file so it has servlet wide scope
ServletContext has application wide scope so define
outside of servlet tag in web.xml file.
getServletConfig() method is used to get the config
object
getServletContext() method is used to get the context
object.
E.g. Shopping cart of a user is a specific to particular
user so here we can use servlet config
To get the MIME type of a file or application session
related information is stored using servlet context
object.

Q25. What is the life-cycle of a servlet?

Q25. What is the life-cycle of a servlet?
There are 5 stages in the lifecycle of a servlet:
➢ Servlet is loaded
➢ servlet is instantiated
➢ servlet is initialized
➢ service the request
➢ servlet is destroyed

Q26. What is Request Dispatcher?

Q26. What is Request Dispatcher?
➢ RequestDispatcher interface is used to forward the
request to another resource that can be HTML, JSP
or another servlet in same application.
➢ We can also use this to include the content of
another resource to the response.
➢ There are two methods defined in this interface:
1. void forward()
2. void include()

Q27. How does Cookies work in Servlets?

Q27. How does Cookies work in Servlets?
➢ Cookies are text data sent by server to the client and it gets saved at the client local machine.
➢ Servlet API provides cookies support through javax.servlet.http.Cookie class that implements Serializable and
Cloneable interfaces.
➢ HttpServletRequest getCookies() method is provided to get the array of Cookies from request, since there is no
point of adding Cookie to request, there are no methods to set or add cookie to request.
➢ Similarly HttpServletResponse addCookie(Cookie c) method is provided to attach cookie in response header,
there are no getter methods for cookie.

Basic Questions
OOPS Questions
Servlets
JDBC
Hibernate
Spring

Q28. What is JDBC Driver?

Q28. What is JDBC Driver?
JDBC Driver is a software component that enables java
application to interact with the database. There are 4
types of JDBC drivers:
➢JDBC-ODBC bridge driver
➢Native-API driver (partially java driver)
➢Network Protocol driver (fully java driver)
➢Thin driver (fully java driver)

Q29. What are the steps to connect to the database in java?

Q29. What are the steps to connect to the database in java?
There are 5 steps we need to follow to connect
to a database in Java
➢ Registering the driver class
➢ Creating connection
➢ Creating statement
➢ Executing queries
➢ Closing connection

Q30. What are the different JDBC API components?

Interfaces Classes
Q30. What are the different JDBC API components?
Interfaces
Connection
Statement
Prepared
Statement
ResultSet
ResultSet
MetaData
Database
MetaData
Callable
Statement

Q31. What is a JDBC Connection interface?

Q31. What is a JDBC Connection interface?
The Connection interface maintains a session with the database. It can be used for transaction management.
Connection Interface
createStatement()
createStatement(result
SetType,
resultSetConcurrency)
setAutoCommit(
boolean status)
commit() rollback() close()

Q32. What is the difference between execute, executeQuery, executeUpdate?

Q33. What is Spring?

Q33. What is Spring?
➢ It is an application framework and inversion of control container for the Java platform.
➢ The framework’s core features can be used by any Java application, but there are extensions for building web
applications on top of the Java EE platform.”
➢ Spring is essentially a lightweight, integrated framework that can be used for developing enterprise applications
in java.

Q34. What are the different modules of the Spring framework.

Q34. What are the different modules of the Spring framework.
Some of the important Spring Framework modules are:
➢ Spring Context – for dependency injection.
➢ Spring AOP – for aspect oriented programming.
➢ Spring DAO – for database operations using DAO pattern
➢ Spring JDBC – for JDBC and DataSource support.
➢ Spring ORM – for ORM tools support such as Hibernate
➢ Spring Web Module – for creating web applications.
➢ Spring MVC – Model-View-Controller implementation for
creating web applications, web services etc.

Q35. List some of the important annotations in annotation-based Spring configuration

Q35. List some of the important annotations in annotation-based Spring configuration
Annotation
@Required
@Autowired
@Qualifier
@Resource
@PostConstruct
@PreDestroy

Q36. What is a Bean in Spring and Explain the different scopes of bean in Spring?

Q36. What is a Bean in Spring and Explain the different scopes of bean in Spring?
➢ .A bean is an object that is instantiated, assembled, and managed by a Spring IoC container.
➢ They are managed by the Spring IoC container.
➢ There are 5 scopes of beans in Spring :
Scope
Singleton Prototype Request Session Global-Session

Q37. How is a bean added to a Spring application?

Q38. Explain the role of DispatcherServlet and ContextLoaderListener.

Q38. Explain the role of DispatcherServlet and ContextLoaderListener.
DispatcherServlet
DispatcherServlet is the front controller in the Spring MVC
application as it loads the spring bean configuration file and
initializes all the beans that have been configured.
ContextLoaderListener
ContextLoaderListener, the listener to start up and shut
down the WebApplicationContext in Spring root.

Q39. What is the difference between constructor injection and setter injection?

Q39. What is the difference between constructor injection and setter injection?
Constructor Injection Setter Injection
No Partial Injection Partial Injection
Desn't override the setter property
Overrides the constructor property if
both are defined.
Creates new instance if any
modification occurs
Doesn't create new instance if you
change the property value
Better for too many properties Better for few properties.

Q40. What is autowiring in spring? What are the autowiring modes?

Q40. What is autowiring in spring? What are the autowiring modes?
Autowiring enables the programmer to inject the bean automatically. We don't need to write explicit injection logic.
Let's see the code to inject bean using dependency injection.
1. <bean id="emp" class="com.javatpoint.Employee" autowire="byName" />
Mode Description
no This is the default mode, it means autowiring is not enabled.
byName
injects the bean based on the property name. It uses setter
method.
byType
injects the bean based on the property type. It uses setter
method.
constructor It injects the bean using constructor

Q41. How to handle exceptions in Spring MVC Framework?

Q41. How to handle exceptions in Spring MVC Framework?
Spring MVC Framework provides following ways to help us
achieving robust exception handling.:
➢ Controller Based – We can define exception handler
methods in our controller classes.
➢ Global Exception Handler – Exception Handling is a cross-
cutting concern and Spring provides .
➢ HandlerExceptionResolver –Any Spring bean declared in
the DispatcherServlet’s application context that
implements HandlerExceptionResolver will be used to
intercept and process any exception raised in the MVC
system and not handled by a Controller.

Q42. What are some of the important Spring annotations used?

Q42. What are some of the important Spring annotations used?
@Controller
@RequestMapping @ResponseBody
@PathVariable @Qualifier
@Autowired @Service
@Scope
@Aspect
@Configuration

Q43. How to integrate Spring and Hibernate Frameworks?

Q43. How to integrate Spring and Hibernate Frameworks?
➢ We can use Spring ORM module to integrate Spring and
Hibernate frameworks
➢ Spring ORM also provides support for using Spring
declarative transaction management,

Q44. What is Hibernate Framework?

Q44. What is Hibernate Framework?
➢ Hibernate is java based ORM tool that provides framework for mapping application domain objects to the
relational database tables and vice versa.
➢ Hibernate provides reference implementation of Java Persistence API, that makes it a great choice as ORM tool
with benefits of loose coupling.
➢ Hibernate configurations are flexible and can be done from XML configuration file as well as programmatically.

Q45. What are the important benefits of using Hibernate Framework?

Q45. What are the important benefits of using Hibernate Framework?
1. Hibernate eliminates all the boiler-plate code.
2. Hibernate framework provides support for XML as well as JPA
annotations.
3. Hibernate provides a powerful query language (HQL) that is
similar to SQL.
4. Hibernate is an open source project from Red Hat Community
and used worldwide.
5. For database vendor specific feature, hibernate is suitable
because we can also execute native sql queries.
6. 7. Hibernate cache helps us in getting better performance.

Q46. Explain hibernate architecture?

Q46. Explain hibernate architecture?
Hibernate

Q47. What is the difference between get and load method?

Q47. What is the difference between get and load method?
get() load()
Returns null if object is not found. Throws ObjectNotFoundException if
object is not found.
get() method always hit the database. load() method doesn't hit the database.
It returns real object not proxy. It returns proxy object.
It should be used if you are not sure
about the existence of instance.
It should be used if you are sure that
instance exists.

Q48. What are the advantages of Hibernate over JDBC?

Q48. What are the advantages of Hibernate over JDBC?
1. Hibernate removes boiler-plate code that comes with JDBC API
2. Hibernate supports inheritance, associations and collections which are not
present with JDBC API.
3. Hibernate implicitly provides transaction management.
4. JDBC API throws SQLException that is a checked exception, so we need to
write a lot of try-catch block code.
5. Hibernate Query Language (HQL) is more object oriented and close to java
programming language. For JDBC, we need to write native sql queries.
6. Hibernate supports caching that is better for performance, JDBC queries
are not cached hence performance is low.

Thank You
Questions/Queries/Feedback

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