if at that point you know that an error has occurred, then 
why not write the proper code to handle that error instead 
of passing a new Exception object to the catch block? 

Throwing your own exceptions signifies some design flaws in 
the project.

Hi Swapna,

throwing our Own Exception does not Means that there is
Design Flaws,

Assume that your application Involves DB Operation,

EG: 

It Reads Data from an MSACCESS file,

and you are connecting the D.B through you program,

but can u tell me, what will happen if somebody/some other
application Exclusively opened the Access file before ur
Program,
----------------
A wise Programmer will foresee this Issue, and will Create
his own Exception Handler, which will instruct his User to
close that MSACCESS file,

----

So SWAPNA pls Grow UP, and try to think like how MEN Do,..