A proxy can become invalid if its corresponding MBean is unregistered. For
example, if monitoring is disabled, most monitoring MBeans are unregistered
from the MBeanServer and no longer exist.
Return the Java classname of the interface that this
implements. This classname may then subsequently be used
to create a standard JMX proxy if desired. If no such
classname is appropriate, then null will be returned.
return
the classnames of all implemented interfaces (usually 1) or null