All MBeans must be given an object name that is unique. It can be assigned by the MBean's preregistration method, if the MBean supports preregistration (see the Javadoc API of the MBeanRegistration interface). Or it can be assigned by the object that creates or registers the MBean, which overrides the one given during preregistration. However, if neither of these assign an object name, the MBean server will not create the MBean and will raise an exception. Once an MBean is instantiated and registered, its assigned object name cannot be modified.
You can encode any meaning into the domain and key strings. The MBean server handles them as literal strings. The contents of the object name should be determined by your management needs. Keys can be meaningless serial numbers if MBeans are always handled programmatically. On the other hand, the keys can be human-readable to simplify their translation to the graphical user interface of a management application. With the HTML protocol adaptor, object names are displayed directly to the user.