Jasper Reports is used to Generate the reports from the 
Database. A powerful report-generating tool that has the 
ability to deliver rich content onto the screen, to the 
printer or into PDF, HTML, XLS, CSV and XML files.

by just putting .jar extension

As far as I am aware about jar files, they are used to 
archive the class files and not java files...
If you want to create a jar file for class files, you can 
use following command:

 cmd:\> jar cvf <name>.jar .

 where (.) is for the current directory.

Static is a keyword in java,
static means only one copy exists for entire class 
irrespective of the number of objects that exists for that 
class.
The static variables are initialized when the class is 
loaded and the non-static variables are initialized just 
before the constructor is called.

access specifiers will specify the scope of the members of 
access
public,protected,private,default.


access modifiers will support the functionality of a method.
abstract,final,native,synchronized,static,volatile.

Threads also have some disadvantages:

Threads are not reusable as they are dependent on a process 
and cannot be separated from the process.

Threads are not isolated as they don't have their own 
address space.

The error cause by the thread can kill the entire process 
or program because that error affects the entire memory 
space of all threads use in that process or program.

Due to the shared resources by the threads with in the 
process can also affect the whole process or program when a 
resource damage by the thread.

For concurrent read and write access to the memory thread 
will required synchronizations. Data of the process can 
easily damage by the thread through data race because all 
the threads with in the process have write access to same 
piece of dat

String is immutable whereas StringBuffer and StringBuilder 
can change their values.

The only difference between StringBuffer and StringBuilder 
is that StringBuilder is unsynchronized whereas 
StringBuffer is synchronized. So when the application needs 
to be run only in a single thread then it is better to use 
StringBuilder. StringBuilder is more efficient than 
StringBuffer.

Criteria to choose among String, StringBuffer and 
StringBuilder

If your text is not going to change use a string Class 
because a String object is immutable. 
If your text can change and will only be accessed from a 
single thread, use a StringBuilder because StringBuilder is 
unsynchronized. 
If your text can changes, and will be accessed from 
multiple threads, use a StringBuffer because StringBuffer 
is synchronous.

our lines of code can be executed by many requests at a 
time, this is the main advantage of the thread.
but the performance will slow down, so threading will be 
used where it's needed.

basically You can make best use of your CPU, by ensuring that its always processing some or the other things. And threading makes the execution faster not slower as it divides the whole work into chunks and processes them parallel. finally unites then to give result. correct me if I am wrong.

Thread is a small part of a program when a program enter in the executed state threads will be execute  concurrently and maximum use of cpu.

Java runtime exception handler 
can not catch all type of exceptions. As such we need 
to explicitly deal with them to prevent abrupt program 
termination.Some of the examples for this could be 
ArrayIndexOutOfBounds, ArithmeticExceptions etc. The 
key factor to remember is that checked exceptions are 
the ones where we need to use the try and catch blocks 
to get the exception problem solved. The same is not 
mandatory for the unchecked exceptions and are caught 
well and good by the Java run time Exception Handler

caching concept in hibernate is performed internally in 
stages...
        1)firstlevel(Session) caching
        2)Secondlevel(SessionFactory) caching
1)firstlevel(Session) caching:
     First-level cache always Associates with the Session 
object. Hibernate uses this cache by default. Here, it 
processes one transaction after another one, means wont 
process one transaction many times. Mainly it reduces the 
number of SQL queries it needs to generate within a given 
transaction. That is instead of updating after every 
modification done in the transaction, it updates the 
transaction only at the end of the transaction. 

2)Secondlevel(SessionFactory) caching
     Second-level cache always associates with the Session 
Factory object. While running the transactions, in between 
it loads the objects at the Session Factory level, so that 
those objects will available to the entire application, 
don’t bounds to single user. Since the objects are already 
loaded in the cache, whenever an object is returned by the 
query, at that time no need to go for a database 
transaction. In this way the second level cache works.

A JSP page can't directly implement an interface. If you 
really need to do this you'll have to define a superclass 
for your page which implements the interface. If you 
declare this superclass to be abstract you can defer the 
implementation of the interface to the JSP page. This 
superclass will have to implement the interfaces 
HttpJspPage and Servlet too, otherwise you will get a 
compilation error from the JSP compiler.

Java is apure object-oriented progrmaing language.here one 
beter feature we have i.e multiple inheritance and pointer 
concepets are not used.

In java the primitivw datatypes like(int,float,double,short)
these values can be represented in objects of classes.

there are following diff between java and c++
1) one of the most important diff is there is no pointre in 
java but pointer is hidden from programmer.
2) java is pure object oriented programming language where 
as c++ is not pure object oriented language is also support 
c feature.
3) in java everything should be within class includin  main 
function where as it can be in calss or not.
4) java doesn't support operator overloading where as c++ 
souuprt
5)there is no global variable in java where as it is in c++
6) there is no distructor in java but threr is finally key 
work 
7)there is no multipal inharitance but is can be achived by 
interface

Locale locale = Locale.GERMANY;
    String string =
NumberFormat.getCurrencyInstance(locale).format(123.45);

you can use java regex pattern matchers to achieve that.

When start method is called , JVM calls run method of this 
object

Thread in a java inbuilt Object.
So if you are implementing threads in your system by using
Thread class or runnable interface, the JVM will look at
that and keep an eye on your code. As soon as you call the
start method it will go and call the run method on its own.
The funda here is that this is something that the JVM if
fully responsible of handling.