> 1. diffrences between interface & absrtact class?
An abstract class is one that is partially defined and requires that
another class extend it to complete all of the method implementations.
An interface is like a class skeleton or blueprint. Any classes that
implement an interface must implement all of the methods described by
the interface.

> 2.diffrences between servlets & jsp?
A jsp  page is just an HTML page  with embedded java  code that tomcat
will compile into a servlet  before sending the page to the client. So
in effect a servlet is just a compiled JSP page. JSP just gives a
development team the ability to separate the HTML coding from the Java
coding.

> 3. if ten threads r of same priority which will run first?
I believe either the system kernel or the JVM would pick any one of
them since they are all the same priority. Depends on the way threads
are scheduled.

> 4.is there data  base pool in tomcat ?
yes. go to the apache site and look at the tomcat JDNI pages.