Java APIs

My application has a server that periodically makes changes in the class files located in the codebase (the changes are in a function implementation, not the structure of the class)

but only the first time the client loads the class from the codebase then always use the local classpath whenever it can find these classes locally

my Question is.. how to force the client to load the classes from the server codebase and not to use the one which exists locally??

thanks in advance,