Java Interview Questions - 3

Here are some more Questions..

       65. What
are wrapper classes?

       Wrapper classes are classes that allow
primitive types to be accessed as objects.
 

 66. 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.
 

 67.  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.
 

 68. 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.
 



69. What is
the difference between Reader/Writer and InputStream/Output Stream?
The Reader/Writer class is
character-oriented and the InputStream/OutputStream class is
byte-oriented. 



70. 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.
 



71. 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 objects.



72. 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 applications. 



73. 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
 



74. 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 ODBC.
 



75. 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 above.



76. 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).
 



77. 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.
 



78. 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.
 



79. 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();



80. 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.
 



81. What
are the classes and interfaces for servlets?

There are two packages in servlets and
they are javax. servlet and
 



82. 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. 



83. 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 client. 



84. 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.
 



85. Who is
loading the init() method of servlet?

Web server
 



86. 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
 



87. 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 Cookies.
 



88. 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.
 



89. 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.
 



90. 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().  



91. 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
 



92. 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 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.



93. 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)
 



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
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 communication.



98. what is
UnicastRemoteObject? 


 All remote objects must extend
UnicastRemoteObject, which provides functionality that is needed to make
objects available from remote machines.
 



99. 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.
 



100. 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.
 



101. 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.
 



102. 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. 



103. What
are Predefined variables or implicit objects?

To simplify code in JSP expressions and
scriptlets, we can use eight automatically defined variables, sometimes called
implicit objects. They are request, response, out, session, application,
config, pageContext, and page.
 

104. 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

      
105. 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.