I hate to say this, but RTFM. This is all covered in the InfoCenter.
If you go to the online InfoCenter:
http://www-4.ibm.com/software/webservers/appserv/doc/v40/aes/infocenter/index.html and do a search for "Hot deployment" it will send you to section 6.5.1: Hot deployment and dynamic reloading.
Kyle
P.S. If you are in WebSphere 3.5 we did not support the same level of hot deployment we do in WebSphere 4.0. In the 3.5 InfoCenter search for "dynamic reloading".
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Kyle Brown,
Author of
Enterprise Java (tm) Programming with IBM Websphere
See my homepage at
http://members.aol.com/kgb1001001 for other WebSphere information.