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- Can we use the constructor, instead of init(), to
initialize servlet? -
Yes , of course you can use the constructor instead of init(). There’s
nothing to stop you. But you shouldn’t. The original reason for init()
was that ancient versions of Java couldn’t dynamically invoke
constructors with arguments, so there was no way to give the constructur
a ServletConfig. That no longer applies, but servlet containers still
will only call your no-arg constructor. So you won’t have access to a
ServletConfig or ServletContext.
- How can a servlet refresh automatically if some new
data has entered the database? -
You can use a client-side Refresh or Server Push.
- The code in a finally clause will never fail to
execute, right? -
Using System.exit(1); in try block will not allow finally code to
execute.
- How many messaging models do JMS provide for and what
are they? - JMS provide for two
messaging models, publish-and-subscribe and point-to-point queuing.
- What information is needed to create a TCP Socket? - The Local System?s IP
Address and Port Number. And the Remote System’s IPAddress and Port
Number.
- What Class.forName will do while loading drivers? - It is used to create an
instance of a driver and register it with the DriverManager. When you have
loaded a driver, it is available for making a connection with a DBMS.
- How to Retrieve Warnings? - SQLWarning objects are a
subclass of SQLException that deal with database access warnings.
Warnings do not stop the execution of an application, as exceptions do;
they simply alert the user that something did not happen as planned. A
warning can be reported on a Connection object, a Statement object
(including PreparedStatement and CallableStatement objects), or a
ResultSet object. Each of these classes has a getWarnings method, which
you must invoke in order to see the first warning reported on the
calling object
SQLWarning warning = stmt.getWarnings();
if (warning != null)
{
while
(warning != null)
{
System.out.println("Message:
" + warning.getMessage());
System.out.println("SQLState:
" + warning.getSQLState());
System.out.print("Vendor
error code: ");
System.out.println(warning.getErrorCode());
. warning
= warning.getNextWarning();
}
}
- How many JSP scripting elements are there and what
are they? - There are three scripting
language elements: declarations, scriptlets, expressions.
- In the Servlet 2.4 specification SingleThreadModel
has been deprecates, why? -
Because it is not practical to have such model. Whether you set
isThreadSafe to true or false, you should take care of concurrent client
requests to the JSP page by synchronizing access to any shared objects
defined at the page level.
- What are stored procedures? How is it useful? - A stored procedure is a set
of statements/commands which reside in the database. The stored
procedure is precompiled and saves the database the effort of parsing
and compiling sql statements everytime a query is run. Each Database has
it’s own stored procedure language, usually a variant of C with a SQL
preproceesor. Newer versions of db’s support writing stored procedures
in Java and Perl too. Before the advent of 3-tier/n-tier architecture it
was pretty common for stored procs to implement the business logic( A
lot of systems still do it). The biggest advantage is of course speed.
Also certain kind of data manipulations are not achieved in SQL. Stored
procs provide a mechanism to do these manipulations. Stored procs are
also useful when you want to do Batch
updates/exports/houseKeeping kind of stuff on the db. The overhead of a
JDBC Connection may be significant in these cases.
- How do I include static files within a JSP page? - Static resources should
always be included using the JSP include directive. This way, the
inclusion is performed just once during the translation phase. The
following example shows the syntax: Do note that you should always
supply a relative URL for the file attribute. Although you can also
include static resources using the action, this is not advisable as the
inclusion is then performed for each and every request.
- Why does JComponent have add() and remove() methods
but Component does not? -
because JComponent is a subclass of Container, and can contain other
components and jcomponents.
- How can I implement a thread-safe JSP page? - You can make your JSPs
thread-safe by having them implement the SingleThreadModel interface.
This is done by adding the directive <%@ page
isThreadSafe="false" % > within your JSP page.
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What
is an abstract method?
An abstract method is a method which
doesn’t have a body, just declared with modifier abstract.
Explain
the use of the finally block.
Finally block is a block which
always executes. The block executes even when an exception is occurred. The
block won't execute only when the user calls System.exit()
What
is the initial state of a thread?
It is in a ready state.
What
is time slicing?
In time slicing, the task continues
its execution for a predefined period of time and reenters the pool of ready
tasks.
What
are Wrapper Classes?
Wrapper Classes allow to access
primitives as objects.
What
is List interface?
List is an ordered collection of
objects.
Can
you explain transient variables in java?
They are the variables that cannot
be serialized.
What
is synchronization?
Synchronization ensures only one
thread to access a shared resource, thus controls the access of multiple
threads to shared resources.
What
is serialization?
Serialization helps to convert the
state of an object into a byte stream.
What
is HashMap and Map?
Map is Interface and Hashmap is
class that implements that.