Web Programming FAQ
Mention the benefits of JavaScript.
JavaScript is primarily a client-side
language. Advantages of JavaScript are
Simple and versatile – can be used with
other languages and in a huge variety of applications
Speed – code functions can be run
immediately in client machine instead of having to contact the server and wait
for an answer.
Reduces Server Load
What is a session? What is session
management and why it is required?
Session is an interval of time during which
a connection exists between a server and a client. The state of the client is
maintained at the server during the session and since http is a stateless
protocol the state information does not persist when the connection is
terminated.
Session management also called as session
tracking is a way to maintain state (data) of an user across multiple sessions.
There are four techniques used in Session tracking:
Cookies
Hidden Form Field
URL Rewriting
HttpSession
Define RMI.
RMI is remote Method Invocation. RMI allows
remote communication and is used to build distributed applications in Java. RMI
allows a Java object residing in one machine to invoke a method which resides
in another (Remote) machine.
What are stub and skeletons?
Stub is a Java object that resides on the
client machine. Its function is to provide the same interface as the remote
server. A skeleton is a Java object that resides on the server machine. It
receives request performs serialization and invokes the appropriate code on the
server.
What is the function of bind(), rebind()
and lookup() methods?
bind() – register an object and name in RMI
registry
rebind()
– modify the existing registered object.
lookup() – search for an object using name.
Define marshalling and unmarshalling.
Marshalling is the process of converting
data or object into a byte stream. The reverse process of converting the byte
stream into original data or object is called as unmarshalling. The conversion
is achieved through serialization.
What is the use of 'param' variable in JSP?
‘param’ is one of the implicit objects in
JSP. It maps the request parameter to a single value. Example
<jsp:param name=”first_name”
value=”xyz”/>
What are the types of directives in JSP?
Types of directive tags
page directive – defines page dependent
attributes example the scripting language used by the JSP
include directive – include file in the JSP
during the translation page
taglib directive – allows to create user
define tags that implement custom behavior
List any 4 taglib directives available in
JSP and their use.
Tag library contains a set of user defined
tags that implement custom behavior. The taglib directive declares that JSP
page uses a set of custom tags, identifies the location of the library and
provides a means of identifying the custom tags in the JSP page.
Differentiate Http and generic servlet
|
GenericServlet
|
HttpServlet
|
|
Abstract class
|
Abstract class
|
|
Direct subclass of servlet class
|
Direct subclass of GeneriServlet class
|
|
Defines a generic protocol independent
servlet – It handles all types of protocol like http, smtp, ftp
etc.
|
Defines a HTTP protocol specific servlet
– It handles only http protocol.
|
What is namespaces in XML? Give an example.
What are Namespaces? Why is it useful?
Explain with an example.
Justify the need for namespaces in XML.
In XML, element names are defined by the
developer. This often results in a conflict when trying to use XML documents
from different applications together. XML Namespace is used to avoid element
name conflict in XML documents. It provide a means for document authors to
unambiguously refer to elements with the same name (i.e., prevent collisions).
For example,
<subject>Geometry</subject> and
<subject>Cardiology</subject>
use element subject to mark up data.
In the first case, the subject is something
one studies in school, whereas in the second case, the subject is a field of
medicine.
Namespaces can differentiate these two
subject elements—for example:
<highschool:subject>Geometry</highschool:subject> and
<medicalschool:subject>Cardiology</medicalschool:subject>
What is XML Parser?
An XML parser is a software library or
package that provides interface for client applications to work with an XML
document.
It is designed to read XML document and
create a way for programs to use the XML
It validates the documents and checks if
the document is well formed.
State the function of DTD.
Document Type Definition (DTD) is used to
define the structure of an XML document. It contains a list of legal elements
and defines the structure with the help of them. It can also be used to define
special characters and character strings used in the document.
Explain the use of DTD for structuring the
XML document.
What are the benefits of using XML Schema?
State the differences between XML Schema
and DTD.
Compare DTD and XML schema.
Both DTD and XML schema provides the basic
structure for defining a XML document. In addition XML schema also provides
methods to define constraints on the data contained in the document. XML schema
is considered to be richer and more powerful than DTD.
Drawback in DTD
DTDs are not flexible enough to meet
today’s programming needs. For example, DTDs lack a way of indicating what
specific type of data (e.g., numeric, text) an element can contain,
DTDs are not themselves XML documents, forcing
developers to learn multiple grammars and developers to create multiple types
of parsers.
Unlike DTDs, schemas do not use EBNF
grammar. Instead, they use XML syntax and are actually XML documents that
programs can manipulate. Like DTDs, schemas are used by validating parsers to
validate documents.
Advantage of using Schemas over DTD
It is easier to describe document content
It is easier to define restrictions on data
It is easier to validate the correctness of
data
It is easier to convert data between
different data types
What is the function of XSLT?
What is the use of XSLT?
eXtensible Stylesheet Language
Transformation (XSLT) is used to transform an XML document into other type of
document like HTML. With XSLT we ca add / remove elements and attributes to or
from an output file. We can also rearrange and sort elements, perform tests and
make decisions about which element to hide, display etc.
What are the various transformation
technologies?
XSL Transformations (XSLT) – is a
technology for transforming XML documents into other documents – i.e.,
transforming the structure of the XML document data to another structure.
XSLT provides elements that define rules
for transforming one XML document to produce a different XML document.
Transforming an XML document using XSLT involves two tree structures – the
source tree (XML document to transform) and the result tree (XML document to
create).
To perform transformations, an XSLT
processor is required. Popular XSLT processors include Microsoft’s MSXML and
the Apache Software Foundation’s Xalan 2 (xml.apache.org).
What are presentation technologies of XML?
Explain each one briefly.
Extensible Stylesheet Language (XSL)
documents specify how programs are to render XML document data. XSL is a group of three technologies—XSL-FO
(XSL Formatting Objects), XPath (XML Path Language) and XSLT (XSL
Transformations).
XSL-FO is a vocabulary for specifying
formatting
XPath is a string-based language of
expressions used by XML and many of its related technologies for effectively
and efficiently locating structures and data (such as specific elements and
attributes) in XML documents.
XSL Transformations (XSLT) – is a
technology for transforming XML documents into other documents – i.e.,
transforming the structure of the XML document data to another structure.
What is Xpath?
Xpath is syntax for defining path of a XML
document. Xpath uses a string-based language of expressions to navigate in XML
documents. It is used for effectively and efficiently locating structures and
data (such as specific elements and attributes) in XML documents
What is XSL and why is it used?
eXtensible Stylesheet Language (XSL) is
used for expressing stylesheets in XML. An XSL is a file that describes how to
display an XML document of a given type.
Java FAQ
What is Java Virtual Machine? State its
purpose. (Or)
Is Java platform independent? Justify. (Or)
How is a Java bytecode interpreted? (Or)
What is the need for bytecode generation?
A programming language is said to be
platform independent if it can create an application program that can be
executed on any platform. Java Virtual Machine (JVM) provides platform
independence to Java.
When a Java program is compiled it generates
a bytecode file. The JVM is available with all operating systems and can be
installed in any host machine. It takes the bytecode file as an input,
interprets it generates an output corresponding to the underlying platform (OS)
of the host machine and then executes it. Hence Java is platform independent.
Differentiate static binding and dynamic
binding.
Static binding
|
Dynamic binding
|
Also called early binding
|
Also called a slate binding
|
Binding happens at compile time
|
Binding happens at run time.
|
Actual object is not used for binding
|
Actual object used for binding
|
What is the use of ‘extends’ keyword?
‘extends’ keyword is used in inheritance in
Java. It allows the public and protected variables and methods of the super
class to be inherited by the subclass.
Example:
class A
{
}
class B extends A
{
}
What is static in Java?
Static is a keyword in Java used with
variables, methods and block of code. Static belongs to the class and not
the object. It has only one instance and is shared by all the objects of
the class.
Static block of code in a class will be
executed before the objects are created for the class. Static variables and
methods can be accessed using the class name. Static methods can use /
manipulate only static variables.
What is a StringBuffer? How does it differ
from String class?
StringBuffer is a peer class of String that
provides much of the functionality of Strings. StringBuffer have characters and
substrings inserted in the middle or appended to the end. StringBuffer is
mutable whereas String class is immutable. StringBuffer is fast and consumes
less memory when compared to String class.
What is the use of super keyword?
How is super used in constructors?
‘super’ is a keyword in Java used to access
the super class variables and constructors.
Example
import java.io.*;
class A
{
int
x;
A(int
i)
{
x = i;
}
}
class B extends A
{
int
y;
B(int
i, int j)
{
super(i); // calls the super class
constructor
y = j;
}
void
fnDisplay()
{
// Accesses the super class
variable
System.out.println("x = "+ super.x);
System.out.println("y = " +
y);
}
}
class pgm1
{
public
static void main(String as[])
{
B
obj = new B(5, 6);
obj.fnDisplay();
}
}
Differentiate constructors and
methods.
Constructor
|
Method
|
Special member function of class
|
Member function of a class
|
Same name as class name
|
Any name can be used
|
Always public.
|
May be public, private or protected.
|
No return values
|
May or may not have return values.
|
Automatically invoked when objects are created.
|
Have to be explicitly invoked using the object of a class
|
Mainly used to initialize the variables of a class
|
Performs a specific task
|
Syntax – constructor
<Class name> (<Argument list>)
{
}
Syntax – method
<Return type> <Method name>
(<Argument list>)
{
}
What is an interface? How is it defined?
Interface in Java is a mechanism to achieve
abstraction. An interface is declared using the keyword interface. It has only
method declarations without body. A class can implement the interface using the
keyword ‘implements’. Each method of the interface has to be defined in the
class.
Interface cannot be instantiated. Multiple
inheritance in Java can be partially implemented using interface.
Syntax:
interface <interface name>
{
//
Method declarations
}
What is an abstract class? List its
characteristics.
A class that is declared with ‘abstract’
keyword is known as abstract class. It cannot be instantiated. They are used to
declare common characteristics of subclass. An abstract class can include
methods that contain no implementation. If an abstract class is inherited, then
the derived class must provide the implementations for all the methods of the
abstract class.
How do you create and initialize arrays in
Java?
An array is a set of related elements of
same datatype which share a common name and are stored in contiguous memory
locations. Each value is identified by its index.
Syntax for declaration
<data
type> [] <array name> = new <datatype>[array size];
Declaration and initialization
<data
type> [] <array name> = {value1, value2, ….};
What is exception handling?
An exception is an abnormal condition that
arises during run time and disrupts the normal flow of the program. Java
provides a mechanism called exception handling for handling such situations. Its
implemented using keywords try, catch, throw, throws and finally.
What is event delegation model?
Event handling in Java involves source and
listener. A source is an awt component like button, checkbox, list, etc. which
may generate several types of events. A listener is an object which may
register to receive an event. When an event occurs, the event source invokes
the appropriate method defined by the listener and provides an event object as
its argument.
To implement the event delegation Model
Implement the appropriate interface in the
listener so that it will receive the type of event desired.
Implement code to register and unregister
(if necessary) the listener as a recipient for the event notifications.
What is inner class and anonymous inner class?
A class declared inside another class is
known as inner class. The inner class can access all the members of the outer
class including its private members.
An anonymous inner class is a type of inner
class that has no name and can be instantiated only once. It is declared inside
the method and terminated by a semicolon.
Example – Inner class
Class
A
{
Class
B // inner class
{
}
}
Example – Anonymous Inner class –
MouseAdapter
public class AnonymousInnerClassDemo
extends Applet
{
public void init()
{
addMouseListener (new MouseAdapter()
{
public void
mousePressed(MouseEvent me)
{
showStatus("Mouse
Pressed");
}
});
}
}
Differentiate between choice and list
objects.
Choice
|
List
|
Type of AWT control
|
Type of AWT control
|
Pull down menu.
|
Pull down menu
|
Choice is displayed in compact form. Only one item is visible.
|
Multiline display. Multiple items may be visible.
|
Allows selection of one item only
|
Multiple selections possible.
|
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