I want to change a class file from the application that is deployed on j2ee server but don�t want to restart the server. Is there any tool available which can change the deployed class file on the fly without restarting the server?
Again, most application servers support hot deployment, so consult your application server documentation.
That aside, a production server shouldn't have hot deployment enabled, nor would a change to production code normally be run out via hot deployment: too much scope to mess live data up. An prudent update to an application in production would be done by taking the application down.