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VIVA questions & Answers
Internet Programming Lab
What is the difference between procedural and object-oriented programs?- a) In
procedural program, programming logic follows certain procedures and the instructions
are executed one after another. In OOP program, unit of program is object, which is
nothing but combination of data and code. b) In procedural program, data is exposed to
the whole program whereas in OOPs program, it is accessible with in the object and
which in turn assures the security of the code.
What are Encapsulation, Inheritance and Polymorphism?- Encapsulation is the
mechanism that binds together code and data it manipulates and keeps both safe from
outside interference and misuse. Inheritance is the process by which one object acquires
the properties of another object. Polymorphism is the feature that allows one interface to
be used for general class actions.
What is the difference between Assignment and Initialization?- Assignment can be
done as many times as desired whereas initialization can be done only once.
What is OOPs?- Object oriented programming organizes a program around its data, i. e.
, objects and a set of well defined interfaces to that data. An object-oriented program can
be characterized as data controlling access to code.
What are Class, Constructor and Primitive data types?- Class is a template for
multiple objects with similar features and it is a blue print for objects. It defines a type of
object according to the data the object can hold and the operations the object can perform.
Constructor is a special kind of method that determines how an object is initialized when
created. Primitive data types are 8 types and they are: byte, short, int, long, float, double,
boolean, char.
What is an Object and how do you allocate memory to it?- Object is an instance of a
class and it is a software unit that combines a structured set of data with a set of
operations for inspecting and manipulating that data. When an object is created using new
operator, memory is allocated to it.
What is the difference between constructor and method?- Constructor will be
automatically invoked when an object is created whereas method has to be called
What are methods and how are they defined?- Methods are functions that operate on
instances of classes in which they are defined. Objects can communicate with each other
using methods and can call methods in other classes. Method definition has four parts.
They are name of the method, type of object or primitive type the method returns, a list of
parameters and the body of the method. A method’s signature is a combination of the first
three parts mentioned above.
What is the use of bin and lib in JDK?- Bin contains all tools such as javac,
appletviewer, awt tool, etc., whereas lib contains API and all packages.
What is casting?- Casting is used to convert the value of one type to another.
How many ways can an argument be passed to a subroutine and explain them?- An
argument can be passed in two ways. They are passing by value and passing by reference.
Passing by value: This method copies the value of an argument into the formal parameter

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of the subroutine. Passing by reference: In this method, a reference to an argument (not
the value of the argument) is passed to the parameter.
12. What is the difference between an argument and a parameter?- While defining
method, variables passed in the method are called parameters. While using those
methods, values passed to those variables are called arguments.
13. What are different types of access modifiers?- public: Any thing declared as public can
be accessed from anywhere. private: Any thing declared as private can’t be seen outside
of its class. protected: Any thing declared as protected can be accessed by classes in the
same package and subclasses in the other packages. default modifier : Can be accessed
only to classes in the same package.
14. What is final, finalize() and finally?- final : final keyword can be used for class, method
and variables. A final class cannot be subclassed and it prevents other programmers from
subclassing a secure class to invoke insecure methods. A final method can’t be
overridden. A final variable can’t change from its initialized value. finalize() : finalize()
method is used just before an object is destroyed and can be called just prior to garbage
collection. finally : finally, a key word used in exception handling, creates a block of
code that will be executed after a try/catch block has completed and before the code
following the try/catch block. The finally block will execute whether or not an exception
is thrown. For example, if a method opens a file upon exit, then you will not want the
code that closes the file to be bypassed by the exception-handling mechanism. This
finally keyword is designed to address this contingency.
15. What is UNICODE?- Unicode is used for internal representation of characters and
strings and it uses 16 bits to represent each other.
16. What is Garbage Collection and how to call it explicitly?- When an object is no longer
referred to by any variable, java automatically reclaims memory used by that object. This
is known as garbage collection. System. gc() method may be used to call it explicitly.
17. What is finalize() method?- finalize () method is used just before an object is destroyed
and can be called just prior to garbage collection.
18. What are Transient and Volatile Modifiers?- Transient: The transient modifier applies
to variables only and it is not stored as part of its object’s Persistent state. Transient
variables are not serialized. Volatile: Volatile modifier applies to variables only and it
tells the compiler that the variable modified by volatile can be changed unexpectedly by
other parts of the program.
19. What is method overloading and method overriding?- Method overloading: When a
method in a class having the same method name with different arguments is said to be
method overloading. Method overriding : When a method in a class having the same
method name with same arguments is said to be method overriding.
20. What is difference between overloading and overriding?- a) In overloading, there is a
relationship between methods available in the same class whereas in overriding, there is
relationship between a superclass method and subclass method. b) Overloading does not
block inheritance from the superclass whereas overriding blocks inheritance from the
superclass. c) In overloading, separate methods share the same name whereas in
overriding, subclass method replaces the superclass. d) Overloading must have different
method signatures whereas overriding must have same signature.
21. What is meant by Inheritance and what are its advantages?- Inheritance is the
process of inheriting all the features from a class. The advantages of inheritance are

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reusability of code and accessibility of variables and methods of the super class by
22. What is the difference between this() and super()?- this() can be used to invoke a
constructor of the same class whereas super() can be used to invoke a super class
23. What is the difference between superclass and subclass?- A super class is a class that
is inherited whereas sub class is a class that does the inheriting.
24. What modifiers may be used with top-level class?- public, abstract and final can be
used for top-level class.
25. What are inner class and anonymous class?- Inner class : classes defined in other
classes, including those defined in methods are called inner classes. An inner class can
have any accessibility including private. Anonymous class : Anonymous class is a class
defined inside a method without a name and is instantiated and declared in the same place
and cannot have explicit constructors.
26. What is a package?- A package is a collection of classes and interfaces that provides a
high-level layer of access protection and name space management.
27. What is a reflection package?- java. lang. reflect package has the ability to analyze
itself in runtime.
28. What is interface and its use?- Interface is similar to a class which may contain
method’s signature only but not bodies and it is a formal set of method and constant
declarations that must be defined by the class that implements it. Interfaces are useful for:
a)Declaring methods that one or more classes are expected to implement b)Capturing
similarities between unrelated classes without forcing a class relationship. c)Determining
an object’s programming interface without revealing the actual body of the class.
29. What is an abstract class?- An abstract class is a class designed with implementation
gaps for subclasses to fill in and is deliberately incomplete.
30. What is the difference between Integer and int?- a) Integer is a class defined in the
java. lang package, whereas int is a primitive data type defined in the Java language
itself. Java does not automatically convert from one to the other. b) Integer can be used as
an argument for a method that requires an object, whereas int can be used for
31. What is a cloneable interface and how many methods does it contain?- It is not
having any method because it is a TAGGED or MARKER interface.
32. What is the difference between abstract class and interface?- a) All the methods
declared inside an interface are abstract whereas abstract class must have at least one
abstract method and others may be concrete or abstract. b) In abstract class, key word
abstract must be used for the methods whereas interface we need not use that keyword for
the methods. c) Abstract class must have subclasses whereas interface can’t have
33. Can you have an inner class inside a method and what variables can you access?-
Yes, we can have an inner class inside a method and final variables can be accessed.
34. What is the difference between String and String Buffer?- a) String objects are
constants and immutable whereas StringBuffer objects are not. b) String class supports
constant strings whereas StringBuffer class supports growable and modifiable strings.
35. What is the difference between Array and vector?- Array is a set of related data type
and static whereas vector is a growable array of objects and dynamic.

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36. What is the difference between exception and error?- The exception class defines
mild error conditions that your program encounters. Exceptions can occur when trying to
open the file, which does not exist, the network connection is disrupted, operands being
manipulated are out of prescribed ranges, the class file you are interested in loading is
missing. The error class defines serious error conditions that you should not attempt to
recover from. In most cases it is advisable to let the program terminate when such an
error is encountered.
37. What is the difference between process and thread?- Process is a program in
execution whereas thread is a separate path of execution in a program.
38. What is multithreading and what are the methods for inter-thread communication
and what is the class in which these methods are defined?- Multithreading is the
mechanism in which more than one thread run independent of each other within the
process. wait (), notify () and notifyAll() methods can be used for inter-thread
communication and these methods are in Object class. wait() : When a thread executes a
call to wait() method, it surrenders the object lock and enters into a waiting state. notify()
or notifyAll() : To remove a thread from the waiting state, some other thread must make a
call to notify() or notifyAll() method on the same object.
39. What is the class and interface in java to create thread and which is the most
advantageous method?- Thread class and Runnable interface can be used to create
threads and using Runnable interface is the most advantageous method to create threads
because we need not extend thread class here.
40. What are the states associated in the thread?- Thread contains ready, running, waiting
and dead states.
41. What is synchronization?- Synchronization is the mechanism that ensures that only one
thread is accessed the resources at a time.
42. When you will synchronize a piece of your code?- When you expect your code will be
accessed by different threads and these threads may change a particular data causing data
43. What is deadlock?- When two threads are waiting each other and can’t precede the
program is said to be deadlock.
44. What is daemon thread and which method is used to create the daemon thread?-
Daemon thread is a low priority thread which runs intermittently in the back ground
doing the garbage collection operation for the java runtime system. setDaemon method is
used to create a daemon thread.
45. Are there any global variables in Java, which can be accessed by other part of your
program?- No, it is not the main method in which you define variables. Global variables
is not possible because concept of encapsulation is eliminated here.
46. What is an applet?- Applet is a dynamic and interactive program that runs inside a web
page displayed by a java capable browser.
47. What is the difference between applications and applets?- a)Application must be run
on local machine whereas applet needs no explicit installation on local machine.
b)Application must be run explicitly within a java-compatible virtual machine whereas
applet loads and runs itself automatically in a java-enabled browser. d)Application starts
execution with its main method whereas applet starts execution with its init method.
e)Application can run with or without graphical user interface whereas applet must run
within a graphical user interface.

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48. How does applet recognize the height and width?- Using getParameters() method.
49. When do you use codebase in applet?- When the applet class file is not in the same
directory, codebase is used.
50. What is the lifecycle of an applet?- init() method - Can be called when an applet is first
loaded start() method - Can be called each time an applet is started. paint() method - Can
be called when the applet is minimized or maximized. stop() method - Can be used when
the browser moves off the applet’s page. destroy() method - Can be called when the
browser is finished with the applet.
51. How do you set security in applets?- using setSecurityManager() method
52. What is an event and what are the models available for event handling?- An event is
an event object that describes a state of change in a source. In other words, event occurs
when an action is generated, like pressing button, clicking mouse, selecting a list, etc.
There are two types of models for handling events and they are: a) event-inheritance
model and b) event-delegation model
53. What are the advantages of the model over the event-inheritance model?- The event-
delegation model has two advantages over the event-inheritance model. They are: a)It
enables event handling by objects other than the ones that generate the events. This
allows a clean separation between a component’s design and its use. b)It performs much
better in applications where many events are generated. This performance improvement
is due to the fact that the event-delegation model does not have to be repeatedly process
unhandled events as is the case of the event-inheritance.
54. What is source and listener?- source : A source is an object that generates an event.
This occurs when the internal state of that object changes in some way. listener : A
listener is an object that is notified when an event occurs. It has two major requirements.
First, it must have been registered with one or more sources to receive notifications about
specific types of events. Second, it must implement methods to receive and process these
55. What is adapter class?- An adapter class provides an empty implementation of all
methods in an event listener interface. Adapter classes are useful when you want to
receive and process only some of the events that are handled by a particular event listener
interface. You can define a new class to act listener by extending one of the adapter
classes and implementing only those events in which you are interested. For example, the
MouseMotionAdapter class has two methods, mouseDragged()and mouseMoved(). The
signatures of these empty are exactly as defined in the MouseMotionListener interface. If
you are interested in only mouse drag events, then you could simply extend
MouseMotionAdapter and implement mouseDragged() .
56. What is meant by controls and what are different types of controls in AWT?-
Controls are components that allow a user to interact with your application and the AWT
supports the following types of controls: Labels, Push Buttons, Check Boxes, Choice
Lists, Lists, Scrollbars, Text Components. These controls are subclasses of Component.
57. What is the difference between choice and list?- A Choice is displayed in a compact
form that requires you to pull it down to see the list of available choices and only one
item may be selected from a choice. A List may be displayed in such a way that several
list items are visible and it supports the selection of one or more list items.

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58. What is the difference between scrollbar and scrollpane?- A Scrollbar is a
Component, but not a Container whereas Scrollpane is a Conatiner and handles its own
events and perform its own scrolling.
59. What is a layout manager and what are different types of layout managers available
in java AWT?- A layout manager is an object that is used to organize components in a
container. The different layouts are available are FlowLayout, BorderLayout,
CardLayout, GridLayout and GridBagLayout.
60. How are the elements of different layouts organized?- FlowLayout: The elements of a
FlowLayout are organized in a top to bottom, left to right fashion. BorderLayout: The
elements of a BorderLayout are organized at the borders (North, South, East and West)
and the center of a container. CardLayout: The elements of a CardLayout are stacked, on
top of the other, like a deck of cards. GridLayout: The elements of a GridLayout are of
equal size and are laid out using the square of a grid. GridBagLayout: The elements of a
GridBagLayout are organized according to a grid. However, the elements are of different
size and may occupy more than one row or column of the grid. In addition, the rows and
columns may have different sizes.
61. Which containers use a Border layout as their default layout?- Window, Frame and
Dialog classes use a BorderLayout as their layout.
62. Which containers use a Flow layout as their default layout?- Panel and Applet classes
use the FlowLayout as their default layout.
63. What are wrapper classes?- Wrapper classes are classes that allow primitive types to be
accessed as objects.
64. What are Vector, Hashtable, LinkedList and Enumeration?- Vector : The Vector
class provides the capability to implement a growable array of objects. Hashtable : The
Hashtable class implements a Hashtable data structure. A Hashtable indexes and stores
objects in a dictionary using hash codes as the object’s keys. Hash codes are integer
values that identify objects. LinkedList: Removing or inserting elements in the middle of
an array can be done using LinkedList. A LinkedList stores each object in a separate link
whereas an array stores object references in consecutive locations. Enumeration: An
object that implements the Enumeration interface generates a series of elements, one at a
time. It has two methods, namely hasMoreElements() and nextElement().
HasMoreElemnts() tests if this enumeration has more elements and nextElement method
returns successive elements of the series.
65. What is the difference between set and list?- Set stores elements in an unordered way
but does not contain duplicate elements, whereas list stores elements in an ordered way
but may contain duplicate elements.
66. What is a stream and what are the types of Streams and classes of the Streams?- A
Stream is an abstraction that either produces or consumes information. There are two
types of Streams and they are: Byte Streams: Provide a convenient means for handling
input and output of bytes. Character Streams: Provide a convenient means for handling
input & output of characters. Byte Streams classes: Are defined by using two abstract
classes, namely InputStream and OutputStream. Character Streams classes: Are defined
by using two abstract classes, namely Reader and Writer.
67. What is the difference between Reader/Writer and InputStream/Output Stream?-
The Reader/Writer class is character-oriented and the InputStream/OutputStream class is

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68. What is an I/O filter?- An I/O filter is an object that reads from one stream and writes to
another, usually altering the data in some way as it is passed from one stream to another.
69. What is serialization and deserialization?- Serialization is the process of writing the
state of an object to a byte stream. Deserialization is the process of restoring these
70. What is JDBC?- JDBC is a set of Java API for executing SQL statements. This API
consists of a set of classes and interfaces to enable programs to write pure Java Database
71. What are drivers available?- a) JDBC-ODBC Bridge driver b) Native API Partly-Java
driver c) JDBC-Net Pure Java driver d) Native-Protocol Pure Java driver
72. What is the difference between JDBC and ODBC?- a) OBDC is for Microsoft and
JDBC is for Java applications. b) ODBC can’t be directly used with Java because it uses
a C interface. c) ODBC makes use of pointers which have been removed totally from
Java. d) ODBC mixes simple and advanced features together and has complex options for
simple queries. But JDBC is designed to keep things simple while allowing advanced
capabilities when required. e) ODBC requires manual installation of the ODBC driver
manager and driver on all client machines. JDBC drivers are written in Java and JDBC
code is automatically installable, secure, and portable on all platforms. f) JDBC API is a
natural Java interface and is built on ODBC. JDBC retains some of the basic features of
73. What are the types of JDBC Driver Models and explain them?- There are two types
of JDBC Driver Models and they are: a) Two tier model and b) Three tier model Two tier
model: In this model, Java applications interact directly with the database. A JDBC driver
is required to communicate with the particular database management system that is being
accessed. SQL statements are sent to the database and the results are given to user. This
model is referred to as client/server configuration where user is the client and the
machine that has the database is called as the server. Three tier model: A middle tier is
introduced in this model. The functions of this model are: a) Collection of SQL
statements from the client and handing it over to the database, b) Receiving results from
database to the client and c) Maintaining control over accessing and updating of the
74. What are the steps involved for making a connection with a database or how do you
connect to a database?a) Loading the driver : To load the driver, Class. forName()
method is used. Class. forName(”sun. jdbc. odbc. JdbcOdbcDriver”); When the driver is
loaded, it registers itself with the java. sql. DriverManager class as an available database
driver. b) Making a connection with database: To open a connection to a given database,
DriverManager. getConnection() method is used. Connection con = DriverManager.
getConnection (”jdbc:odbc:somedb”, “user”, “password”); c) Executing SQL statements :
To execute a SQL query, java. sql. statements class is used. createStatement() method of
Connection to obtain a new Statement object. Statement stmt = con. createStatement(); A
query that returns data can be executed using the executeQuery() method of Statement.
This method executes the statement and returns a java. sql. ResultSet that encapsulates
the retrieved data: ResultSet rs = stmt. executeQuery(”SELECT * FROM some table”);
d) Process the results : ResultSet returns one row at a time. Next() method of ResultSet
object can be called to move to the next row. The getString() and getObject() methods are

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used for retrieving column values: while(rs. next()) { String event = rs.
getString(”event”); Object count = (Integer) rs. getObject(”count”);
75. What type of driver did you use in project?- JDBC-ODBC Bridge driver (is a driver
that uses native(C language) libraries and makes calls to an existing ODBC driver to
access a database engine).
76. What are the types of statements in JDBC?- Statement: to be used createStatement()
method for executing single SQL statement PreparedStatement To be used
preparedStatement() method for executing same SQL statement over and over.
CallableStatement To be used prepareCall() method for multiple SQL statements over
and over.
77. What is stored procedure?- Stored procedure is a group of SQL statements that forms a
logical unit and performs a particular task. Stored Procedures are used to encapsulate a
set of operations or queries to execute on database. Stored procedures can be compiled
and executed with different parameters and results and may have any combination of
input/output parameters.
78. How to create and call stored procedures?- To create stored procedures: Create
procedure procedurename (specify in, out and in out parameters) BEGIN Any multiple
SQL statement; END; To call stored procedures: CallableStatement csmt = con.
prepareCall(”{call procedure name(?,?)}”); csmt. registerOutParameter(column no. , data
type); csmt. setInt(column no. , column name) csmt. execute();
79. What is servlet?- Servlets are modules that extend request/response-oriented servers,
such as java-enabled web servers. For example, a servlet might be responsible for taking
data in an HTML order-entry form and applying the business logic used to update a
company’s order database.
80. What are the classes and interfaces for servlets?- There are two packages in servlets
and they are javax. servlet and
81. What is the difference between an applet and a servlet?- a) Servlets are to servers
what applets are to browsers. b) Applets must have graphical user interfaces whereas
servlets have no graphical user interfaces.
82. What is the difference between doPost and doGet methods?- a) doGet() method is
used to get information, while doPost() method is used for posting information. b)
doGet() requests can’t send large amount of information and is limited to 240-255
characters. However, doPost()requests passes all of its data, of unlimited length. c) A
doGet() request is appended to the request URL in a query string and this allows the
exchange is visible to the client, whereas a doPost() request passes directly over the
socket connection as part of its HTTP request body and the exchange are invisible to the
83. What is the life cycle of a servlet?- Each Servlet has the same life cycle: a) A server
loads and initializes the servlet by init () method. b) The servlet handles zero or more
client’s requests through service() method. c) The server removes the servlet through
destroy() method.
84. Who is loading the init() method of servlet?- Web server
85. What are the different servers available for developing and deploying Servlets?- a)
Java Web Server b) JRun g) Apache Server h) Netscape Information Server i) Web Logic

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86. How many ways can we track client and what are they?- The servlet API provides
two ways to track client state and they are: a) Using Session tracking and b) Using
87. What is session tracking and how do you track a user session in servlets?- Session
tracking is a mechanism that servlets use to maintain state about a series requests from
the same user across some period of time. The methods used for session tracking are: a)
User Authentication - occurs when a web server restricts access to some of its resources
to only those clients that log in using a recognized username and password. b) Hidden
form fields - fields are added to an HTML form that are not displayed in the client’s
browser. When the form containing the fields is submitted, the fields are sent back to the
server. c) URL rewriting - every URL that the user clicks on is dynamically modified or
rewritten to include extra information. The extra information can be in the form of extra
path information, added parameters or some custom, server-specific URL change. d)
Cookies - a bit of information that is sent by a web server to a browser and which can
later be read back from that browser. e) HttpSession- places a limit on the number of
sessions that can exist in memory. This limit is set in the session. maxresidents property.
88. What is Server-Side Includes (SSI)?- Server-Side Includes allows embedding servlets
within HTML pages using a special servlet tag. In many servlets that support servlets, a
page can be processed by the server to include output from servlets at certain points
inside the HTML page. This is accomplished using a special internal SSINCLUDE,
which processes the servlet tags. SSINCLUDE servlet will be invoked whenever a file
with an. shtml extension is requested. So HTML files that include server-side includes
must be stored with an . shtml extension.
89. What are cookies and how will you use them?- Cookies are a mechanism that a servlet
uses to have a client hold a small amount of state-information associated with the user. a)
Create a cookie with the Cookie constructor: public Cookie(String name, String value) b)
A servlet can send a cookie to the client by passing a Cookie object to the addCookie()
method of HttpServletResponse: public void HttpServletResponse. addCookie(Cookie
cookie) c) A servlet retrieves cookies by calling the getCookies() method of
HttpServletRequest: public Cookie[ ] HttpServletRequest. getCookie().
90. Is it possible to communicate from an applet to servlet and how many ways and
how?- Yes, there are three ways to communicate from an applet to servlet and they are:
a) HTTP Communication(Text-based and object-based) b) Socket Communication c)
RMI Communication
91. What is connection pooling?- With servlets, opening a database connection is a major
bottleneck because we are creating and tearing down a new connection for every page
request and the time taken to create connection will be more. Creating a connection pool
is an ideal approach for a complicated servlet. With a connection pool, we can duplicate
only the resources we need to duplicate rather than the entire servlet. A connection pool
can also intelligently manage the size of the pool and make sure each connection remains
valid. A number of connection pool packages are currently available. Some like
DbConnectionBroker are freely available from Java Exchange Works by creating an
object that dispenses connections and connection Ids on request. The ConnectionPool
class maintains a Hastable, using Connection objects as keys and Boolean values as
stored values. The Boolean value indicates whether a connection is in use or not. A

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program calls getConnection() method of the ConnectionPool for getting Connection
object it can use; it calls returnConnection() to give the connection back to the pool.
92. Why should we go for interservlet communication?- Servlets running together in the
same server communicate with each other in several ways. The three major reasons to use
interservlet communication are: a) Direct servlet manipulation - allows to gain access to
the other currently loaded servlets and perform certain tasks (through the ServletContext
object) b) Servlet reuse - allows the servlet to reuse the public methods of another servlet.
c) Servlet collaboration - requires to communicate with each other by sharing specific
information (through method invocation)
93. Is it possible to call servlet with parameters in the URL?- Yes. You can call a servlet
with parameters in the syntax as (?Param1 = xxx || m2 = yyy).
94. What is Servlet chaining?- Servlet chaining is a technique in which two or more servlets
can cooperate in servicing a single request. In servlet chaining, one servlet’s output is
piped to the next servlet’s input. This process continues until the last servlet is reached.
Its output is then sent back to the client.
95. How do servlets handle multiple simultaneous requests?- The server has multiple
threads that are available to handle requests. When a request comes in, it is assigned to a
thread, which calls a service method (for example: doGet(), doPost() and service()) of the
servlet. For this reason, a single servlet object can have its service methods called by
many threads at once.
96. What is the difference between TCP/IP and UDP?- TCP/IP is a two-way
communication between the client and the server and it is a reliable and there is a
confirmation regarding reaching the message to the destination. It is like a phone call.
UDP is a one-way communication only between the client and the server and it is not a
reliable and there is no confirmation regarding reaching the message to the destination. It
is like a postal mail.
97. What is Inet address?- Every computer connected to a network has an IP address. An IP
address is a number that uniquely identifies each computer on the Net. An IP address is a
32-bit number.
98. What is Domain Naming Service(DNS)?- It is very difficult to remember a set of
numbers(IP address) to connect to the Internet. The Domain Naming Service(DNS) is
used to overcome this problem. It maps one particular IP address to a string of characters.
For example, www. mascom. com implies com is the domain name reserved for US
commercial sites, moscom is the name of the company and www is the name of the
specific computer, which is mascom’s server.
99. What is URL?- URL stands for Uniform Resource Locator and it points to resource files
on the Internet. URL has four components: http://www. address. com:80/index.html,
where http - protocol name, address - IP address or host name, 80 - port number and
index.html - file path.
What is RMI and steps involved in developing an RMI object?- Remote
Method Invocation (RMI) allows java object that executes on one machine and to invoke
the method of a Java object to execute on another machine. The steps involved in
developing an RMI object are: a) Define the interfaces b) Implementing these interfaces
c) Compile the interfaces and their implementations with the java compiler d) Compile
the server implementation with RMI compiler e) Run the RMI registry f) Run the

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What is RMI architecture?- RMI architecture consists of four layers and each
layer performs specific functions: a) Application layer - contains the actual object
definition. b) Proxy layer - consists of stub and skeleton. c) Remote Reference layer -
gets the stream of bytes from the transport layer and sends it to the proxy layer. d)
Transportation layer - responsible for handling the actual machine-to-machine
what is UnicastRemoteObject?- All remote objects must extend
UnicastRemoteObject, which provides functionality that is needed to make objects
available from remote machines.
Explain the methods, rebind() and lookup() in Naming class?- rebind() of the
Naming class(found in java. rmi) is used to update the RMI registry on the server
machine. Naming. rebind(”AddSever”, AddServerImpl); lookup() of the Naming class
accepts one argument, the rmi URL and returns a reference to an object of type
What is a Java Bean?- A Java Bean is a software component that has been
designed to be reusable in a variety of different environments.
What is a Jar file?- Jar file allows to efficiently deploying a set of classes and
their associated resources. The elements in a jar file are compressed, which makes
downloading a Jar file much faster than separately downloading several uncompressed
files. The package java. util. zip contains classes that read and write jar files.
What is BDK?- BDK, Bean Development Kit is a tool that enables to create,
configure and connect a set of set of Beans and it can be used to test Beans without
writing a code.
What is JSP?- JSP is a dynamic scripting capability for web pages that allows
Java as well as a few special tags to be embedded into a web file (HTML/XML, etc). The
suffix traditionally ends with .jsp to indicate to the web server that the file is a JSP files.
JSP is a server side technology - you can’t do any client side validation with it. The
advantages are: a) The JSP assists in making the HTML more functional. Servlets on the
other hand allow outputting of HTML but it is a tedious process. b) It is easy to make a
change and then let the JSP capability of the web server you are using deal with
compiling it into a servlet and running it.
What are JSP scripting elements?- JSP scripting elements lets to insert Java
code into the servlet that will be generated from the current JSP page. There are three
forms: a) Expressions of the form <%= expression %> that are evaluated and inserted
into the output, b) Scriptlets of the formthat are inserted into the servlet’s service method,
and c) Declarations of the form <%! Code %>that are inserted into the body of the servlet
class, outside of any existing methods.
What are JSP Directives?- A JSP directive affects the overall structure of the
servlet class. It usually has the following form:<%@ directive attribute=”value” %>
However, you can also combine multiple attribute settings for a single directive, as
follows:<%@ directive attribute1=”value1″ attribute 2=”value2″ . . . attributeN
=”valueN” %> There are two main types of directive: page, which lets to do things like
import classes, customize the servlet superclass, and the like; and include, which lets to
insert a file into the servlet class at the time the JSP file is translated into a servlet
What are Predefined variables or implicit objects?- To simplify code in JSP
expressions and scriptlets, we can use eight automatically defined variables, sometimes

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called implicit objects. They are request, response, out, session, application, config,
pageContext, and page.
What are JSP ACTIONS?- JSP actions use constructs in XML syntax to control
the behavior of the servlet engine. You can dynamically insert a file, reuse JavaBeans
components, forward the user to another page, or generate HTML for the Java plugin.
Available actions include: jsp:include - Include a file at the time the page is requested.
jsp:useBean - Find or instantiate a JavaBean. jsp:setProperty - Set the property of a
JavaBean. jsp:getProperty - Insert the property of a JavaBean into the output. jsp:forward
- Forward the requester to a newpage. Jsp: plugin - Generate browser-specific code that
makes an OBJECT or EMBED
How do you pass data (including JavaBeans) to a JSP from a servlet?- (1)
Request Lifetime: Using this technique to pass beans, a request dispatcher (using either
“include” or forward”) can be called. This bean will disappear after processing this
request has been completed. Servlet: request. setAttribute(”theBean”, myBean);
RequestDispatcher rd = getServletContext(). getRequestDispatcher(”thepage. jsp”); rd.
forward(request, response); JSP PAGE:<jsp: useBean id=”theBean” scope=”request”
class=”. . . . . ” />(2) Session Lifetime: Using this technique to pass beans that are
relevant to a particular session (such as in individual user login) over a number of
requests. This bean will disappear when the session is invalidated or it times out, or when
you remove it. Servlet: HttpSession session = request. getSession(true); session.
putValue(”theBean”, myBean); /* You can do a request dispatcher here, or just let the
bean be visible on the next request */ JSP Page:<jsp:useBean id=”theBean”
scope=”session” class=”. . . ” /> 3) Application Lifetime: Using this technique to pass
beans that are relevant to all servlets and JSP pages in a particular app, for all users. For
example, I use this to make a JDBC connection pool object available to the various
servlets and JSP pages in my apps. This bean will disappear when the servlet engine is
shut down, or when you remove it. Servlet: GetServletContext(). setAttribute(”theBean”,
myBean); JSP PAGE:<jsp:useBean id=”theBean” scope=”application” class=”. . . ” />
How can I set a cookie in JSP?- response. setHeader(”Set-Cookie”, “cookie
string”); To give the response-object to a bean, write a method setResponse
(HttpServletResponse response) - to the bean, and in jsp-file:<% bean. setResponse
(response); %>
How can I delete a cookie with JSP?- Say that I have a cookie called “foo, ” that
I set a while ago & I want it to go away. I simply: <% Cookie killCookie = new
Cookie(”foo”, null); KillCookie. setPath(”/”); killCookie. setMaxAge(0); response.
addCookie(killCookie); %>
How are Servlets and JSP Pages related?- JSP pages are focused around
HTML (or XML) with Java codes and JSP tags inside them. When a web server that has
JSP support is asked for a JSP page, it checks to see if it has already compiled the page
into a servlet. Thus, JSP pages become servlets and are transformed into pure Java and
then compiled, loaded into the server and executed.
What is the difference between application server and web server?

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An web server is responsible for handling HttpRequests whereas appliation server is responsible
for handling business logics. app server has inbuilt features like load balancing, clusters, caches
and resource & connection pooling etc. Using application server we can develop reusable
components. Application server is a super set of web server.
web server is used for executing JSP and servlets. application server is used for executing EJB
related components
Difference between throw and throws :
throw -- to explicitly throw an exception
throws --- means that exception will be handled by the called method.
1. Difference between HashTable and hashMap ?
Both provide key-value access to data. The Hashtable is one of the original collection
classes in Java. HashMap is part of the new Collections Framework, added with Java 2, v1.2.
The key difference between the two is that access to the Hashtable is synchronized on the table
while access to the HashMap isn't. You can add it, but it isn't there by default. Another difference
is that iterator in the HashMap is fail-safe while the enumerator for the Hashtable isn't. If you
change the map while iterating, you'll know. And, a third difference is that HashMap permits
null values in it, while Hashtable doesn't. For new code,we can use HashMap.
2.What is the diffrence between Array,Vector,ArryList,LinkedList and HashTable with
HashMap with example and situation?
Once u create an array (of any type) u can't change the array size at dynamically. it is not
synchronized. U can view a Vector as a dynamic array. U can resize the vector at runtime. u can
add/remove element in a vector at runtime. it is synchronized. An ArrayList is a class which
implements the List interface. This again is resizable and u hav all the functionalities of a list. it
is not synchronized. Note : u can hav duplicates in ArrayList. A LinkedList is an implementation
of the calssical 'C' linked list. U can get, remove or insert elements. HashTable is basically a key-
value pair collection. Key has to be unique. U can do get and put. HashMap is implementation of
Map interface. U can hav null key or null value. Use when u require constant time performance.

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3.What is the difference between servlet & CGI?
For each HTTP request, CGI will start a new process. whereas in servlet, init() method
will be called, only when first HTTP request came. for subsequent request an thread is created.
4.What is the difference between the Serlvet single threaded model and multi threaded
Typically, a servlet class is instantiated the first time it is invoked. The same instance will
be used over several client requests, so all members that are declared in that servlet are shared
accross clients. That is what is meant by multi threaded model, multiple clients that access the
same instance.
There are situations where you want to protect your servlet member variables from being
modified by different clients. In this case, you can have your servlet implement the marker
interface SingleThreadModel. Every time a client makes a request to a servlet that implements
this interface, the engine will create a new instance of the servlet. For performance reasons, the
engine can also maintain a instance pool, handing out instances as they are needed. Or it could
also serialize client requests, executing one after another.
5. How to read environment variables from a Servlet?
A:ServletConfig.getParameter(String param_name)
Q: What is the difference between an Interface and an Abstract class?
A: An Abstract class declares have at least one instance method that is declared abstract which
will be implemented by the subclasses. An abstract class can have instance methods that
implement a default behavior. An Interface can only declare constants and instance methods, but
cannot implement default behavior.
All memeber variable of an interface is "public static final"
Q: What is the purpose of garbage collection in Java, and when is it used?
A: The purpose of garbage collection is to identify and discard objects that are no longer needed
by a program so that their resources can be reclaimed and reused. A Java object is subject to
garbage collection when it becomes unreachable to the program in which it is used.
Q: Describe synchronization in respect to multithreading.
A: With respect to multithreading, synchronization is the capability to control the access of
multiple threads to shared resources. Without synchonization, it is possible for one thread to
modify a shared variable while another thread is in the process of using or updating same shared
variable. This usually leads to significant errors.

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Q: Explain different way of using thread?
A: The thread could be implemented by using runnable interface or by inheriting from the
Thread class. The former is more advantageous, 'cause when you are going for multiple
inheritance..the only interface can help.
Q: What are pass by reference and passby value?
A: Pass By Reference means the passing the address itself rather than passing the value. Passby
Value means passing a copy of the value to be passed.
Q: What is HashMap and Map?
A: Map is Interface and Hashmap is class that implements that.
Q: Difference between HashMap and HashTable?
A: The HashMap class is roughly equivalent to Hashtable, except that it is unsynchronized and
permits nulls. (HashMap allows null values as key and value whereas Hashtable doesnt allow).
HashMap does not guarantee that the order of the map will remain constant over time. HashMap
is non synchronized and Hashtable is synchronized.
Q: Difference between Vector and ArrayList?
A: Vector is synchronized whereas arraylist is not.
Q: Difference between Swing and Awt?
A: AWT are heavy-weight componenets. Swings are light-weight components. Hence swing
works faster than AWT.
Q: What is the difference between a constructor and a method?
A: A constructor is a member function of a class that is used to create objects of that class. It has
the same name as the class itself, has no return type, and is invoked using the new operator.
A method is an ordinary member function of a class. It has its own name, a return type (which
may be void), and is invoked using the dot operator.
Q: What is an Iterators?
A: Some of the collection classes provide traversal of their contents via a java.util.Iterator
interface. This interface allows you to walk a collection of objects, operating on each object in
turn. Remember when using Iterators that they contain a snapshot of the collection at the time the
Iterator was obtained; generally it is not advisable to modify the collection itself while traversing
an Iterator.

Page 16
Q: What is an abstract class?
A: Abstract class must be extended/subclassed (to be useful). It serves as a template. A class that
is abstract may not be instantiated (ie, you may not call its constructor), abstract class may
contain static data. Any class with an abstract method is automatically abstract itself, and must
be declared as such.
A class may be declared abstract even if it has no abstract methods. This prevents it from being
Q: What is static in java?
A: Static means one per class, not one for each object no matter how many instance of a class
might exist. This means that you can use them without creating an instance of a class.Static
methods are implicitly final, because overriding is done based on the type of the object, and
static methods are attached to a class, not an object. A static method in a superclass can be
shadowed by another static method in a subclass, as long as the original method was not declared
final. However, you can't override a static method with a nonstatic method. In other words, you
can't change a static method into an instance method in a subclass.
Q: What is final?
A: A final class can't be extended ie., final class may not be subclassed. A final method can't be
overridden when its class is inherited. You can't change value of a final variable (is a constant).
Q: What if the main method is declared as private?
A: The program compiles properly but at runtime it will give "Main method not public."
Q: What if the static modifier is removed from the signature of the main method?
A: Program compiles. But at runtime throws an error "NoSuchMethodError".
Q: What if I write static public void instead of public static void?
A: Program compiles and runs properly.
Q: What if I do not provide the String array as the argument to the method?
A: Program compiles but throws a runtime error "NoSuchMethodError".
Q: What is the first argument of the String array in main method?

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A: The String array is empty. It does not have any element. This is unlike C/C++ where the first
element by default is the program name.
Q: If I do not provide any arguments on the command line, then the String array of Main
method will be empty of null?
A: It is empty. But not null.
Q: How can one prove that the array is not null but empty?
A: Print args.length. It will print 0. That means it is empty. But if it would have been null then it
would have thrown a NullPointerException on attempting to print args.length.
Q: What environment variables do I need to set on my machine in order to be able to run
Java programs?
A: CLASSPATH and PATH are the two variables.
Q: Can an application have multiple classes having main method?
A: Yes it is possible. While starting the application we mention the class name to be run. The
JVM will look for the Main method only in the class whose name you have mentioned. Hence
there is not conflict amongst the multiple classes having main method.
Q: Can I have multiple main methods in the same class?
A: No the program fails to compile. The compiler says that the main method is already defined
in the class.
Q: Do I need to import java.lang package any time? Why ?
A: No. It is by default loaded internally by the JVM.
Q: Can I import same package/class twice? Will the JVM load the package twice at
A: One can import the same package or same class multiple times. Neither compiler nor JVM
complains abt it. And the JVM will internally load the class only once no matter how many times
you import the same class.
Q: What are Checked and UnChecked Exception?

Page 18
A: A checked exception is some subclass of Exception (or Exception itself), excluding class
RuntimeException and its subclasses.
Making an exception checked forces client programmers to deal with the possibility that the
exception will be thrown. eg, IOException thrown by's read() method·
Unchecked exceptions are RuntimeException and any of its subclasses. Class Error and its
subclasses also are unchecked. With an unchecked exception, however, the compiler doesn't
force client programmers either to catch the
exception or declare it in a throws clause. In fact, client programmers may not even know that
the exception could be thrown. eg, StringIndexOutOfBoundsException thrown by String's
charAt() method· Checked exceptions must be caught at compile time. Runtime exceptions do
not need to be. Errors often cannot be.
Q: What is Overriding?
A: When a class defines a method using the same name, return type, and arguments as a method
in its superclass, the method in the class overrides the method in the superclass.
When the method is invoked for an object of the class, it is the new definition of the method that
is called, and not the method definition from superclass. Methods may be overridden to be more
public, not more private.
Q: What are different types of inner classes?
A: Nested top-level classes, Member classes, Local classes, Anonymous classes
Nested top-level classes- If you declare a class within a class and specify the static modifier, the
compiler treats the class just like any other top-level class.
Any class outside the declaring class accesses the nested class with the declaring class name
acting similarly to a package. eg, outer.inner. Top-level inner classes implicitly have access only
to static variables.There can also be inner interfaces. All of these are of the nested top-level
Member classes - Member inner classes are just like other member methods and member
variables and access to the member class is restricted, just like methods and variables. This
means a public member class acts similarly to a nested top-level class. The primary difference
between member classes and nested top-level classes is that member classes have access to the
specific instance of the enclosing class.
Local classes - Local classes are like local variables, specific to a block of code. Their visibility
is only within the block of their declaration. In order for the class to be useful beyond the
declaration block, it would need to implement a
more publicly available interface.Because local classes are not members, the modifiers public,
protected, private, and static are not usable.
Anonymous classes - Anonymous inner classes extend local inner classes one level further. As
anonymous classes have no name, you cannot provide a constructor.

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Q: What is the difference between declaring a variable and defining a variable?
A: In declaration we just mention the type of the variable and it's name. We do not initialize it.
But defining means declaration + initialization.
e.g String s; is just a declaration while String s = new String ("abcd"); Or String s = "abcd"; are
both definitions.
Q: What is the default value of an object reference declared as an instance variable?
A: null unless we define it explicitly.
Q: What type of parameter passing does Java support?
A: Java supports both pass by value as well as pass by reference.
Q: Primitive data types are passed by reference or pass by value?
A: Primitive data types are passed by value.
Q: Objects are passed by value or by reference?
A: Objects are always passed by reference. Thus any modifications done to an object inside the
called method will always reflect in the caller method.
Q: What is serialization?
A: Serialization is a mechanism by which you can save the state of an object by converting it to a
byte stream.
Q: Which methods of Serializable interface should I implement?
A: The serializable interface is an empty interface, it does not contain any methods. So we
do not implement any methods.
Q: What is the common usage of serialization?
A: Whenever an object is to be sent over the network, objects need to be serialized. Moreover if
the state of an object is to be saved, objects need to be serilazed.
Q: What is Externalizable interface?
A: Externalizable is an interface which contains two methods readExternal and writeExternal.
These methods give you a control over the serialization mechanism. Thus if your class
implements this interface, you can customize the serialization process by implementing these

Page 20
Q: What happens to the object references included in the object?
A: The serialization mechanism generates an object graph for serialization. Thus it determines
whether the included object references are serializable or not. This is a recursive process. Thus
when an object is serialized, all the included objects are also serialized alongwith the original
Q: What one should take care of while serializing the object?
A: One should make sure that all the included objects are also serializable. If any of the objects
is not serializable then it throws a NotSerializableException.
Q: What happens to the static fields of a class during serialization? Are these fields
serialized as a part of each serialized object?
A: Yes the static fields do get serialized. If the static field is an object then it must have
implemented Serializable interface. The static fields are serialized as a part of every object. But
the commonness of the static fields across all the instances is maintained even after serialization.
Q: Does Java provide any construct to find out the size of an object?
A: No there is not sizeof operator in Java. So there is not direct way to determine the size of an
object directly in Java.
[ Received from Sandesh Sadhale] TOP
Q: What are wrapper classes?
A: Java provides specialized classes corresponding to each of the primitive data types. These are
called wrapper classes. They are e.g. Integer, Character, Double etc.
Q: Why do we need wrapper classes?
A: It is sometimes easier to deal with primitives as objects. Moreover most of the collection
classes store objects and not primitive data types. And also the wrapper classes provide many
utility methods also. Because of these resons we need wrapper classes. And since we create
instances of these classes we can store them in any of the collection classes and pass them
around as a collection. Also we can pass them around as method parameters where a method
expects an object.
Q: What are checked exceptions?

Page 21
A: Checked exception are those which the Java compiler forces you to catch. e.g. IOException
are checked Exceptions.
Q: What are runtime exceptions?
A: Runtime exceptions are those exceptions that are thrown at runtime because of either wrong
input data or because of wrong business logic etc. These are not checked by the compiler at
compile time.
Q: What is the difference between error and an exception?
A: An error is an irrecoverable condition occurring at runtime. Such as OutOfMemory error.
These JVM errors and you can not repair them at runtime. While exceptions are conditions that
occur because of bad input etc. e.g. FileNotFoundException will be thrown if the specified file
does not exist. Or a NullPointerException will take place if you try using a null reference. In
most of the cases it is possible to recover from an exception (probably by giving user a feedback
for entering proper values etc.).
Q: How to create custom exceptions?
A: Your class should extend class Exception, or some more specific type thereof.
Q: What happens to an unhandled exception?
A: One can not do anytihng in this scenarion. Because Java does not allow multiple inheritance
and does not provide any exception interface as well.
Q: How does an exception permeate through the code?
A: An unhandled exception moves up the method stack in search of a matching When an
exception is thrown from a code which is wrapped in a try block followed by one or more catch
blocks, a search is made for matching catch block. If a matching type is found then that block
will be invoked. If a matching type is not found then the exception moves up the method stack
and reaches the caller method. Same procedure is repeated if the caller method is included in a
try catch block. This process continues until a catch block handling the appropriate type of
exception is found. If it does not find such a block then finally the program terminates.
Q: What are the different ways to handle exceptions?
A: There are two ways to handle exceptions,
1. By wrapping the desired code in a try block followed by a catch block to catch the exceptions.
2. List the desired exceptions in the throws clause of the method and let the caller of the method
hadle those exceptions.

Page 22
1. How can you achieve Multiple Inheritance in Java?
Java's interface mechanism can be used to implement multiple inheritance, with one important
from c++ way of doing MI: the inherited interfaces must be abstract. This obviates the need to
between different implementations, as with interfaces there are no implementations.
3. Searching a String
String string = "aString";
// First occurrence.
int index = string.indexOf('S'); // 1
// Last occurrence.
index = string.lastIndexOf('i'); // 4
// Not found.
index = string.lastIndexOf('z'); // -1
4. Connecting to a Database and Strings Handling
Constructing a String
If you are constructing a string with several appends, it may be more efficient to construct it
using a
StringBuffer and then convert it to an immutable String object.
StringBuffer buf = new StringBuffer("Initial Text");
// Modify
int index = 1;
buf.insert(index, "abc");
// Convert to string
String s = buf.toString();
Getting a Substring from a String
int start = 1;
int end = 4;
String substr = "aString".substring(start, end); // Str
5. What is a transient variable?
A transient variable is a variable that may not be serialized. If you don't want some field not to
be serialized,
you can mark that field transient or static.
6. What is the difference between Serializalble and Externalizable interface?
When you use Serializable interface, your class is serialized automatically by default. But you
can override
writeObject() and readObject()two methods to control more complex object serailization process.
When you
use Externalizable interface, you have a complete control over your class's serialization process.
7. How many methods in the Externalizable interface?
There are two methods in the Externalizable interface. You have to implement these two
methods in order
to make your class externalizable. These two methods are readExternal() and writeExternal().
8. How many methods in the Serializable interface?

Page 23
There is no method in the Serializable interface. The Serializable interface acts as a marker,
telling the
object serialization tools that your class is serializable.
9. How to make a class or a bean serializable?
By implementing either the interface, or the interface.
As long as
one class in a class's inheritance hierarchy implements Serializable or Externalizable, that class is
10. What is the serialization?
The serialization is a kind of mechanism that makes a class or a bean persistence by having its
or fields and state information saved and restored to and from storage.
11. What are synchronized methods and synchronized statements?
Synchronized methods are methods that are used to control access to an object. A thread only
executes a
synchronized method after it has acquired the lock for the method's object or class. Synchronized
statements are similar to synchronized methods. A synchronized statement can only be executed
after a
thread has acquired the lock for the object or class referenced in the synchronized statement.
12. What is synchronization and why is it important?
With respect to multithreading, synchronization is the capability to control the access of multiple
threads to
shared resources. Without synchronization, it is possible for one thread to modify a shared object
another thread is in the process of using or updating that object's value. This often causes dirty
data and
leads to significant errors.
13. What is the purpose of finalization?
The purpose of finalization is to give an unreachable object the opportunity to perform any
processing before the object is garbage collected.
14. What classes of exceptions may be caught by a catch clause?
A catch clause can catch any exception that may be assigned to the Throwable type. This
includes the
Error and Exception types.
15. What is the difference between the Reader/Writer class hierarchy and the
class hierarchy?
The Reader/Writer class hierarchy is character-oriented, and the InputStream/OutputStream class
is byte-oriented.
16. What happens when a thread cannot acquire a lock on an object?

Page 24
If a thread attempts to execute a synchronized method or synchronized statement and is unable to
an object's lock, it enters the waiting state until the lock becomes available.
17. What restrictions are placed on method overriding?
Overridden methods must have the same name, argument list, and return type. The overriding
method may
not limit the access of the method it overrides. The overriding method may not throw any
exceptions that
may not be thrown by the overridden method.
18. What restrictions are placed on method overloading?
Two methods may not have the same name and argument list but different return types.
19. How does multithreading take place on a computer with a single CPU?
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The operating system's task scheduler allocates execution time to multiple tasks. By quickly
between executing tasks, it creates the impression that tasks execute sequentially.
20. How is it possible for two String objects with identical values not to be equal under the
== operator?
The == operator compares two objects to determine if they are the same object in memory. It is
possible for
two String objects to have the same value, but located indifferent areas of memory.
21. How are this() and super() used with constructors?
this() is used to invoke a constructor of the same class. super() is used to invoke a superclass
22. What class allows you to read objects directly from a stream?
The ObjectInputStream class supports the reading of objects from input streams.
23. What is the ResourceBundle class?
The ResourceBundle class is used to store locale-specific resources that can be loaded by a
program to
tailor the program's appearance to the particular locale in which it is being run.
24. What interface must an object implement before it can be written to a stream as an
An object must implement the Serializable or Externalizable interface before it can be written to
a stream as
an object.
25. What is Serialization and deserialization?
Serialization is the process of writing the state of an object to a byte stream. Deserialization is the
of restoring these objects.
26. What are the Object and Class classes used for?
The Object class is the highest-level class in the Java class hierarchy. The Class class is used to
the classes and interfaces that are loaded by a Java program.
27. Can you write Java code for declaration of multiple inheritance in Java ?
Class C extends A implements B

Page 25
28. What do you mean by multiple inheritance in C++ ?
Java Interview Questions
Multiple inheritance is a feature in C++ by which one class can be of different types. Say class
teachingAssistant is inherited from two classes say teacher and Student.
29. Write the Java code to declare any constant (say gravitational constant) and to get its
Class ABC
static final float GRAVITATIONAL_CONSTANT = 9.8;
public void getConstant()
system.out.println("Gravitational_Constant: " + GRAVITATIONAL_CONSTANT);
30. What are the disadvantages of using threads?
31. Given two tables Student(SID, Name, Course) and Level(SID, level) write the SQL
statement to get the
name and SID of the student who are taking course = 3
and at freshman level.
FROM Student, Level
WHERE Student.SID = Level.SID
AND Level.Level = "freshman"
AND Student.Course = 3;
32. What do you mean by virtual methods?
virtual methods are used to use the polymorhism feature in C++. Say class A is inherited from
class B. If we
declare say fuction f() as virtual in class B and override the same function in class A then at
appropriate method of the class will be called depending upon the type of the object.
33. What do you mean by static methods?
By using the static method there is no need creating an object of that class to use that method.
We can
directly call that method on that class. For example, say class A has static function f(), then we
can call f()
function as A.f(). There is no need of creating an object of class A.
34. What do mean by polymorphism, inheritance, encapsulation?
Polymorhism: is a feature of OOPl that at run time depending upon the type of object the
method is called.
Inheritance: is a feature of OOPL that represents the "is a" relationship between different

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Say in real life a manager is a employee. So in OOPL manger class is inherited from the
employee class.
Encapsulation: is a feature of OOPL that is used to hide the information.
35. What are the advantages of OOPL?
Object oriented programming languages directly represent the real life objects. The features of
inhreitance, polymorphism, encapsulation makes it powerful.
36. How many methods do u implement if implement the Serializable Interface?
The Serializable interface is just a "marker" interface, with no methods of its own to implement.
37. Are there any other 'marker' interfaces?
38. What is the difference between instanceof and isInstance?
instanceof is used to check to see if an object can be cast into a specified type without throwing a
cast class
exception. isInstance() determines if the specified object is assignment-compatible with the
represented by this Class. This method is the dynamic equivalent of the Java language instanceof
The method returns true if the specified Object argument is nonnull and can be cast to the
reference type
represented by this Class object without raising a ClassCastException. It returns false otherwise.
39. why do you create interfaces, and when MUST you use one?
You would create interfaces when you have two or more functionalities talking to each other.
Doing it this
way help you in creating a protocol between the parties involved.
40. What's the difference between the == operator and the equals() method? What test does
use, and why?
The == operator would be used, in an object sense, to see if the two objects were actually the
same object.
This operator looks at the actually memory address to see if it actually the same object. The
method is used to compare the values of the object respectively. This is used in a higher level to
see if the
object values are equal.
Of course the the equals() method would be overloaded in a meaningful way for whatever object
that you
were working with.
42. Given a text file, input.txt, provide the statement required to open this file with the
appropriate I/O
stream to be able to read and process this file.
43. Name four methods every Java class will have.
public String toString();
public Object clone();

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public boolean equals();
public int hashCode();
44. What does the "abstract" keyword mean in front of a method? A class?
Abstract keyword declares either a method or a class. If a method has a abstract keyword in front
of it, it is
called abstract method.Abstract method has no body. It has only arguments and return type.
methods act as placeholder methods that are implemented in the subclasses. Abstract classes
can't be
instantiated.If a class is declared as abstract,no objects of that class can be created.If a class
contains any
abstract method it must be declared as abstract.
45. Does Java have destructors?
No garbage collector does the job working in the background
46. Are constructors inherited? Can a subclass call the parent's class constructor? When?
You cannot inherit a constructor. That is, you cannot create a instance of a subclass using a
constructor of
one of it's superclasses. One of the main reasons is because you probably don't want to overide
superclasses constructor, which would be possible if they were inherited. By giving the
developer the ability
to override a superclasses constructor you would erode the encapsulation abilities of the
49. Does Java have "goto"? No
50. What does the "final" keyword mean in front of a variable? A method? A class?
FINAL for a variable : value is constant
FINAL for a method : cannot be overridden
FINAL for a class : cannot be derived
Reference Books
1. Web Programming, building Internet applications, Chris Bates 2nd edition, WILEY
2. The complete Reference Java 2 Fifth Edition by Patrick Naughton and Herbert Schildt.
3. Java Server Pages Hans Bergsten, SPD O’Reilly
4. Internet and World Wide Web How to program by Dietel and Nieto PHI/Pearson
Education Asia.
5. Jakarta Struts Cookbook, Bill Siggelkow, S P D O’Reilly.