Its a *very important setting* that effects static objects (or singletons) as well a versioning of jars.
I'll give you a common example. Lets say you have a utility jar that you want every module on the server to use so you add it to the server's WAS_HOME library folder. Next, one of your users (say you have hundreds) adds the same jar to their EAR for deployment on the server.
Now, if the jars are of different versions, then the PARENT_FIRST or PARENT_LAST will have a big impact on which run time version files are use. Assume the versions are the same though, static objects will still be affected since singletons are created at the level the class loader is declared so. So PARENT_FIRST would have them all sharing the same singleton and PARENT_LAST would have them creating their own if they had a local copy of the jar.
Hi Rathi, beware of the classloader, since Parent_Last would give higher priority to your web app classloader over the server classloader. Remember that when Websphere loads a class A, every class being instanced from that class are going to be loaded by the classloader that loaded class A...if they aren't in the same classloader environment then an Exception would be trown.
SCJP 1.4, <br />IBM Certified System Administrator Websphere Application Server 5.0, IBM Certified DB2 UDB Database Associate